Maximum Power Of A Drag Based Wind Turbine

Chapter 1
1.1 Background
Energy is one of the essential needs of a functional society. As the demand for energy is
increasing globally, strenuous efforts are required to increase the efficiency of energy use. The
most available and affordable sources of energy in today’s economic structure are fossil fuels
(about 85% of all commercial energy is derived from them). Efficiency improvement and new
technologies are a part of the solution. Renewable Energy technologies can meet much of
growing demands lower than those usually forecast for conventional energy. By the middle of the
21st century renewable sources of energy could account for three fifth of the world electricity
market and two fifth of the market for the conventional fuels [1]. Moreover making the transition
to renewable-intensive energy economy would provide environmental and other benefits.
This outlook for renewable energy reflects impressive technical gains made during the past
decade. Renewable energy system has benefited from developments in electronics, biotechnology, material science and other energy areas. For example fuel cells developed originally
for space programs have opened doors to the use of hydrogen as a nonpolluting fuel for
Such concerns have led to the creation of political movements pressing for changes in our
demand for the environment. These pressures have ranged from criticism of individual practices
(growth in the heavy vehicle portion of the passenger automobiles economy) to demands that the
overall structure and economic basis of societies be changed. Many pressures are focused on
energy, in terms of its uses, supply technologies and efficiencies. These concerns have often been
expressed in demands for less use, greater end use efficiencies, and more reliance on solar and
geothermal powered technologies rather than fossil and nuclear energy, which extract their fuel
from finite earth resources [1].
In the most extreme guise sustainable energy is that which can be provided without change in the
earth’s biosphere. However no such form of energy supply exists. All require some kind of land
use, with attended disruptions of the associated eco-system extractions, which can be disruptive
for nuclear ones. Ultimately all this extracted material re-enter the biosphere as wastes where
their sequestration practices are at least as important as their masses in determining the
accompanying ecological disruptions.
Energy production or utilization is often intertwined with consumption of other precious natural
resources, such as mineral, forest, water, food and land. Further the everyday use of energy can
damage human health and earth’s ecosystem over wide length and timescale. Yet in the
developed countries the availability of stable supplies of energy at manageable prices has
propelled has propelled economic development and enfranchised most of the populace with
mobility and a host of life style which were unimaginable a century ago. Development countries
are now dramatically expanding there to extend economic prosperity within their borders. At the
same time continued dominance of the world’s energy by fossil fuels is expected to be challenged
not by the red herring of scarcity but by concern that emission of fossil derived CO2 and fugitive
CH4 to the atmosphere will cause serious global climatic modifications.
For more sustainable energy future we need to develop a rich set of energy technology and
technology intensive policy options. These options include increased efficiency of energy
production and use, reduced consumption, a new generation of renewable energy technologies,
nuclear options that can retain public acceptance, and means to use fossil fuels in a climate
friendly way. If fossil fuel prices rise to include cost of carbon management, consumers may also
modify their consumption patterns. Environmental and ethical concerns may also contribute to
new attitudes about unconstrained economic growth patterns. Sustainability concepts provide a
framework to focus the evaluation of energy technology and policy options and their tradeoffs
and to guide the decision making on energy futures. The key to these concepts right is to develop
a solid understanding of the multi facet technological, geopolitical, sociological, and the
economic impacts of energy use and abuse.
Sustainability is necessary subjective because it reflects human values- the relative importance
stakeholders assign to the activity to be sustained, to the perceived benefits of the activity, and to
other values “tradeoffs” to sustain the activity in question. Many sustainability tradeoffs are an
inevitable result of tension between the benefits derived and the adverse consequences of the
activity that provides those benefits for instance the tension includes time horizons for reform i.e.
taking the best now versus preserving it from future generations, individual versus national verses
global interest and expansion of economic opportunity versus stewardship of resources [1].
1.2 Objective
The objective of this project is to provide information on the various types of renewable energy
resources available, with major focus on the wind energy. The project outlines what is renewable
and sustainable energy alone with brief discussion on the available resources such as Biomass,
Hydropower, Solar and major focus on Wind Energy and research review on “Energy Generation
in Tall Buildings”. The review ‘Energy Generation in Tall Buildings” is focused on latest concept
of producing energy by wind turbine augmented/mounted in tall buildings. The project mainly
summarizes how the resources are used in energy production, what has been done till now in that
field of development and what is the research which is going on in that field of development for
future. It also details the meaning of Sustainable and Renewable resources.
The research review on Energy Generation in Tall Building is the latest concept which got
recognition due to the energy losses in transmission from wind mills. The research review
discusses all the latest research in the field along with feasibility features design and complete
assessment of wind flow characteristics.
1.3 Methodology
To achieve the above mentioned objective the concept of Sustainable/Renewable energy
requirements is explained from the very basic fundamental as to what is energy, and the how is it
related to the first and second law of thermodynamics. Explanation of Sustainable Energy and
Renewable Energy and the relationship they share. A brief introduction to the resources such as
biomass, hydro-power and solar which provides us this Sustainable/Renewable energy. As Wind
Energy from the economic stand is the most deserving green supply option for more widespread
deployment is discussed at length along-with the wind resources, wind speed and the factors
attributed to technological aspects to see the advances of the sort that improved the rotor
efficiency to 30% over past two decades. Last but not the least a research review on Energy
Generation in Tall Building is discussed as to the elaborate the modern concept of wind energy.
Chapter 2
2.1 What is Sustainable Energy?
Energy is one of the essential needs of functioning society. With the increasing population of the
world which has tripled since 1930 there is more need for energy. The most available and
affordable sources of energy in today’s world are fossil fuels, efficiency improvements and new
technologies are part of the solution. Concerns have often been expressed in demands of less use,
greater end use efficiencies and more reliance on solar and geothermal powered technologies
rather than fossil and nuclear energy. In most extreme guise, sustainable energy is that which can
be provided without change to the earth’s biosphere.
Sustainable energy is the provision of energy that meets the needs of the present without
compromising the ability of future generations to meet their needs. Sustainable energy sources are
most often regarded as including all renewable sources, such as plant matter, solar power, wind
power, wave power, geothermal power and tidal power. It usually also includes technologies that
improve energy efficiency.
Energy technologies are being considered as sustainable if their net effects upon the biosphere
don’t significantly degrade its capabilities for supporting existing species in their current
abundance and diversity.
Energy efficiency and renewable energy are said to be the twin pillars of sustainable
energy. Some ways in which sustainable energy has been defined are [1]:
"Effectively, the provision of energy such that it meets the needs of the future without
compromising the ability of future generations to meet their own needs. ...Sustainable
Energy has two key components: renewable energy and energy efficiency."
"Dynamic harmony between equitable availability of energy-intensive goods and services
to all people and the preservation of the earth for future generations." And, "the solution
will lie in finding sustainable energy sources and more efficient means of converting and
utilizing energy."
"Any energy generation, efficiency & conservation source where: Resources are available
to enable massive scaling to become a significant portion of energy generation, long
term, preferably 100 years"
"Energy which is replenish able within a human lifetime and causes no long-term damage
to the environment."
2.2 Defining Energy- Scientific and Engineering Foundation
To understand the energy suitable for quantitative study for sustainability we must understand
the, energy
2.2.1 What is Energy?
Basically energy embodies animated and possible productive physical or mental activity
presumably by humans, animals, machines, nature, electricity etc. The first definition of energy
which came out in 1805 and was given by Thomas Young was “ability to do work” We think of
work as physical or mental exertion, to comprehend the concept of sustainable energy we need to
understand 4 key concepts namely energy, work, heat and power.
Observation has shown that a certain quantities remain constant during physical, chemical and
biological changes. This conserved or immutable quantity is energy. First of all let us understand
the meaning or conservation of energy which means we cannot get rid of the energy. Let us
divide the entire universe into specific regions with well-defined boundaries and other particular
characteristics. We define such a region into a system for example – (System 1 – combustion
chamber of an automobile engine and all the rest of the universe as System 2 which we define as
the surroundings). What is important here is not the absolute energy content of the universe or the
system or even set of systems but rather the change in energy content of particular system within
the universe and their interaction with their surroundings during the course of that change. In such
analysis it is important to know foe particular circumstances the total amount of energy a system
can give to or take from its surroundings and what fraction of that changed energy can be
converted to useful purpose such as the motion of an automobile or generation of electricity[1].
The first and second law of thermodynamics provides useful the theory to explain this concept
assuming that we have necessary data to implement the tool of thermodynamics for practical
calculation. It is important to know the how rapidly the energy can be generated within or
assimilated by or released from one or more systems example to this is how fast the chemical
energy of fuel be converted to kinetic energy of an automobile or thrust that propels a rocket. To
address these questions we need to rely on thermodynamics chemical kinematics, physical
transport and fluid mechanics to describe the rates of chemical reaction and the exchange of heat
material and the momentum within and between a single and multi-phase media. [4]
The position or motion of matter causes energy to exhibit diverse forms. Many of them are
rapidly observed such as (changes in pressure, temperature, volume, surface area and
electromagnetic properties). Thermodynamically heat and all forms of energy are related to
mechanical work such as raising and lowering of weights in a gravitational field.
A closed thermodynamic system is completely surrounded by movable boundaries permeable to
heat but no matter example of this is a vertical cylinder filled with gas and covered with piston
that can be moved up and down. By adding weights to the piston we can compress the gas and
store energy in analogy to pushing on a coiled spring. This addition of weights is a example of
work performed by the surroundings on our system. The resulting downward movement of the
piston is the work obtained by the system from its surroundings regardless of how meticulously
the weights were added. The amount of work taken by the system is always less than the work
done on the system by its surroundings by an amount of energy exactly equal to the heat gained
by the system which is the basic concept of second law of thermodynamics. Hence we can say
heat is a form of energy. In the example of the piston it arises from wasted of lost work. Thus we
can say that heat is a mode of energy transfer to or from a system by virtue of contact with
another system at higher or lower temperature. “Work is a defined as any mode of energy transfer
other than heat that changes the energy of the system”. Power is a energy change between two
systems it has units of energy per time and may represent a flow of work heat or both. [3]
Thus formal thermodynamic statement of law of conservation of energy is the First Law of
Thermodynamics. Thus mathematically for a closed system
∆E = Q + W
Where ∆E is the change in energy content of a system, Q is the amount of heat transferred to the
system from its surroundings and W is the amount of work done on the system by its
In many practical problems we come across problems where system is not closed but is a open
system where matter can flow inward outward or in both directions across the system boundaries.
∆E = ∆U + ∆Ep + ∆Ek = Q + Wsh – Wpv
This expression tells us that the change in the energy content E of a closed system can be divided
into chances in the internal energy U , potential energy Ep and kinetic energy Ek of the system .
The internal energy of the system can be changed by modifying the system temperature, changing
its phase (solid or liquid), by chemical reaction (ie by changing its molecular architecture) or
changing its atomic structure (ie by fragmenting (fission) or coalescing (fusion) nuclear particles.
The potential energy is changed by shifting the system location in the force field (gravitational ,
magnetic or electric).The kinetic energy of a system is varied by increasing or decreasing the
system velocity. The above equation disintegrates in to PV Work and SH Work.
Shaft work can be defined as any work other than PV work and it may involve rotation of the
shaft but may not include electrical work and other forms. PV work arises from the fact that every
system, however small, has some volume. As previously discussed applying weights on the
piston at the cylinder head we concluded that the change in system volume changes the system
potential energy. So any system at equilibrium (i e fixed temperature, pressure and composition)
has a constant volume. To attain that volume the system has to push its surroundings out of the
way to make room for itself. The work done by the system to reach the volume V by showing
back a pressure P is PV work and is given by the expression.
Wpv = ʃ PdV
It is often convenient to combine the systems internal energy U with the energy it has by virtue of
its volume V and pressure P. The resulting thermodynamic quantity is the enthalpy H which is
mathematically defined as
H = U + PV
Where P is the pressure in the system in some cases it may also
include the pressure of the surroundings (atmospheric pressure) but this is not always the case. As
with other forms of energy we are interested in the change in enthalpy when the system changes
from state 2.1 to state 2.2
∆H = H2 – H1 = ∆U + ∆(PV)
= (U2 + P2V2) – (U1 + P1V1)
Equation 2.1 and 2. 2 apply to closed and open system. If a
closed system undergoes a change in energy but remains at constant volume, there is no PV work
and the basic equation at constant volume for a closed system reduces to
∆U + ∆Ep + ∆Ek = Q + Ws
The second case is when pressure remains constant so the equation becomes
∆U + ∆Ep + ∆Ek = Q + Wsh – (P2V2 –P1V1)
(U2 + P2V2) – (U1 + P1V1) + ∆Ep + ∆Ek = Q +Wsh
∆H + ∆Ep + ∆Ek = Q + Wsh
For change in energy content of a closed system at constant pressure we can write the law of
energy conservation directly in terms of change in the system enthalpy, potential energy and
kinetic energy. Further to that is if the system is at rest and moves at a constant velocity or any
motion in a forced field which does not modify its potential energy which means the system
remains at the same height in the gravitational field than the enthalpy change accounts for all the
change in energy brought by addition and removal of shaft work.
2.3 What is Renewable Energy?
Renewable Energy- Any energy resource that is naturally regenerated over a short time scale and
derived directly from the sun (such as thermal, photochemical, and photoelectric), indirectly from
the sun (such as wind, hydropower, and photosynthetic energy stored in biomass), or from other
natural movements and mechanisms of the environment (such as geothermal and tidal energy).
Renewable energy does not include energy resources derived from fossil fuels, waste products
from fossil sources, or waste products from inorganic sources."
Renewable energy flows involve natural phenomena such as sunlight, wind, tides, plant growth,
and geothermal heat.
Renewable energy is derived from natural processes that are replenished constantly. In its various
forms, it derives directly from the sun, or from heat generated deep within the earth. Included in
the definition is electricity and heat generated from solar, wind, ocean, hydropower, biomass,
geothermal resources, and bio-fuels and hydrogen derived from renewable resources.
2.4 Kinds of Renewable Energy
Renewable energy is the energy which comes from the natural resources such as sunlight, wind,
rain tides and geothermal heat which are renewable. Classifying an energy form as “renewable”
encompasses a range of assumptions regarding the time scale. The implication is that the
renewable energy is available continuously without depleting and degrading. For example solar
energy is available for some time period every day virtually everywhere on the surface of the
earth. There is a natural 24 hour diurnal cycle, as well as seasonal vibration due to the changes in
the relative angle of our rotating earth tilted on its axis as it makes its yearly orbit around the sun.
Due to these effects are the daily fluctuations that result because of the cloud cover. Other
renewable types such as Biomass, Hydro Power and Wind Energy have analogous variations over
different time scale [6].
2.5 Bio Mass Energy
Biomass (plant material) is a renewable energy source because the energy it contains comes from
the sun. Through the process of photosynthesis, plants capture the sun's energy. When the plants
are burned, they release the sun's energy they contain. In this way, biomass functions as a sort of
natural battery for storing solar energy. As long as biomass is produced sustainable, with only as
much used as is grown, the battery will last indefinitely.
In general there are two main approaches to using plants for energy production: growing plants
specifically for energy use, and using the residues from plants that are used for other things. The
best approaches vary from region to region according to climate, soils and geography.
Biomass, a renewable energy source, is biological material from living, or recently living
organisms, such as wood, waste, (hydrogen) gas, and alcohol fuels. Biomass is commonly plant
matter grown to generate electricity or produce heat. In this sense, living biomass can also be
included, as plants can also generate electricity while still alive. The most conventional way in
which biomass is used however it, still relies on direct incineration. Industrial biomass can be
grown from numerous types of plants, including miscanthus, switch grass, hemp, corn, poplar,
willow, sorghum, sugarcane, and a variety of tree species, ranging from eucalyptus to oil palm
(palm oil). Biomass qualifies as a renewable energy resource because commercially meaningful
quantities are generated in time scale that is comparable to or less than typical time scale for
human use of resources.
