Energy Resources

The high-pressure steam pushes against the blades of the turbine, causing it to spin; the rotating turbine drives the generator; which transfers kinetic energy into electrical energy.

Fossil fuels take millions of years to form from the remains of dead organisms; they are used up much faster than they are replaced; so once consumed, they cannot be replenished within a human lifetime.

The biofuel is burned in a boiler to heat water and produce steam; the steam drives a turbine; which turns a generator to produce electrical energy.

Advantage — biofuels are renewable because new crops can be grown to replace those used; this means the supply does not run out. Disadvantage — growing biofuel crops requires large areas of land; this reduces land available for food production and can cause deforestation.

Water stored behind a dam has gravitational potential energy; when released, the water flows downhill and gains kinetic energy; the moving water drives a turbine; which spins a generator to produce electrical energy.

Tidal power is highly reliable because tides occur predictably twice a day regardless of weather conditions; wave power is less reliable because wave size depends on wind strength, which varies. Tidal power requires building a barrage across an estuary, which disrupts habitats and blocks migration routes for aquatic species; wave power devices are placed on the ocean surface and cause less habitat disruption, though they may affect shipping routes.

Cold water is pumped down into hot underground rocks; the water absorbs thermal energy and turns to steam; the steam rises and drives a turbine; which spins a generator to produce electrical energy.

Geothermal energy is renewable because the thermal energy in the Earth's interior is continuously produced by radioactive decay and is not depleted by extraction at practical rates. However, geothermal energy is only available in locations where hot rocks are close enough to the surface to heat water effectively; in most regions the rocks are too deep, making geothermal power stations impractical.

Nuclear fuel undergoes fission in a reactor, releasing thermal energy; this energy heats water in a boiler to produce steam; the steam drives a turbine; which turns a generator to produce electrical energy.

Advantage — nuclear power stations produce no carbon dioxide during operation; therefore they do not contribute to the enhanced greenhouse effect or climate change during generation. Disadvantage — nuclear power stations produce radioactive waste; this waste remains dangerous for thousands of years and requires secure long-term storage, posing environmental and safety risks.

A solar cell converts light energy from the Sun directly into electrical energy; no turbine or generator is needed.

Solar cells are renewable because the Sun continuously provides light, which is not depleted by use. However, solar cells only produce electricity during daylight hours; their output depends on sunlight intensity, which decreases on cloudy days and at night; therefore in regions with frequent cloud cover or short daylight hours, solar cells are unreliable as a sole energy source.

A solar cell converts light directly into electrical energy; a solar panel absorbs infrared radiation to heat water.

The Sun heats the Earth's surface unevenly; different surfaces absorb radiation at different rates, creating temperature differences. These temperature differences cause convection currents in the atmosphere; the moving air (wind) carries kinetic energy. Therefore, the kinetic energy harnessed by wind turbines originates from solar radiation heating the atmosphere.

Advantage 1 — hydroelectric power is renewable because the water cycle continuously replenishes the water supply. Advantage 2 — it is reliable because water can be released from the dam on demand to generate electricity when needed. Disadvantage 1 — building the dam floods large areas of valley, destroying habitats and displacing communities. Disadvantage 2 — suitable river valleys with sufficient height difference are not available everywhere, limiting geographic availability.

Fossil fuels are reliable because they can be burned on demand at any time, so the power station produces a predictable and controllable output. They are non-renewable because they formed over millions of years and are consumed far faster than they can be replaced. Wind energy is renewable because wind is caused by solar heating of the atmosphere, which is continuous and will not run out. However, wind energy is unreliable because wind speed varies unpredictably; when the wind drops, turbines produce little or no electricity, so output cannot be guaranteed.

Efficiency is the proportion of the total energy input that is transferred to useful energy output; a higher efficiency means less energy is wasted / transferred to non-useful stores.

In every energy transfer, some energy is transferred to non-useful stores, usually the thermal store of the surroundings; this occurs because of friction, air resistance, or electrical resistance in the device. Therefore, the useful energy output is always less than the total energy input, so efficiency is always less than 100%.

Radiation from the Sun is the main source of energy for all energy resources except geothermal, nuclear, and tidal.

Wind energy depends on the Sun because the Sun heats the Earth's surface unevenly; this creates temperature differences that drive convection currents in the atmosphere, producing wind. Tidal energy does not depend on the Sun because tides are caused by the gravitational pull of the Moon on the Earth's oceans; this gravitational effect occurs regardless of solar radiation.