Hydroelectricity is a long word which means generating electric power from water. Sometimes we just call it hydro. Just like the water wheel used in the traditional mill for thousands of years it uses the power of flowing water to turn a wheel or turbine. The turbine is connected to an electric generator and this produces electricity.

Hydroelectric stations can be massive dams or small units on the edge of the local river. Hydroelectric stations are a mature technology: they are well-understood and reliable and we’ve many years experience of running them. However, some schemes in the past have been controversial when we didn’t think enough about the effect of large dams on the local environment and on local people who depend on water, especially in areas where water is a precious resource.

One type of hydroelectric station worth a closer look is called pumped hydro. This is where there are two water reservoirs: one high up and one low down. When electricity is needed, the station generates electricity by the water flowing down from the top reservoir to the bottom reservoir turning the turbines. When there is too much electricity in the grid, the station can use some of that extra available electricity to pump water uphill back to the top reservoir. This is clever because it is a bit like a big battery. It allows that extra electricity we don’t need right now to be stored for later.

In the UK, pumped hydro has been very useful to manage day and night usage for decades. The challenge now is to manage the grid with intermittent renewables of wind and solar as well as the varying demand from homes, schools, offices, factories and electric car charging. Pumped hydro can help with that but more storage will be required.

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