Renewable Energy Technologies
(TECC3792)
Lecture Notes - 2021
AT Ndapuka
CH7 Outline
 Other forms of Renewable Energy
•
•
•
•
•
•
Introduction
Wave Energy
Tidal Power
Hydroelectric Power
• Pumped Hydro
Biomass for Electricity
Geothermal
AT Ndapuka
TECC3792
Introduction
 RE Technologies
AT Ndapuka
TECC3792
Introduction

Present and Future Trends
• Global Installed Capacity
AT Ndapuka
TECC3792
Introduction

Present and Future Trends (cont’d)
• Global Installed Capacity (cont’d)
2019 Additions
Total power capacity rose 8.4%
2,588 GW including hydropower
Non hydropower: 14.7% increase
5% growth in biofuel
production
AT Ndapuka
TECC3792
Introduction

Present and Future Trends (cont’d)
• Global Installed Capacity (cont’d)
AT Ndapuka
TECC3792
Other RE Forms
 Wave Energy
• Ocean energy - Energy captured from ocean waves, tides, currents,
salinity gradients and ocean temperature differences.
• Solar energy on earth causes varying temperatures, which in turn
cause winds to blow and create waves on the surface of the ocean.
• These waves are a powerful source of energy.
• Ocean waves are a more predictable resource with a higher energy
density compared to solar and wind. However, harvesting this energy
is a challenge.
• Wave energy converters capture the energy of surface waves to
generate electricity.
• Wave energy projects are still in pilot stage.
AT Ndapuka
TECC3792
Other RE Forms
 Wave Energy (cont’d)
• Wave Energy Resource
• If the waves are assumed to be sinusoidal, then their power per
meter is given by [W/m]:
𝜌𝑔2 𝐻2 𝑇
𝑃=
32𝜋
• Where:
𝜌 − density of sea water (1025 kg/m3)
𝑔 − gravitational acceleration (9.8 m/s2)
𝐻 − trough-to-crest height (m)
𝑇 − wave period (s)
• However, actual waves in the ocean are more complex to be
represented in this way. Several factors still need to be
considered.
AT Ndapuka
TECC3792
Other RE Forms
 Wave Energy (cont’d)
•
Harvesting methods
AT Ndapuka
Terminator
Attenuator
Point Absorbers
Overtopping Device
TECC3792
Other RE Forms
 Methods of harvesting wave energy
• Terminator – partially submerged structures oriented perpendicular
to the direction of the wave to force water into the device.
• Incoming wave compresses the air trapped inside a chamber which in
turn spins the turbine.
AT Ndapuka
TECC3792
Other RE Forms
 Methods of harvesting wave energy (cont’d)
• Attenuator – These are long devices aligned parallel to the
•
•
direction of the wave such that their front end points into the
oncoming wave.
Hydraulic pumps convert the flexing into shaft power for the
generator.
Works with both
vertical and horizontal
waves.
Pelamis Attenuator
AT Ndapuka
TECC3792
Other RE Forms
 Methods of harvesting wave energy (cont’d)
• Point Absorbers –These are floating platforms, not oriented in a
•
particular way toward the waves.
They utilise rise and falls of waves to run the generator.
AT Ndapuka
TECC3792
Other RE Forms
 Methods of harvesting wave energy (cont’d)
•
•
Overtopping Device – Made up of a reservoir, and water is forced
onto the resevoir by the waves.
Water is then rejected from the reservoir through the turbine.
•
Self Study Topic: Predicting Wave Energy Performance (8.3.3)
AT Ndapuka
TECC3792
Other RE Forms
 Wave Energy (cont’d)
Advantages
Disadvantages
• It is highly predictable
compared to wind and
solar.
• It is a renewable form of
energy.
• It is environmental friendly.
• High initial capital.
• Equipment rating and
wave magnitude
complications.
• It can cause damage to
sea life ecosystem.
• Location disadvantage.
• May lead to high
transmission losses.
• Noise and visual concerns.
