POWER PLANT ENGINEERING-Unit 4

UNIT IV
POWER FROM RENEWABLE ENERGY
Hydro Electric Power Plants – Classification, Typical
Layout and associated components including
Turbines. Principle, Construction and working of
Wind, Tidal, Solar Photo Voltaic (SPV), Solar Thermal,
Geo Thermal, Biogas and Fuel Cell power systems.

Hydro Electric
Converts Hydraulic Energy to Electrical Energy
• The water falls through a certain height, its
potential energy is converted into kinetic energy
and this kinetic energy is converted to the
mechanical energy by allowing the water to flow
through the hydraulic turbine runner. This
mechanical energy is utilized to run an electric
generator which is coupled to the turbine shaft.

Site Selection
• Water Available
• Water-Storage
• Head of Water
• Distance from Load Center
• Access to Site

Classification
The hydro-power plants can be classified as below:
1. Storage plant
(a) High head plants
(b) Low head plants
(c) Medium head plants.
2. Run-of-river power plants
(a) With pondage
(b) Without pondage.
3. Pumped storage power Plants.

Layout of Hydro Electric Power Plant

Components of Hydro Electric Power
Plant

1) Dam The dam is the most important
component of hydroelectric power plant. The
dam is built on a large river that has
abundant quantity of water throughout the
year. It should be built at a location where
the height of the river is sufficient to get the
maximum possible potential energy from
water.
2) Water Reservoir The water reservoir is the
place behind the dam where water is stored.
The water in the reservoir is located higher
than the rest of the dam structure. The
height of water in the reservoir decides how
much potential energy the water possesses.
The higher the height of water, the more its
potential energy. The high position of water
in the reservoir also enables it to move
downwards effortlessly. The height of water
in the reservoir is higher than the natural
height of water flowing in the river, so it is
considered to have an altered equilibrium.
This also helps to increase the overall
potential energy of water, which helps
ultimately produce more electricity in the
power generation unit.

3) Intake or Control Gates These are the
gates built on the inside of the dam. The
water from reservoir is released and
controlled through these gates. These are
called inlet gates because water enters the
power generation unit through these
gates. When the control gates are opened
the water flows due to gravity through the
penstock and towards the turbines. The
water flowing through the gates possesses
potential as well as kinetic energy.
4) The Penstock The penstock is the long
pipe or the shaft that carries the water
flowing from the reservoir towards the
power generation unit, comprised of the
turbines and generator. The water in the
penstock possesses kinetic energy due to
its motion and potential energy due to its
height. The total amount of power
generated in the hydroelectric power
plant depends on the height of the water
reservoir and the amount of water flowing
through the penstock. The amount of
water flowing through the penstock is
controlled by the control gates.

5) Water Turbines Water flowing from the penstock is
allowed to enter the power generation unit, which houses
the turbine and the generator. When water falls on the
blades of the turbine the kinetic and potential energy of
water is converted into the rotational motion of the blades
of the turbine. The rotating blades causes the shaft of the
turbine to also rotate. The turbine shaft is enclosed inside
the generator. In most hydroelectric power plants there is
more than one power generation unit. There is large
difference in height between the level of turbine and level
of water in the reservoir. This difference in height, also
known as the head of water, decides the total amount of
power that can be generated in the hydroelectric power
plant. There are various types of water turbines such as
Kaplan turbine, Francis turbine, Pelton wheels etc. The type
of turbine used in the hydroelectric power plant depends
on the height of the reservoir, quantity of water and the
total power generation capacity
6) Generators It is in the generator where the electricity is
produced. The shaft of the water turbine rotates in the
generator, which produces alternating current in the coils of
the generator. It is the rotation of the shaft inside the
generator that produces magnetic field which is converted
into electricity by electromagnetic field induction. Hence
the rotation of the shaft of the turbine is crucial for the
production of electricity and this is achieved by the kinetic
and potential energy of water. Thus in hydroelectricity
power plants potential energy of water is converted into
electricity.

