mecahnical engineering

1. UNIT 4 POWER FROM RENEWABLE ENERGY

2. WIND ENERGY

3. Wind energy :-
 Airflows can be used to run wind turbines.
 Wind energy is used in wind mills which converts the kinetic energy of
the wind into mechanical or electrical energy.
 The kinetic energy of wind can be used to do mechanical work like lifting
water from wells or grinding grains in flour mills.
 A single wind mill produces only a small amount of electricity.
 large number of wind mills in a large area are coupled together to
produce more electricity in wind energy farms.
 The minimum wind speed required is15km/hr.
 At presentWind power potential of India is 1020 MW
 Largest wind farm is near Kanyakumari inTamilnadu generate 380 MW
electricity

4. Wind farm

5. Advantages :-
 It is a renewable source of energy.
 It does not cause pollution.
 The recurring cost is less.
 Once the wind turbine is built the
energy it produces does not cause
green house gases
Disadvantages :-
 Wind is not available at all times.
 It requires a large area of land.
 A minimum wind speed of 15 km/h is
required.

6. What is tidal energy?
• Tidal power facilities harness the energy
from the rise and fall of tides.
• Two types of tidal plant facilities.
– Tidal barrages
– Tidal current turbines
• Ideal sites are located at narrow channels and
experience high variation in high and low
tides.

7. Tides
• Tidal power utilizes the twice-daily variation in
sea level caused primarily by the gravitational
effect of the Moon and, to a lesser extent the
Sun on the world's oceans. The Earth's rotation
is also a factor in the production of tides.
• The interaction of the Moon and the Earth
results in the oceans bulging out towards the
Moon Lunar Tide . The sun’s gravitational field
pulls as well (Solar Tide)
• As the Sun and Moon are not in fixed positions
in the celestial sphere, but change position
with respect to each other, their influence on
the tidal range (difference between low and
high tide) is also effected.
• If the Moon and the Sun are in the same plane
as the Earth, the tidal range is the
superposition of the range due to the lunar
and solar tides. This results in the maximum
tidal range (spring tides). If they are at right
angles to each other, lower tidal differences
are experienced resulting in neap tides.
• Tidal power utilizes the twice-daily variation in
Sea level caused primarily by the gravitational
effect of the Moon and, to a lesser extent the Sun
on the world's oceans. The Earth's rotation is also
a factor in the production of tides.
• The interaction of the Moon and the Earth results
in the oceans bulging out towards the Moon
Lunar Tide . The sun’s gravitational field pulls as
well (Solar Tide)
• As the Sun and Moon are not in fixed positions in
the celestial sphere, but change position with
respect to each other, their influence on the tidal
range (difference between low and high tide) is
also effected.
• If the Moon and the Sun are in the same plane as
the Earth, the tidal range is the superposition of
the range due to the lunar and solar tides. This
results in the maximum tidal range (spring tides).
If they are at right angles to each other, lower
tidal differences are experienced resulting in neap
tides.

8. TIDAL POWER PLANT

11. Basic physics of tides
• There are two high tides and two
low tides during each period of
rotation of the earth.
• Spring and Neap tides depend on the
orientation of the sun, moon, and the
earth.
▫ High spring tides occur when the
sun and moon line up with the
earth. This occurs whether they are
either on same or opposite side.
▫ Low neap tides occur when the sun
and moon line up at 90 ͦ to each
other.
• Flood Currents: currents moving
in the direction of the coast.
• Ebb Currents: the current
receding from the coast
•Gravitational pull of the sun and
moon and the pull of the centrifugal
force of rotation of the earth-moon
system.
•When a landmass lines up with the
earth-moon system, the water
around it is at high tide.
•When a landmass is at 90 ͦ to the
earth-moon system, the water
around it is at low tide.

