CIEM 2013
A NEW CONCEPT OF RENEWABLE POWER PLANT,
SWPP-STO
1
VIOREL SERBAN , ANA MARIA ANDRONACHE1, RALUCA DINCA1,
MARIAN ANDRONE1, MADALINA ANGELA ZAMFIR1, GEORGE
ALEXANDRU CIOCAN1, CARMEN ANCA SAFTA2, LAURA ELENA
SERBAN3, VIORELA MARIA POSTOLACHE3, LIVIU DAN POSTOLACHE3
The objective of this paper is to present a new concept of an efficient power
plant which collects and transforms solar and wind power into electric energy, has
the capacity to store the energy in the form of pressure energy and then, when is
need it, to produce electricity from the stored energy. Collection of solar and wind
energy is achieved by high-efficiency and environmental friendly technologies. The
power plant can be placed in any location, including in urban areas because its
architecture is not in contradiction with the traditional urban architecture. The
power plant can serve restricted collectivities and can be connected to the power
system and be used in the regulation of load curve.
Keywords: power plant, wind, solar, energy storage, energy integration strategy
1. Overview
Generation of wind and solar energy is random, on short-term,
determining instability problems for the power system. These problems lead to
power cuts or to the stopping of conventional (thermal and hydro) power
generating units. Low efficiency, under these operating conditions, has caused the
enhancement of the environment pollution and the wear of the electricity
generating equipment from the conventional power plants. Thus, the operating
costs have increased. Besides these, there is also the fact that the large power
transfers from the solar or wind farms determine system losses and technical
issues related to the development of the high-voltage transmission line system.
This is why, the necessity to find effective and reliable solutions, for the
renewable energy storage and energy reuse, came out worldwide, [1].
The paper presents the concept of a compact solar and wind power plant
which can store and reuse the energy, SWPP-STO (Solar and Wind Power Plant
with Storage). SWPP-STO collects the renewable energy, uses the known
1
Subsidiary of Technology and Engineering for Nuclear Projects, str. Atomistilor, no. 409,
Magurele, Romania
2
Assoc. Prof., Power Engineering Faculty, University “Politehnica” of Bucharest, Romania
3
SC SIGMA PATENT STUDIO SRL, str. Barbat Voievod , no. 45A, Bucharest, Romania
Viorel Serban, A. M. Andronache, R. Dinca, M. Androne, M. A. Zamfir, G. A. Ciocan,
C. A. Safta, L. E. Serban, V. M. Serban, L. D. Postolache
technologies of solar energy conversion, by means of photovoltaic panels, and of
wind energy conversion, by means of new wind turbines (NWT), but also
promotes a new indirect collection technology for the solar energy. Difference
between the conversion and collection concept is made.
SWPP-STO consists of a cylindrical tank made of reinforced concrete, and
provided inside with a metal lining. Wind energy is collected by means of newly
developed wind turbines - NWT, installed on the upper side of the tank. Solar
energy is indirectly collected by means of the greenhouse effect and chimney
effect. Energy is stored using the compressed air as storage technology. Stored
energy can be reused, on request, depending on the system demands, employing
the related equipment and discharging the compressed air into the NWT.
SWPP-STO power plants can be effectively used for the adjustment of the
load curve, by means of the electricity consumption during the night and day gap
period and electricity generation during the evening and morning peaks of the
load curve, as the electricity generation can be virtually instantaneously started or
stopped.
Energy storage is the best renewable energy integration strategy.
2. The current system for conversion and storage of renewable energy
Collection of wind energy, as currently carried out, can be done only for
the areas with a high and relatively continuous energy potential. The disadvantage
of wind energy collection is that the wind energy conversion has a low efficiency
and generates a number of problems that affect the environment. This is why in
nowadays the wind energy is operated only on-shore and off-shore, by building
large farms of wind turbines, of which blade diameter can reach up to 150m
(Vestas V164-8.0 MW with 164m rotor diameter), [2]. These areas are located far
away from the electric energy users, causing issues with regard to its transmission
and the related losses. Large sizes also generate manufacturing, transportation and
installation issues, and the component parts in operation involve risks determined
by high centrifugal forces occurring on the blades.
Wind parks that randomly feed and interrupt high capacities, generate
issues as regards the power system stability. In order to maintain a balance
between the capacity supplied and the capacity consumed, capacities equal to the
capacity generated by the wind turbines have to be taken out from the power
system. These operating conditions lead to power cuts at the conventional power
plants, or to their shut-down. When the wind turbines are randomly stopped, the
restarting of the conventional equipment is needed, in order to cover the power
deficit. Start-ups and shut-downs and the capacity variations increase the fuel
consumption in the conventional power plants, meanwhile increasing their
pollution level, decreasing their efficiency and increasing their wear.