Indeed biomass is the natural engine for conversion of solar energy to high energy content
products that are stored that can be stored, transported and used conveniently. To explain this
better plants grow by the process of photosynthesis in which sunlight transforms two naturally
abundant raw materials water and carbon did oxide , to carbohydrates and other complex organic
compounds of great natural and commercial value by photosynthesis which is as follows
6CO2 + 6H2O → C6H12O6 + 6O2 (with sunlight and catalyst)
The above equation represents the process of pumping energy “uphill” because carbon di oxide
and water have zero heating value and reside at one extreme of the energy spectrum. The energy
content comes from solar input , which plants convert to biomass energy with conversion
efficiencies of about 1-2%. The catalyst chlorophyll and other plant ingredients facilitate in the
2.5.1 Bio-Mass Relevance to Energy Production
There are thermal and biological routes can be converted into wide range of useful forms of
energy, including process heat, steam, motive power, liquid fuels and electricity as well as
synthesis gas (syngas) and fuel gases of various heating value. Syngas is a precursor to many
other useful products such as methanol, substitute natural gas, ammonia (for fertilizers) and other
liquid transportation fuel.
2.5.2 Conversion of Bio-Mass to Fuels
Thermal and Hydrothermal processes can also be used to convert various biomass
feedstock’s into gaseous and liquid fuels. Pyrolysis involves thermal treatment in the
absence of oxygen to gasify the biomass to carbon monoxide and hydrogen (syngas). The
mixture could be chemically converted to the liquid and gaseous fuels using suitable
catalyst. Alternatively food processing waste that have high level of fats and oils can be
easily hydrolyzed to produce low Btu gas and high bio-diesel grade liquid fuel.[7]
Figure 2.1 Gasification process [38]
2.5.3 Bioconversion
Bioconversion or biochemical processing refers to the direct or adaptive use of the chemistry of
living things to transform one substance to another. Fermentation is a bio-conversion process
known for centuries as a means to transform carbohydrates (sugar) to ethyl alcohol. It is a basis of
production of a host of beverages as well as ethanol for production of fuel. Bioconversion is
appealing as is it accepts feed materials that vary appreciable in chemical composition and
generates useful products moreover it enables the human understanding in biology and
biochemistry to be applied to the manufacture of fuels and other energy producing products such
as chemicals. This provides engineers and scientists with tools to devise processes that will run at
milder conditions synthesis chemically complex products from structurally simple starting
materials. The disadvantage of bioconversion is that the fuels manufactured are dramatically
slower rates than thermal processes and the need to separate the desired products from the dilute
mixtures. Slower rates translate to lower throughputs per unit time or the need for large process
vessels, resulting in higher capital costs. Moreover recovery from dilute mixtures consumes
energy and increase operating expense. [5]
2.5.4 Bio-Gas
Biogas typically refers to a gas produced by the biological breakdown of organic matter in the
absence of oxygen. Biogas originates from biogenic material and is a type of bio-fuel. Biogas is
produced by anaerobic digestion or fermentation of biodegradable materials such as biomass,
manure, sewage, municipal waste, green waste, and plant material and energy crops. This type of
biogas comprises primarily methane and carbon dioxide. Other types of gas generated by use of
biomass are wood gas, which is created by gasification of wood or other biomass. This type of
gas consists primarily of nitrogen, hydrogen, and carbon monoxide, with trace amounts of
Table 2.5 Schematic of overall process chemistry for production of biogas by
anaerobic digestion of wet bio mass..
promotes acids,
fermentation and hydrogen etc
alcohols, promotes
that CH4, CO2,
Even though CO2 has zero heating value (for combustion in air or oxygen) biogas is still a high
quality fuel gas because pure methane has HHV of 1000 Btu/SCF giving typical biogas a 500
2.5.5 Bio-Gas Grid Injection
Gas-grid injection is the injection of biogas into the methane grid (natural gas grid). Injections
includes biogas until the breakthrough of micro combined heat and power two-thirds of all the
energy produced by biogas power plants was lost (the heat), using the grid to transport the gas to
customers, the electricity and the heat can be used for on-site generation resulting in a reduction
of losses in the transportation of energy. Typical energy losses in natural gas transmission
systems range from 1–2%. The current energy losses on a large electrical system range from 5–
Figure 2.2 SCADA system for pipe lines [39]
The SCADA system at the Main Control Room receives all the field data and presents it to the
pipeline operator through a set of screens or Human Machine Interface, showing the operational
conditions of the pipeline. The operator can monitor the hydraulic conditions of the line, as well
as send operational commands (open/close valves, turn on/off compressors or pumps, change set
points, etc.) through the SCADA system to the field.
To optimize and secure the operation of these assets, some pipeline companies are using what is
called Advanced Pipeline Applications, which are software tools installed on top of the SCADA
system, that provide extended functionality to perform leak detection, leak location, batch
tracking (liquid lines), pig tracking, composition tracking, predictive modeling, look ahead
modeling, operator training and more
2.5.6 Environmental Issues of Bio-Mass Energy
There have been various researches in the field of environmental issues of biomass energy to
evaluate the assessment and implementation of biomass energy options. Environmental control
becomes more challenging with smaller installations such as residential wood stoves; new units
are equipped with catalytic convertors to reduce the adverse emissions. On the positive side
carefully managed growth and harvesting biomass for energy and other application can be used to
restore forests and other sensitive ecosystem. Thus we can say that utilization of biomass are
important in designing comprehensive strategies to reduce atmospheric buildup of greenhouse
gases while preserving options for supply and use of clean energy and energy intensive consumer
2.5.7 Summary
Biomass currently contributes about 3% of total US energy consumption. Since some biomass is
used commercially it represents a slightly higher percentage of total primary energy use. The
major use of combustion of various bio-fuels roughly 2 quads in the industrial and 0.5 quads in
the residential sector. Biomass has several potential benefits in electric power sector. It has low
Sox (sulphur oxide) emission, better co firing with coal or other fossil fuels for smooth supply
disruptions and facilitate gradual transitioning to reduce fossil dependency and the potential to be
CO2 neutral. In long term it may be possible to apply innovations in biotechnology to breed
plants that directly convert sunlight to directly gasoline and other premium products. To achieve
this goal methods are yet to be discovered that utilize the modern tools of bio-technology
including genomics, metabolic engineering and molecular level understanding of biocatalysts.
2.6 Hydro-Power
Hydropower is a renewable energy resource resulting from stored energy in water that flows
from a higher to a lower elevation under the influence of earth gravitational field. Hydropower or
water power is power that is derived from the force or energy of moving water, which may be
harnessed for useful purposes. Prior to the widespread availability of commercial electric power,
hydropower was used for irrigation, and operation of various machines, such as watermills, textile
machines, sawmills, dock cranes, and domestic lifts.
2.6.1 Basic Energy Conversion Principles
The primary energy source for hydropower is solar and gravitational. The overall process is tied
to the natural hydrologic cycle of evaporation and condensation in the earth atmosphere which
redistributes water from lower elevations (sea level at the oceans) to the higher elevations on the
land. The redistribution increases the potential energy of the water which then flows back to the
rivers and then to the oceans under the influence of gravity. Due to the rainfalls and the snow falls
the water stored or flowing at any times varies diurnally and seasonally. The change in potential
energy that occurs as the water makes its way back to the oceans provides an opportunity to
extract a portion of that energy in form of hydropower. Hydropower can be produced from any
change in water elevation but for practical purpose the tidal flows and ocean waves or currents
are classified differently.
In today’s hydropower application, changes in both potential and kinetic energy of the flowing
water are used to generate mechanical power to drive a generator to produce electric power.
Before 1900 direct mechanical power applications were prevalent in number of industries such as
weaving, fiber spinning and grain grinding.[8]
Types of Hydro-Power System
1. Impoundment which uses a natural or manmade dam for maintaining a water supply.
Figure 2.3 An impoundment hydro-power plant dams water in a reservoir [40].
The most common type of hydroelectric power plant is an impoundment facility. An
impoundment facility, typically a large hydropower system, uses a dam to store river water in a
reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn
activates a generator to produce electricity. The water may be released either to meet changing
electricity needs or to maintain a constant reservoir level.
2. Diversion or a run of river system that intercept a portion of natural flow of a river without
employing an artificial dam.
Figure 2.4 The Tazimina project in Alaska[40] This is an example of a diversion
hydropower plant. No dam was required
3. Pumped Storage is an application which depends on the demand of electric power. It is used when
the demand of electric power is low water is pumped from a source to storage reservoir located at
a higher elevation. During peak load period, the stored water is released, passing through a
hydraulic turbine to generate power.
Facilities range in size from large power plants that supply many consumers with electricity to
small and micro plants that individuals operate for their own energy needs or to sell power to
The main device used to capture hydro energy is the hydraulic turbine, which produces rotating
shaft work that powers the electric generator. Although there are many types of hydraulic
turbines, the basic approach is similar. They use the change in potential energy to increase the
fluid pressure and/or velocity and then deposit a portion of this hydraulic or kinetic energy on a
turbine bucket to rotate a centrally located shaft. Thus, as the fluid passes through the turbine the
change in its potential energy is continuously converted mechanical power. The step to electric
power is straightforward and is achieved by connecting the rotating shaft from the hydraulic
turbine to an electric generator. The hydro generator operates in similar manner to those used in
fossil-fired, gas turbine or steam or even wind power applications . Hydro machines tend to be
larger and slower in rotation speed than vapor or gas turbo expanders and may be oriented
vertically or horizontally [1].
The overall power that can be extracted from any device will depend on the available potential or
kinetic energy as reflected by magnitude of the total (static plus dynamic) hydraulic head and
conversion efficiency of the particular hydraulic turbine/ device – electric generator combination.
Power output can be represented by a simple formula.
Power = (total hydraulic head) x (volumetric flow rate) x (efficiency)
gZ + ½
The first term on the right hand sidecontains the static head
gZ and the dynamic head
contributions in units kg/m
height of the water head in “m”,
gravity 9.8 m/
. Q is the volumetric flow rate in units
is the density of water in kg/
. Z is the net
and g is the acceration due to
is the difference in square of the inlet and existing fluid velocity
across energy converter. A is the cross-sectional area of energy converter that is open to flow. For
the hydro installations that are impounment structure with the static head providing the energy,
the dynamic head given by ½
term is effectively zero. For a low head run of river system
the dynamic head could be comparable to or greater than the static head,
The efficiency of the conversion process is represented by term
≤ 1 which captures the losses
that occur due to friction and other disspatative effects . The latest state of art technology turbine
generator efficiencies can approch 0.9 for large flow machines
Conversion Equipment and Civil Engineering Operations
The natural condition that exist at site, including surface topography, river flows, water quality
and annual rainfall and snow fall determines the paticular design for a hydropower installation.
When suiatble hydraulic heads are not present , dams are construction across the rivers to store
water and create the hydraulic head needed to drive the turbo machinery. Dams are typically
designed to last for 50 to 100 years and, as such, are constructed of durable materials such as
reinforced concrete, earth and crushed rock. There are several design approches that are used for
concrete dams, including solid and hallow, gravity and arch geometries. On life cycles basis the
CO2 emmissions associated with the production of concrete for dams should be considered, many
of the largest disasters associated with the energy system and their infrastructure has been a result
of dam failure. Due to improved construction methods and materials and new technology for
diagnostic testing the realiablity and intergerity of dam structure has improved drasstically [1].
In addition to the actual dam strcture there are number of other major factors of design to be taken
into consideration. Foe example turbine inlet manifold or penstock which usually include screens
to keep debris and fish out from entering the turbine and the discharge or tailrace system must be
designed to maintain the hydraulic head and minimize the effects of sedimentation and silt
Figure 2.5 The characteristic components of hydroelectric plant [40]
2.6.5 Potential for Growth
Although hydropower is currently the largest and most important producer of electricity from
renewable energy source with over 600Gwe of capacity and 2600TWhr annually its future role is
less certain in long term. While the potential for adding additional hydropower stations
worldwide is substantial in terms of availability and reasonable capital investment but the other
factors like environmental related concerns related with mega-scale projects that involve dams
and their subsequent land inundation pose subsequent barriers to deployment and growth of
hydropower as a renewable energy resource.
Environmental concerns can be addressed by accelerating the level of scientific attention being
directed at by achieving quantitative understanding the impacts and benefits of hydro and to
develop me technologies that will mitigate these effects. More sustainable opportunities can be
achieved from hydropower system but one must keep in mind the low level of R&D support for
such undertakings.
Advance technology needs can be divided in to 2 categories a) near term improvements and
improvements for the existing hydro stations to address varies issue such as fish migration and
oxygen depletion issues and the b) long term innovations for utilizing low head and run of water
resources in an environmentally and economically sustainable manner.[9]
Near term improvements- Many people have this perception that as hydropower is a mature
technology with sustainable capital investment in place it cannot be influenced by modern
technology but this is not true, the problems of fish migration and oxygen depletion are being
dealt with number of new technological approaches such as understanding the reason for cause of
such high level of mortality rate of young fish, followed by the turbine design which is more fish
friendly. Various research labs have been working on improving hydro technology for a few
years and the research has led to better understanding of what causes fish morality in hydro
turbines and has generated a lot of innovations that would reduce the problem.
Advanced modeling methods employing computational fluid dynamics have identified location
and conditions inside existing turbines that are problematic to successful fish migration. The main
injury to the fish is due to rapid pressure changes, impingement and abrasion of turbine blades
and damage induces by cavitation’s. One optimistic approach that causes both CFD modeling and
experimental validation methods with electronically tagged fish has resulted in proposed design
of internal turbine bladding that could be retrofitted in Fransis and Kaplan units to reduce
morality. Another important aspect of these proposed fish friendly retrofits is that the conversion
efficiency would be preserved or even increased. Another concept of designing a new turbine is
worked on where the turbine would use a centrifugal fuel concept that would facilitate migration
of small fish and operate at efficiencies which is approx. 90%.
Oxygen depletion in the water discharge from hydro turbines also is a problem in installations.
Aerating weirs and turbine runners are being developed by scientist to increase oxygen content.
Development is being carried out on smaller dams with existing low heads that increase power
output with little environmental damage.
LONG TERM INNOVATIONS- If the ultra-low head (1 m) or run-of-river energy converters
concepts could be developed economically then there could have been large jump in potential of
hydro power which would fulfill if not all but desirable sustainability attributes of energy system.
These concepts would allow for fish migration, maintain the natural flow and flooding cycles of
river by eliminating or minimizing impoundment and keep water quality at high levels.
Matrix turbines are specially designed for ultra-low heads turbines are being considered by a
number of groups. Many researches are going on to develop several low cost alternatives such as
slow rpm turbines made of composite plastics that operate efficiently with ultra-low heads (less
than 1 m) and can capture both the potential and kinetic energy of flowing water in rivers or tidal
basins. Another development is design of high rpm, air driven Fransis turbine that are powered by
hydraulically activated chambers that compress air using river flows and using low hydraulic
heads (1-3m).
Schneider and associates have taken a different approach in which a river or tidal basin’s hydro
energy is captured directly as kinetic energy ½
using a hydro-engine that consist of a
horizontal cascade of foils that are mechaniically connected to the drive mechanism by looping
around two axles resembling a venetian blind structure. Schneider hydro-engine utilizes natural
river flows enhanced by two hydraulic heads (less than 3m) while keeping fluid pressure changes
and velocity and accelration levels within safe ranges for fish passage. Some other renouned
companies are also working on ultra low head machines employing matrix turbines and a desired
power wheel concept. Although initial testing of these concepts have been successful but
durability, validated performance including efficiency and to ensure reasonable cost remians to be
done before these advanced machines will be deployed commercially.[10]
2.7 Solar Energy
Thought-out the human history, solar energy has been utilized for domestic use in heating and
cooking. . In general, its ubiquitous nature and ability to be effectively used over a range of scales
makes solar the popular choice among popular renewable enthusiast. The Sun’s energy incident
on the earth is the intrinsic source for many forms of renewable energy (including wind, ocean
thermal, and bio energy) and over a long time scales all of the fossil energy.