12. Tidal Barrage
•Two types:
• Single basin system-
Ebb generation: During flood tide basin is
filled and sluice gates are closed , trapping
water. Gates are kept closed until the tide has
ebbed sufficiently and thus turbines start
spinning and generating electricity.
Flood generation: The basin is filled through
the turbine which generate at flood tide.
Two way generation: Sluice gates and turbines
are closed until near the end of the flood tide
when water is allowed to flow through the
turbines into the basin creating electricity. At
the point where the hydrostatic head is
insufficient for power generation the sluice
gates are opened and kept open until high
tide when they are closed. When the tide
outside the barrage has dropped sufficiently
water is allowed to flow out of the basin
through the turbines again creating
electricity.
Double-basin system: There are two basins, but
it operates similar to en ebb generation,
single-basin system. The only difference is a
proportion of the electricity is used to pump
water into the second basin allowing storage.
• Utilize potential energy
• Tidal barrages are typically dams built across an
estuary or bay.
• consist of turbines, sluice gates, embankments, and
ship locks.
Basin

13. Working principle of Tidal power plants
Tide or wave is periodic rise and fall of water level of the sea. Tides occur due to the
attraction of sea water by the moon. Tides contain large amount of potential energy
which is used for power generation. When the water is above the mean sea level, it is
called flood tide. When the water level is below the mean level it is called ebb tide.
Working
The arrangement of this system is shown in figure. The ocean tides rise and fall and
water can be stored during the rise period and it can be discharged during fall. A dam is
constructed separating the tidal basin from the sea and a difference in water level is
obtained between the basin and sea.
During high tide period, water flows from the sea into the tidal basin through the
water turbine. The height of tide is above that of tidal basin. Hence the turbine unit
operates and generates power, as it is directly coupled to a generator.

14. During low tide period, water flows from tidal basin to sea, as the water level in the basin
is more than that of the tide in the sea. During this period also, the flowing water rotates the
turbine and generator power.
The generation of power stops only when the sea level and the tidal basin level
are equal. For the generation of power economically using this source of energy
requires some minimum tide height and suitable site. Kislaya power plant of 250 MW
capacity in Russia and Rance power plant in France are the only examples of this
type of power plant
Advantages of tidal power plants.
1.It is free from pollution as it does not use any fuel.
•It is superior to hydro-power plant as it is totally independent of rain.
•It improves the possibility of fish farming in the tidal basins and it can provide
recreation to visitors and holiday makers.
Disadvantages
•Tidal power plants can be developed only if natural sites are available on the bay.
•As the sites are available on the bays which are always far away from load centres,
the power generated has to be transmitted to long distances. This increases the
transmission cost and transmission losses.

15. The tidal power plants are generally classified on the basis of the number of basins used for
the power generation. They are further subdivided as one-way or two-way system as per the
cycle of operation for power generation.
The classification is represented with the help of a line diagram as given below.
Working of different tidal power plants
1. Single basin-one-way cycle
This is the simplest form of tidal power plant. In this system a basin is allowed to get filled
during flood tide and during the ebb tide, the water flows from the basin to the sea passing
through the turbine and generates power. The power is available for a short duration ebb tide.
Figure: (a) Tidal region before construction of the power plant and tidal variation

16. Figure: (b) Single basin, one –way tidal power plant
Figure (a) shows a single tide basin before the construction, of dam and figure (b) shows the
diagrammatic representation of a dam at the mouth of the basin and power generating during the
falling tide.
2. Single-basin two-way cycle
In this arrangement, power is generated both during flood tide as well as ebb tide also. The
power generation is also intermittent but generation period is increased compared with one-
way cycle. However, the peak obtained is less than the one-way cycle. The arrangement of the
basin and the power cycle is shown in figure.
Figure: Single –basin two-way tidal power plant
The main difficulty with this arrangement, the same turbine must be used as prime mover as
ebb and tide flows pass through the turbine in opposite directions. Variable pitch turbine and
dual rotation generator are used of such scheme.

