Hydroelectric power plants do not release carbon dioxide while generating electricity – this occurs mostly during their construction and decommissioning.
UK Government research has found that a large hydroelectric power station emits 10 to 30 grams of carbon dioxide for each kilowatt-hour (kWh) of electricity it generates.
Building a dam may require the removal of trees that absorb carbon from the atmosphere. When land is cleared for construction, greenhouse gases escape from the soil and future capacity to absorb carbon is lost too.
The carbon footprint involved in making and transporting the concrete used to construct a large-scale hydroelectric power station is significant.
Hydroelectricity is a low-carbon and renewable energy source. Increasing the proportion of UK electricity generated from low-carbon energy sources can reduce the proportion that must be generated by higher-carbon sources.
The working life of a large-scale hydroelectric power station can exceed 100 years – so when we calculate the average lifetime emissions of a hydroelectric power station, initial CO2 emissions will be offset by subsequent decades of zero-carbon electricity generation.
In 2014, the UK generated around 1.9% of its energy from hydroelectric power stations, according to EDF Energy analysis based on Elexon data.
Smaller-scale run-of-river schemes that use the natural flow of rivers or streams to drive a turbine have a much smaller carbon footprint than large-scale schemes. Typically, they produce less than 5 grams of CO2 for each kilowatt-hour (kWh) of electricity they generate, because construction of a run-of-river project releases less CO2 than that of a hydroelectric power station.