Solar radiation, along with secondary solar-powered resources such as wind and wave power,
hydroelectricity and biomass, account for most of the available renewable energy on earth. Only a
minuscule fraction of the available solar energy is used.
Solar technologies are broadly characterized as either passive solar or active solar depending on
the way they capture, convert and distribute solar energy. Active solar techniques include the use
of photovoltaic panels and solar thermal collectors to harness the energy. Passive solar techniques
include orienting a building to the Sun, selecting materials with favorable thermal mass or light
dispersing properties, and designing spaces that naturally circulate air. [4]
The Sun’s energy incident on the earth is the intrinsic source for many forms of renewable energy
(including wind, ocean thermal, and bio energy) and over a long time scales all of the fossil
2.7.1 Resource Assessment
As we all appreciates the variability of suns intensity during the day as the sun passes overhead
and as its radiations encounters through the clouds and reaches the earth surface. Seasonal
variations are then superimposed on the top of these diurnal changes. Fortunately the daily and
seasonal movements of the sun are both predictable and known in precise mathematical form.
Changes in weather are less regular, but can be averaged from estimating the solar potential in
different regions. The intermittent and variable characteristics of the solar energy must be
reckoned with to make effective use of it as a source of thermal and electrical energy. Passive and
active storage is always coupled to the solar energy system.
The intrinsic source of the sun’s energy is a direct result of thermonuclear fusion of hydrogen
nuclei to form helium, which occurs at phenomenally high rate of about 4000000000 Kg of mass
conversion per sec. Solar fusion reaction results in temperature of about 6000 degree Celsius at
the sun’s surface, induces a large solar radiative flux that travels 93 million miles to the earth.
The distribution of solar energy flux that intercept the earth is a strong function of wavelength of
incident light, as the variation in the absorption and reflection characteristics of different
molecules contained in the earth’s atmosphere, the distribution changes from the top of the
atmosphere to the earth surface. Most of the short wavelength ultraviolet is absorbed by the
oxygen (O2), ozone (O3) and nitrogen (N2) in the upper atmosphere while water (H2O) and
carbon-mono-oxide (CO2) captures a good portion of the longer wavelength radiation in the
visible and infrared region.
Figure 2.6 Schematic of Incoming solar energy [41]
About half of the incoming solar energy reaches the Earth Surface
The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper
atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds,
oceans and land masses. The spectrum of solar light at the Earth’s surface is mostly spread across
the visible and near-infrared ranges with a small part in the near-ultraviolet.
Earth’s land surface, oceans and atmosphere absorb solar radiation, and this raises their
temperature. Warm air containing evaporated water from the oceans rises, causing atmospheric
circulation or convection. When the air reaches a high altitude, where the temperature is low,
water vapor condenses into clouds, which rain onto the Earth’s surface, completing the water
cycle. The latent heat of water condensation amplifies convection, producing atmospheric
phenomena such as wind, cyclones and anti-cyclones. Sunlight absorbed by the oceans and land
masses keeps the surface at an average temperature of 14 °C. By photosynthesis green plants
convert solar energy into chemical energy, which produces food, wood and the biomass from
which fossil fuels are derived.
Table 2.8 Yearly solar fluxes and Human energy Consumption [4]
Yearly Solar fluxes & Human Energy Consumption
3,850,000 EJ
2,250 EJ
3,000 EJ
Primary energy use (2005)
487 EJ
Electricity (2005)
56.7 EJ
The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately
3,850,000 (EJ) per year. In 2002, this was more energy in one hour than the world used in one
year. Photosynthesis captures approximately 3,000 EJ per year in biomass. The amount of solar
energy reaching the surface of the planet is so vast that in one year it is about twice as much as
will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and
mined uranium combined.
In mathematical terms the capture efficiency (η solar) of the solar collector can be represented as
η solar = useful energy recovered/ total solar flux incident on the collector x 100%
Recovered energy can be in the form of thermal energy (heat) or electrical energy (current x
voltage). In thermal energy recovery applications, efficiencies can be high ranging from 30-60%
or more whereas in photovoltaic efficiencies are considerably low 8-15%.
An operating variable that can influence the capture efficiency of the solar collector is the
pointing error ψ which can be represented as
Ψ = pointing error = € - β in degrees
And α = collector tilt relative to the latitude = β – φ
β = tilt angle of the collector in degrees from the horizontal
Φ = latitude in degrees, € = pointing angle of the sun, θ = altitude angle in degrees
ω = azimuth in degrees
The altitude angle θ and azimuth ω are defined as the angle of the sun above the horizon and the
angle from true south, respectively. The hourly variation of the sun’s position are usually
represented by the azimuth or hour angle, ω that varies about 15 degrees per hour and ranges
from 0 to a maximum value that changes depending on the time of the year. The value of ω is
zero at solar noon when the sun reaches its highest position in the sky for its specific location and
reaches its maximum value when the sun sets below the horizon. The maximum value is less than
90 degrees in fall and winter months and greater than 90 during spring and summer months.
Seasonal variations are usually given as a function of declination angle δ, which provides a
qualitative measure of tilted earth’s position relative to the sun as the earth moves around the sun
annually. Value of δ is zero at autumn and vernal equinoxes September 21 and March 21
respectively and in northern latitude +23.5 degrees and at summer solstice on june21 and -23.5
degrees at winter solstice on December 21.
Figure 2.7 Sun’s Position Vector[42]
The sun’s position vector relative to the earth-center frame, in the earthcenter frame, CM, CE and CP represent three orthogonal axes from the
center of the earth pointing towards meridian, east and Polaris,
Figure 2.8 Collector reference frame[42]
In the collector-center frame, the origin O is defined at the center of the collector
surface and it coincides with the origin of earth-surface frame. OV is defined as vertical axis
in this coordinate system and it is parallel with first rotational axis of the solar collector.
Meanwhile, OR is named as reference axis and the third orthogonal axis, OH, is named as
horizontal axis. The OR and OH axes form the level plane where the collector surface is
driven relative to this plane. The simplest structure of solar collector that can be driven in
two rotational axes: the first rotational axis that is parallel with OV and the second rotational
axis that is known as EE′ dotted line (it can rotate around the first axis during the sun tracking
but must always remain perpendicular with the first axis). From the diagram, θ is
the amount of rotational angle about EE′ axis measured from OV axis, whereas β is the
amount of rotational angle about OV axis measured from OR axis. Furthermore, α is solar
altitude angle in the collector-center frame, which is expressed as π/2 - θ
2.7.2 Passive and Active Solar Thermal Energy for the Buildings
About one third of the energy we consume is used to heat, cool and humidify/dehumidify the
building we live and work in. In developed countries and mega cities worldwide people send 80%
of their time inside such buildings. As such indoor air quality can be significant health issue that
is strongly linked to the energy use. The amount and type of energy required to condition
buildings depends on the dependent on the climatic conditions of the region where they are
located. Solar thermal energy utilization in buildings usually involves one or more of the
following approaches:
1. Passive thermal gain and reuse
2. Active capture of solar heat using solar collectors
3. Direct and indirect day lighting.
The first two require the same type of thermal energy storage and a means for distributing the
thermal energy. All require in corporation in the design of the building. In most instances both
direct and diffuse solar radiation are collected on a flat surface exposed to the sun radiation where
the absorber area is equal to the collector area. In some cases a concentrating approach may be
used to achieve higher storage temperatures where the collector is larger than the absorber area.
In addition to capturing a portion of solar spectrum for use, proper building design should strive
for high performance by maximizing energy efficiency. This approach usually leads to increased
building insulation (higher R values, reduced air infiltration and leakage) in the walls floor and
roof and better window placements and materials. There are tradeoffs with the given the cost
associated with the reducing heat losses or heat gains that must be balanced against the benefits of
having lower energy demands. For instance indoor air quality can be compromised in a wellinsulated building, with air infiltration rates. In these cases properly designed system for air
exchange with energy recovery are needed. Nonetheless it is safe to assume that a building that
has a passive or active solar thermal system is also designed for high energy efficiency.
Passive System
The basic approach with passive system is to utilize the building structure to capture solar heat
and transmit light, where appropriate, to reduce artificial lighting needs. The natural characteristic
of certain building materials, such as stone, cement or concrete and adobe clay are ideally suited
to capture and store heat. In the daily cycle, heat is collected during the day and transferred by
natural convection of air or water to condition the inside of the building over a period of time that
extends into the evening.
Location and orientation relative to the sun’s movement is important in determining exactly what
type of passive design will work best. In addition the type of building gives different challenges.
For instance the windowless or closed commercial office building that are loaded with people,
lighting and fixtures and their computer workstation represent a discrete set of small heat sources
that introduce a substantial cooling load even in winter months. Residential units with a lower
density of people greater opportunity for natural ventilation and day lighting are better suited for
classical passive design.
Adobe and Trombe walls represent popular options for certain locations. These options take
advantage of relatively high heat capacity and lower thermal diffusivity of the solid stone and
masonry material to store and transfer heat to the inside of the building. Normally the wall is
placed on the south facing side of the building and may be placed and may be coated with black
or darkened surface to increase the solar absorptivity and covered with glass on the side facing
outward with an air space between it and the solid wall. To reduce heat losses the back and side
surface may be insulated. A roof overhanging is often used to limit the amount of solar gain
during the hotter summer months. Most recently the variation of Trombe wall concept has made
them more flexible and adaptable to the wider variety of building applications. The transpiring
wall is one such idea which was introduces by scientists at National Renewable Energy
Laboratory, transpiring wall has been effective for both passive heating and cooling applications.
Figure 2.9 Modified Trombe Wall [43]
Hot Air
Figure 2.10 Transpired Collector [43]
Active System
Active solar thermal system is usually applied in residences and commercial buildings for
providing hot water, heating and air conditioning. What makes them different from passive
system is that they employ collectors that capture solar energy and rapidly transfer thermal energy
to circulating working fluid which can be used immediately in the dwelling or stored for later use.
Control systems are almost always employed to turn circulating pumps on and off and to divert
fluid to storage vessel when collector temperature reaches specified levels. Active system has
been in operation for over 80 years mostly employed in homes. Here we see a flat plate collector
that consists of a selectively coated metal plate with attached channels. A circulating fluid is
heated as it is pumped through the channels on the collector and then passed through coil
contained inside of a hot water storage tank where it transfer heat to the water in a tank, an
antifreeze mixture (typically a propylene glycol- water mixture) is used as the working fluid to
avoid freezing and subsequent damage to the collector system during the winter. Alternatively
water could be employed with a gravity drain back loop to eliminate concerns about freezing.
The most flat collectors are modules that can be mounted on the roof or can be build in the roof
structure. Each one contains a metal receiver that has been coated with special material to
produce a selective surface that has a high absorbtivity for solar energy in the visible and
ultraviolet region at shorter wavelength and low emissivity in longer wavelength, thermal infrared
region. This selectivity lowers the radiative heat loss from collector surface. As many materials
have been used as selective surface a favored material is black chrome oxide Cr2O3. To reduce
the heat losses from the collector, insulation surrounds the sides and back, and one or two
transparent glass or plastic plates are positioned on the top side of the collector with an air gap of
1 cm or more. The choice of a transparent cover material is based on a number of factors,
including its ability to transmit solar energy with small losses, durability to weather and cost.
Tempered glass is often selected for solar hot water heaters given its low cost and durability even
though it is opaque to radiation in the infrared region. An electronic control unit regulates the
flow of working fluid and operates in response to a difference in temperature between the
measured storage tank temperature and temperature of the collector surface on the roof.
Figure 2.11 Solar Hot Water System [41]
Although the reliability of the commercial solar hot waters heater was not universally good when
they were extensively deployed in the 1970’s and early as 1980’s, today’s system are very robust,
carrying warranties of 20+ years. Beside hot water heating solar flat plate system can be used for
space heating and cooling. In heating applications air is often circulated through channels in the
panel to capture the solar energy. It can then be used immediately for heating rooms by being
forced through a set of room by room registers to distribute the heat or stored in a crushed rocking
bed for later night time use. Alternatively water can be used as a heat transfer fluid in a similar
manner; only difference is that the set of room radiators would be used to distribute the heat. Air
has an advantage over water in that it does not freeze and/or cause corrosion problems, but it has
lower heat capacity and higher parasitic losses in distribution and storage system.
For cooling, both vapor compression refrigeration and absorption cycle can be used. In vapor
compression cycle, solar energy can be used as heat source to power a turbine in a closed loop
Rankine cycle, which in turns drives the compressor of the refrigeration cycle. A disadvantage of
these cycles is that they need to be fairly large to have reasonable operating efficiencies. For both
large and scale cooling loads a lithium bromide (LiBr) absorption cycle can be employed. Here
solar thermal energy at temperatures 70-80 degrees is used to evaporate water from the low
pressure LiBr solution in the generator section of the cycle. Heat is rejected from the system as
the water is condensed while cooling occurs in the evaporator section, again operated under
vacuum condition at about 40 degrees. The cycle is completed as the LiBr solution reabsorbs the
water vapor to complete the cycle.
It is to estimate the cost for passive solar system because they often become a integral part of the
building structure. For example partial cost offsets results when a passive solar greenhouse,
Trombe or transpiring wall is incorporated into a design of a new building. In addition
guaranteeing trouble free performance or other desirable attributes, such as enhanced day lighting
is as importance as reducing heating costs in determining whether passive system are deployed.
Seasonal storage of captured solar energy would enhance its value for space heating
Several innovative concepts have been proposed for using the earth sub-surface in form of water
contained in a confined aquifer or as heat rock. While both of these concepts are technically
possible there are drawbacks. For example additional cost is incurred to put such storage system
in place. Give these limitations and constraints deployment of existing passive and active solar
heating and cooling technology for building has been severely limited by the high front end
capital cost that are incurred when the building is constructed. The potentially lower net life-cycle
cost for the solar system cannot be realized. The traditional low cost of the conventional fuels and
base load electricity
with the exception of occasional price shocks is often the single most
important factor that deflates interest in investing in energy and solar energy capture.
There are several ways of making solar heating system more attractive. One is to achieve lower
unit cost by improving and scaling up production levels and the other is by introducing policy
incentives. The high capital cost of solar hot water system is partly driven by limited production
to the million units per year in US which would have substantial impact-reducing the current cost
for these systems by 30-40% or more to levels of $2500-$5000 or less, depending on the size of
the system. Introducing incentives to home owners of commercial operators to install a solar
system would also have an impact. Such incentives could be in form of tax credits or lower
mortgage rates.
2.7.3 Recent Patents of Solar Energy Collectors
The first patent included in this review concerns an alterable solar collector. A solar collector of a
solar water heating system comprises a conduit formed by two circular cross-sectioned manifolds
running parallel with each other. The manifolds are able to rotate vertically about the central line
of the manifolds. The manifolds have
(I). a number of T-shaped members
(II). a number of seal means connecting the T-shaped members together in a watertight way
(III). at least one heat insulating means covering outside of the T-shaped members and the seal
means, and
(IV). at least one cover means supporting and protecting the heat insulating means, as well as the
T – shaped members and the seal means inside the heat insulating means.
The solar collector also comprises a number of solar absorbers perpendicularly positioned along
the conduit and connected to the side holes of the T-shaped members of the manifolds of the
conduit, at least one bottom support means at each side of the conduit holding the low ends of the
solar absorbers to keep them in position and at least two connection means riding on a roof on
which the solar collector is installed to connect the bottom support means to the manifolds.
