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Renewables

Intro

Impulse Style Water Turbines

An impulse turbine operates on the same principle as a toy pinwheel. Water strikes the turbine runner, and pushes it in a circle. The water is delivered to the runner through a pipeline, and out a small nozzle that maximizes the force available to operate the turbine.

These types of water generator work best in sites where the water source has high head (20 feet or more). Head is the vertical distance between where the water enters the turbine system (in this case, into a pipeline) and where it reaches the turbine runner. These water turbines require minimal water flow volume, so they are ideal for sites where a relatively small amount of water runs down a fairly steep hill, as in a hillside stream or small waterfall. The most well known type of impulse turbine is the Pelton-wheel style as used in Harris Pelton turbines. But in higher flow sites, a Turgo style runner such as the one use in the Stream Engine has a higher output potential.

Reaction Style Water Turbines
Reaction turbines require a much larger amount of water flow than impulse styles, but can operate with as little as two feet of head, making them ideal for sites where there may be relatively flat land, but a large water flow.

These route water either through a pipeline into an enclosed housing, or through a canal to an open flume, (note: most open-flume designs can be modified to use a pipeline and enclosed housing if it better suits your installation site). The turbine runner is immersed in the water, which exits the housing through the turbine, turning the alternator as it 'drops' through the runner blades. No matter which runner style a reaction turbine uses, a specially designed outlet tube increases the turbine power output by creating suction as the water exits the system.

Submersible Propeller Water Turbines
These turbines are the least efficient of the three styles, but also the simplest design. A propeller mounted on the front of the turbine is attached to an alternator inside the main turbine housing. When submerged in a fast moving water source, the force of the passing water rotates the propeller. Propeller style generators work well for locations with a fast moving, relatively deep stream or river, where a water diversion system is not possible, or when mounted on a moving boat.

Advice
For people with a good source of year-round running water, one or two water turbines may be all they need to power their homes. However, for those with seasonal, winter-only streams available, a small water generator may be the perfect back up for a solar system's off-peak season.

Cost
Hydro costs are very site specific. For low head systems (not including the civil works - so assuming there was 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. These schemes are generally more expensive as they require bigger turbines and more civil works.

For medium heads, 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-£25,000. Unit costs drop for larger schemes