Renewable Electric Capacity
Worldwide

Theoretical Power Generated by Wind Turbine
Power = ½ (ρ)(A)(V)3
A = swept area = (radius)2
, m2
V = Wind Velocity, m/sec.
ρ = Density of

• Rotor- The hub and the blades together are referred to as
the rotor. Wind turns the blades which turn the drive shaft.
• Shaft- Two different shafts turn the generator. One is used
for low speeds while another is used in high speeds.
• Gear Box- Gears connect the high and low speed shafts and
increase the rotational speeds from about 10-60 rotations
per minute to about 1200-1800 rpm, the rotational speed
required by most generators to produce power.
• Generator- The generator is what converts the turning
motion of a wind turbine's blades into electricity.
• Controller- Turns the blades on at 8-16 mph and shuts them
down around 65 to prevent any high wind damage.
• Tower- Tall tubular metal shaft. The taller the tower, the
more power produced.
• Yaw Drive - To ensure the wind turbine is producing the
maximal amount of electrical energy at all times, the yaw
drive is used to keep the rotor facing into the wind as the
wind direction changes.

Turbines: Two Types
• Horizontal Axis Wind Turbines
• Vertical Axis Wind Turbines

Advantages and Disadvantages
• Vertical Axis Advantages
– Can place generator on
ground
– You don’t need a yaw
mechanism for wind
angle
• Disadvantages
– Lower wind speeds at
ground level
– Less efficiency
– Requires a “push”
• Horizontal Advantages
– Higher wind speeds
– Great efficiency
• Disadvantages
– Angle of turbine is
relevant
– Difficult access to
generator for repairs

TIDAL POWER PLANT
1. Single Basin Arrangement
•Low Tide
•High Tide
2. Double Basin Arrangement

Solar Photovoltaic (PV)
A photovoltaic system, also solar PV power system, or PV
system, is a power system designed to supply usable solar
power by means of photovoltaics. It consists of an
arrangement of several components, including solar
panels to absorb and convert sunlight into electricity

Solar Thermal
A photovoltaic system, also solar PV power system, or PV
system, is a power system designed to supply usable solar
power by means of photovoltaics. It consists of an
arrangement of several components, including solar
panels to absorb and convert sunlight into electricity

Solar heating
Water Heating with solar energy
A surface faces the sun’s rays and absorbs them, converting
the radiation into warmth. The temperature of this
surface, the so-called absorber,
therefore rises. Every object placed
in the sun exhibits this effect to
a greater or lesser degree.
A black surface shows the greatest
rise in temperature, it absorbs about 90% of the sun’s
incident radiation and reflects very little.

classification of solar collectors
1 - Flat-plate collectors – The absorbing surface is approximately
as large as the overall collector area that intercepts the sun
rays .
2 - Concentrating collectors – Large areas of mirrors or lenses
focus the sun light onto a smaller absorber .
cross section of typical liquid flat plate collector concentrating solar collector

Solar concentrators
solar concentrator is a device that allows the collection of
sunlight from large area and focusing it on a smaller receiver.
The cost per unit area of a solar concentrator is therefore
much cheaper than the cost per unit area of a PV material. By
introducing this concentrator, not only the same amount of
energy could be collected from the sun, the total cost of the
effect of concentrator on the PV cell solar cell could also be
reduced .
effect of concentrator on the PV cell

Benefits and drawbacks of using the
solar concentrators
Benefits:
- Reduce the dependency on silicon cell and increase the
intensity of solar.
- Irradiance, hence increase the cell efficiency.
- Reduce the total cost of the whole system.
Drawbacks:
- Degrade the PV cell lifespan.
- Need to cool down the PV to ensure the performance
of the PV is optimum.
- Mechanical tracking system may required.

Design of solar concentrator
parabolic concentrator hyperboloid concentrator
Fresnel Concentrator general design of DTIRC

APPLICATIONS
1 - Water distillation :
The solar distiller purifies water by first
evaporating and then condensing it.