Solar and wind energy power plant with energy storage and reuse it
As a result of these shortcomings, in order to reduce the negative effect of
wind energy operation system, the development of effective technologies for
small and relatively evenly distributed capacity within the power system is
encouraged [3]. A new wind turbine technology was developing to enable the
efficient conversion and collection of the wind energy from the urban area. Small
wind turbines have known a sustainable development over the last decade, [4].
According to the “Small Wind World Report, 2012”, there were more than 330
worldwide manufacturing companies of small wind turbines, at the end of 2011.
Small horizontal axis turbines are usually turbines with propeller rotor,
having one, two, three blades (commercial type) or several blades (farmer’s
wheel), [5]. Rotor has to be oriented in the wind direction, by means of additional
mechanical systems. These turbines are sensitive to the change of wind direction,
and their performances are negatively influenced by the continuous adjustment of
the turbine according to the wind direction. Figure 1 shows several commercial
types of such turbines, being indicated their commercial name.
Small vertical axis turbines, figure 2, are designed for urban areas of wind
energy conversion.
Swift
Turby
Eclectic
Fortis Montana
Fig. 1. – Small Horizontal Axis Wind Turbine, HAWTs
WindSide
Fig. 4. – Small Vertical Axis Wind Turbines, VAWTs
Ropatec
The advantage of these turbines is represented by their robust structure, which,
when the wind direction changes, has no negative effects on the wind turbine
Viorel Serban, A. M. Andronache, R. Dinca, M. Androne, M. A. Zamfir, G. A. Ciocan,
C. A. Safta, L. E. Serban, V. M. Serban, L. D. Postolache
efficiency. However, the efficiency of these turbines, no matter their (high or low)
capacity, is lower as compared to the horizontal axis turbines, [6].
As a disadvantage of the currently used wind turbines is the high wind
velocity of starting the wind turbine (between 3m/s and 5m/s), and also the
necessity of braking of the turbine at very high wind velocities.
Noise level of a wind turbine placed at 250m distance, as compared to
other noise sources, is of 50 dB, according to the American Wind Energy
Association [7], but once the wear of the mechanical parts increases, this value
may also increase, also determining an enhancement of the vibration level. Thus,
there are added a shorter lifetime, as compared to the hydraulic turbines or steam
turbines, and the need for a well-structured maintenance service.
Energy storage technologies can be divided into three main groups:
mechanical, electrochemical and electromagnetic storage [8]. Mechanical storage
includes pumped hydro storage, compressed air energy storage and flywheels.
Electrochemical storage includes all types of batteries. Electromagnetic storage
includes super capacitors and superconducting magnetic energy storage.
Regarding the storage time the energy storage technologies are energy storage
systems with short storage period (from which the storage time is less than 10
minutes) and energy storage systems on long periods, figure 3.
Fig. 3. Discharge times of different energy storage technologies, [8]. The short storage systems are
summarized in SMES, Superconducting Magnetic Energy Storage, SCES super capacitor energy
storage and FES flywheel storage systems. The long-term storage systems are known as BES,
Battery Energy Storage, HES, hydrogen energy storage, PHES pumped hydroelectric energy
storage and CAES, compressed air energy storage.
According to the relevant literature, there are no solar-wind power plants
enabling the storage and reuse of the renewable energy so far.
Solar and wind energy power plant with energy storage and reuse it
3. Solar and wind power plant with energy storage and
reuse, SWPP-STO
Power plant SWPP-STO is develop on the technologies based on the
efficient operation of renewable energy, solar and wind, through sustainable
processes and cleans with low specific investment.
Electricity storage is a topical issue and meet a balanced and stable energy
system, for which the intermittent nature of solar and wind energy resources is no
longer a problem and a "burden", [9, 10].
SWPP-STO power plant is a watertight structure made of reinforced
concrete, of tower type, which represents both the compressed air tank for energy
storage, as well as the support for the renewable energy collecting equipment,
wind turbines and photovoltaic panels, respectively. Reinforced concrete structure
also supports the air compression equipment and the one generating electric
energy from the compressed air, and the equipment for the power plant operation
control and command, as well, figure 4.
Main body of SWPP-STO has a cylindrical shape with thick walls, bottom
and cover of convex shape and is provided inside with a metal lining, forming the
main tank for the energy as compressed air. Newly developed wind turbines,
NWT, are installed on the upper side of the main body. Technological chain for
the energy storage and for the reuse of the stored energy is also installed on the
upper side of the main cylindrical body. Technological chain consists of the
compressors, compressed air turbines and NWT.
On the outside the main body, channels are built on vertical plane, evenly
distributed and closed by sloping membrane sections, transparent to the solar
radiation, by means of which the greenhouse and chimney effects occur with
maximum intensity. Channels also collect the wind energy from the vertical
surface of the building and direct it towards the NWT, installed on the SWPP-STO parapet.