Another patent in stationary collectors concern a heliothermic flat plate collector module. The
heliothermic flat plate collector module comprises a sheet metal panel, whose rear face lies
opposite to the face exposed to solar radiation. It is covered by a bonded grid type arrangement of
capillary tubes, positioned at a distance one below the other, permitting the passage of a liquid
medium, in addition to connections for admitting and evacuating the liquid to and from the gridtype arrangement. The capillary tubes are attached to the rear face of the sheet metal panel by
means of a coating that encases the capillary tubes, or an accumulation of thermally sprayed
metal particles, which adhere to the rear face of the sheet metal panel and to the surface of the
capillary tubes.
The first invention relating to concentrating collectors concerns a parabolic trough collector,
whose supporting structure is configured as a dual-shell torsion box, which increases the rigidity
of the collector. The objective of a second patent in this area is to provide a tubular cover for a
parabolic trough collector for helping accumulation of sun radiation more than a conventional
receiver tube and having an uptake factor of the best capability. In the case that the absorption
tube is provided in the tubular cover, the tubular cover of the parabolic trough collector has four
structure elements at which sunlight is focused, at the absorption tube provided in the tubular
cover. Another invention on parabolic trough collectors concerns a collector which includes a
single-axis parabolic mirror and a receiver tube arranged at the focal point (F) of the parabolic
mirror. The receiver tube includes an absorber tube and an outer tubular glass jacket around it. To
compensate for focusing errors in the parabolic collector and thus to reduce associated geometric
optical losses, the tubular jacket is provided by four structural elements, which focus the sunlight
on the absorber tube arranged in the tubular jacket by reflection and/or refraction. The receiver
tube is preferably arranged relative to the parabolic mirror, so that its center is displaced from the
focal point (F) in the direction of the mirror by a distance equal to half the spacing between the
tubular jacket and the absorber tube.
In another patent, the parabolic trough collector has a receiver formed by several single absorber
tubes. The single absorber tubes are supported by absorber tube supports and surrounded by a
glass tube. Because of different expansion behavior of the absorber tube and the glass tube during
collector operation flexible unions are foreseen between absorber tube and glass tube. In order to
use the radiation coming to the non-active-area where the absorber tube supports and the flexible
unions are located, a mirror collar is installed. The mirror collar is able to reflect the solar
radiation, which is coming from different directions, to the active absorber part of the single
absorber tubes even when the sun incident angle is changing. A high concentration central
receiver system and a method which provides improved reflectors and a unique heat removal
system is presented. The central receiver has a number of interconnected reflectors coupled to a
tower structure at a predetermined height above ground for reflecting solar radiation. A number
of concentrators are disposed between the reflectors and the ground such that the concentrators
receive reflective solar radiation from the reflectors. The central receiver system further includes
a heat removal system for removing heat from the reflectors and an area immediately adjacent to
the concentrators. Each reflectors use mirror, a facet and an adhesive is disposed between the
mirror and the facet such that the mirror is fixed to the facet under a comprehensive stress[1].
2.7.4 Recent Patents of Tracking Mechanism
As we know that the tracking mechanism are required in concentrating mechanism for following
the trajectory of the sun in the sky with certain accuracy. In fact, the concentrating collector
performance depends on the effectiveness of the tracking mechanism as any large deviations will
focus solar radiation away from the receiver.
The first invention in this category, concerns a solar tracking mechanism utilized in connection
with a solar energy collection system. The collection system includes a light reflective shell
shaped to focus solar radiation on a radiation absorbing segment of a tube which carries a heat
transfer fluid. The shell is pivotally mounted on a support frame. An actuator mounted between
the support frame and the shell is able to rotate the shell. A solar sensor is mounted deep within a
sighting tube which is fixed to the shell such that a line of sight through the sighting tube is at
least parallel to the optical axis of the shell. The solar sensor generates a sensor signal which is
used as a control input to an actuator control system. End limit switches generate a limit stop
signals when the shell reaches maximum angular positions. The actuator control system generates
fluid flows to the actuator based on the solar sensor signal and the limit stop signals. The method
of tracking the sun includes the provision of a solar cell array, which activates the solar collection
system when solar radiation illuminating the array exceeds a predetermined threshold. This
provides a solar sensor shielded from the solar radiation except for direct, aligned radiation,
pivotally rotating the shell westward based upon the solar sensor signal, stopping the shell at a
maximum angular positions, and rotating the shell westward if the shell does not reach the
maximum westward angular orientation during a predetermined daylight time period. The solar
energy collection system may be further configured to include a bisected shell, which is hinged
together. The shell halves can be collapsed onto each other thereby protecting the light reflective
surface and the radiation absorbing segment of the tube carrying heat transfer fluid.
In another invention, the solar tracking mechanism is employed in relation with a solar energy
captivation system. The captivation system includes a light reflective cover, with a shape to focus
solar radiation over a segment of radiation absorption from a tube that carries a heat transfer fluid.
The cover is mounted by pivot over a support structure. An actuator mounted between the support
structure and the cover is able to rotate around the cover. A solar sensor is mounted inside a visor
tube fixed to the cover, so that the visual line through the visor tube is at least parallel to the
optical axis of the cover. The solar sensor generates a sensor signal used as a control inlet for a
control system of the actuator. Limiting switches generate end thrust block signals when the
cover reaches maximum angular positions. The actuator control system generates fluid flows in
the actuator according to the solar sensor signal and to the end thrust block signals. The sun
tracking method includes also an arrangement of solar cells, actuating the solar captivation
system when the solar radiation that illuminates the arrangement surpasses a predetermined
threshold value. In this way the solar sensor is protected against solar radiation, except from
direct radiation, aligned radiation, turning with pivot the cover to the west, according to the signal
of the solar sensor, stopping the cover in maximum angular positions and turning the cover to the
west if the cover does not reach the maximum angular orientation to the west, during a
predetermined period of daylight. The solar energy captivation can also be configured to include
a bisected cover joined by means of hinges. The cover halves can be folded one against the other
to protect the light reflective surface and the radiation absorption segment of the tube that carries
the heat transfer fluid.
2.7.5 Conclusion
It is evident from the above discussion that a large variety of collectors have been developed over
the period of time, which can be used in variety of applications depending from the temperature
variation. Some areas in the field of solar energy are fully developed and needs less attention like
the flat plate collectors and parabolic collectors but still a lot of research is required in this field to
make it one of the major source of energy production. The major focus of the research should be
application based focusing on the particular application like pharmaceutical application where
solar reforming of low hydro-carbon fuels such as LPG and natural gas into syngas which can be
used in gas turbines for better efficiency and manufacture of solar aluminum which is a very
energy intensive process, moreover the production of solar zinc which is a very valuable
commodities. Solar photochemical process is a detoxification technology that can provide
environmental waste management industry with a powerful tool to destroy waste with clean
energy from the sun. The approach of research is more of application based rather than general
based application. The research on new materials for reflectors and heat absorption is important
for development in this field. The objective is to create materials with high reflectivity
approaching unity and high heat absorption and low emittance as to enhance the thermal behavior
of solar energy collectors. The ongoing research is the use of nanotechnology in various areas of
material science for more efficient solar conversion by employing Nano-structured collectors on
the solar energy collectors.
Chapter 3
3.1 What is Wind Energy?
Wind power is the conversion of wind energy into a useful form of energy, such as using wind
turbines to make electricity, wind mills for mechanical power, wind pumps for pumping water or
drainage, or sails to propel ships. Humans have been using wind power for at least 5,500 years to
propel sailboats and sailing ships. Windmills have been used for irrigation pumping and for
milling grain since the 7th century AD in what is now Afghanistan, India, Iran and Pakistan.
In the United States, the development of the "water-pumping windmill" was the major factor in
allowing the farming and ranching of vast areas otherwise devoid of readily accessible water.
Wind pumps contributed to the expansion of rail transport systems throughout the world, by
pumping water from water wells for the steam locomotives. The multi-bladed wind turbine atop a
lattice tower made of wood or steel was, for many years, a fixture of the landscape throughout
rural America. When fitted with generators and battery banks, small wind machines provided
electricity to isolated farms.
The first commercial machine of this genre in the US was constructed in Vermont starting in
1939 which had a rotor diameter of 53 m and full power rating of 1.25 megawatts of electric
wartime exigencies and cheaper alternatives led to its demise in 1945. However the oil supply
crisis of 1973 ignited widespread interest in and commitment to the wind turbines as a potential
major component of the future electric energy generation system.
The Earth is unevenly heated by the sun, such that the poles receive less energy from the sun than
the equator; along with this, dry land heats up (and cools down) more quickly than the seas do.
The differential heating drives a global atmospheric convection system reaching from the Earth's
surface to the stratosphere which acts as a virtual ceiling. Most of the energy stored in these wind
movements can be found at high altitudes where continuous wind speeds of over 160 km/h
(99 mph) occur. Eventually, the wind energy is converted through friction into diffuse heat
throughout the Earth's surface and the atmosphere [1].
The total amount of economically extractable power available from the wind is considerably
more than present human power use from all sources. The most comprehensive study as of 2005
found the potential of wind power on land and near-shore to be 72 TW, equivalent to 54,000
MToE (million tons of oil equivalents) per year, or over five times the world's current energy use
in all forms. The potential takes into account only locations with mean annual wind speeds ≥
6.9 m/s at 80 m. The study assumes six 1.5 megawatt, 77 m diameter turbines per square
kilometer on roughly 13% of the total global land area (though that land would also be available
for other compatible uses such as farming). The authors acknowledge that many practical barriers
would need to be overcome to reach this theoretical capacity.
3.2 Wind Resources
As winds are produces by uneven solar heating of the earth’s land and sea surface. Thus they are
a form of solar energy. On average the ratio of total wind power to incident solar power is on the
order of 2 percent, reflecting a balance between input and dissipation by turbulence and drag on
the surface. Only a small fraction is close enough to earth surface to be practically accessible and
only certain locations have winds that are sufficiently strong and steady to be attractive for
exploitation. The figure below shows the wind resource map for the US as well as the potential in
the whole world.
The overview from the map shows that the best wind fields are generally near the coast and there
is commonly an overall decline in average quality in central regions of large continental land
masses. However the great plains of the US Midwest has extensive resources. If fully exploited
those in North Dakota and South Dakota alone can be used to generate enough electricity to equal
half of current US consumption and the totality of the US landscape could produce several times
today’s needs.
While the potential resources are immense there are several constraints on use that limit near term
exploitation to perhaps 20% or so of total electric grid capacity [1].
1. Winds vary in speed, hence incident energy flux, during the day and from season to
season and not necessarily in concert with demand for electricity.
2. This non-dispatch able nature limits the portion of wind power in a utility generator mix,
with provision for spinning inexpensive way, at present to store energy for future use.
3. Other than the fortuitous proximity of pumped storage hydro installation there is no
sufficiently inexpensive way, at present to store energy for future use.
4. The best wind fields may not be in reasonable proximity to large population centers,
which necessitates the construction of expensive high-voltage transmission system and
results in large line losses of the input energy.
Figure 3.1 Wind Resources and Transmission Lines. Map of available wind power for the
United States. Color codes indicate wind power density Class [44]
As with other solar-electric technology, advances in storage technologies, whether centralized or
dispersed, could greatly expand the prospects for market penetration by wind turbine generators.
Compressed air energy storage, superconducting magnets, super capacitors, advanced batteries and
flywheels are potentials candidates. In addition connecting spatially dispersed winds plants, together with
an enhanced transmission system, could expand wind expand the wind generated contribution beyond
20%. The quality of wind is sufficiently variable and localized that accurate long term site survey is
requisite to deployment. As soon as we see power in moving air is proportional to cube of velocity
moreover velocity spectra can vary to the extent that for the same average velocity, spectrum averaged
power can differ by as much as 50%.
Wind Speed- The power per unit area transported by a fluid system is proportional to the cube of
the fluid velocity. The strength of wind varies, and an average value for a given location does not
alone indicate the amount of energy a wind turbine could produce there. To assess the frequency
of wind speeds at a particular location, a probability distribution function is often fit to the
observed data. Different locations will have different wind speed distributions. The Weibull
model closely mirrors the actual distribution of hourly wind speeds at many locations. The
Weibull factor is often close to 2 and therefore a Rayleigh distribution can be used as a less
accurate, but simpler model.
Because so much power is generated by higher wind speed, much of the energy comes in short
bursts. The 2002 Lee Ranch sample is telling; half of the energy available arrived in just 15% of
the operating time. The consequence is that wind energy from a particular turbine or wind farm
does not have as consistent an output as fuel-fired power plants.
Weibull Distribution is a continuous probability distribution in terms probability theory and
statistics. It is defined as
The probability density function of a Weibull random variable x is[1]:
Where k > 0 is the shape parameter and λ >0 is the scale parameter of the distribution. Its
complementary cumulative distribution function is a stretched exponential function. The Weibull
distribution is related to a number of other probability distributions; in particular, it interpolates
between the exponential distribution (k = 1) and the Rayleigh distribution (k = 2).
If the quantity x is a "time-to-failure", the Weibull distribution gives a distribution for which the
failure rate is proportional to a power of time. The shape parameter, k, is that power plus one, and
so this parameter can be interpreted directly as follows:
A value of k<1 indicates that the failure rate decreases over time. This happens if there is
significant "infant mortality", or defective items failing early and the failure rate
decreasing over time as the defective items are weeded out of the population.
A value of k=1 indicates that the failure rate is constant over time. This might suggest
random external events are causing mortality, or failure.
A value of k>1 indicates that the failure rate increases with time. This happens if there is
an "aging" process, or parts that are more likely to fail as time goes on.
In the field of materials science, the shape parameter k of a distribution of strengths is known as
the Weibull modulus
Reyleigh Distribution- In probability theory and statistics, the Rayleigh distribution is
continuous probability distribution. A Rayleigh distribution is often observed when the
overall magnitude of a vector is related to its directional components. One example where
the Rayleigh distribution naturally arises is when wind speed is analyzed into its
orthogonal 2-dimensional vector components. Assuming that the magnitude of each
component is uncorrelated and normally distributed with equal variance, then the overall
wind speed (vector magnitude) will be characterized by a Rayleigh distribution. A second
example of the distribution arises in the case of random complex numbers whose real and
imaginary components are i.i.d. (independently and identically distributed) Gaussian. In
that case, the absolute value of the complex number is Rayleigh-distributed. The
distribution is named after Lord Rayleigh.The Rayleigh probability density function is
for parameter σ
> 0, and cumulative distribution function.
Table 3.1 Graphical representation of wind speed versus hours [45]
Distribution of wind speed (red) and energy (blue) for all of 2002 at the Lee Ranch facility in
Colorado. The histogram shows measured data, while the curve is the Rayleigh model
distribution for the same average wind speed.
Wind Gradient-In common usage, wind gradient, more specifically wind speed gradient or
wind velocity gradient, or alternatively shear wind, is the vertical gradient of the mean horizontal
wind speed in the lower atmosphere. It is the rate of increase of wind strength with unit increase
in height above ground level. In metric units, it is often measured in units of meters per second of
speed, per kilometer of height (m/s/km), which reduces to the standard unit of shear rate, inverse
seconds (s−1).
The atmospheric effect of surface friction with the winds aloft force the surface wind to slow and
turn near the surface of the Earth, blowing inward across isobars, when compared to the winds in
the nearly frictionless flow well above the Earth’s surface. This layer, where surface friction
slows the wind and changes the wind direction, is known as the planetary boundary layer.
Daytime solar heating due to insolation thickens the boundary layer as winds at the surface
become increasingly mixed with winds aloft. Radiative cooling overnight decouples the winds at
the surface from the winds above the boundary layer, increasing vertical wind shear near the
surface, also known as wind gradient.
Typically, due to aerodynamic drag, there is a wind gradient in the wind flow just a few hundred
meters above the Earth’s surface—the surface layer of the planetary boundary layer. Wind speed
increases with increasing height above the ground, starting from zero due to the no-slip condition.
Flow near the surface encounters obstacles that reduce the wind speed, and introduce random
vertical and horizontal velocity components at right angles to the main direction of flow. This
turbulence causes vertical mixing between the air moving horizontally at one level, and the air at
those levels immediately above and below it, which is important in dispersion of pollutants and in
soil erosion.
