[font=Arial] If you have a suitable water source, installing a hydro-power system will allow you to create green, clean energy. Hydro-power systems convert the potential energy stored in water to rotate a turbine which in turn produces electricity. How does it work? Power may be produced from even a small stream, and a micro （small） hydro plant is classified as one that generates less than 100 kilowatts （kW）. Systems range from a few hundred watts （possibly for use with batteries） for domestic schemes, to over 25kW for commercial schemes. The Energy Saving Trust says that improvements in small turbine and generator technology mean that small hydro schemes are an attractive means of producing electricity. Hydro systems can be connected to the national electricity grid or be part of a stand-alone （off-grid） power system. In a grid-connected system, any electricity generated, but not used, can be sold to electricity companies. In an off-grid hydro system, electricity can be supplied directly to the devices powered or through a battery. A back-up power system may be needed to compensate for variations in water flow throughout the year. What are the practicalities? Hydro power requires the water source to be relatively close to where you will use the electricity generated, or to a suitable grid connection. The amount of energy generated depends on how fast the water flows and how far the water falls – so you need a fast flow and a good drop. In small systems around half of the power of the water is actually converted to electrical power. You will need to talk to the relevant planning authorities to ensure the site and design are acceptable and identify any other permissions required. How much does it cost? Hydro costs depend very much on the site and energy output. For small systems using an existing pond or weir, costs may be in the region of £4,000 per kW installed up to about 10kW - and would drop per kW for larger schemes. For medium sized systems, there is a fixed cost of about £10,000 and then about £2,500 per kW up to around 10kW - so a typical 5kW domestic scheme might cost £20,000 to £25,000, according to the Energy Saving Trust.[/font]