AT Ndapuka
TECC3792
Other RE Forms
 Tidal Power
• Tides are created by the gravitational effect of the sun and the moon
on the earth.
• The occurrence of tides is highly predictable, but harvesting tidal
energy is a serious challenge.
• Tidal energy is produced through the use of tidal energy generators
which are placed in areas with high tidal movements.
• Generators are designed to capture the kinetic motion of the ebbing
and surging of ocean tides in order to produce electricity.
• Tidal barrages are dams that cross tidal estuaries and capture energy
as tides ebb and flow.
• Tidal Range - The difference between high and low tides. Must be at
least 5 meters.
AT Ndapuka
TECC3792
Other RE Forms
 Tidal Power (cont’d)
• Spring tides (max)
• Neap tides (min)
Source: Alternative Energy Tutorials
AT Ndapuka
TECC3792
Other RE Forms
 Tidal Power (cont’d)
•
Tidal Energy is more developed than wave energy, about 536 MW of
installed capacity by 2016.
•
Major plants in operation:
• 254 MW Sihwa plant in the Republic of Korea (2011).
• 240 MW La Rance tidal power station in France (1966).
•
320 MW Swansea Bay Tidal Lagoon in Wales, was proposed at a
cost of £1.3 billion. The construction was postponed because UK
gov rejected funding the project.
•
At the start of 2017, China released its 13th Five-Year Plan on
Ocean Energy, which targets 50 MW of installed capacity by 2020.
AT Ndapuka
TECC3792
Other RE Forms
 Tidal Technologies
Barrages or Dams
Tidal Fences
Tidal Turbines
AT Ndapuka
TECC3792
Other RE Forms
 Tidal Technologies (cont’d)
• Barrages or Dams
• They use the difference in the vertical height between the
incoming high tides and the outgoing low tides.
• As the tide ebbs and flows, sea water is allowed to flow in or out
of the reservoir.
AT Ndapuka
TECC3792
Other RE Forms
 Tidal Power Technologies
• Barrages or Dams (cont’d)
Source: Alternative Energy Tutorials
AT Ndapuka
TECC3792
Other RE Forms
 Tidal Power Technologies (cont’d)
• Tidal Fences
• These are vertical axis turbines mounted in a fence or row
placed on the sea bed.
AT Ndapuka
TECC3792
Other RE Forms
 Tidal Power Technologies (cont’d)
• Tidal Turbines
• Tidal turbines are similar to wind turbines.
• They are normally placed on the sea floor where the tidal flow is
strong.
• They are heavier than WT.
• Also expensive to build.
AT Ndapuka
TECC3792
Other RE Forms
 Tidal Power (cont’d)
• Tidal Turbines: Operating Principle
• A tidal current generator operates exactly in the same way as the
wind turbine.
• The only difference is that here, the driving force is water which is
more denser than air.
• Therefore, the wind equations also do apply here.
• Power in the water:
1
𝑃𝑤 = 𝜌𝐴𝑣 3
2
where
AT Ndapuka
𝜌 = 1025 kg/m3
TECC3792
Other RE Forms
 Tidal Power (cont’d)
Advantages
• It is a renewable energy resource.
• Produces free and green energy.
• Low visual impact as the tidal turbines are mainly if not totally
submerged beneath the water.
• Low noise pollution as any sound generated is transmitted through
the water.
• High predictability as high and low tides can be predicted years in
advance, unlike wind.
• Tidal barrages provide protection against flooding and land damage.
• Large tidal reservoirs have multiple uses and can create recreational
lakes and areas.
AT Ndapuka
TECC3792
Other RE Forms
 Tidal Power (cont’d)
Disadvantages
• Disturbs sea life migration.
• Build up of silt, sediments and
pollutants within the tidal barrage.
• Requires a suitable site, where
the tides are consistently strong.
• Higher capital costs (construction
and maintenance costs/W).
• High power distribution costs.
Long undersea cables.
• Intermittency in nature.
• Danger to fish and other sea-life
as they get stuck in the barrage
or sucked through the tidal
turbine blades.
