Saving energy, money and the environment

Hydro-power is the largest source of renewable energy, providing about 16 per cent of the world’s electricity. 

Hydro-power is not used so much at a domestic level because it needs the right site; most people have not got a stream handy. Also, it is expensive to install. The term ‘micro-hydro’ is used for domestic size systems, and generally refers to those which generate between 5 and 100kW of power. 

• Water with some flow is taken from a river or stream. Usually, it comes from behind a weir or a small dam 
• The water runs down a canal (or leat) to a head tank, where it settles and fish, silt and other debris are filtered out 
• From there the water drops down a pipe (called the penstock) to turn a turbine. The height of the drop (called the head) is one of the significant aspects of whether your site will be suitable. The greater the head, the more power is generated 
• A turbine is located in a powerhouse with the generator, transformer and the control equipment. From there the power generated can be used directly to power your house, stored in batteries or exported to the grid. One advantage of hydro-power is that with a good site you may not need batteries or an inverter (to convert DC to AC voltage), as the turbine can produce a constant 240 volts when turned on.  
• Once it has left the turbine, the water returns to the river along another canal (the tailrace).  

Advantages of Hydro-power are:

• cheap heating and hot water 
• affordable option for off grid homes 
• cut your carbon footprint 
• works 24/7 

If you have a good site, hydro-power is one of the most efficient and reliable forms of renewable energy. Micro systems tend to be between 60 and 90 per cent efficient – where efficiency measures how well the water’s power is converted into electrical power. Hydro also has good predictability, and in the UK output is generally greatest in the winter months when energy demand is highest.

In Hydro terms a good site generally means one on a steep hill with fast flowing water. The head (or maximum vertical drop) of water is key. Less than 10m is normally classed as low head, from 10-50m medium, and more than 50m, high. If the head and flow are good enough, useful power can be generated from small streams.

Somewhat surprisingly, old watermills are not necessarily suitable hydro electricity sites. Although they may have an old canal drawing water off the stream, many do not have a strong enough flow or high enough head to generate electricity effectively. This is because they were designed to operate machinery directly. It is estimated that up to 15 per cent may be suitable for upgrading.

If your site is suitable, it is also important that it is reasonably close to where the power is going to be used, and to a connection point to the grid, if you plan to export any surplus.

If you are off-grid, and have a good site, you can use power directly from the turbine, turning it on and off as you need it. Alternatively you can use batteries to store the excess.

Costs for installing micro-hydro vary, largely depending on the location and equipment required for install. The basic equipment for a 1kW off-grid battery charging system might cost £5,000 to £6,000 plus installation costs, according to the Centre for Alternative Technology. The total cost of a Pelton turbine producing 5kW from a 25m head might cost £25,000 when installed by a professional. 

You will need planning permission to install any hydro-power system. You should contact your local planning department at an early stage. They will be able to advise you on other organisations that need to be consulted, such as the Environment Agency, and the process you need to go through.

The Smart Export Guarantee (SEG) means you can get paid for the surplus energy your micro-hydro system generates and exports back to the grid. You should shop around for the best SEG tariff. For more on the SEG see here

• Case study: Devon Wildlife Trust
• Community hydro power project close to realisation (Nov 2013)