Water as a source of energy was first used to provide the power for mill wheels to grind corn and lathes to shape wood into all manner of gadgets of the times - hubs for carriage/cart wheels etc. These were the huge multi-paddled wooden water wheels that one can still see in renovated mills across the country. Here the water was lead to the mill in a built up leat from higher up the stream and then shot over the wheel,thus turning the paddles, and so down into a pool beneath the wheel and back to the main stream. Only after the invention of electricity was it realized that these water wheels could also generate power for lighting. Huge hydro-power schemes followed and each housed several large metal turbine wheels capable of providing enough power for industrial as well as domestic use. However, this same technology can be scaled down for use in small streams for the provision of electricity to domestic and farm premises.

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How might it work for you

Obviously any form of Hydro-power, requires access to moving water. It will also require liaison with the Environment Agency, whether the device is set directly into the stream; or whether the water is directed through a Race to the device, and is then returned to the main stream. This all counts as water abstraction; and although in the latter case the removal is temporary, the water level in the main stream will necessarily be lowered for a short stretch.

Concerns are twofold and concern both: the welfare of fish and the other biota in the stream; and the natural water feed to neibouring farms and minor streams that lead off the stretch of reduced water flow, due to the redirection of water through the mill. Lowered water levels in winter could result in a dry bed, as could low flow periods in a dry summer; and it is this eventuality that is of most concern. The type of turbine is also crucial; some, but not all, are be fish friendly. Archimedes Screws are considered 'Fish Friendly' and most authorities will allow them to be sited in the main stream, provided that this does not interfere with other water users. However, most turbines/Pelton wheels are liable to chop fish and must be fitted with Fish Excluders with a side 'fish race' if they are in the main stream, or more simply a fish excluder at the start of the leat leading to the mill race. Therefore, it is best to site these in a race system from which fish can easily be excluded at both ends. This of course means that the main river bed must always have enough water to allow for the passage of fish in the short section parallel to the Race.

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Facts - Energy Produced and Costs of Production

Up to a rating of 10kW, these cost approx. £4,000/kW and anything up to 100kW is considered to be a Micro Hydro generation scheme. A 100kW installation will cost anywhere between £85,000 and £280,000. The variation in cost has a lot to do with the type of preparatory works and building required to house the turbine. Probably the cheapest to set up would be a small under or overshot Pelton wheel; or an Archimedes Screw. These were originally devised to draw water up to the fields from the River Nile; its use for electrical generation when reversed was only established in the 1990s.

An Archimedes Screw rated at 5kW could be set up in a stream with a fall of 2.4m and a flow of 0.36cu.m/sec. This will produce 27MW/year, which with FiTs and Grid payments will have a payback time of just over 9 years at present costs.


Schemes of up to 15kW attract a 20 year payment of 19.9p/kWh/year, plus a 5p Export Tariff. This falls with the size of the scheme, so that at 2MW the FiT is 11p/kWh/year; and at 5MW the FiT is down to 4.5p/kWh/year. The Export Tariff of 5p/kWh does not change.

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Pros and Cons


  • These schemes are low maintenance and easy to service.
  • Archimedes Screws are particularly Fish Friendly.
  • With the Archimedes Screw, at no stage is water abstracted from the stream bed, not even for a short distance
  • Several Archimedes Screws or Pelton Wheels can be sited at the sides of larger rivers and set into weirs without disrupting the flow of the river in the main channel.
  • Water provides most power in the winter months when it is most needed.
  • There are no carbon emissions once up and running.
  • The amount of power provided means that electrical heating for old houses becomes very economical.


  • The initial installation costs are high.
  • Planning permission will have to be obtained.
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Variations on the theme

Turbines can be set under the flow of water over a weir (Overshot Wheel); or can be set into a wheel house above the flow, with the water pushing against the underside of the wheel (Undershot Wheel).

The Archimedes Screw is usually pushed around by water flowing down its underside for the length of the screw. The metal screw itself being laid in a sloping concrete Race. This is well suited to even very small mountain and moorland streams.

Another variation is the Kaplan Turbine, for the workings of which see the entry in Wikipedia.en.wikipedia.org/wiki/Kaplan_turbine

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How and Why it works

Water Wheels almost certainly pre-date Windmills; but they too started life with different functions, being used to power Grind Stones to mill grain, and to raise water from a river bed to irrigate the fields. In the case of raising water the paddles were more like buckets and the wheel was turned using rope warps with a draught animal to pull them.

The combination of basic metal working, together with the use of wood, lead to the possibility of the Archimedes Screw (Archimedes lived from 287BC to 212BC). This then took over as the most economical way of raising water, since the screw kept on working as long as the draught animal walked its circle without any need to change ropes.

However, in recent years it was realized that if water is poured into the top of an Archimedes' screw, it will force the screw to rotate. This system is also known as a 'Reverse Screw'. The rotating shaft can then be attached to a gear system and used to drive an electric generator. This type of installation is not damaged by dirty, silt laden flood water, nor by the odd bit of gravel; but the biggest plus of all is that it is Fish Friendly. Settle Hydro and Torrs Hydro are two of the reverse screw micro hydro schemes operating in England.

Water wheels now have a variety of shaped paddles designed to maximize the force of the water; and, in the same way as the modern wind turbines, the main shaft is connected to a series of gears, to speed up the rotation of the generator.

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