Hydroelectricity

How do hydropower systems work?

All streams and rivers flow downhill. Before the water flows down the hill, it has potential energy because of its height. Hydro power systems convert this potential energy into kinetic energy in a turbine, which drives a generator to produce electricity. The greater the height and the more water there is flowing through the turbine, the more electricity can be generated.

The amount of electricity a system actually generates also depends on how efficiently it converts the power of the moving water into electrical power.

Find out more about different kinds of technology at the British Hydro Association website.

The benefits of hydro systems

• Cut your electricity bills
  A hydro system can generate 24 hours a day, often generating all the electricity you need and more.
• Be paid to generate energy 
  If eligible, you'll get payments from the Feed In Tariff for all the electricity you generate, as well as for any surplus electricity you sell back to the grid.
• Cheap heating and hot water
  A hydro system may generate more electricity than you need for lighting your home and powering your electrical appliances – so you can use the excess to heat your home and your hot water too. 

• A cheaper option for off-grid homes
  Installing a hydro system can be expensive, but in many cases it's less than the cost of getting a connection to the National Grid if you don’t already have one. Find out more about off-grid options.
• Cut your carbon footprint
  Hydroelectricity is green, renewable energy and doesn't release any harmful carbon dioxide or other pollutants.

Will hydropower work for me?

Hydropower is very site specific. Most homes will not have access to a suitable resource even if they have a water course running nearby. Assessing a hydro site properly is a job for a professional. If you think you might have a suitable site the next step is to contact a certificated installer, who will have a look at your site for you.

To be suitable for electricity generation, a river needs to have a combination of

• flow – how much water is flowing down the river per second, and 
• head – a difference in height over a reasonably short distance

You could have either lots of flow and not much head (such as a river flowing over a weir) or lots of head and not much flow (such as a mountain stream).

It’s also important to consider what happens to the river in summer. The minimum flow during dry periods is usually the deciding factor, no matter how impressive the river looks when it is in flood.

If there is a good hydro resource in or near your community it might be worth developing it as a community energy project, rather than as a system to supply just one home. Download our guide to hydropower, for individuals or communities.

If you don’t think a hydro system is suitable for your home, use our Home Energy Generation Selector Tool to look at other options.

Off grid

Is your home connected to the National Grid? If not, hydro schemes are one of the most reliable alternatives to mains supply for isolated properties, and can sometimes be cheaper to install than a new mains connection. More about off-grid options.

Costs, savings and earnings

Costs

Costs for installing a hydro system vary a lot, depending on the location and the amount of electricity you can generate. A typical 5kW scheme suitable for an average home might cost around £25,000 including installation. Some sites cost less than this to develop; others cost much more due to the nature of the site, and so will be less financially attractive and less likely to be developed.

Maintenance costs vary but are usually low as hydro systems are very reliable.

Savings

Savings will depend on the number of hours the turbine is able to run in a year, which in turn will depend on how often the level of the river is high enough to supply the system. Your installer will be able to predict this for you and estimate the amount of electricity that will be generated.

Making the most of hydroelectricity

To make the electricity you produce go further:

• use low energy bulbs throughout your home - these produce the same amount of light as conventional bulbs and use up to 80% less electricity. Find out more about energy-saving bulbs.
• invest in energy-efficient appliances. Find out how to spot the best energy-saving products.

If you can reduce your energy demand so much that you don’t use all the electricity you generate:

• you can sell the surplus back to the grid, if you're connected, to earn extra money
• you can store some of the surplus in batteries to use later if you're off grid.

Earnings

If your system is less than 15kW, all the electricity you generate will earn 20.9p/kWh from the Feed In Tariff and every surplus unit you sell to the grid will earn 3.1p (2011/12 prices). Off-grid systems will earn the 20.9p generation tariff.