AT Ndapuka
Other issues
• Higher payback periods.
• Therefore, not cost effective
compared to conventional
sources.
TECC3792
Other RE Forms
 Hydro Power
• Hydro forms up a significant part of the global electricity supply.
• Over 1 TW installed global capacity (16.5%).
• The largest hydro plants are Three Gorges 22.4 GW (China) and
Itaipu 14 GW (Brazil).
• About 350 GW installed in China.
• 330 MW installed in Namibia, Ruacana Hydro Power Station.
• Hydro is a mature and established technology.
• It is flexible; can provide baseload power, peaking power, spinning
reserve or even storage.
• Small hydro is becoming attractive and cost effective.
AT Ndapuka
TECC3792
Other RE Forms
 Hydro Power (cont’d)
• Global Capacity
• 19.4 GW were
added to reach a
total of 1,170 GW
• China continues to
lead the market.
Hydropower Global Capacity, Shares of Top 10 Countries
and Rest of World, 2020 (GSR2021)
AT Ndapuka
TECC3792
Other RE Forms
 Hydro Power (cont’d)
• Hydropower Configurations
1. Run-of-the-river plants
2. Hydro with Storage
3. Pumped Hydro
AT Ndapuka
TECC3792
Other RE Forms
 Hydro Power (cont’d)
• Operating Principle
• Potential, pressure and kinetic energy associated with hydro
plants.
• Energy Head: (pressure and velocity head)
𝑝 𝑣2
𝐸𝑛𝑒𝑟𝑔𝑦 𝐻𝑒𝑎𝑑 = 𝑧 + +
𝛾 2𝑔
• Where:
𝑧 − elevation above reference height [m].
𝑝 − pressure [N/m2]
𝛾 − specific weight [N/m3]
𝑣 − average velocity [m/s]
g − gravitational acceleration [9.81 m/s2)
AT Ndapuka
TECC3792
Other RE Forms
 Hydro Power (cont’d)
• Operating Principle (cont’d)
• Q – Flow rate [m3/s)
• HG – Gross Head [m]
• Without considering losses:
𝑃 = 9.81 × 𝑄 × 𝐻𝐺
[kW]
• Considering losses:
𝑃 = 9.81 × 𝜂 × 𝑄 × 𝐻𝑁
[kW]
• 𝐻𝑁 = 𝐻𝐺 − 𝑃𝑖𝑝𝑖𝑛𝑔 𝑙𝑜𝑠𝑠𝑒𝑠
AT Ndapuka
TECC3792
Other RE Forms
 Hydro Power (cont’d)
• Operating Principle (cont’d)
• H – Gloss Head [m]
AT Ndapuka
TECC3792
Other RE Forms
 Hydro Power (cont’d)
• Types of Turbines
• Impulse Turbines – uses the velocity (kinetic energy) of the
water to move the runner and discharges to atmospheric
pressure. Ideal for sites with head.
• Pelton and cross flow turbines.
AT Ndapuka
TECC3792
Other RE Forms
 Hydro Power (cont’d)
• Types of Turbines (cont’d)
• Reaction Turbines – Gets power from the combined action of
pressure and moving water.
• Good for sites with lower head and higher flows compared with
the impulse turbines.
• Propeller
• Kaplan
• Straflo
• Bulb Turbine, etc.
• Francis Turbine
AT Ndapuka
TECC3792
Other RE Forms
 Pumped Hydro
• Water is pumped from low reservoir to upper reservoir when surplus
power is available.
• Reversible pump-turbine/motor-generator assemblies can act as both
pumps and turbines.
• Fully commercialized utility-scale storage technology.