Photovoltaic panels can be installed, as well, on solar radiation transparent
support, instead of the transparent membranes.
Fig. 4. SWPP-STO general view and new wind turbine detail (last foto)
Circular secondary body is placed on the lower side of the main body. This
Viorel Serban, A. M. Andronache, R. Dinca, M. Androne, M. A. Zamfir, G. A. Ciocan,
C. A. Safta, L. E. Serban, V. M. Serban, L. D. Postolache
consists of a basement or basement and ground floor, forming a rigid box along
with the main body, in order to provide the SWPP-STO stability.
In the northern part of the main body there is the tower auxiliary body,
where there are installed the equipment, the batteries used to create a buffer stock
of small power electric energy, such as to re-store it in the main tank, and
auxiliary equipment serving the SWPP-STO power plant, as well. The three
structural elements (the main body, the circular secondary body and the tower
auxiliary body) have a common foundation between them.
Power plant bodies are made of reinforced concrete with granite
aggregates that have a high heating capacity to store the energy from solar
radiation, being of black color outside in order to capture, with maximum
efficiency, the energy from the solar radiation.
SWPP-STO can be also coupled to other adjacent renewable energy
generating units, to store the energy generated due to its existing wind or solar
potential. Stored energy shall be released on demand (of the National Power
System or from the independent users of local urban communities).
Collection of renewable energy, its storage and reuse, by means of
SWPP-STO, are performed as follows:
Wind energy is collected by NWT installed at the upper side, on the
circular parapet of the main body and in the central area. NWT turbines from the
central area are mounted on a metal structure, self-oriented, depending on the air
currents direction. NWT are newly developed, carried out within the project, and
consist of a modular rotor with blades, with gradual drive and response, and of a
twin stator made of fixed and mobile deflectors directing the air currents.
Constructively, the NWT turbines control the air flow acting on the rotor;
therefore they are not to be stopped at high velocities of the air currents, as
compared to the horizontal wind turbines, with propeller, currently on the market.
Wind energy related to the surface of a vertical section through the SWPP-STO
axis is collected by re-directing the air currents towards the NWT by means of
outdoor canals covered by inclined panels, on sections.
Solar energy is indirectly collected as kinetic energy given by the air
currents caused by the chimney effect and greenhouse effect. During the daylight,
the power plant walls and the tapered covering capture and store large amounts of
thermal energy from the solar radiation, with an efficiency of 85 – 95%, which
increases the temperature of the main body walls outside channels. Heating of
walls and of the tapered covering generates air currents known as chimney
currents, of which kinetic energy is converted into electric energy by means of
NWT turbines. Heating is also accelerated by the greenhouse effect caused by the
outside channels closed with solar radiation transparent membranes. Tapered
covering of the circular secondary body is equipped with trapezoidal channels on
the upper side, in order to increase the solar radiation capture surface. Mirrors can
Solar and wind energy power plant with energy storage and reuse it
be placed near the power plant, in order to concentrate the solar radiation on the
power plant walls, and in particular on the tapered covering. Efficiency of these
turbines is of 40 - 50%. By means of this procedure, solar energy is converted into
electric energy with an average efficiency of 30% - 45%, which is about 2 to 4
times higher than the solar energy conversion into electric energy by means of
6/54 regular photovoltaic panels.
Pressure energy is stored as compressed air in the sealed tank inside the
main body. Energy is stored at pressures between 4 to 10bar of overpressure. Air
is compressed by means of a set of compressors, with a relatively wide capacity
range, randomly supplied, depending on the available renewable energy. For
electric capacities of up to 2kW, the energy is stored within a buffer tank of
batteries, up to a capacity of 200kWh, afterwards being transferred to the main
tank, as pressure energy, for the actuation of the compressors, whether in parallel
or not with the presence of direct renewable energy.
Electric energy generation from the pressure energy by discharging the
compressed air into the compressed air turbines, up to a pressure between 0.2 –
0.5 bar, afterwards it is discharged in cornice wind turbines, whether in parallel or
not with the presence of natural air currents caused by the chimney effect and
greenhouse effect.
If the energy storing tank has a diameter of 21 m and a height of 40 m, the electric
energy generated from the stored pressure energy is between 4 and 10MWh,
depending on the compressed air pressure. If the tank has a diameter of 40 m and
the height of 60 m, the electric energy generated from the stored pressure energy
is between 23 and 58MWh. A flow diagram of SWPP-STO is shown in figure 5.
Depending on the power demand of the community served by the solarwind power plant, the unit capacity for the generation of electric energy from the
stored energy can be between 0.5 and 2MW, providing a continuous operation
time of SWPP-STO, between 8 and 12 hours, only by means of the stored energy.
An operation time of up to 180 hours is expected for SWPP-STO power plant,
taking into account the solar and wind renewable energy potential, available in the
area, as well.
