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

2

Fossil fuel

• Increased global pollution• Ozone depletion/acid rain• Global warming• Health issues• Available in limited areas• Inefficient processes; <50-60%

thermal efficiency

3

Fossil fuel

• Foreign source• Depleting sources

Oil

Gas

Coal

0 10 20 30 40 50 60 70 80 90 100 110 120

35

37

107

World Fossil Fuel Reserves Depletion Times

Shahriar Shafiee and Erkan Topal, Energy Policy, 37 (2009) 181–189

What is renewable energyEnergy that comes from resources which are naturally refilled on a human timescale, such as sunlight, wind, rain, tides, waves, and geothermal heat.

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

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.

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.

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

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.

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.

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

Hydro energyWave 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.

Hydro energy

Hydroelectric powerLike 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.

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 futureBut• No established

infrastructure• Not mature technology• Energy storage issues

Ideal Future Fuel

i) Abundanceii) Non-toxic and environment friendly emissionsiii) Easy accessibilityiv) 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 typeEnergy densitiesMJ/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   14Gaur S, Reed T (1998) Thermal data for natural and synthetic fuels. Marcel Dekker, New York

18

Hydrogen as fuel

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

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

Renewable sources

Hydrogen from renewable sources

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

Hydrogen from renewable sources

• Biomass• Thermo-chemical processes (Gasification)• Biochemical process: Anaerobic digestion (micro-algea), fermentation

• Water electrolysis• Wind• Hydroelectric• Geothermal• Wave/tidal

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