The reduction in velocity near the surface is a function of surface roughness, so wind velocity
profiles are quite different for different terrain types. Rough, irregular ground, and man-made
obstructions on the ground, retard movement of the air near the surface, reducing wind velocity.
Because of low surface roughness on the relatively smooth water surface, wind speeds do not
increase as much with height above sea level as they do on land. Over a city or rough terrain, the
wind gradient effect could cause a reduction of 40% to 50% of the geostrophic wind speed aloft;
while over open water or ice, the reduction may be only 20% to 30%.
For engineering purposes, the wind gradient is modeled as a simple shear exhibiting a vertical
velocity profile varying according to a power law with a constant exponential coefficient based
on surface type. The height above ground where surface friction has a negligible effect on wind
speed is called the “gradient height” and the wind speed above this height is assumed to be a
constant called the “gradient wind speed” For example, typical values for the predicted gradient
height are 457 m for large cities, 366 m for suburbs, 274 m for open terrain, and 213 m for open
Although the power law exponent approximation is convenient, it has no theoretical basis.] When
the temperature profile is adiabatic, the wind speed should vary logarithmically with height,
Measurements over open terrain in 1961 showed good agreement with the logarithmic fit up to
100 m or so, with near constant average wind speed up through 1000 m.
The shearing of the wind is usually three-dimensional, that is, there is also a change in direction
between the ‘free’ pressure-driven geostrophic wind and the wind close to the ground.] This is
related to the Ekman spiral effect. The cross-isobar angle of the diverted geostrophic flow near
the surface ranges from 10° over open water, to 30° over rough hilly terrain, and can increase to
40°-50° over land at night when the wind speed is very low.
After sundown the wind gradient near the surface increases, with the increasing stability.
Atmospheric stability occurring at night with radiative cooling tends to contain turbulent eddies
vertically, increasing the wind gradient. The magnitude of the wind gradient is largely influenced
by the height of the convective boundary layer and this effect is even larger over the sea, where
there is no diurnal variation of the height of the boundary layer as there is over land. ] In the
convective boundary layer, strong mixing diminishes vertical wind gradient.
The design of buildings must account for wind loads, and these are affected by wind gradient.
The respective gradient levels, usually assumed in the Building Codes, are 500 meters for cities,
400 meters for suburbs, and 300 m for flat open terrain. For engineering purposes, a power law
wind speed profile may be defined as follows:
= speed of the wind at height
= gradient wind at gradient height
= exponential coefficient
Maximum Wind Turbine Efficiency- Bertz Ratio
The efficiency of a wind turbine is measured as the ratio between the energy extracted from the
wind to perform useful work (e.g., electricity) and the total kinetic energy of the wind without the
presence of a wind turbine. To understand the reasoning behind Betz'’Law, consider a 100%
efficiency, i.e., extracting all the kinetic energy from the wind and thus bringing the air to a
standstill. The paradox of bringing the air to a stop means that there'’ no way for the air to drive a
rotating machine, so no useful work can be extracted. Now consider the other extreme, i.e., the
wind turbine doesn'’ reduce the wind speed at all. Again conservation of energy dictates that no
useful work will be accomplished by the wind turbine. Clearly the maximum theoretical
efficiency lies somewhere between these two extremes. Betz'’Law simply and elegantly proves
the maximum efficiency of a wind turbine can'’ exceed 59%.
The latest horizontal-axis wind turbines typically have efficiencies in the range of 35-40%, so
clearly there'’ no conflict there between theory and practice. If electricity generators and
distribution are taken into consideration, then efficiency drops to the 10-30% range.
A recent article entitled "“FD Modeling for Wind Turbines" cites efficiencies for a shrouded
wind turbine way in excess of the Betz Law limit (shown by Figure 4 in the article). Straightaway
this should be a cause for the kind of skepticism usually reserved for perpetual motion devices.
Now, maybe Betz'’Law is flawed and the researchers have found a loophole, or more likely, they
have made a mistake in their calculations. To make such an extraordinary claim against a wellregarded theory requires extraordinary evidence. Their study is based on Computational Fluid
Dynamics (CFD) calculations. I believe this is an excellent example of how not to use advanced
Computer-Aided Engineering (CAE) tools, such as CFD.
Figure 3.2 Horizontal Axis Wind Turbine(Reference No.46)
CAE tools are only as good as the engineers and researchers that know when and where to apply
them. Good practitioners know that when a simulation contradicts a well-proven law, such as
conservation of energy, or in this case Betz'’Law, there is likely a problem with their simulation
and not vice-versa. It is relatively easy to use CAE tools to perform virtual simulations that have
no real world equivalent. There are a number of reasons why a good simulation can turn bad:
Underlying assumptions of the tool and the physical models it supports are not met, for
instance a linear stress analysis model is no use if the stresses are likely to exceed the
elastic limit and make a material deform plastically
Specification of inappropriate boundary conditions and material properties can produce
subtle inaccuracies in simulation results
Low fidelity (coarse mesh) model representation
Mistyped numbers or incorrect unit conversions can cause a simulation to produce results
that are off by orders of magnitude.
3.3 Wind Machinery and Generating System
The primary application of wind turbines is to extract energy from the wind. Hence, the
aerodynamics is a very important aspect of wind turbines. Like many machines, there are many
different types all based on different energy extraction concepts. Similarly, the aerodynamics of
one wind turbine to the next can be very different.
Overall the details of the aerodynamics depend very much on the topology. There are still some
fundamental concepts that apply to all turbines. Every topology has a maximum power for a
given flow, and some topologies are better than others. The method used to extract power has a
strong influence on this. In general all turbines can be grouped as being lift based, or drag based
with the former being more efficient. The difference between these groups is the aerodynamic
force that is used to extract the energy.
The most common topology is the Horizontal Axis Wind Turbine. It is a lift based wind turbine
with very good performance, accordingly it is a popular for commercial applications and much
research has been applied to this turbine. In the latter part of the 20t h century the Darrieus wind
turbine was another popular lift based alternative but is rarely used today. The Savonius wind
turbine is the most common drag type turbine, despite its low efficiency it is used because it is
simple to build and maintain and very robust.
The governing equation for power extraction is given below:
Where: P is the power, F is the force vector, and U is the speed of the moving wind
turbine part.
The force F is generated by the wind interacting with the blade. The primary focus of wind
turbine aerodynamics is the magnitude and distribution of this force. The most familiar type of
aerodynamic force is Drag; this is the same force that is felt pushing against you on a windy day.
Another type of force is lift; this is the same force that allows most aircraft to fly. The direction of
the drag force is parallel to the relative wind, while the lift force is perpendicular. Typically, the
wind turbine parts are moving so this alters the flow around the part. An example of relative wind
is the wind one would feel cycling on a calm day.
To extract power, the turbine part must move in the direction of the force. In the drag force case,
the relative wind speed decreases subsequently so does the drag force. The relative wind aspect
dramatically limits the maximum power that can be extracted by a drag based wind turbine. Lift
based wind turbine typically have lifting surfaces moving perpendicular to the flow. Here, the
relative wind will not decrease in fact it increases with rotor speed. Thus the maximum power
limits of these machines is much higher than drag based machines
Different wind turbines will come in different sizes. Then once the wind turbine is operating it
will experience a wide range of conditions. This variability complicates the comparison of
different types of turbines. To deal with this, non dimensionalization is applied to various
qualities. One of the qualities of non dimensionalization is that when geometrically similar
turbines will produce the same non-dimensional results, while because of other factors (difference
in scale, wind properties) produce very different dimensional properties. This allows one to make
comparisons between different turbines, while eliminating the effect of things like size and wind
conditions from the comparison.
The coefficient of power is the most important variable in wind turbine aerodynamics.
Buckingham π theorem can be applied to show that non-dimensional variable for power is given
by the equation below. This equation is similar to efficiency, so values between 0 and less than
one are typical. However this is not the exactly the same as efficiency so in practice some
turbines can exhibit greater than unity
power coefficients. In these circumstances one cannot conclude the first law of thermodynamics
is violated because this is not an efficiency term by the strict definition of efficiency.
CP is the coefficient of power, ρ is the air density, A is the area of the wind turbine,
finally V is the wind speed.
Equation (1) shows two important dependents. The first is the speed that the machine is going
(U). This variable is non-dimensional zed by the wind speed, to get the speed ratio:
The force vector is not straightforward, as stated earlier there are two types of aerodynamic
forces, lift and drag. Accordingly there are two non-dimensional parameters. However both
variables are non-dimensional zed in a similar way. The formula for lift is given below; the
formula for drag is given after:
is the lift coefficient,
is the drag coefficient,
is the relative wind as
experienced by the wind turbine blade, A is the area but may not be the same area used in the
power non-dimensionalization of power.
The aerodynamic forces have a dependency on W, this speed is the relative speed and it is given
by the equation below. Note that this is vector subtraction.
Maximum power of a drag based wind turbine
Equation (1) will be the starting point in this derivation. Equation (CD) is used to define the
force, and equation (Relative Speed) is used for the relative speed. These substitutions give the
following formula for power.
The formulas (CP) and (Speed Ratio) are applied to express (Drag Power) in no dimensional
It can be shown through calculus that equation (SpeedRatio) achieves a maximum at λ = 1 / 3. By
inspection one can see that equation (DragPower) will achieve larger values for λ > 1. In these
circumstances, the scalar product in equation (1) makes the result negative. Thus, one can
conclude that the maximum power is given by:
Experimentally it has been determined that a large CD is 1.2, thus the maximum CP is
approximately 0.1778
Wind Blade Technology- Today’s machines are much different from the frame supported sails of
the predecessors. The new style blades are much akin to the air plane propellers or wings and
helicopter rotors, and designers have made good use of prior theory and experiences in this area.
It is perhaps more than just coincidence that the largest airplane wingspan and the largest wind
turbine rotor is diameter were both approximately 100 m and the widely deployed successful
commercial units in both the fields are about 2/3rd of a span of these one of a kind behemoths.
Nevertheless there are also important differences.
Two and three blade design is common. Three bladed units are predominant today. Two bladed
turbines may find favor from very large offshore machines. Considerable sophistication has been
introduced into the blade airfoil design process to optimize the performance in the appropriate
wind field range and to satisfy other requirements including-
1. Intentionally stalling at storm force wind velocities to protect the rotor, gears and
generator against over stress.
2. Avoiding loss of performance due to roughening by debris deposits.
3. Tapering of hub to tip blade shape and twisting the angle of pitch in the horizontal plane
to allow for the increase in circumferential speed as a function of radius.
4. Substitution lightweight composite materials for the metal blade design.
Good blade design is a challenge because efficient power extraction is only one goal. Wind gusts
and changes in direction give rise to cyclic stresses in the blades, and through them, to the rest of
the drive train. Blades and gear failure due to fatigue have been a continuing problem, even in the
next generating machines [1].
The simplest model for horizontal axis wind turbine (HAWT) aerodynamics is Blade Element
Momentum (BEM) theory. The theory is based on the assumption that the flow at a given annulus
does not affect the flow at adjacent annuli. This allows the rotor blade to be analyzed in sections,
where the resulting forces are summed over all sections to get the overall forces of the rotor. The
theory uses both axial and angular momentum balances to determine the flow and the resulting
forces at the blade.
The momentum equations for the far field flow dictate that the thrust and torque will induce a
secondary flow in the approaching wind. This in turn affects the flow geometry at the blade. The
blade itself is the source of these thrust and torque forces. The force response of the blades is
governed by the geometry of the flow, or better known as the angle of attack. Refer to the Airfoil
article for more information on how airfoils create lift and drag forces at various angles of attack.
This interplay between the far field momentum balances and the local blade forces requires one to
solve the momentum equations and the airfoil equations simultaneously. Typically computers and
numerical methods are employed to solve these models.
There is a lot of variation between different version of BEM theory. First, one can consider the
effect of wake rotation or not. Second, one can go further and consider the pressure drop induced
in wake rotation. Third, the tangential induction factors can be solved with a momentum
equation, an energy balance or orthogonal geometric constraint; the latter a result of Biot-Savart
law in vortex methods. These all lead to different set of equations that need to be solved. The
simplest and most widely used equations are those that consider wake rotation with the
momentum equation but ignore the pressure drop from wake rotation. Those equations are given
below. a is the axial component of the induced flow, a' is the tangential component of the induced
flow. σ is the solidity of the rotor, φ is the local inflow angle. Cn and Ct are the coefficient of
normal force and the coefficient of tangential force respectively. Both these coefficients are
defined with the resulting lift and drag coefficients of the airfoil:
Corrections to Blade Element Momentum theory- Blade Element Momentum (BEM) theory
alone fails to accurately represent the true physics of real wind turbines. Two major shortcomings
are the effect of discrete number of blades and far field effects when the turbine is heavily loaded.
Secondary short-comings come from dealing with transient effects like dynamic stall, rotational
effects like coriolis and centrifugal pumping, finally geometric effects that arise from coned and
yawed rotors. The current state of the art in BEM uses corrections to deal with the major
shortcoming. These corrections are discussed below. There is as yet no accepted treatment for the
secondary shortcomings. These areas remain a highly active area of research in wind turbine
The effect of the discrete number of blades is dealt with by applying the Prandtl tip loss factor.
The most common form of this factor is given below where B is the number of blades, R is the
outer radius and r is the local radius. The definition of F is based on actuator disk models and not
directly applicable to BEM. However the most common application multiplies induced velocity
term by F in the momentum equations. As in the momentum equation there are many variations
for applying F, some argue that the mass flow should be corrected in either the axial equation, or
both axial and tangential equations. Others have suggested a second tip loss term to account for
the reduced blade forces at the tip. Shown below are the above momentum equations with the
most common application of 'F':
The typical momentum theory applied in BEM is only effective for axial induction factors up to
0.4 (thrust coefficient of 0.96). Beyond this point the wake collapses and turbulent mixing occurs.
This state is highly transient and largely unpredictable by theoretical means. Accordingly, several
empirical relations have been developed. As the usual case there are several version, however a
simple one that is commonly used is a linear curve fit given below, with ac = 0.2. The turbulent
wake function given excludes the tip loss function, however the tip loss is applied simply by
multiplying the resulting axial induction by the tip loss function.
When a > ac
CT and Ct, the first one is the thrust coefficient of the rotor, which is the one which should be
corrected for high rotor loading (i.e. for high values of a), whilst the second one (ct) is the
tangential aerodynamic coefficient of an individual blade element, which is given by the
aerodynamic lift and drag coefficients
Tower- We have previously noted that the wind energy flux increases approximately as the 3/7
power of height or 0.43% for every 1% increase in rotor hub height, hence taller the tower better.
However cost increases with height which leads to compromise. A rough rule of thumb is for hub
height to equal rotor diameter. Two types of tower design are common steel truss lattice work and
tabular pole. The latter is more popular due to lower drag and downstream turbulence and
improved aesthetics.
3.4 Turbine
The amount of power transferred to a wind turbine is directly proportional to the density of the
air, the area swept out by the rotor, and the cube of the wind speed.
The usable power
available in the wind is given by:
Where P = power in watts, _ = an efficiency factor determined by the design of the turbine, _ =
mass density of air in kilograms per cubic meter, r = radius of the wind turbine in meters, and v =
velocity of the air in meters per second.
As the wind turbine extracts energy from the air flow, the air is slowed down, which causes it to
spread out. Albert Betz, a German physicist, determined in 1919 (see Betz' law) that a wind
turbine can extract at most 59% of the energy that would otherwise flow through the turbine's
cross section, that is _ can never be higher than 0.59 in the above equation. The Betz limit applies
regardless of the design of the turbine.