AT Ndapuka
TECC3792
Other RE Forms
 Pumped Hydro (cont’d)
• China is the leading installer of pumped storage in 2016, 3.7 GW of
27 GW, followed by South Africa, Switzerland, Portugal and the
Russian Federation. [GSR 2017]
• In 2017, pumped storage capacity grew by 1.8 GW (2%) to 28.5 GW,
and a further 39 GW is under construction. [GSR 2018]
• South Africa completed the installation of three turbines (333 MW
each) of the 1.3 GW Ingula pumped storage plant in 2016; the fourth
and final turbine became operational in January 2017
• Pumped storage hydropower is the dominant source of largescale
energy storage, accounting for an estimated 96% of global energy
storage capacity.
AT Ndapuka
TECC3792
Other RE Forms
 Pumped Hydro (cont’d)
• Advantages
• Peak power supply capability.
• Can start and shutdown very quickly ( in minutes).
• Can switch between pumping and generation in half an hour.
• Ideal for load following and grid stabilisation.
• The most cost-effective bulk grid storage.
• Acts as a good way to deal with excess power from intermittent
sources.
AT Ndapuka
TECC3792
Other RE Forms
 Pumped Hydro (cont’d)
• Two-Penstock Pumped Storage System
AT Ndapuka
TECC3792
Other RE Forms
 Pumped Hydro (cont’d)
• Two-Penstock Pumped Storage System (cont’d)
• The energy available in the upper reservoir relative to the lower
one is expressed as [kWh]:
𝑉 × 𝑔 × 𝐻 𝜌𝐴𝑔∆ℎ × 𝐻
𝐸=
=
3.6 × 106
3.6 × 106
224 m
224 m piping
30 m
AT Ndapuka
TECC3792
Other RE Forms
 Biomass Power
• Biomass is fuel that is developed from organic materials (plants or
animals), a renewable and sustainable source of energy.
• Biomass energy is carbon neutral.
AT Ndapuka
TECC3792
Other RE Forms
 Biomass Power (cont’d)
• Market Share (Biomass for power)
• 6.5% global increase in 2018, 7% in 2017.
AT Ndapuka
TECC3792
Other RE Forms
 Biomass Power (cont’d)
• Market Share (Biomass for power)
AT Ndapuka
TECC3792
Other RE Forms
 Biomass Power (cont’d)
• Market Share (Biomass for power)
AT Ndapuka
TECC3792
Other RE Forms
 Biomass Power (cont’d)
• Biomass Fuels
AT Ndapuka
TECC3792
Other RE Forms
 Biomass Power (cont’d)
• Biomass Fuels (cont’d)
• Energy density comparison
AT Ndapuka
TECC3792
Other RE Forms
 Biomass Power (cont’d)
• Biomass Conversion Processes
• Combustion – Is when the biomass is being burned in higher
pressure boiler to generate steam.
• Gasification – This is achieved by partial combustion of biomass
in low oxygen environment, leading to the release of a gaseous
product. The resulting gas can then be used in combustion
engines, micro-turbines, fuel cells or gas turbines.
• Pyrolysis - In pyrolysis, the partial combustion is stopped at a
lower temperature (450°C to 600°C), resulting in the creation of a
liquid bio-oil. The pyrolysis oil can then be used as a fuel to
generate electricity.
AT Ndapuka
TECC3792
Other RE Forms
 Biomass Power (cont’d)
• Biomass Conversion Processes (cont’d)
• Solid biomass can be burned directly to produce heat.
• Biomass can also be converted into a gas called biogas or into
liquid biofuels such as ethanol and biodiesel.
• Biogas can also be produced by processing sewage and animal
manure in special vessels called biodigesters.
• Ethanol is made from crops such as corn and sugar cane that are
fermented to produce fuel ethanol for use in vehicles.
AT Ndapuka
TECC3792
Other RE Forms
 Biomass Power (cont’d)
• Combined Heat and Power (CHP)
• CHP is the simultaneous production of electricity and heat from
one source of energy.
• It can achieve higher overall efficiencies.
AT Ndapuka
TECC3792
Other RE Forms
 Biomass Power (cont’d)
Advantages
Disadvantages
• Improved forest health,
• Carbon Neutrality (O2 in, CO2
out),
• Reliable (comparable to
coal),
• Value addition to some
products,
• Affordable.