2 - Solar boiler :
A solar boiler with a collector surface of 3 to 4 m2and a
storage capacity of 200 liters can provide 300 to 400 liters per
day of water between 400c and 600c in temperature. The yield
is naturally dependent on the amount of sun and on a
judicious of the installation.
solar boiler

3 - The Parabolic Solar Cooker :
The parabolic or concentrating solar cooker reflects the sun’s
rays in such a way that these are converged onto a small area,
in this area a dark metal cooking pot is fixed. Because of the
small size of the area of convergence there is room for only
one pot. It can be warmed up between 150 and 3500c,
enough to fry.
Solar Cooker

Working of Geothermal Power Plant

Geothermal Energy
Geothermal power is an alternative source of energy that
harnesses the Earth’s heat in order to generate electricity. In
locations with shallow ground water at high temperatures,
wells are drilled in order to extract the steam or hot water.
There are three types of geothermal energy generation plants
•Dry Steam Power Plant
•Flash Power Plant
•Binary Power Plant

Flash Steam Power Plant
The heated water is sprayed into a tank held at much lower pressure than the
fluid. This causes the fluid to vaporize rapidly, or “flash.” The vapor then drives a
turbine to run the generator.

Geothermal fossil systems(Hybrid systems):
 Low-temperature of geothermal sources in the low temp
.
 High-temperature of geothermal sources in the high temp.
Arrangement of hybrid plants
 Geothermal –preheat hybrid systems
 Fossil-superheat hybrid systems

Geothermal –Preheat hybrid systems

APPLICTIONS OF GEOTHERML ENERGY AT DIFFERENT TEMPARATURES

TEMPERATURES REGIMES
Geothermal energy can be divided into three temp regimes.
i. High =>150°c
ii. Moderate =90-150°c
iii. Low=<90°c

Application of Geothermal Energy
Space Heating Air Conditioning Drying
Hot Water
Greenhouses
Melting Snow
Aquaculture

ADVANTAGES
Environment friendly.
Renewable energy source.
High potential.
Low operational cost.
More reliable than other alternatives.

DIS ADVANTAGES
High installation cost .
May release harmful gases
.
Earthquakes .
Transportation .

What is biogas?
• A mixture of methane and
carbon dioxide
CH4
CO2 • Methane or ‘swamp gas’,
produced naturally in
swampy ponds

Aerobic and Anaerobic Digestion

Biogas
plants
Conventional
Domed
shape
Floating
type
Modern
Nisargruna
biogas
62

• A fixed-dome plant comprises of a closed, dome-shaped
digester with an immovable, rigid gas-holder and a
displacement pit, also named 'compensation tank'.
• When gas production starts, the slurry is displaced into
the compensation tank.
• Gas pressure increases with the volume of gas stored.
• If there is little gas in the gas-holder, the gas pressure is
low.
63

• Relatively low construction costs.
• The absence of moving parts and rusting steel parts.
• If well constructed, fixed dome plants have a long life
span.
• The underground construction saves space and protects the
digester from temperature changes.
• The construction provides opportunities for skilled local
employment.
65

• Fluctuating gas pressure complicates gas utilization.
• Amount of gas produced is not immediately visible.
• Fixed dome plants need exact planning of levels.
• Excavation can be difficult and expensive in bedrock.
66

• A floating-drum plant consists of a cylindrical or dome-
shaped digester and a moving, floating gas-holder, or drum.
• The gas-holder floats either directly in the fermenting
slurry or in a separate water jacket.
• The drum in which the biogas collects has an internal
and/or external guide frame that provides stability and
keeps the drum upright.
• If biogas is produced, the drum moves up, if gas is
consumed, the gas-holder sinks back.
67

• Floating-drum plants are easy to understand and operate.
• They provide gas at a constant pressure.
• The stored gas-volume is immediately recognizable by the
position of the drum.
• Gas-tightness is no problem, provided the gasholder is de-
rusted and painted regularly.
69

• The steel drum is relatively expensive and maintenance-
intensive.
• Removing rust and painting has to be carried out regularly.
• The life-time of the drum is short (up to 15 years; in
tropical coastal regions about five years).
• If fibrous substrates are used, the gas-holder shows a
tendency to get "stuck" in the resultant floating scum.
70