This equation shows the effects of the mass rate of flow of air traveling through the turbine, and
the energy of each unit mass of air flow due to its velocity. As an example, on a cool 15 °C (59
°F) day at sea level, air density is 1.225 kilograms per cubic metre. An 8 m/s (28.8 km/h or
18 mi/h) breeze blowing through a 100 meter diameter rotor would move almost
77,000 kilograms of air per second through the swept area. The total power of the example breeze
through a 100 meter diameter rotor would be about 2.5 megawatts. Betz' law states that no more
than 1.5 megawatts could be extracted.
Figure 3.3 Principal element of a wind turbine electric generator (Reference No.47)
3.5 Type of Wind Turbines
Wind turbines can be separated into two types based by the axis in which the turbine rotates.
Turbines that rotate around a horizontal axis are more common. Vertical-axis turbines are less
frequently used.
Horizontal-axis wind turbines (HAWT) have the main rotor shaft and electrical generator at the
top of a tower, and must be pointed into the wind. Small turbines are pointed by a simple wind
vane, while large turbines generally use a wind sensor coupled with a servo motor. Most have a
gearbox, which turns the slow rotation of the blades into a quicker rotation that is more suitable to
drive a generator.
Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower.
Turbine blades are made stiff to prevent the blades from being pushed into the tower by high
winds. Additionally, the blades are placed a considerable distance in front of the tower and are
sometimes tilted up a small amount. [14]
Downwind machines have been built, despite the problem of turbulence, because they don't need
an additional mechanism for keeping them in line with the wind, and because in high winds, the
blades can be allowed to bend which reduces their swept area and thus their wind resistance.
Since turbulence leads to fatigue failures, and reliability is so important, most HAWTs are
upwind machines.
HAWT Subtypes
1. Windmills
These squat structures, typically (at-least) four-bladed, usually with wooden shutters or fabric
sails, were developed in Europe. These windmills were pointed into the wind manually or via a
tail-fan and were typically used to grind grain. In the Netherlands they were also used to pump
water from low-lying land, and were instrumental in keeping its polders dry. Windmills were also
located throughout the USA, especially in the Northeastern region.
2. Modern Rural Windmills
The Eclipse windmill factory was set up around 1866 in Beloit. Wisconsin and soon became a
huge success building mills for farm water pumping and railroad tank filling. Other firms like
Star, Dempster, and Aero motor also entered the market. Hundreds of thousands of these mills
were produced before rural electrification and small numbers continue to be made. They typically
had many blades, operated at tip speed ratios (defined below) not better than one, and had good
starting torque. Some had small direct-current generators used to charge storage batteries, to
provide a few lights, or to operate a radio receiver. The American rural electrification connected
many farms to centrally-generated power and replaced individual windmills as a primary source
of farm power by the 1950s. They were also produced in other countries like South Africa and
Australia (where an American design was copied in 1876). Such devices are still used in locations
where it is too costly to bring in commercial power.
In Schiedam, the Netherlands, a traditional style windmill (the Noletmolen) was built in 2005 to
generate electricity.[4] The mill is one of the tallest Tower mills in the world, being some
139.434 Feet (42.5 meters) tall.
Common modern wind turbines- Turbines used in wind farms for commercial production of
electric power are usually three-bladed and pointed into the wind by computer-controlled motors.
This type is produced by Danish and other manufacturers. These have high tip speeds of up to six
times the wind speed, high efficiency, and low torque ripple which contributes to good reliability.
The blades are usually colored light gray to blend in with the clouds and range in length from 65–
130 feet (19.8–39.6 meters) or more. The tubular steel towers range from about 200–300 feet
(61–91.4 meters) high. The blades rotate at 10-22 revolutions per minute. A gear box is
commonly used to step up the speed of the generator, though there are also designs that use direct
drive of an annular generator. Some models operate at constant speed, but more energy can be
collected by variable-speed turbines which use a solid-state power converter to interface to the
transmission system. All turbines are equipped with high wind shut down features to avoid over
speed damage.
HAWT Advantages
Blades are to the side of the turbine's center of gravity, helping stability.
Ability to wing warp, which gives the turbine blades the best angle of attack. Allowing
the angle of attack to be remotely adjusted gives greater control, so the turbine collects
the maximum amount of wind energy for the time of day and season.
Ability to pitch the rotor blades in a storm, to minimize damage.
Tall tower allows access to stronger wind in sites with wind shear. In some wind shear
sites, every ten meters up, the wind speed can increase by 20% and the power output by
HAWT Disadvantages
HAWTs have difficulty operating in near ground, turbulent winds.
The tall towers and long blades up to 90 meters long are difficult to transport on the sea
and on land. Transportation can now cost 20% of equipment costs.
Tall HAWTs are difficult to install, needing very tall and expensive cranes and skilled
The FAA has raised concerns about tall HAWTs effects on radar near Air Force bases.
Their height can create local opposition based on impacts to view sheds.
Downwind variants suffer from fatigue and structural failure caused by turbulence.
Cyclic stresses and vibration -Cyclic stresses fatigue the blade, axle and bearing material failures
were a major cause of turbine failure for many years. Because wind velocity often increases at
higher altitudes, the backward force and torque on a horizontal-axis wind turbine (HAWT) blade
peaks as it turns through the highest point in its circle. The tower hinders the airflow at the lowest
point in the circle, which produces a local dip in force and torque. These effects produce a cyclic
twist on the main bearings of a HAWT. The combined twist is worst in machines with an even
number of blades, where one is straight up when another is straight down. To improve reliability,
teetering hubs have been used which allow the main shaft to rock through a few degrees, so that
the main bearings do not have to resist the torque peaks.
When the turbine turns to face the wind, the rotating blades act like a gyroscope. As it pivots,
gyroscopic precession tries to twist the turbine into a forward or backward somersault. For each
blade on a wind generator's turbine, percussive force is at a minimum when the blade is
horizontal and at a maximum when the blade is vertical. This cyclic twisting can quickly fatigue
and crack the blade roots, hub and axle of the turbines.
Vertical-axis -Vertical-axis wind turbines (or VAWTs) have the main rotor shaft arranged
vertically. Key advantages of this arrangement are that the turbine does not need to be pointed
into the wind to be effective. This is an advantage on sites where the wind direction is highly
variable. VAWTs can utilize winds from varying directions.
With a vertical axis, the generator and gearbox can be placed near the ground, so the tower
doesn't need to support it, and it is more accessible for maintenance. Drawbacks are that some
designs produce pulsating torque. Drag may be created when the blade rotates into the wind.
It is difficult to mount vertical-axis turbines on towers, meaning they are often installed nearer to
the base on which they rest, such as the ground or a building rooftop. The wind speed is generally
slower at a lower altitude, so less wind energy is available for a given size turbine. Air flow near
the ground and other objects can create turbulent flow, which can introduce issues of vibration,
including noise and bearing wear which may increase the maintenance or shorten the service live.
However, when a turbine is mounted on a rooftop, the building generally redirects wind over the
roof and this often doubles the wind speed at the turbine. If the height of the rooftop mounted
turbine tower is approximately 50% of the building height, this is near the optimum for maximum
wind energy and minimum wind turbulence.
VAWT subtypes
Figure 3.4 World's tallest Darrieus wind turbine, Quebec, Canada[46]
Darrieus wind turbine -"Eggbeater" turbines. They have good efficiency, but produce large
torque ripple and cyclic stress on the tower, which contributes to poor reliability. Also, they
generally require some external power source, or an additional Savonius rotor, to start turning,
because the starting torque is very low. The torque ripple is reduced by using 3 or more blades
which results in a higher solidity for the rotor. Solidity is measured by blade area over the rotor
area. Newer Darrieus type turbines are not held up by guy wires but have an external
superstructure connected to the top bearing.
Gorlov helical turbine -Essentially, a Darrieus turbine in a helical configuration was patented in
2001. It solves most of the problems of the Darrieus rotor. It is self-starting, has lower torque
ripple, low vibration and noise, and low cyclic stress. High reliability is expected from tested or
matured designs. At least two wind turbine products are on the market as of 2002, including the
Turby wind turbine and the Quietr evolution wind turbine. It is up to 35% efficient, which is
competitive with the most efficient VAWT's.
Giromill - Subtype of Darrieus turbine, with straight, as opposed to curved, blades. The cycloturbine variety have variable pitch to reduce the torque pulsation and are self-starting. The
advantages of variable pitch are: high starting torque; a wide, relatively flat torque curve; a lower
blade speed ratio; a higher coefficient of performance; more efficient operation in turbulent
winds; and a lower blade speed ratio which lowers blade bending stresses. Straight, V, or curved
blades may be used. Recently , this type of turbine has been advanced by former Russian rocket
scientists who claim to have increased the efficiency of the VAWT up to 38% . A company , SRC
Vertical Ltd. has been formed , and has begun selling the new turbine .
Savonius wind turbine -These are drag-type devices with two- (or more) scoops that are used in
anemometers, the Flettner vents (commonly seen on bus and van roofs), and in some highreliability low-efficiency power turbines. They are always self-starting if there are at least three
scoops. They sometimes have long helical scoops to give a smooth torque. The Banesh rotor and
especially the Rahai rotor improve efficiency with blades shaped to produce significant lift as
well as drag. A new variety uses sails that can open or close with changes in wind speed.
VAWT advantages
Can be easier to maintain if the moving parts are located near the ground.
As the rotor blades are vertical, a yaw device is not needed, reducing cost.
VAWTs have a higher airfoil pitch angle, giving improved aerodynamics while
decreasing drag at low and high pressures.
Straight bladed VAWT designs with a square or rectangular crossection have a larger
swept area for a given diameter than the circular swept area of HAWTs.
Mesas, hilltops, ridgelines and passes can have faster winds near the ground because the
wind is forced up a slope or funneled into a pass and into the path of VAWTs situated
close to the ground.
Low height useful where laws do not permit structures to be placed high.
Does not need a free standing tower so is much less expensive and stronger in high winds
that are close to the ground.
Usually have a lower Tip-Speed ratio so less likely to break in high winds.
Does not need to turn to face the wind if the wind direction changes making them ideal in
turbulent wind conditions.
They can potentially be built to a far larger size than HAWT's , for instance floating
VAWT's hundreds of meters in diameter where the entire vessel rotates , can eliminate
the need for a large and expensive bearing.
There may be a height limitation to how tall a vertical wind turbine can be built and how
much sweep area it can have. However, this can be overcome by connecting a multiple
number of turbines together in a triangular pattern with bracing across the top of the
structure. Thus reducing the need for such strong vertical support, and allowing the
turbine blades to be made much longer.
VAWT Disadvantages
Most VAWTs produce energy at only 50% of the efficiency of HAWTs in large part
because of the additional drag that they have as their blades rotate into the wind. This can
be overcome by using structures to funnel more and align the wind into the rotor (e.g.
"stators" on early Windstar turbines) or the "vortex" effect of placing straight bladed
VAWTs closely together.
Most VAWTS need to be installed on a relatively flat piece of land and some sites could
be too steep for them but are still usable by HAWTs.
Most VAWTs have low starting torque, and may require energy to start the turning.
A VAWT that uses guy wires to hold it in place puts stress on the bottom bearing as all
the weight of the rotor is on the bearing. Guy wires attached to the top bearing increase
downward thrust in wind gusts. Solving this problem requires a superstructure to hold a
top bearing in place to eliminate the downward thrusts of gust events in guy wired
While VAWTs' parts are located on the ground, they are also located under the weight of
the structure above it, which can make changing out parts near impossible without
dismantling the structure if not designed properly.
Cost of Externalities-During the operation of wing turbine emits no noxious gases and unlike
the heat engine type system requires no cooling water. Thus most of the environmental costs not
reflected in conventional accounting are associated with initial construction. Again the steel
components impose the lion share of the burden. We are to calculate the externalities associated
with the 2000 KWh of energy consumed to produce the steel components of the wind turbine per
unit of rated power. Estimates range widely but 2 cents/KWh is a plausible compromise value at a
generous 40% efficiency that translates into 0.8 cents/KWh thermal.
If the wing turbine unit has a specific cost of $1000 per rated KW, which translates this translates
into a lifetime leveled capital cost components of 5 cents/KWh. This is vanishingly small and of a
comparable order of magnitude. [13]
3.6 Environmental Impact of Wind Turbine
Compared to the environmental impact of traditional energy sources, the environmental impact of
wind power is relatively minor. Wind power consumes no fuel, and emits no air pollution, unlike
fossil fuel power sources. The energy consumed to manufacture and transport the materials used
to build a wind power plant is equal to the new energy produced by the plant within a few
months. While a wind farm may cover a large area of land, many land uses such as agriculture are
compatible, with only small areas of turbine foundations and infrastructure made unavailable for
There are reports of bird and bat mortality at wind turbines, as there are around other artificial
structures. The scale of the ecological impact may or may not be significant, depending on
specific circumstances. Prevention and mitigation of wildlife fatalities, and protection of peat
bogs, affect the sitting and operation of wind turbines.
There are conflicting reports about the effects of noise on people who live very close to a wind
turbine. Undesirable features include-
1. Aesthetic Impact-Newer wind farms have larger, more widely spaced turbines, and have a less
cluttered appearance than older installations. Wind farms are often built on land that has already
been impacted by land clearing and they coexist easily with other land uses (e.g. grazing, crops).
They also have a smaller footprint than other forms of energy generation such as coal and gas
plants. However, wind farms may be close to scenic or otherwise undeveloped areas, and
aesthetic issues are important for onshore and near-shore locations.
Aesthetic issues are subjective and some people find wind farms pleasant and optimistic, or
symbols of energy independence and local prosperity. While some tourism officials predict wind
farms will damage tourism, some wind farms have themselves become tourist attractions, with
several having visitor centers at ground level or even observation decks atop turbine towers.
2. Noise-Modern wind turbines produce significantly less noise than older designs. Turbine
designers work to minimize noise, as noise reflects lost energy and output. Noise levels at nearby
residences may be managed through the sitting of turbines, the approvals process for wind farms,
and operational management of the wind farm.
3. Birds- Danger to birds is often the main complaint against the installation of a wind turbine.
However, a study estimates that wind farms are responsible for 0.3 to 0.4 fatalities per gigawatt-
hour (GWh) of electricity while fossil-fueled power stations are responsible for about 5.2
fatalities per GWh.
4. Land use- Although wind energy fluxes through a horizontal plane are often several hundred
watts per sq meter, comparable the vertical solar energy fluxes the large front to front and side to
side spacing need to avoid interferences make wind power a dilute resource.
5. Maintenance Workers Hazard- The dangers associated with windmill maintenance are similar
to those faced by steeplejacks and high rise construction iron workers. However associated added
costs are presumable reflected in the bus bar price as higher workplace insurance premium are
paid by the wind farm owner/operators.
3.7 Current Status and Future Prospects
At the end of the 20th century wind farm electric energy generation has come to a crucial
crossroad. From an economic stand point, it has been the most deserving of all of the green
supply options for more widespread deployment. However, like virtually all other candidates it
cannot complete with CCGT unless there are significant taxes and/or credits assigned to CO2
release/avoidance. In part this helps to explain why demand is stagnant in the US which once had
over 90% of wind power capacity while it is growing at a moderate rate in Western Europe,
where it is currently responsible for approx. 20% of Denmark electricity generation. Other
impediment includes:
1. A lingering lack of confidence in reliability because of the high failure rate experience by
some product lines in recent past.
2. The turmoil brought about by electric utility deregulation.
3. Historically low prices for coal, oil, gas and uranium which is lower than at anytime in
the past century.
4. The lack of consistent, coordinated, stable national energy policy and the resulting
vacillation between acceptance and rejection of subsidies such as tax credit allowance
and R&D support
Since the technological aspects of the wind energy system has attained near maturity we are
unlikely to see further advances of the sort that improved rotor blade efficiency by 30% over
the past 2 decades. Incremental improvements foreseeable in the near term include-[1]
1. Still better power electronics to improve wind generation interference with the grid.
2. Cheaper, better understood composite materials for blade construction.
Power train simplification, for example elimination of gear boxes (which accounts for
30% of unit cost) by use of multi-pole generators.
