Hydro-electric energy
Hydroelectric power is the energy derived from the flowing water in rivers, or from a man-made installations where water Sows from a high RESERVOIR down through a tunnel Water power was used for centuries to power machinery, for example for grinding corn in mills and factories, but was largely replaced by steam power in the Industrial Revolution. Hydroelectric power is now mainly used to generate electrical energy.
The UK currently generates about 1.8% of its electricity from to large-scale hydroelectric schemes - most of which are found in the Scottish Highlands. Hydroelectric is a proven technology. It is efficient - the most modem plants have energy conversion efficiencies of up to 90%. Many smaller schemes exist, and as interest in this clean power increases more schemes are becoming operational.
Future development
Opportunities to increase large-scale hydroelectric power stations in the UK-are limited as most commercially-attractive and environmentally-acceptable sites have by now been utilized. Two new small-scale hydroelectric schemes in Scotland have been recently approved at Kin-gairloch in Lochaber and Braevallih in Argyll, which will provide 3.5 and 2.2 MW respectively, providing enough electricity to meet the demand of 5,250 households.
Some old water mills are being refurbished and bought back into the energy supply network. If small-scale hydroelectric power station from all of the streams and rivers in the UK could be tapped it would be possible to produce 10,000GWh (1GWh = 1,000,000 kWH) per year - enough to meet just over 3% of our total electrical needs and making significant contribution to the Government's renewable energy target of 10% by 2010.
River ecology
Hydroelectric power schemes need an abstraction license from the Environment Agency. Under this license, the effect of the turbine on a river's ecosystem will be investigated. The river's ecology is protected by restricting the proportion of the total flow diverted through the turbine. Large hydroelectric power scheme may include fish ladders to allow migrating salmon and sea trout to pass into the upper river to spawn.
Energy balance
With small scale hydroelectric schemes, the embodied energy (the energy used in the manufacture of the components) of a scheme is typically equaled by the energy generated by the scheme within 9 months of commissioning.
Emissions
Emissions are not a problem on small-scale schemes. In larger schemes which have involved flooding, some carbon dioxide emissions may come from decaying vegetation in the short term.