What is hydro power?
Hydro power is one of the longest established renewables in our current energy mix.
Water wheels were developed for irrigation over two thousand years ago, and were applied to the milling industry. They became extensive by the Industrial Revolution, driving machinery in mills, factories and foundries.
The development of water turbines made the energy potential from moving water suitable for electricity generation. Hydropower currently supplies 2% of the electricity used in the UK (2004 figures). This is mostly from old, large dam projects.
How does the technology work?
Hydro power works by placing a turbine in a flow of water to extract energy and convert it to electricity through a generator.
The amount of electricity that can be generated is related to the rate of flow of the water and the distance (known as 'head') the water falls.
There are three types of of hydro schemes: pumped storage; storage; and run-of-river schemes.
Storage schemes involve damming a river and incorporating a turbine and generator in the dam itself.
Run-of-river schemes enchance the flow of a river and maintain its natural flow by using a weir.
Storage and run-of-river schemes can divert water from a river, lake or dam down a low pressure channel to a remote turbine and generator, returning the water back to the river afterwards.
Micro and small-scale hydro
Small-scale hydro was used before the introduction of large distribution schemes to generate a few thousand watts of electricity locally from sluices and dams of old mills.
With improvements in generating technology, small-scale hydro is now once again being looked at as a green source of electricity.
How can the technology be used?
It is feasible to generate a few kilowatts of electricity from 'heads' as low as 2 to 3 metres. It is possible to generate useful power from anything upwards of a small stream. This is likely to be a few hundred watts for domestic schemes, or a 25kW minimum for commercial schemes.
Suitable for the UK?
The UK's potential to generate energy from small-scale hydro is largely untapped. If the potential for small-scale hydro in the UK were realised it could generate over 2.5% of current UK electricity demand.
Small-scale hydro, unlike some large-scale hydro, which have created huge environmental problems, has negligable ecological effects if properly managed.
It is one of the most cost-effective and reliable technologies for green energy generation and can be grid connected or part of a decentralised system.
Small-scale hydro has a high efficiency of 70-90%, is reasonably predictable (varies gradually with rainfall), and the technology is long-lasting and robust, with systems engineered to last up to 50 years.
How does the technology work?
Pumped storage systems are a means of storing energy for later use when it needs to be used quickly, such as at peak demand times.
The system uses two reservoirs and, at times of low demand, water is pumped (using electricity) from the lower to the upper basin. The water is then used to generate electricity at a time when demand is high.
The UK already has 2788MW of installed pumped storage capacity.
This technology is not a source of energy as it is reliant upon electricity to pump the water up to the higher reservoir. However, it is a useful way of storing energy for times when the demand is high, as it can rapidly respond to sudden changes in demand.
Dinorwig pumped storage station in Wales is one example of a pumped storage scheme in the UK.
Large-scale hydro projects currently contribute 4000GWh of the electricity used in the UK. Most of these schemes are found in the Scottish Highlands.
Opportunities to increase large-scale hydro in the UK are limited, but a 100MW scheme at Glendoe on Loch Ness has been given planning permission, and will provide enough electricity to meet the needs of 37,000 homes.
Other green energy sources