4. Intelligent online monitoring, diagnostic and control system to maximize power
extraction and minimize the susceptibility to damage from off normal condition.
5. In the policy area, more widespread promotion of green power at a voluntary premium
6. Improved modeling in all respects aerodynamics and fluid dynamics structural, power
conditioning, grid integration, system planning and environmental benefits.
In the longer term, the single most beneficial development would be better, cheaper
means of transmission and storage of energy, a need common to most other types of
solar energy.
3.8 Energy Generation in Tall Buildings
3.8a Introduction and Background
Over the past few decades, ideas for the environmental tall buildings have explored the
generations of clean energy in buildings, Bringing together architecture and technology to take
advantage in wind and solar radiation. The exposure of the tall building typology to sun and wind
forces inspired research projects and utopian design proposal, with the possibility of large
unobstructed façade areas to catch solar radiation and the top floors to harvest wind at high
The awareness in public regarding the impact of climate change on environment and harmful
effects of dependency on fossil fuels was noticed. [16]
This increase in awareness led to actions in many sectors to mitigate climate change such as
integration of renewable sources of energy in buildings [17]
According to the Intergovernmental Panel on Climate Change (IPCC), buildings are responsible
for one third of global energy related CO2 because of their dependency on conventional sources
of energy which are the main source of harmful carbon gas emissions. So for reducing this
harmful carbon gas emission from the building the concept of generating electricity which is
cleaner came into effect. Integrating wind turbines on the buildings can reduce reliance on grid
supplied energy and hence would be source of greener energy.[18]
Discussions on the generation of clean energy in tall buildings, especially regarding the
introductions of wind turbine, raise a series of questions:
1) What are the current and future possibilities for wind generation in tall buildings?
2) Is the wind power definitely worthwhile?
3) What are the real challenges- economic, political, technical or architectural, or are they
all have an impact together?
Although technology has advanced dramatically over the last decade and architectural has
shown ways of bringing the technology of wind turbine and building designs together though
there is no consensus on the possibilities and advantages of generating clean energy and
incorporating wind turbines in tall buildings. In early stage majority of proposals with
photovoltaic cells and wind turbines were removed as projects develops, mainly due to
economic reasons but also due to technical issues and urban planning restrictions. Specialists
in the field confirm that the reason for the limited number of wind turbine around the world is
not lack of know-how, but due to economics and possibly also aesthetics.
Some of the first examples of design (not built) of tall buildings with the incorporation of
energy generation appeared in the late 1980’s for China Tower in Malaysia, Tokyo Turbine
Tower and Sky ZED zero energy development proposal for London. All three projects
incorporated an aerodynamic architectural form to catch wind and direct it to a turbine
incorporated in the buildings, with photo-voltaic penal covering extensive areas of facades,
challenging conventional architectural ideas.
One of the most publicized research projects on the topic was the project ZED in 1994
promoted by European Commission involving architects and engineers. The main objective
project was to achieve zero carbon emission for buildings in three cities of London, Toulouse
and Berline. With the respective climatic conditions proposal for London turned out to be tall
buildings whereas the other two were low rise buildings.
Project ZED led to a second research initiative, Wind Energy for Built Environment (WEB)
in 2001 also prompted by European Commission. With the aim of exploring the potential of
wind energy generation in integrated design solutions, the energy target of project WEB was
to meet a minimum of 20% of energy demand of tall building with wind turbine. Simulations
of case studies at windy sites in coastal areas gave a payback time of 6 years.
Considered in the field of research as a
pioneering design exercise, with its 3
integrated 35 m diameter horizontal axis
wind turbines in twin tower building.
Project WEB has become the iconic form,
making the case for tall building and energy
generation through wind turbines.
In the last decade a significant number of
different proposals for tall buildings around
the world have been published showing
ideas for incorporation of wind turbines and
Figure 3.5 Digital Model of Project WEB [36]
photovoltaic cells. Building integrated
wind turbine is the latest field of wind turbine these days. Electricity is being produced right
where it is needed, eliminating the transmission problem. Installing wind turbines especially tall
buildings allows one to take advantage of height without an expensive full size tower.
3.9 Practical Usage of Electrical Output
The installed wind turbine output electricity is connected to the electric grid and this is not the
only way that the energy from the wind can be used. This implies that the output of the turbine
can be employed in other ways such as water and space heating
As the wind turbine is either used as an isolated machine or is connected to the grid irrespective
of the size of the unit. Assuming that we are dealing with the wind turbine on the top of the
building catching a lot of wind energy without having any problem. How can we use the
harnessed energy?
Assuming that relatively small turbine and the generator is a single phase alternator or it is a DC
generator. Talking in account the fact that wind is not necessarily blowing at this time, energy is
needed and the rate of energy generation is neither constant nor uniform, the harnessed energy
can be used in the following ways.
1) Connect the turbine output to the building electricity.
2) Use an independent circuit for generated electricity.
3) Use the harnessed energy for heating water or for space heating in the winter.
4) Store electricity for using when required, for instance for lighting at night.
5) Combination of 1) and 3).
6) Combination of 2) and 4).
Connect the turbine output to the building electricity is the best and most preferred choice and
most expensive too. In such an arrangement the voltage and frequency of the generated electricity
must match those of the main electric supply to the building and the generated electricity must be
in perfect synchronization with the main grid. The equipment to take care of and satisfy these
conditions adds to the price of the turbine. Use an independent circuit for generated electricity is a
separate circuit which is used for the generated electricity from the turbine mainly for lightening
purpose only. As lights are not sensitive to frequency and voltage variation and nor importantly
the synchronization is not necessary at all.
3.10 Parameters for Implementation of Wind Turbine on Buildings
The implementation of wind turbines into tall buildings has become increasingly common
footprint in making the public statement about the green energy. However there are number of
parameters which need to be taken in consideration for determining long term benefits of these
implementations. The implementation is dependent on various parameters which are as follows1. Wind Climate
2. Modification of Wind Climate by Urban Environment
3. Building Aerodynamics
4. Shape of Tall Building to Increase Efficiency of Wind Turbine
5. Tools for Predicting the Wind Power Generation ( through wind climate analysis)
6. Tools for Predicting the Wind Power Generation ( through computation fluid dynamics)
7. Tools for Predicting the Wind Power Generation (through wind tunnel analysis)
8. Wind Turbine Selection Process.
1. Wind Climate-The requirements for optimizing the performance of wind generators in an
urban environment are quite different from those pertaining to wind farms in open sites. This
entails the use of different design approaches to assess the optimum placement of wind turbines
within the building envelope, the most suitable generator types for the building environment, and
to estimate annual energy production for the wind turbines.
As the urban areas consist of houses, apartments buildings, office buildings, high raising
buildings so there is no free land or undeveloped space so in other words the only spots to mount
a wind turbine can be on the building roofs. In fact in windy regions there is a lot of wind on the
top of high rise building roofs; moreover the roof top turbine is necessarily much smaller than
those in wind farms. As due to lot of hindrances in the swift wind flow the speed of the wind is
relatively less than in an open space. Thus the wind turbine for this purpose must be able to catch
and use the low speed wind. This implies having a high starting torque usually not the case with
all wind turbines. Moreover at the edge of high rise building roofs upward wind is also possible.
This wind which doesn’t have the stream parallel to the roof called skew wind is not suitable for
propeller types of turbines but can be used with other type of turbines.
According to Coleman & Preston Revolutionary Power (2008)[35] the idea of exploiting wind
energy in the built environment is attractive because wind energy is considered one of the most
reliable clean sources of energy on the planet and wind turbines are likely to be in operation for
about 85% of the year, and have a service life of at least 20 years.
2. Modification of Wind Climate by Urban Environment- When contemplating the incorporation
of wind power generation into a tall building design, the first consideration must be the local
wind climate of the area. Bluntly, if there is no wind to start with then the potential for successful
use of turbines will be very limited.
The most common statistic that is quoted when assessing wind power potential is average wind
speed. This is the average wind speed throughout each day throughout the year. Due to the cubic
relationship between wind and wind power, this on its own is not a particularly useful statistic as
it does not reveal anything about the characteristics of the underlying wind climate. For instance,
many locations around the world experience seasonal trade winds that mean that while high wind
speeds will be experienced at some times of year, much calmer conditions, with limited power
generation potential, will be experienced for other larger parts of the year. Similarly, many
locations experience large diurnal effects with wind speed varying greatly throughout the day, for
example as a result of afternoon sea breezes. A better metric for determining the power potential
is the annual average wind power density of a site. The wind power density is the average amount
of power that is in the wind on a yearly basis, which takes into account not only the mean wind
speed for a site, but also the frequency distribution of wind speeds.
The directionality of the wind is also important. As the incorporation of turbines into tall
buildings tends to favor limited wind directions, perhaps within a 45° sector, depending upon the
building configuration and the location of the wind turbines on the building Wind conditions in
urban environments tend to be very different. The effect of urban environments on a boundarylayer is shown in Figure 3.6. This shows how buildings slow the wind near to the ground, and
increase the turbulence in the wind. Turbines work most efficiently in low-turbulence
environments so care needs to be taken in specifying turbine types that will cope with both
existing turbulence and likely future changes in turbulence as a result of urban development.
Urban development is likely to pose one of the greatest challenges to increasing use of turbines
on tall buildings. In city center locations, height restrictions often mean that many tall buildings
are of similar heights. Even if a building is very tall, if all the surrounding buildings are of similar
height then the potential for seeing suitable conditions for efficient turbine installation is
significantly reduced.
Figure 3.6 Mean Velocity Profiles for Various Types of Environments [37]
Urban development is likely to pose one of the greatest challenges to increasing use of turbines
on tall buildings. In city center locations, height restrictions often mean that many tall buildings
are of similar heights then potential for seeing suitable conditions for efficient turbine installation
is significantly reduced.
As discussed by Müller, G., Jentsch, M. F., & Stoddart, E high-rise buildings have the largest
potential for wind turbine integration when compared to low-rise structures. In locating the
building wind turbine, the building roof should be approximately 50% higher than its
surroundings, and the turbine located near the center of the roof on the most common wind
direction for the location, with the lowest position of the rotor at least 30% of the building height
above the roof level.)[25].
Another research came up with the concept that turbine height has a significant effect on
capturing higher mean wind speed and power generated, while output varied considerably with
wind direction. [30]
3. Building Aerodynamics- As discussed above, it is desirable to locate turbines in regions of
high wind speed and low turbulence. Describing the wind flow around a tall buildings can be
quite complex and has been studied in depth for many years. A simplified sketched of the mean
flow phenomenon is shown in Figure 3.7.
There will be positive pressure on the windward face and negative pressure on the side and
leeward faces. As air, or any fluid, will naturally flow from areas of high pressure to low pressure
this implies that the most effective locations for wind turbines will be either in the accelerated
shear layers around the edge and top of the building or in specially developed passages linking
the areas of positive and negative pressure. The wind speeds close to the center of the roof may
be low as this area is often in a region of separated flow. Number of new developments that were
based on the principle of aerodynamic building, to enhance the performance of the integrated
wind turbines. For example Bahrain World Trade, Centre, Pearl River Tower in China etc.
It was also observed that it cannot be assumed that such projects will become the norm as urban
wind turbines may not always be visually appropriate and hence not be put forward by architects
and designers. Therefore, a successful wind turbine design would be integrated to add to the
architectural value of the building. [25]
Figure 3.7 Wind flow around the Tall Building[37]
It was found that wind speed increases at the edges of the building and wind turbines could be
implemented to take advantage of the speeding effect of wind hitting the sharp edges. However,
these turbines should be designed to operate within urban areas where air flow is
4.Shape of the Tall Building to Increase efficiency of Wind Turbine- Shaping of tall buildings
can be used effectively to enhance the performance of wind turbines. Examples of this are the
Bahrain World Trade Center. As shown in Fig 3.8
Figure 3.8 Design of the Bahrain World Trade Center [37]
The two 50 storey sail shaped office towers taper to a height of 240m and support three 29m
diameter horizontal-axis wind turbines. The towers are harmoniously integrated on top of a three
story sculpted podium and basement which accommodate a new shopping center, restaurants,
business centers and car parking.
The elliptical plan forms and sail-like profiles act as aero-foils, funneling the onshore breeze
between them as well as creating a negative pressure behind, thus accelerating the wind velocity
between the two towers. Vertically, the sculpting of the towers is also a function of airflow
dynamics. As they taper upwards, their aero foil sections reduce. This effect when combined with
the increasing velocity of the onshore breeze at increasing heights creates a near equal regime of
wind velocity on each of the three turbines.
Basically Bahrain World Trade Centre Tower is formed to create a venture effect, placing the
horizontal axis turbines between two wings of the buildings. This approach clearly works for only
a limited number of wind directions, but may be useful in a location with a dominant prevailing
wind direction. Restricting the orientation of horizontal axis turbines, however, severely limits the
efficiencies gained from using this type of turbine. (For more in depth knowledge regarding the
Bahrain World Trade Centre Tower [31]
Another example of the shape of the tall building is the Pearl River Tower. In the Pearl River
Tower slots through the tower are used to relieve the pressure between the front and rear faces of
the tower with these slots being aerodynamically shaped to increase flow through them. Again,
this approach is most efficient for only a few wind directions but has the advantages of not only
accelerating the flow but by the compressing the air, decreasing turbulence. The 2.3-million
square-foot Pearl River Tower redefines what is possible in sustainable design by incorporating
the latest green technology and engineering advancements. The 309-meter tower's sculpted body
directs wind to a pair of openings at its mechanical floors, where traveling winds push turbines
which generate energy for the building.
Figure 3.9 Pearl River Tower [48]
The design for the tower incorporates a series of other integrated sustainable and engineering
elements, including solar panels, double skin curtain wall, chilled ceiling system, under floor
ventilation air, and daylight harvesting, all of which contribute to the building’s energy
In 2008 it was observed that lens and aero foil building forms can overcome wind loads and
minimize their effect on laminar air flow. Two examples of this are the Bahrain World Trade
Centre and the Pearl River Tower in China. The Bahrain World Trade Centre Tower is formed to
collect and squeeze wind flow between the two towers where the horizontal axis wind turbines
are placed.[26]
5. Tool for predicting wind power generation- Wind Climate Analysis- The first part of
assessing the suitability of a tall building for wind power incorporation is to understand
the local wind climate. Unlike rural wind farms, where the nearest anemometer may be
located many miles away, most cities have reasonable lengths of records from nearby
airports. This is not, however, to say these are necessarily good or reliable records. It is
not at all uncommon to see obscure directionality characteristics due to poor anemometer
sitting close to buildings. Wherever possible, records from multiple stations should be
used as a check. A rule of thumb is to use a minimum of 10 years of records to ensure
statistical robustness.
In areas where the availability anemometer records are suitable to describe the local wind
environment a simple wind speed transfer approach can be utilized. In this approach the wind
speed at the anemometer are extended to a gradient height (200 m to 600 m above grade) where
the little terrain has no impact on wind speeds using a power law relationship (A power law is a
special kind of mathematical relationship between two quantities. When the frequency of an event
varies as a power of some attribute of that event, the frequency is said to follow a power law).
The same wind speed is then assumed to exist at gradient height above the site. The winds speeds
are then transferred down to site either using the power law with the site specific exponent or by
measuring the vertical velocity in an atmospheric boundary layer wind tunnel.
When there are no reliable anemometers records within a reasonable distance of the site mesoscale modeling can be used to determine the wind climate of the area. This uses input from
historical meteorological record from may be hundreds of kilometers away to regenerate the
weather system affecting the site.
The directionality of the wind is also important. Incorporation of the turbines into tall buildings
tends to favor limited wind direction usually within a 45 degree sector depending upon the
building configuration and the location of wind turbines on the buildings.
