Sources of Energy
What the exam tests
Sources of Energy tests the classification of energy sources, the working and limitations of conventional and non-conventional sources, and environmental consequences. Expect comparisons of fuels, solar devices, wind energy, biogas and nuclear energy.
Core rules
- A good energy source should be available, affordable, easy to store and transport, and have a high energy output per unit mass.
- Fossil fuels (coal, petroleum, natural gas) are non-renewable and release CO2, SO2 and particulates.
- Thermal power plants burn fuel to make steam, which drives a turbine. Hydro plants use falling water; dams affect ecosystems and displace people.
- Wind energy is renewable and does not need water, but wind speed must exceed about 15 km/h and the turbines cause noise and bird hazards.
- Solar energy can be used directly for heating or converted by photovoltaic cells. A solar cooker uses a black surface and a glass cover to trap heat.
- Biogas is mainly methane, produced by anaerobic decomposition of biomass. It gives a clean fuel and enriched slurry.
- Tidal, wave and ocean-thermal energy use the sea; geothermal uses heat from the Earth.
- Nuclear fission releases large energy from heavy nuclei; fusion is the Sun's process but is not yet a commercial power source.
Worked example
A 200 W solar panel receives sunlight for 5 hours a day. Energy per day = power × time = 200 W × 5 h = 1000 Wh = 1 kWh. Over 30 days it gives 30 kWh. This is the unit used on electricity bills, so the calculation is directly useful for sizing a rooftop system.
Traps that cost marks
- Calling biogas mainly CO2; it is mainly methane.
- Saying hydro power has no environmental cost; submergence and displacement are real costs.
- Treating nuclear fusion as a working commercial source.
- Confusing renewable with clean; a renewable source can still have ecological costs.