17. 3. Single – basin two-way cycle with pump storage
In this system, power is generated both during flood and ebb tides. Complex
machines capable of generating power and pumping the water in either directions
are used. A part of the energy produced is used for introducing the difference in the
water levels between the basin and sea at any time of the tide and this is done by
pumping water into the basin up or down. The period of power production with this
system is much longer than the other two described earlier. The cycle of operation
is shown in figure.
Figure: Single-basin, two-way tidal plant coupled with pump storage system.
4. Double basin type
In this arrangement, the turbine is set up between the basins as shown in figure. One basin
is intermittently filled tide and other is intermittently drained by the ebb tide. Therefore, a small
capacity but continuous power is made available with this system as shown in figure. The main
disadvantages of this system are that 50% of the potential energy is sacrificed in introducing the
variation in the water levels of the two basins.
Figure: Double basin, one-way tidal plant.

18. 5. Double basin with pumping
In this case, off peak power from the base load plant in a interconnected transmission
system is used either to pump the water up the high basin. Net energy gain is possible with
such a system if the pumping head is lower than the basin-to-basin turbine generating head.

19. Geothermal energy :-
 It means the energy harnessed from the hot rocks present inside the earth .
 High temperature, high pressure steam fields exit below the earth’s surface in
many places.
 At the core, temperatures may reach over 9,000 degrees Fahrenheit.
 This heat comes from the fission of radioactive material naturally present in
the rocks.
 The deeper regions of the earth’s crust is very hot.This heat melts rocks and
forms magma.
 The magma moves up and collects below at some places called Hot spots.
 The underground water in contact with hot spot gets heated into steam at
high pressure.
 By drilling holes into hot spots the steam coming out can be used to rotate
turbines of generators to produce electricity.

20. Contd..
 There are 46 hydrothermal areas in India where the water
temperature normally exceeds 150 degree centigrade.
 Electricity can be generated from these hot springs.
 In many places the the hot water comes out of the ground
through cracks in the form of Natural geysers:E.g. Manikaran,
Kullu and sohana, Haryana.
 Earth's geothermal energy originates from the original
formation of the planet (20%) and from radioactive decay of
minerals (80%).

22. Advantages of Geothermal Energy
Significant Cost Saving : Geothermal energy generally involves low running costs
since it saves 80% costs over fossil fuels and no fuel is used to generate the power.
 Reduce Reliance on Fossil Fuels : Dependence on fossil fuels decreases with the
increase in the use of geothermal energy. With the sky-rocketing prices of oil, many
countries are pushing companies to adopt these clean sources of energy.
 Environmental Benefits : helped in reducing global warming and pollution , does not
create any pollution as it releases some gases from deep within the earth which are
not very harmful to the environment.
 Direct Use : Since ancient times, people having been using this source of energy for
taking bath, heating homes, preparing food and today this is also used for direct
heating of homes and offices.
 Job Creation and Economic Benefits .

23. Energy:
 Energy broadly means the capacity of something, a person, an animal or a physical
system to do work and produce change.
 Used in science to describe how much potential a physical system has to change.
Sources of Energy.
Conventional sources of
energy
Non conventional sources
of energy

24. Non Conventional Energy sources:
• Those energy sources which are renewable
and ecologically safe.
• such as solar energy, wind energy, biomass
energy, ocean energy (tidal energy, wave
energy, ocean thermal energy), geothermal
energy, nuclear energy etc.
• Some sources of energy are non renewable
like coal, petroleum and natural gas.

25. • About 16% of global final energy consumption comes from
renewable, with 10% coming from traditional biomass, which
is mainly used for heating, and 3.4% from hydroelectricity.
 New renewable (small hydro, modern biomass, wind, solar,
geothermal, and biofuels) accounted for another 3% and are
growing very rapidly.
 The share of renewable in electricity generation is around
19%, with 16% of global electricity coming from
hydroelectricity and 3% from new renewable.

