Hydropower uses the flow of water to generate electricity. This flow of water is often created by building a dam to block a valley or river.
In MegaWatt hydropower has a high capacity with a moderate cost and environmental impact.
Hydropower is one of the oldest forms of renewable energy, with evidence of water wheels in the Middle East dating back to 4th century BC. Most modern hydropower plants use a dam to create a reservoir of water. Once the water has built up, it is released by valves which allow the water pass through the dam under gravity. This flow of water passes through turbines which turn generators, producing electricity.
It is a reliable and flexible source of electricity, unless the area suffers from a prolonged period of drought. It can also reduce the chance of severe flooding downstream of the dam by controlling the water flow.
Building a hydropower plant along a river can have a big impact on the local environment, in particular for the aquatic ecosystems. Large areas of land are flooded, and fish can no longer migrate upstream. It also requires a lot of concrete and steel in its construction.
There are only a limited number of places where hydropower can be built, as it is very dependent on the local geography, therefore it is not expected to be a growth industry.
Now for some stats from the UK grid in 2019.
The total installed capacity for hydropower is 4363 MW (de-rated), of which 2744 MW is pumped storage generation.
Hydropower provided around 1.8% of the electricity generation (5.9 TWh), which is 9% more than the year before. Capacity for hydro generation was unchanged; this increase was due to an increase in capacity factor to 36.2%, due to increased rainfall and changes in weather patterns.
Hydropower generation in the UK has remained quite stable, and is not likely to increase much in the future. Most of the potential for further hydropower plants are in Scotland, but due to the remote location of the sites, often located in national parks and areas of outstanding beauty, environmental concerns mean it is unlikely that these sites will be developed.
This time lapse of the Three Gorges Dam shows just how quickly China has developed in recent years, including in securing its electricity supply.
The Dinorwig Power station in North Wales is the largest hydropower project in the UK. It is a pumped storage facility, with a maximum capacity of 1728 MW and a storage capacity of around 9.1 GWh. Construction began in 1974 and was completed 10 years later, using over 1 million tonnes of concrete, 200,000 tonnes of cement and 4,500 tonnes of steel!
The Dinorwig dam is tiny in comparison to the biggest hydropower plant in the world. The Three Gorges Dam, built along the Yangtze river in China, is the worlds biggest hydropower project, with an installed capacity of 22500 MW.
The size of this dam and the reservoir it created are enormous. The reservoir it created is 600 km long, holds almost 40 km cubed of water and displaced 1.25 million people from their homes. The amount of water it holds is so big, NASA calculated that the shift of water mass stored by the dams would increase the total length of the Earth's day by 0.06 microseconds!
All of the numbers we used for the UK statistics can be found in the Digest of United Kingdom Energy Statistics 2020 which is from the Department for Business, Energy & Industrial Strategy (the people in government who look after our energy policy). Other statistics are from the International Energy Agency overview of electricity.