Responding to demand

The demand for electricity varies throughout the day.

Graph titled Electricity demand on 30 January 2014. It plots megawatts from 0 to 60,000 against time of day.

When the demand for electricity is greater than the base load, the National Grid reacts by providing additional electricity.

Nuclear power stations and coal-fired power stations usually provide base load electricity. They run all the time because they take the longest time to start up. Hydroelectric power stations have a very short start-up time and are used to provide additional electricity at peak times. Electricity is also imported from other European countries to meet the demand at peak. It can also be exported at other times.


Discuss why the demand for electricity varies throughout the day and how the National Grid responds to this change in demand.

The demand for electricity changes throughout the day. It is at its lowest during the early hours of the morning as the majority of people are in bed. It increases between 06:00 and 09:00 when many people get up and switch on electrical appliances such as lights, kettles and electric showers. The demand increases again at around 17:00 when many people return home from work.

The National Grid monitors this power use in order to respond to the change in demand during the day. The National Grid provides a base load of electricity using coal and nuclear power stations, and when the demand exceeds the base load, hydroelectric power stations are used in order to supply electricity quickly in order to meet the demand. Electricity can also be imported from other European countries at peak times.


Explain why transformers are used in the National Grid.

A step-up transformer increases the voltage in order to decrease the current before it travels through the transmission lines. A lower current ensures that less energy is wasted as heat in the transmission lines, and makes the process more efficient. A step-down transformer decreases the voltage in order to make it safer for the consumer.

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