Fuel Cells: Components and Functions
• MEA = membrane
electrode assembly
(electrolyte and
electrodes)
• Anode = fuel electrode;
electronic conductor and
catalyst
• Cathode = air electrode;
electronic conductor and
catalyst
• Electrolyte = oxygen-ion
conductor, electron
inhibitor

Parts of a Fuel Cell
• Anode
– Negative post of the fuel cell.
– Conducts the electrons that are freed from the hydrogen molecules so that they
can be used in an external circuit.
– Etched channels disperse hydrogen gas over the surface of catalyst.
• Cathode
– Positive post of the fuel cell
– Etched channels distribute oxygen to the surface of the catalyst.
– Conducts electrons back from the external circuit to the catalyst
– Recombine with the hydrogen ions and oxygen to form water.
• Electrolyte
– Proton exchange membrane.
– Specially treated material, only conducts positively charged ions.
– Membrane blocks electrons.
• Catalyst
– Special material that facilitates reaction of oxygen and hydrogen
– Usually platinum powder very thinly coated onto carbon paper or cloth.
– Rough & porous maximizes surface area exposed to hydrogen or oxygen
– The platinum-coated side of the catalyst faces the PEM.

Fuel Cell Operation
• Pressurized hydrogen gas (H2) enters cell on anode side.
• Gas is forced through catalyst by pressure.
– When H2 molecule comes contacts platinum catalyst, it splits into two
H+ ions and two electrons (e-).
• Electrons are conducted through the anode
– Make their way through the external circuit (doing useful work such as
turning a motor) and return to the cathode side of the fuel cell.
• On the cathode side, oxygen gas (O2) is forced through the
catalyst
– Forms two oxygen atoms, each with a strong negative charge.
– Negative charge attracts the two H+ ions through the membrane,
– Combine with an oxygen atom and two electrons from the external
circuit to form a water molecule (H2O).

Proton-Exchange Membrane Cell
http://www.news.cornell.edu/releases/Nov03/Fuelcell.institute.deb.html

Fuel Cells: Types
– Electrolyte Types
• Alkaline
• Polymer Electrolyte Membrane (Proton Exchange
Membrane)
• Direct Methanol
• Phosphoric Acid
• Molten Carbonate
• Solid Oxide

Alkaline Fuel Cell
• First AFC developed by Francis Bacon (1930s)
• In the Apollo missions
– 85% KOH
– 200-230oC
– Ni anode and NiO cathode
– Acidic fuel cells had been used, but alkaline had faster oxygen
reduction kinetics
– Fuel cells were used to provide electricity, cool the ship, and
provide potable water

35%
KOH
O2
H2
H2O
OH-
Alkaline Fuel Cell
Anode: C/Pt or
C/Raney Ni/Pt
Cathode: C/Pt
H2 + 2OH-  H2O + 2e-
O2 + H2O + 2e-  HO2
- + OH-
HO2
- + H2O + 2e- 3OH-
1 A/cm2 at 0.7 V
r.t.-80oC

Alkaline Fuel Cell
 Advantages:
Low cost electrolyte solution (KOH 30-35%)
Non-noble catalyst withstand basic conditions
O2 kinetics faster in alkaline solution

Polymer Electrolyte Membrane Fuel Cell
• Used by NASA in Gemini mission
– employed polystyrene sulfonate (PSS) polymer (unstable)
• Nafion – developed by Dupont (1960s)
– Currently used in most PEMs
– Polytetrafluoroethylene (PTFE) backbone with a perfluorinated side chain
that is terminated with a sulfonic acid group
– More stable, higher conductivity
• The Dow Chemical Company
– Developed a polymer similar to Nafion
• Shorter side chain and only one ether oxygen
• No longer available

H2  2H+ + 2e- O2 + 2H+ + 2e-  H2O2
H2O2 + 2H+ + 2e-  H2O
Anode: C/Pt Cathode: C/Pt
N A F I O N
1 A/cm2 at 0.7 V
85-105oC
H2 O2
H+
H2O

• Advantages:
– Nonvolatile membrane
– CO2 rejecting electrolyte
– few material problems

