How does Hydro Electric Power Work?

Hydro-power uses a turbine powered by the flow of water to turn a generator and produce power

Hydro power

Basically, hydropower is any system that generates electricity from water. On a commercial scale, the UK has had hydro dams for many, many years, mostly in Scotland and Wales. For the purposes of the tariffs, the most common technology will involve turbines placed in running water all of which is explained below. However, if you don’t have access to running water then the below won’t be relevant to you other than to satisfy simple curiosity, of course!

How it works

Hydropower systems use falling water to drive a turbine which generates electricity. The amount of energy which a system generates depends on a combination of the flow rate – the volume of water flowing – and the ‘head’ – the vertical height difference between the incoming and outgoing water. Hydro scheme are generally described as being either ‘high head systems’ or ‘low head systems’

A high head system will typically be sited to have a water intake above a weir or a dam. The water is then redirected into the intake, down a channel or pipe (known as the penstock) and into one or more turbines. A screen will be positioned within the intake to prevent fish or other debris going through the turbines.

Low head systems, as their name implies, has a smaller drop. They tend to be positioned on old mill sites for this reason but do note that simply converting a water wheel to generate low amounts of electricity (sub 45kW) does not qualify under the Feed-In Tariffs.

There are several different designs of turbine with different ways of converting the water flow to rotation of the generator. The most suitable will depend mainly on the flow and head characteristics of the site.

Most systems are connected to the grid which is important as it allows electricity to be ‘imported’ when the system isn’t producing enough power and ‘exported’ when your system produces more electricity than you need. The exported surplus electricity is sold back to the grid at 3p/kwh under the Feed-In Tariffs.

Where it works best

You will need access to a water course, ideally with a ‘head’ of at least a metre. For this reason, many hydropower generators are installed at old mill sites.

Often the water flow varies throughout the year, so hydro systems may not be able to supply all your electricity when you need it. If you’re not connected to the electricity grid, you will need a backup power system.

Consents are required to install hydropower systems because they affect the water flow. Typically abstraction and impoundment licences are required from the Environment Agency. We can help customers with this requirement.

Helpfully, the Environment Agency has also produced this interactive map of the 26,000 sites in England and Wales that are deemed suitable for small scale hydropower.

How much energy it produces

For any given head, the output of a hydro-turbine will be closely related to the flow rate. You may be able to control this with sluices and match the output to your needs. In most cases, however, the flow rate will depend on the recent rainfall and perhaps the requirements of other users of the stream or river. It is useful, therefore, to have historical data to be able to project the output of a hydro-power system.

What maintenance it needs

The maintenance requirements depend on the design of the turbine but typically we recommend a service visit once a year to check on the performance of the system.

Tariff levels

… are shown here.