27. Biogas plant :-
• Mixture of gases containing methane, carbon dioxide, hydrogen and
hydrogen sulphide.
• It is produced by anaerobic degradation of animal waste.
• Anaerobic degradation means break down of organic matter by bacteria in
the absence of oxygen.
• The biogas plant has a large underground tank made of bricks and
cement.
• The lower part is the digester and the upper part has a dome with a gas
outlet.

28. • Animal dung is mixed with water in the mixing tank and the slurry is sent
into the digester.
• The gas is taken out through the gas outlet and used for heating and
lighting purposes.
• The slurry left behind is rich in nitrogen and phosphorus and is used as
manure for crops.
• From cattle dung alone we can produce biogas of a magnitude of 22,500
MW annually.
• A sixty cubic feet gobar gas plant can serve the needs of one average
family.
• This gas contains 55 – 70 percent methane, which is inflammable and it is
generally used as cooking gas and for generation of electricity.

29. FIXED DOME TYPE BIOGAS PLANT

30. Advantages of Biogas
• Clean, non-polluting and cheap
• Direct supply of gas from tank.
• No maintence cost
• Does not cause any health hazard.
• provides us both the fuel and the manure.

31. Fuel cells are electrochemical
cells consisting of two electrodes and an
electrolyte which convert the chemical
energy of chemical reaction between fuel
and oxidant directly into electrical energy.
Fuel
cells

32.  Ordinary Combustion process of fuel is
Fuel Oxygen
Combustion
Products
Heat

33.  The process of fuel cell is
Fuel Oxygen
Oxidation
Products
Electricity

34. Chemical
Energy
Heat
Mechanical
Energy
Electrical
Energy

35. • Fuel cell consists of electrodes, electrolyte & catalyst to
facilitate the electrochemical redox reaction.
• The basic arrangement in a fuel cell can be represented as
follows:
Fuel Electrode Electrolyte Electrode Oxidant

36. Fuel cell consist of
Anode
•A layer of anodic catalyst.
Electrolyte
Cathode
•A layer of cathodic catalyst.

37. • Materials which have high electron conductivity &
zero proton conductivity in the form of porous
catalyst (porous catalyst or carbon).
Anode & Cathode
• Platinum
Catalyst
• High proton conductivity & zero electron
conductivity.
Electrolyte
Fuel cell consist of

38.  Fuel Cell System:
1. The fuel (direct H2 or reformed H2) undergoes oxidation at
anode and releases electrons.
2. These electrons flow through the external circuit to the
cathode.
3. At cathode, oxidant (O2 from air) gets reduced.
4. The electrons produce electricity while passing through the
external circuit. Electricity is generated continuously as long as
fuel and the oxidant are continuously and separately supplied
to the electrodes of the cell from reservoirs outside the
electrochemical cell.

39.  The Fuel cell can be represented as:
• 2H2 → 4H+ + 4e-
At
anode
• O2 + 4H+ + 4e- → 2H2O
At
Cathode
• 2H2 + O2 → 2H2O
Overall
Reaction
 Large number of these cells are stacked together in series to
make a battery called as fuel cell battery or fuel battery.

41. Advantages of Fuel Cells
1. High efficiency of energy conversion (approaching 70%)
from chemical energy to electrical energy.
2. Low noise pollution & low thermal pollution.
3. Fuel cell power can reduce expensive transmission lines &
minimize transmission loses for a disturbed system.
4. Fuel cells gives excellent method for efficient use of fossil
fuels hence saves fossil fuels.
5. Fuel cells are less polluting. The chemical process involved
in it is clean. It does not produce polluting exhaust. Mostly
the byproducts are water & waste heat, which are
environmentally acceptable when hydrogen & air are used
as reactants.

42. Advantages of Fuel Cells
6. In case of fossil fuels, when used as reactants,
environmentally undesirable NOx are not produced since
there is no combustion in the process.
7. Hydrogen-Oxygen fuel cells produce drinking water of
potable quality.
8. Designing is modular, therefore the parts are
exchangeable.
9. Low maintenance cost.
10. Fuel cell performance is independent of power plant size.
The efficiency does not depend on the size of power plant.
It remains same for the plants of MW or kW or W size.