It was concluded that building form manipulation based on wind flow assessments would play an
important role in reducing the turbulence and wind shear around buildings by 10–15% and 15–
30% respectively, which are responsible for reducing energy production from building integrated
wind turbines. This reduction in energy yield from the expected output of the turbines is one of
the main reasons behind a state of uncertainty about the feasibility of integrating wind turbines in
the built environment. In addition to challenges posed to accurately assess wind speeds on site
economic feasibility, environmental and social aspects should also be addressed. [27]
6. Tools for predicting wind power generation by CFD (Computational Fluid Dynamics)Computational fluid dynamics (or CFD) is a vital part of the toolbox of the designer wanting to
efficiently incorporate wind turbines into a building. It is, however, a developmental tool that is
of most use in progress of a design to the stage of experimental testing.
It was asserted that this tool is probably the most accurate tool for assessing wind flow on a
particular site, especially when considering retrofitting wind turbine into an existing building.
However, the major drawback of this tool is the difficultly and expense of even carrying it out
once, let alone having to change measurement locations and times. [32].
The first role that CFD can play is in developing novel turbine forms to best suit the installation
environment. For tall buildings which can, by necessity of space, only incorporate a limited
number of turbines it may not be often that a budget will warrant special turbine designs. CFD is,
however, a useful tool in predicting the comparative efficiency of different designs or the efficacy
of design modifications.
When alternative building shapes are being considered to enhance the efficiency of turbines, CFD
can also be a useful tool in investigating the general benefits of different forms. This can be a
very useful visual tool in identifying flow patterns and aspects of the design leading to them. It
offers a relatively quick way to make and test a substantial number of design options.
The one area where CFD is weakest is in the prediction of flows in very dense urban
environments. At the moment, there is simply not sufficient computational power to accurately
model the effects of turbulence in the built environment. As turbulence is one of the key items
affecting how wind flows around buildings this makes CFD an unsuitable tool for use beyond a
general comparison of alternative designs. It certainly can’t accurately account for the effects of
surrounding, buildings or give outright quantitative advice on expected power outputs. For those
tasks, a combined analysis using both CFD and the wind tunnel is needed.
Many researchers considered mathematical models difficult to use, extremely time consuming
and requires a thorough knowledge of fluid dynamics. In addition, CFD modeling is considered
the development of the mathematical models as it relies on solving the Navier-Stoke equations
which are still the cornerstone of CFD codes applied in practical studies. However, there is
currently a considerable effort in research to develop other simulation models to solve the
turbulence problem. One of these techniques is the use of Large Eddy simulation (LES)
techniques in CFD which successfully simulates wind flow at pedestrian level; another model is
the Reynolds-averaged Navier-Strokes. [29]
7. Prediction of Wind Power Generation- Wind Tunnel Measurement- Wind tunnel
measurements are used first as a design tool in the development of turbines. It is common to test a
number of different design modifications during a test. It is, however, difficult to accurately
model the full effects of turbulence in the wind tunnel; as the scale of turbulence that can be
generated is limited by the physical size of the tunnel.
The wind tunnel can also be used to determine the effects of surrounding buildings and terrain on
conditions at a proposed site. [33]
A terrain model, at a scale of 1:986, is shown for a rural site in Figure3.10. This is used to
determine the effects of large-scale topography and where there is a large site to determine the
best locations on the site for the installation of turbines.
On the contrary experiments were carried out proving that in situ measurements are loaded with
errors especially at pedestrian level in the built environment which could reach 20%. However,
both CFD and Wind Tunnel Tests have embedded errors.
Currently CFD is used in modeling the potential of introducing natural ventilation in high rise
buildings. This could be taken a step further to look into account enhancing the building form to
improve wind power generation. Swiss Re-building by Fosters and Partners was extensively
modelled to capture natural ventilation in its atriums throughout the building height and assess
reducing the wind turbulences on pedestrians. On the other hand there were theories warning that
the current computational power renders CFD simulation incapable of accurately modeling
turbulent wind flow in very dense urban environments. [34] and [29]
Figure 3.10 A 1986 scale model of terrain installed in a boundary layer wind tunnel to evaluate
the optimum placement of wind turbines.[37].
Figure 2 shows a typical wind tunnel turntable in use during measurements to determine wind
conditions above a tall building in Shanghai. This model is at a scale of 1:300. The blocks, trip
board, and spires upwind of the model are used to generate the expected wind characteristics from
far-field buildings and terrain. The effects of individual buildings within about 400 m of the testsite are accounted for by their inclusion on this surround model. A directional pressure probe is
used to measure wind speed, change in direction, and
Figure 3.11 Photograph of a scale model installed
in an atmospheric boundary layer wind tunnel to evaluate the potential for building integrated
wind turbines[37]
turbulence at the proposed turbine locations . Note that in this case, measurements were made at
a series of locations over the roof to determine both the best locations for sitting turbines, and the
turbine types most suited for installation. The measurements were then used in an analysis to
predict power output from a number of types of turbine.
8. Wind Turbine Selection Process- Three kinds of wind turbines can be integrated into the
building to generate electricity. Horizontal axis wind turbines are normally pole mounted and turn
to face the direction of the wind thus maximizing energy yield. The practical application of such
turbines to buildings in variable direction wind climates is therefore very difficult. The majority
of architectural studies deploying building-integrated, horizontal axis turbines deploy the
principle of a fixed turbine as in the case of the Bahrain World Trade Center. Development for
vertical axis wind turbines is encouraging and of course they benefit from the advantage of being
truly Omni-directional. However, at the time of design development for this project, large scale
proven vertical axis turbines were not available for building application.
Horizontal axis wind turbines with a yawing system may be used allow the turbine to change
direction facing the prevailing wind. However, if the wind frequently changes direction, this
would affect the energy yield of the turbine negatively. A vertical axis wind turbine would be
recommended as it is dependent on the wind speed rather than the wind direction and can
withstand changing wind direction and turbulent wind flow. Reducing the effect of the changing
wind direction could be overcome if the building form is shaped in a way to direct wind towards
the installed turbine. [27]
In 2009 the following research classified three methods of integrating wind turbines into the built
environment; the first is the building integrated wind turbines, where a separate wind turbine is
located on a free-standing tower away from the building itself; the second is the building mounted
wind turbines, where the wind turbine is installed on to the building structure and the third is the
building augmented wind turbines where the building form is shaped to concentrate wind flow
and is shaped towards the wind turbine. [21]
All four of the turbines that can be described as vertical axis Darrieus wind turbines. VAWTs are
expected to have a better chance of withstanding the strong wind shear predicted to exist on the
roof of the building.
The fixed horizontal turbine suffers the drawback of only being able to operate with wind from a
limited azimuth range, if problems with blade deflections and stressing through excessive skew
flow are to be avoided. From the outset of this project, the shape of the towers has been designed
to capture the incoming wind and funnel it between the towers.
Extensive wind tunnel modeling that was latterly validated by CFD modeling, examples of which
are illustrated in Fig.3.12 have shown that the incoming wind is in effect deflected by the towers
in the form of an S-shaped streamline which passes through the space between the towers at an
angle within the wind skew tolerance of the wind turbine. Engineering predictions show that the
turbine will be able to operate for wind.
Fig 3.12 CFD Images by Ramboll showing airflow patterns near towers, simulated at the level of
the top turbine for different free, undisturbed wind incidence angles with respect to an ’x’ axis
(i.e. horizontal line connecting towers)[37]
directions between 270° and 360°, however, caution has been applied and turbine predictions and
initial operating regimes are based a more limited range of between 285° and 345°. At all wind
directions outside of this range the turbine will automatically adopt a standstill mode. It is no
coincidence that the buildings are orientated toward the extremely dominant prevailing wind.
Simulation for wind turbine taken from [31].
3.11 Conclusion
It can be concluded the out of all types of integrating wind turbines in a built environment, it is
the Building Augmented Wind Turbines (BWAT is a turbine augmented in the building and is a
part of it for example Bahrain Trade Center) which gives the opportunity to the architects to
express their concerns towards the environmental friendly design where the part of the building
plays a important role in harnessing energy. However to ensure feasibility of their design a
complete assessment of wind flow characteristics needs to be accessed for which CFD
simulations are carried out for assessing wind flow in the built environment though it has been
noted that CFD simulations is not an accurate tool and should be validated by other available
tools which also are embedded with errors. Calculating these errors and taking them into account
when assessing the feasibility of integrating wind turbines.
As of now all the researches on this area have been focused on environmental and economic
feasibility which were directly related to reduction in carbon emission and energy yield
respectively. High initial cost and long pay back periods of urban wind turbines has not yet let it
to be competitive in the market. This can be overcome by better understanding of the
performance and integration of wind turbines on the buildings. However researchers should
address some public concern about the integration of wind turbine.
As the BAWT offers greatest potential in terms of producing energy a new way of thinking about
the augmentation is required: a new methodology needs to be developed to enable successful
integration of wind energy integration into the buildings we design and use. This is not only about
sculpting the building form to channel the wind through the turbines, it is a holistic approach,
integrating form, structure, fabric, services, space usage and wind energy generation into one
The Bahrain World Trade Centre, the Pearl River Tower and the Strata SE1 building are the first
steps in augmenting the building form to enhance wind generation, but these are just the first
steps, we need to integrate not only energy generation into the design but the whole function of
the building.
As of the existing research there more research which is required in terms of methodology of the
design of the building for generation of electricity. More learning is required in the design
parameter from the past successes and failures. More research is required not only for the purpose
generating more energy or CO2.
Although technology has advanced dramatically over the last decade and architectural has shown
ways of bringing the technology of wind turbine and building designs together though there is no
consensus on the possibilities and advantages of generating clean energy and incorporating wind
turbines in tall buildings. In early stage majority of proposals with photovoltaic cells and wind
turbines were removed as projects develops, mainly due to economic reasons but also due to but
also due to technical issues and urban planning restrictions.
There are a number of issues that must be put into prospective for proper implementation of wind
turbines over tall buildings.
1. Safety
2. Environmental Aspects (noise, views etc.)
3. Economy
4. Technical and Practical Issues.
1. Safety- This implies safety to the surrounding areas and its inhabitants and safety to the
building on which the turbine is installed plus other safety issues related to the electrical
2. Environmental Aspects (noise, views etc.)- Environmental concerns such as noise is
another important issue which needs consideration while designing the building installed
turbine. Another concern is the vibration due continuous operation of the wind turbine.
Depending on the architecture of the building the selection of the turbine should be made
for instance if the building has a prevailing skew wind then a Savonius turbine may be
installed with its axis horizontal instead of vertical.
3. Economy- The economy of the project depends on the cost of commercial wind turbines
(it must be economically viable for the money to be spent on it) unless there are some
other issues to outweigh the economy of the wind project such as health, clean
environment and urgency economic concerns always pay an important role in the
decision making. This however depends on the cost of electric power and also on the
wind speed in the region.
4. Practical and Technical Issues- The installed wind turbine output electricity is connected
to the electric grid and this is not the only way that the energy from the wind can be used.
This implies that the output of the turbine can be employed in other ways such as water
and space heating. In other words the electricity is used in a viable manner.
Technology and the integration of technologies and system thinking develops rapidly, what is
current today will be obsolete in five years’ time. So we will never get ‘a solution’ but we need to
get closer to a solution
Chapter 4
As Sustainable development is defined as living, producing and consuming in the manner
that meets the needs of the present without compromising the ability of future generations
and the word “development” refers to the improvement in quality of life especially
standard of living in less development countries of the world. The concept of sustainable
development was widely accepted following seminal report on the World Commission on
Environment and development in 1987. The commission was set up as unevenness in
economic development and population growth were and are still placing unprecedented
pressure on our planets lands, waters and other natural resources. So for the purpose
saving the natural resources from extinction need for reliable energy resources was
recommended. Sustainable energy resources such as bio-mass, hydro-power, solar and
wind energy have their own in such a way that no quantitative assessment can be made.
The contribution of the bio-mass is 3% of the total US energy consumption and is
considered easily dispatch able have low Sox emission, along with carbon-di-oxide
neutral, moreover in long term prospect it may be possible to apply innovations in
biotechnology to breed plants that directly convert sunlight to gasoline and other
premium products. Although hydro-power is currently the largest producer of electricity
from renewable energy resources but its role is less certain in long term due to reason of
high capital investment and mega-scale project that involves dams and their subsequent
land inundation. Advanced technology for near term improvements needs to focus on the
existing hydro stations to address varies issue such as fish migration and oxygen depletion issues
and the long term innovations for utilizing low head and run of water resources in an
environmentally and economically sustainable manner. Solar energy as discussed has large
potential in producing electricity still more research is required in this field to make it one of the
major source of energy production. The major focus of the research should be application based
focusing on the particular application like pharmaceutical application where solar reforming of
low hydro-carbon fuels such as LPG and natural gas into syngas which can be used in gas
turbines for better efficiency and manufacture of solar aluminum which is a very energy intensive
process, moreover the production of solar zinc which is a very valuable commodities. Solar
photochemical process is a detoxification technology that can provide environmental waste
management industry with a powerful tool to destroy waste with clean energy from the sun. The
approach of research is more of application based rather than general based application. The
research on new materials for reflectors and heat absorption is important for development in this
field. The objective is to create materials with high reflectivity approaching unity and high heat
absorption and low emittance as to enhance the thermal behavior of solar energy collectors.
simply switch energy forms if the alternative will not be able to securely sustain its
people. Thus, for such developing countries, it seems that the only thing that can be done
for the time being is to slowly offer alternatives, to give aid in implementing new forms
of energy, and to suggest laws through international policy that will force the abatement
Wind Energy from an economic stand point is the most deserving green supply option for
more widespread deployment. Earlier there weren’t significant taxes and/or credits
assigned to carbon-di-oxide released or avoidance so wind energy didn’t get that
popularity. Moreover the popularity of wind energy was undermined due to following
A lingering lack of confidence in reliability because of the high failure rate experience by
some product lines in recent past.
The turmoil brought about by electric utility deregulation.
Historically low prices for coal, oil, gas and uranium which is lower than at any time in
the past century.
The lack of consistent, coordinated, stable national energy policy and the resulting
vacillation between acceptance and rejection of subsidies such as tax credit allowance
and R&D support
Since the technological aspects of the wind energy system has attained near maturity we are
unlikely to see further advances of the sort that improved rotor blade efficiency by 30% over
the past 2 decades. Incremental improvements foreseeable in the near term include-
Still better power electronics to improve wind generation interference with the grid.
Cheaper, better understood composite materials for blade construction.
Power train simplification, for example elimination of gear boxes (which accounts for
30% of unit cost) by use of multi-pole generators.
Intelligent online monitoring, diagnostic and control system to maximize power
extraction and minimize the susceptibility to damage from off normal condition.
In the policy area, more widespread promotion of green power at a voluntary premium
Improved modeling in all respects aerodynamics and fluid dynamics structural,
power conditioning, grid integration, system planning and environmental
As the transmission of energy from wind mills is expensive and incurs losses a new concept of
producing electricity from wind turbine over tall buildings was introduced. It gave a opportunity
to the architects to express their concerns towards the environmental friendly design where the
part of the building plays a important role in harnessing energy. However to ensure feasibility of
their design a complete assessment of wind flow characteristics needs to be accessed for which
CFD simulations are carried out for assessing wind flow in the built environment though it has
been noted that CFD simulations is not an accurate tool and should be validated by other
available tools which also are embedded with errors. Calculating these errors and taking them
into account these errors is the major issue when assessing the feasibility of integrating wind
High initial cost and long pay back periods of urban wind turbines has not yet let it to be
competitive in the market. This can be overcome by better understanding of the performance and
integration of wind turbines on the buildings. The Bahrain World Trade Centre, the Pearl River
Tower and the Strata SE1 building are the first steps in augmenting the building form to enhance
wind generation, but these are just the first steps, we need to integrate not only energy generation
into the design but the whole function of the building.
As of the existing research there has to be more research required in terms of methodology of the
design of the building for generation of electricity. More learning is required in the design
parameter from the past successes and failures.
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