Local heating (CHP)

Generating electricity in a power station involves large amounts of waste energy (mainly as hot gases sent up the chimney and into cooling water). It is impossible to avoid this. The photograph shows cooling towers at a power station. These are used to condense steam (which has been used to drive the turbines) back to water, ready to be used again. When a power station is near the sea, the seawater is often used to cool the steam. In general, power stations like these only transfer around one third of the energy from the fuel to the final users.

A few power stations use pipes to transfer some of this energy to local homes and industries where it is used for heating. This system is called 'Combined Heat and Power' (CHP). It can raise the amount of useful energy extracted from the fuel from 30% to 50%.

The need for economical use of the world's energy resources

The world's store of energy is mainly used to help us over the times when the sun's energy is too little (eg Britain in winter). This store is not only used to keep us warm and give us light, but also to enable us to produce buildings, materials, medicines, and all the devices and services which we use. Without stored energy, the life-sustaining areas on Earth would be very much smaller.

Around 90% of the world's energy needs are met by using up our reserves of coal, oil and gas, which are decreasing rapidly.

Grades of energy

Sources of energy can vary in their usefulness. High grade sources like oil, coal and nuclear fuels can be used for nearly every task. Low grade sources like solar energy and wind might well be far more plentiful in total, but their energy is harder for us to put to use.