43. Advantages of Fuel Cells
11. Fast start up time for low temperature system.
12. The heat is cogenerated hence increases efficiency of high
temperature system.
13. The demand for variations in power & energy densities is
easily met as required. e.g. Laptop, computers requires
low power density & high energy density where as
automobile requires high power density, high energy
density. Both can be powered by fuel cells.
14. Fuel cells automotive batteries can render electric
vehicles, efficient & refillable.

44. Disadvantages of Fuel Cells
• High initial cost.
• Life times of the cells are not accurately known.
• Large weight and volume of gas fuel storage
system.
• High cost of pure hydrogen.
• Hydrogen can be stored in lesser volume by
liquefaction but liquefaction itself require 30% of
the stored energy.
• Lack of infrastructure for distributing hydrogen.

45. Applications of Fuel Cells
• The first commercial use of fuel cell was in
NASA space program to generate power for
satellites and space capsules.
• Fuels are used for primary and backup power
for commercial, industrial and residential
buildings in remote and inaccessible area.
• They are used to power fuel cell vehicles
including automobiles, aeroplanes, boats and
submarines.

46. Types of Fuel Cells

47. Two Commercially important Fuel Cells as:
• Phosphoric Acid Fuel Cell
• Polymer Electrode to Membrane Fuel Cell

49. Characteristic
features
PEMFC PAFC
Primary fuel H2 H2
Electrodes Graphite Carbon
Electrolyte Polymer membrane(Per
fluoro sulphonic acid)
Phosphoric acid soaked
in silicon matrix
Catalyst Pt Pt
Operating
temperature
50 – 1000C (typically 800C) 150 – 2000C
Major applications Stationary and automotive
power
Stationary power
Advantages •Solid electrolyte reduce
corrosion & electrolyte
management problems
•Operates at low
temperature
•Quick start up
•Higher temperature
combines heat power
•Increases tolerance to
fuel impurities

50. Comparison of PAFC & PEMFC
• It has H2 as a primary fuel.
• It requires carbon as an electrode.
• Phosphoric acid is used as an
electrolyte.
• Platinum acts as catalyst.
• It’s operating temperature is 150 to
200oC.
• It has major applications in stationary
& automotive power.
• It has H2 as a primary fuel.
• It requires graphite as an electrode.
• Polymer membrane is used as an
electrolyte.
• Platinum acts as catalyst.
• It’s operating temperature is 50 to
100oC (typically 80oC).
• It has major applications in stationary
power.

51. PAFC were the first fuel cells to cross
commercial threshold in the electric power
industry.
• PAFC is considered the First generation of
modern fuel cell.
• These are considered as the most advanced
fuel cells after alkaline fuel cells.
• They operate at around 150 to 200oC.
PAFC

52. Set up of PAFC
• These fuel cell use liquid phosphoric acid as
electrolyte contained in a silicon carbide matrix
placed between electrodes.
• The electrodes are made of carbon paper coated
with a finely dispersed platinum catalyst bonded
with teflon.
• Hydrogen or reformate gas (mixture of H2 + CO)
generated from alcohols or hydrocarbons is used
as the fuel whereas air is used as oxidant.

53. Working of PAFC
• The catalyst strips electron off the hydrogen rich
fuel at the anode.
• Positively charged hydrogen ions then migrate
through the electrolyte from anode to the
cathode.
• Electrons generated at the anode travel through
an external circuit providing electric power &
reach to the cathode.
• At cathode, the electrons, hydrogen ions &
oxygen form water which is discharged from the
fuel cell.

54. The cell reaction can be represented as:
• 2H2 → 4H+ + 4e-
At
anode
• O2 + 4H+ + 4e- → 2H2O
At
Cathode
• 2H2 + O2 → 2H2O
Overall
Reaction

55. Diagram