The energy in water has been harnessed for thousands of years. In prehistoric times, for example, it is probable that felled timber was moved by floating it down rivers. At sea, too, early mariners knew how to exploit the tides to help their passage.

For centuries, watermills were a common feature of riversides in this country, grinding corn and working other basic machinery; tidemills on the coast used the rising and falling of the tides to the same end. Hydro schemes helped power industrialisation in the 19th century, while over the last hundred years, hydroelectric projects, mainly in Scotland and Wales, have been an important source of the UK's electricity.

Today, the power in water can be harnessed in a number of ways:

• Hydro Power
  This uses the flow of water in rivers (or from reservoirs) to generate electricity. Water is fed through a turbine to generate power before being channelled back to the waterway. The amount of electricity that can be produced is determined by how much water is available and how fast it flows is determined by the vertical distance between the point where water from a river or reservoir and the turbines below.

• Wave Power
  The energy in waves can be turned into electricity by devices placed on the shoreline or out to sea. Wave motion can be used to compress air to drive a turbine or hydraulic pump.

• Tidal Energy
  The energy in tides can be captured using turbines built into "tidal barrages" which exploit the natural rise and fall in sea level. Underwater currents, caused by tides, can also be used to drive turbines.

Nearly 200 hyrdo schemes are currently operating in the UK. Most, but not all, are in mountainous or hilly areas. The cost of hydroelectricity has become increasingly competitive with power produced by burning fossil fuels; indeed, large-scale schemes, which provide about 2% of the UK's electricity, produce power for around the same price.

While the high cost of electricity generated by tidal barrages has prevented their development to date, the first prototype wave scheme to produce power for the electricity network has now been built in the UK.

The following are just some examples of UK water power projects:

• Loch Sloy Hyrdo Station
  The UK's largest conventional hydroelectric station, with the exception of pump storage schemes, is on the banks of Loch Lomond, Scotland. Built at the end of the 1940s, and with a capacity of 130MW, it uses water from neighbouring Loch Sloy; this is fed through pipes from a dam down to the power station's turbines 300 metres below.

• Barton Locks Small Hydro Scheme
  Situated on the Manchester Ship Canal, this scheme produces a maximum of 660kW of power - enough for about 600 homes. It won a contract under the UK Government's Non-Fossil Fuel Obligation (NFFO), which made a premium price payable for electricity generated by selected renewables schemes

• LIMPET
  LIMPET (Land-Installed Marine-Powered Energy Transformer) is a shoreline wave energy system on the Scottish island of Islay. The action of the waves is used to make air flow through a turbine, generating electricity. The project, which won a contract under the Scottish Renewables Obligation (SRO), is helping to demonstrate the viability of using waves to produce power.

Although there is little scope to increase the UK's use of large-scale hydro power, potential does exist to develop further small-scale schemes in suitable places. A new UK Government wave power programme is now assessing the extent to which wave power could help meet our energy needs. For economic reasons, tidal power is unlikely to be developed in the short term.

Finding Out More

Complementing the information contained here on the Planet Energy Web site, additional detailed information about water power is available on the main DTI Renewable Energy Programme Web site at www.dti.gov.uk/renewable/index.html, where other links relevant to this important renewable energy technology are also available. Other key sites for this technology include:

• British Hydropower Association
• International Energy Agency
• New Review - The quarterly newsletter for the UK renewable energy industry

In the Classroom