Energy, Power and Climate Change

Energy Sources and Consumption

Fossil Fuels

Energy Conversions

• Production of electrical power often starts with the release of thermal energy from a fuel

• Conversion of energy into work requires a cyclical process, and energy is lost to the surroundings

• Lost energy is unavailable and is known as degraded energy

Efficiency

€

efficiency =useful energy obtained

total energy in

Sankey Diagrams: Electrical Power

Production

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Renewable vs. Nonrenewable Energy

Sources

• Renewable resources - cannot be used up

• Examples:• Hydro (dams/tides)• Solar (Photovoltaic cells, solar heaters)

• Wind• Biofuels• Geothermal

• Non-renewable resources - can be used up and eventually run out

• Examples:• Fossil fuels - coal, oil, natural gas

• Nuclear

Other things to consider:

• Nuclear power sources are non-renewable, but supply available can make the source effectively renewable

• A fuel can be managed in a renewable or nonrenewable way - for example, we can replant trees at the same rate that they are cut down

Possible sources of energy:

•Sun’s radiated energy•Gravitational energy of the Sun and the Moon

•Nuclear energy stored within atoms

•Earth’s internal heat energy

Energy Density:

• Can be used to compare fuels (including transportation costs)

• Energy liberated per unit mass of fuel consumed

• Measured in J kg-1

€

energy density =energy release from fuel

mass of fuel consumed

Comparison of Energy Sources

World’s Energy Consumption

natural gas 24%

coal 24%

nuclear 6%

oil 38%

other 8%

Energy Sources used to Generate Electricity

Renewables include hydro (16.2%), combustible renewables (1.0%), and other (wind, solar, geothermal) (0.8%)

Coal 40.1%

Nuclear 15.1%

Oil 6.7 %

Gas 19.7%

Renewables 18.0%

Waste material 0.3%

Fossil Fuels

• Coal, oil and natural gas• Accumulations of dead matter exposed to high temperatures and pressures over millions of years

• Coal - plant matter in swamps• Oil - dead marine matter• Natural gas - by-product of oil production

Historical and Geographical Factors

• Industrial Revolution - large scale manufacturing

• Textiles, steam engine, iron and steel

• Increased rate of energy usage• Industries developed near fossil fuel deposits

• Growth of cities, increased cost due to transportation of fuels

Energy Transformations

• Solar energy converted by photosynthesis into living plant matter

• Plant matter converted to fossil fuels

• Fuel burned and converted to thermal energy

• Thermal energy converts water to steam

• Steam turns turbines

Flow Chart

Solar EnergyphotosynthesisChemical Energy in Plants

compressionChemical Energy in Fossil Fuels

burningThermal EnergyKE of steamKE of turbinesElectrical Energy

Rate of Fuel Consumption By Power Stations

•Calculate the typical rate (in kg per hour and tons per hour) at which coal must be supplied to a 500 coal MW fired power station. (Coal power stations have a typical efficiency of 35%, and coal has an energy density of 33 MJ per kg).

How much power must be released from the fuel?

• You need 500 MW or 5 x 108 J s-1

• Coal is 35% efficient, so…….

€

efficiency =useful energy obtained

total energy in

€

0.35 =5x108Js−1

total energy in

Energy in = 1.43 x 109 J s-1

How much coal do you need?

• If the energy density of coal is 33 MJ per kg (or 3.3 x 107 J kg-1), then:

€

1.43x109Js−1

3.3x107Jkg−1= 43.4 kg s−1

€

43.4 kg s−1 x 3600 s /hr =1.56 x105 kghr−1

€

1.56 x105 kghr−1 x 0.001 tons /kg =160 tonshr−1

Efficiencies of Fossil Fuels

Fossil Fuel

Typical Efficiency

Current Maximum Efficiency

Coal 35% 42%

Natural Gas

45% 52%

Oil 38% 45%

Advantages of Fossil Fuels

• Very high “energy density” (a lot of energy released from a small mass)

• Easy to transport• Cheap when compared to other sources of energy

• Power plants can be built anywhere with good transport links and water availability

• Can be used directly in the home to provide heating

Disadvantages of Fossil Fuels

• Combustion products produce pollution, esp. acid rain

• Combustion products produce greenhouse gases

• Extraction of fossil fuels can damage the environment

• Nonrenewable• Coal-fired plants require large amounts of fuel