Considering the fact that SWPP-STO can operate as a load curve
regulation power plant, its operation time can be continuous. During the day and
night no-load periods of the load curve, the power plant can be supplied by the
National Power System (NPS), in order to store the energy by compressing the
air. During the morning and evening on-load periods, as then when necessary,
SWPP-STO can generate electric energy from the store pressure energy.
In the literature [11, 12] the energy storage technical solutions are
analyzed economically, too. Comparing different technologies of energy storage
on long term, for example pumped storage power plants where the minimum cost
of achieving is $600/kW installed and maintenance cost is $4.3/kW/year, and a
Viorel Serban, A. M. Andronache, R. Dinca, M. Androne, M. A. Zamfir, G. A. Ciocan,
C. A. Safta, L. E. Serban, V. M. Serban, L. D. Postolache
compressed air storage plant where the minimum cost is $425/kW installed and
maintenance cost is $1.35/kW/year [13], it is obvious that the CAES technology is
more convenient financial.
Fig. 5. Technological diagram of SWPP-STO
SWPP-STO can be performed in any location, in order to fully meet all the
electricity demands of communities, with no connections to NPS. The power
plant, due to its electric energy storage and generation capacity, does not disturb
the power system it is connected to, and may efficiently participate to fine
regulations of the load curves.
4. Conclusions
The paper presents a new concept of power plant for renewable energy,
SWPP-STO.
SWPP-STO power plant has the following advantages:
- efficiently collects the wind energy, including from the urban area, by means of
NWT;
- efficiently collects the solar energy, both by means of photovoltaic panels
installed on the SWPP-STO frontage as well as indirectly by means of the
greenhouse and chimney effects generated in the canals from the SWPP-STO
frontage and covered by photovoltaic panels or membranes, both transparent to
solar radiation;
- enables the renewable energy storage as pressure energy by compressing the air
in a large tank, which represents also the support structure of SWPP-STO;
Solar and wind energy power plant with energy storage and reuse it
- is able to supply electric energy when the renewable energy potential is missing,
at a time, by gradually discharging the compressed air in compressed air turbines,
in NWT, respectively;
- installed capacity of one SWPP-STO of average size is of 1MW up to 2MW and
can be also built in urban areas, which complies with the current requirements
related to the decentralization of the renewable energy generation and to the
sustainable development.
SWPP-STO is a good technical solution to use of renewable energy along
with the current issues of reliability, stability and power quality.
REFERENCES
[1].
[2].
[3].
[4].
[5].
[6].
[7].
[8].
[9].
[10].
[11].
[12].
[13].
Stathis Peteves, Power Storage Options to integrate Renewables - TP Wind 1st EnergyR&D
Event – Grid Integration, Oct 4, 2011 – www.jrc.ec.europa.eu.
http://en.wikipedia.org/wiki/Wind_turbine.
***, Facilitating energy storage to allow high penetration of intermittent renewable energy.
European regulatory and market framework conditions for the development of energy
storage infrastructure, www.store-project.eu..
***, Small Wind World Report, 2012, WWEA World Wind Energy Association.
Adrian Bej, “Turbine de vânt”, Editura Politehnica, Timişoara, 2003.
Erich Hau, Wind turbines: fundamentals, technologies, application, economics, Ed.
Springer, 2006.
Colby W.D., Dobie R., Leventhall G., Lipscourt D.M., McCunney R.J., Scilo M.T.,
Soudergaard B., „Wind turbine sound and helth effects; an expert panel review”, AWEA,
Dec. 2009, http://www.awea.org/_cs_upload/learnabout/publications/5728_1.pdf.
Andrijanovits A., Hoimoja H., Vinnikov D., Comparative Review of Long-Term Energy
Storage Technologies for Renewable Energy Systems, Electronics And Electrical
Engineering, 2012. No. 2(118), http://dx.doi.org/10.5755/j01.eee.118.2.1168.
***, Joint EASE/EERA recomandation for a European energy storage technology
development roadmap towards 2030, European Assoc. for storage of Energy, Technical
Annex, www.ease.eu.
***, Energy storage technologies for wind power integration, Technical Report, Universite
Libre de Bruxelles, Faculte de Science Appligue, Service BEAMS Groupe Energie, March,
2010.
Ibrahim H., Ilinca A., Techno-Economic Analysis of Different Energy Storage
Technologies, http://dx.doi.org/10.5772/52220, 2013.
A. Oberhofer, P. Meisen, “Energy Storage Technologies and Their Role in Renewable
Integration”, Global Energy Network Institute, 2012, July.
Wang H., Wang L., Wang X., Yao E., “A Novel Pumped Hydro Combined with Compressed
Air Energy Storage System”, Energies 2013, 6, 1554-1567; doi:10.3390/en6031554, pp.
1554-1567.