This document discusses various sources of renewable energy including fossil fuels, solar energy, geothermal energy, hydro energy, and hydrogen as a potential future fuel. It notes that while fossil fuels currently provide a reliable energy supply, they are non-renewable and cause environmental issues like pollution and global warming. Renewable sources like solar, geothermal, and hydro provide clean energy alternatives, but technologies are not yet mature and established. Hydrogen is highlighted as an ideal future fuel because it is abundant, non-toxic, and can be produced from renewable resources, though safe storage and transportation of hydrogen remains a challenge.

1. Fossil fuel
• Enormous natural energy
resources
• Available in all three form of
matter
• Well established and mature
infrastructure (industry-
domestic-transportation)
• Reliable supply
• We all are dependent and
used-to
• Cheapest energy source
• Long life
The Scenario
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2. Fossil fuel
• Increased global pollution
• Ozone depletion/acid rain
• Global warming
• Health issues
• Available in limited areas
• Inefficient processes; <50-60%
thermal efficiency
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3. Fossil fuel
• Foreign source
• Depleting sources
35
37
107
0 10 20 30 40 50 60 70 80 90 100 110 120
Oil
Gas
Coa
l
World Fossil Fuel Reserves Depletion Times
Shahriar Shafiee and Erkan Topal, Energy Policy, 37 (2009) 181–189
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4. What is renewable energy
Energy that comes from
resources which are
naturally refilled on a
human timescale, such
as sunlight, wind, rain,
tides, waves, and
geothermal heat.

5. Renewable energy sources
• Biomass energy (biofuel)
• Direct: combustion of biomass (wood, grass)
• Indirect: chemical conversion to biofuel (biomass gasification, bioethanol)
• Hydrogen as fuel
• Radiant solar energy
• Solar heating, solar power plants, photovoltaic cells
• Wind energy
• Hydro energy
• Geothermal energy

6. Solar energy
• On average, every square meter of Earth's surface receives 164 watts of solar
energy
• you could stand a really powerful (150 watt) table lamp on every square meter of
Earth's surface and light up the whole planet with the Sun's energy
• Or, if we covered just one percent of the Sahara desert with solar panels, we
could generate enough electricity to power the whole world.
• This energy is as a mixture of light and heat.
• Light makes plants grow, providing us with food, while the heat keeps us warm
enough to survive
• But we can't use either the Sun's light or heat directly to run a television or a car.

7. Solar energy
• A solar cell is a sandwich of n-type silicon
(blue) and p-type silicon (red).
• When sunlight shines on the cell, photons
(light particles) bombard the upper surface.
• The photons (yellow blobs) carry their energy
down through the cell.
• The photons give up their energy to electrons
(green blobs) in the lower, p-type layer.
• The electrons use this energy to jump across
the barrier into the upper, n-type layer and
escape out into the circuit.
• Flowing around the circuit, the electrons
make the lamp light up.

8. Solar energy
Advantages
• Solar energy is a renewable energy resource and there are no fuel costs.
• No harmful polluting gases are produced.
Disadvantages
• Solar cells are expensive and inefficient, so the cost of their electricity is high.
• Solar panels may only produce very hot water in very sunny climates, and in cooler
areas may need to be supplemented with a conventional boiler.
• Although warm water can be produced even on cloudy days, neither solar cells nor
solar panels work at night
• Lot of space required

9. Geothermal energy
Hot rocks
• In some places, the rocks are hot, but no hot
water or steam rises to the surface.
• In this situation, deep wells can be drilled down
to the hot rocks and cold water pumped down.
• The water runs through fractures in the rocks
and is heated up.
• It returns to the surface as hot water and
steam, where its energy can be used to drive
turbines and electricity generators.
• The diagram below shows how this works.

10. Geothermal energy
Volcanic areas
• Several types of rock contain radioactive
substances such as uranium.
• Radioactive decay of these substances releases
heat energy, which warms up the rocks.
• In volcanic areas, the rocks may heat water so
that it rises to the surface naturally as hot
water and steam.
• Here the steam can be used to
drive turbines and electricity generators.
• This type of geothermal power station exists in
places such as Iceland, California and Italy.

11. Geothermal energy
• Advantages
• Renewable
• Easy to exploit in some cases
• CO2 production less than with fossil fuels
• High net energy yield
• Disadvantages
• Not available everywhere
• H2S pollution

12. Hydro energy
Wave energy
The water in the sea rises and falls because of
waves on the surface. Wave machines use the
kinetic energy in this movement to drive
electricity generators.

13. Hydro energy
Hydroelectric power
Like tidal barrages, hydroelectric power
stations use the kinetic energy in moving water.
But the water comes from behind a dam built
across a river valley. The water high up behind
the dam contains gravitational potential
energy. This is transferred to kinetic energy as
the water rushes down through tubes inside
the dam. The moving water drives electrical
generators, which may be built inside the dam.