• Low energy density,
• Seasonal/annual fluctuation
in biomass supply,
• Land use competition (food or
biomass),
• Risk of deforestation,
• Requires plenty of water.
AT Ndapuka
TECC3792
Other RE Forms
 Geothermal Power
• The use of heat from deep inside the earth to generate electricity.
AT Ndapuka
TECC3792
Other RE Forms
 Geothermal Power (cont’d)
• Global Status
• Slow growth due to high risk of geothermal exploration and
project development (0.5 GW). Global total of 13.3 GW.
AT Ndapuka
TECC3792
Other RE Forms
 Geothermal Power (cont’d)
• Geothermal power plants are similar to conventional steam-power
station with an exception that they do not have furnaces and steam
generators as steam is readily available from the geothermal fields.
• Geothermal power plants are built on the edges of tectonic plates
(geothermal fields) where high temperature geothermal resources are
available near the surface.
• There are two types of Geothermal Plants:
• A dry-steam (vapour dominated).
• A flash-steam (liquid dominated).
AT Ndapuka
TECC3792
Other RE Forms
 Geothermal Power (cont’d)
• Types of Plants
Dry Steam
AT Ndapuka
Flash Steam
TECC3792
Other RE Forms
 Geothermal Power (cont’d)
• A dry-steam power station directly uses the superheated steam of
150oC or greater from the vapor-dominated geothermal fields to drive
a steam turbine that is coupled to an electricity generator.
• The low-pressure and low-temperature steam that comes out of the
turbine is condensed into water in a condenser.
• The condensed water is subsequently discharged or reinjected into
the geothermal fields through reinjection wells.
AT Ndapuka
TECC3792
Other RE Forms
 Geothermal Power (cont’d)
• A flash-steam power station employs a low-pressure tank to allow
high-pressure hot water that comes out of the production well to boil
into steam.
• The saturated (wet) steam is separated from the water, using a
cyclone separator, and used to drive a steam turbine that is coupled
to an electricity generator.
• The low-pressure and low-temperature steam that comes out of the
turbine is condensed into water in a condenser.
• The water from the condenser and the separator is subsequently
discharged or reinjected into the geothermal fields.
AT Ndapuka
TECC3792
Other RE Forms
 Geothermal Power (cont’d)
• A binary-cycle geothermal power station which is the most recent
development, utilizes hot drawn water from a lower-temperature
liquid-dominated geothermal field to heat a secondary working fluid of
much lower boiling point in using a heat exchanger.
• This causes the secondary fluid to flash vaporize which then drives a
Rankine-cycle turbine coupled to an electric generator to produce
electricity.
• The thermal efficiency of the binary geothermal power plant is in the
range of 10-13%.
AT Ndapuka
TECC3792
Other RE Forms
 Geothermal Power (cont’d)
• Steam from geothermal resources is of lower temperatures than that
used in conventional steam power plants.
• The thermal efficiency of geothermal power plants is therefore lower
than that of the conventional power stations, typically in the range of
10-15%.
• Geothermal power requires no fuels, it is therefore immune to fuel
cost fluctuations.
• The capital costs constituting drilling and exploration are high.
• Exploration of deep resources entails significant risks.
• The operating costs are the costs of drilling new production wells to
compensate for the depleted ones.
AT Ndapuka
TECC3792
Other RE Forms
 Geothermal Power (cont’d)
Advantages
•
•
•
•
•
Renewable,
Environmental friendly,
Reliable,
High efficiency,
Relatively low maintenance.
Disadvantages
•
•
•
•
Potential emissions,
Possibility of depletion,
High initial investment,
Highly localised → Transmission and distributions costs.
AT Ndapuka
TECC3792
Other RE Forms
Chapter 7 Summary
 Other forms of Renewable Energy
•
•
•
•
•
•
•
Introduction
Wave Energy
Tidal Power
Hydroelectric Power
Pumped hydro
Biomass for Electricity
Geothermal Power
AT Ndapuka
TECC3792