The heat released from burning fossil fuels is used to boil water to produce steam. The steam is heated to very high temperatures so that it is at high pressure and can turn huge steam turbines. Some of the energy of the steam is transformed into movement, or kinetic energy, as the turbines spin. The turbines are connected to the coils of large generators. The coils carry a current and act as electromagnets. As the turbines spin, they produce an electric current in the fixed coils surrounding them. This is fed into a power supply grid and carried to wherever in the network it is needed.
Power stations cannot store surplus electricity, so electricity generation has to match demand. The power companies have to judge how much power will be required. During periods of hot weather, electricity demand may increase as more people use air conditioning to keep their homes and offices cool. lf power companies’ estimates are wrong, people may experience power cuts.
Power stations are not very efficient, and between 50 and 70 per cent of the energy contained in the fossil fuel is wasted. Some of the heat energy will heat the surrounding air and escape through the boiler chimneys. The heat energy locked up in the steam cannot all be transferred to the spinning turbines. Although the steam is cooler when it leaves compared to when it enters the y turbines, it is still warm. The steam is carried to the cooling towers, where it cools sufficiently to condense back to water. The warm water is then emptied Into a nearby river or sea, where it can cause thermal (heat) pollution. Warm water holds less oxygen than cold water. The addition of a large quantity of warm water can cause animals, such as fish, to ‘suffocate`, as they are unable to extract enough oxygen from the water.