Direct Methanol Fuel Cell
Anode: Pt/Ru/C Cathode: Pt/C
CH3OH + H2O CO2 + 6H+ + 6e-
O2 + 2H+ + 2e-  H2O2
H2O2 + 2H+ + 2e-  H2O
N
A
F
I
O
N
85-105oC
400 mA/cm2 at 0.5V
at 60oC

Direct Methanol Membrane Fuel Cell
• Advantages:
– Direct fuel conversion – no reformer needed, all positive aspects of
PEMFC
– CH3OH – natural gas or biomass
– Existing infastructure for transporting petrol can be converted to MeOH
• Problems:
– High catalyst loading (1-3mg/cm2 v. 0.1-0.3 mg/cm2)
– CH3OH hazardous
– Low efficiency (MeOH crossover – lowers potential)

Phosphoric Acid Fuel Cell
• Most commercially developed fuel cell
– Mainly used in stationary power plants
– More than 500 PAFC have been installed and tested around the
world
– Most influential developers of PAFC
• UTC Fuel Cells, Toshiba, and Fuji Electric

Anode: Pt/C Cathode: Pt/C
H2 – 2e- = 2H+ O2 + 4H+ + 4e-  2H2O
200oC
100%
H2PO4
Si matrix
separator
PTFE binding
CH4 or H2 O2
H+
H2O

• Advantages:
– H2O rejecting electrolyte
– high temps favor H2O2 decomposition
• O2 + H2O +2e-  H2O2
• Stable H2O2 lowers cell voltage and corrodes electrode
• Problems:
– O2 kinetic hindered
– CO catalyst poison at anode
– H2 only suitable fuel
– low conducting electrolyte

Molten Carbonate Fuel Carbonate
• Developed in the mid-20th century
• Developed because all carbonaceous fuel produce
CO2
• Using CO3
2- electrolyte eliminates need to regulate
CO3
2- build up

Molten Carbonate Fuel Carbonate
Anode: Ni/Al or Ni/Cr Cathode: NiO
CH4 + 2H2O  4H2 + CO2 + 4e-
H2 +CO3
2-  H2O + CO2 + 2e-
O2 + 2CO2 + 4e-  2CO3
2-
Li2CO3
and
Na2CO3
LiAlO3 used to
support
electrolyte
580-700oC
150 mA/cm2 at
0.8 V at 600oC
H2, CxH2x+2 O2, CO2
CO3
2-

Molten Carbonate Fuel Cell
• Advantages:
– Higher efficiency (v. PEMFC and PAFC) (50-70%)
– Internal reforming (H2 or CH4)
– No noble metal catalyst (High T increases O2 kinetics)
– No negative effects from CO or CO2
• Problems:
– Materials resistant to degradation at high T
• Ni, Fe, Co steel alloys better than SS
– NiO at cathode leeches into CO3
2- reducing efficiency or crossing
over causing short circuiting
• Dope electrode and electrolyte with Mg
• Kucera and Myles (LiFeO2 or Li2MnO3 stabilize)

Solid Oxide Fuel Cell
Cathode = La1-xSrxMnO3
Y doped
ZrO2
Anode = NiO-YSZ cermet 800-1000oC
H2 + O2-  H2O + 2e- OR
CH4 + 4O2-  2H2O + CO2 + 8e-
O2 + 2e-  2O2-
Interconnector
material = Mg
or Sr doped
lanthanum
chromate
1mA at 0.7V
H2, CxH2x+2 O2
O2-

Solid Oxide Fuel Cell
• Advantages:
– Solid electrolyte eliminates leaks
– H2O management, catalyst flooding, slow O2 kinetic are not
problematic
– CO and CO2 are not problematic
– Internal reforming - almost any hydrocarbon or hydrogen
fuel
• Problems:
– Severe material constraints due to high T
• Stainless steal at lower temperatures
• Alloyed metal or Lanthanum Chromite material

Applications
Fuel cells are being developed for application
in:
Stationary power plants
Automobiles
Portable electronics
To enable mobile power source, fuel must also
be portable

POWER PLANT ENGINEERING-Unit 4

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