14. Hydro energy
Advantages
• Cheap to operate
• Renewable
• High yield
• Pretty plentiful (Some countries depend almost entirely on it)
• Not intermittent (if reservoir is large enough)
• Reservoirs have multiple uses (Flood control, drinking water, aquaculture, recreation)
Disadvantages
• Human population displacement
• Ecosystem impacts
• Barriers to migrating fish
• Loss of biodiversity both upstream and downstream
• Reduces nutrient flow (dissolved and particulate)
• Rotting vegetation underwater releases methane, which is a greenhouse gas

15. RENEWABLE AND SUSTAINABLE ENERGY
• No/low pollution
• Widely available
• Indigenous source
• Lifelong future
But
• No established
infrastructure
• Not mature technology
• Energy storage issues
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16. Ideal Future Fuel
i) Abundance
ii) Non-toxic and environment friendly emissions
iii) Easy accessibility
iv) Sustainability

17. Hydrogen as fuel
• Hydrogen possesses all features of future fuel
• Yields water and 242 kJ/mol of net heat energy at
25oC
• Clean and eco-friendly fuel
• Most abundant element in universe (92%)
• Produced from renewable sources and industrially
• Highest energy per unit mass
• Three times greater than gasoline
• 30% more efficiency with internal combustion
engine
• Potential substitute for
• Gasoline
• Natural gas
• Other fuels
for both stationary and mobile applications
Fuel type
Energy densities
MJ/l MJ/kg
Hydrogen 0.0108 143
Liquefied natural gas (160oC) 22.2 53.6
Natural gas 0.0364 53.6
Gasoline (petrol) 34.2 46.4
LPG (60%Pr. + 40%Bu.) 26.8 46
Liquefied petroleum gas 26.8 46
Diesel 38.6 45.4
Gasohol E10 (ethanol 10% vol.) 33.2 43.5
Biodiesel 33.5 42.2
Butanol 29.2 36.6
Coal, anthracite 72.4 32.5
Ethanol 24 30
Coal, bituminous 20 24
Coal, lignite 14
Gaur S, Reed T (1998) Thermal data for natural and synthetic fuels. Marcel Dekker, New York
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18. Hydrogen as fuel
G. Marbán and T. Valdés-Solís, “Towards the hydrogen economy” Int. J. Hydrogen Energy, 32, 1625–1637, 2007 18
Renewable and non renewable sources

19. Hydrogen as fuel
G. Marbán and T. Valdés-Solís, “Towards the hydrogen economy” Int. J. Hydrogen Energy, 32, 1625–1637, 2007 19
Renewable sources

20. Hydrogen from renewable sources
Renewable Hydrogen Technologies: Production, Purification, Storage ...
edited by Luis M Gandia, Gurutze Arzamedi, Pedro

21. Hydrogen from renewable sources
• Biomass
• Thermo-chemical processes (Gasification)
• Biochemical process: Anaerobic digestion (micro-algea), fermentation
• Water electrolysis
• Wind
• Hydroelectric
• Geothermal
• Wave/tidal

22. Hydrogen from renewable sources
Solar conversion
• Solar-thermal water splitting (solar thermolysis):
At elevated temperatures water molecules split into their atomic components hydrogen and oxygen. For
example at 2200 °C about three percent of all H2O molecules are dissociated into various combinations of
hydrogen and oxygen atoms, mostly H, H2, O, O2, and OH. Other reaction products like H2O2 or HO2 remain
minor. At the very high temperature of 3000 °C more than half of the water molecules are decomposed, but at
ambient temperatures only one molecule in 100 trillion dissociates by the effect of heat.
• Photocatalytic water splitting:
water splitting under visible light irradiation allows obtaining hydrogen from the irradiation of sunlight on water
in the presence of suitable catalyst that reduces the high activation energy of the decomposition reaction. The
process can be carried out more easily by an indirect route, using water in combination with a so-called
sacrificial reducing agent, typically, an alcohol such as methanol. Noble metals such as Pd, Pt, Ir, and Au
supported on a semiconductor such as TiO2 are active catalyst for this process.
• Photobiological water splitting

23. Challenges for hydrogen use as fuel
• Safe storage and transportation
• Poor volumetric energy density i.e., 10 kJ/l at 1 bar and 15oC
• High flammability characteristics
• Present in combined fashion like H2O
• High pressure storage: safety hazards like explosion
• Liquefaction: very low temperatures and abundant amount of energy
• Hydrogen adsorption: inadequate storage capacity, high weight to volume ratio
and limited knowledge
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