Flowing water is a renewable energy source, and the most modern hydroelectric power stations are capable of converting at least 90% of their energy into electricity. However, the number of sites in the UK where this energy source can be harnessed on a large scale is limited.
The Committee on Climate Change which advises the Government estimates that hydroelectric power could theoretically contribute up to 8 billion kilowatt-hours (kWh) of electricity per year to the UK's energy needs.
Large-scale hydroelectric power stations need to dam valleys to create reservoirs in which to store water. For the installation to include pumped storage – a technology that improves the reliability of the power station by storing energy for later use – two reservoirs must be situated close together, but at different heights.
Not many sites in the UK meet these conditions. Most of those that do are in the Scottish Highlands and are already home to large-scale hydropower schemes. These schemes generate about 1.4% of the electricity used in the UK, but due to the lack of other suitable sites, this figure is unlikely to increase significantly.
These are the quantity of supply challenges facing hydro. Read about the possible solutions.