Equipment and installers

What turbine to use?

The turbine has to be carefully chosen so that there is a balance between a larger turbine that is capable of producing lots of power when the water is available, or a smaller, cheaper one which will generate less energy but work flat out most of the year. This is called the load factor. Normally you would choose one which had a load factor of 50% to 70%.

Turbines can be classified as high, medium or low head.

There are two kinds of turbine – reaction and impulse.

Impulse turbines are situated to spin freely in air and the water is directed at the turbine through a spout or nozzle. These are the most common sorts of turbine for micro hydro systems. There are three types – Pelton, Turgo and Cross flow.

Impulse turbine image

Reaction turbines are fully immersed in water and enclosed in housing, so that the pressure of the water turns the turbine. They are most likely to be used where there is a relatively consistent flow throughout the year.

Pelton turbines are used for a low flow and high head. Turgo for medium head and flow, and cross flow are adjustable for variable flow. The Francis turbine was originally designed as a low head turbine and there were thousands of them installed across Europe in the 1920s – 60s. Many of them are still in existence and it is possible to get them refurbished.

Turbine choice guide

 

Most hydro schemes will need at least a short run of pipe to bring the water from the river to the turbine. The pipe's diameter may range from a few centimetres to over 30 cms or more. Losses due to friction must be minimised and so the bigger the pipe the better. Plastic pipe (PVC) is the usual choice and it must be buried to keep the water from freezing and to protect it from damage.

 

Other equipment

Trash Screens

Perhaps one of the most important pieces of equipment is the trashscreen or trashrack. This filters out the debris from the river before it gets to the turbine. Most of the problems in a system can be caused by the screening system and so it is wise to get the best that you can afford.

A pool of water will not increase the output from the turbine, but it will allow the water to cal so any debris can sink or float.

In most cases the first line of protection is a boom which is laid across the river. This will catch large items. A rack of bars is then placed across the intake, which can be cleared with a rake. The distance between the bars will affect the head and so they need to be the maximum possible whilst still being able to stop debris entering the turbine.

Fish screens

In any river where the Environment Agency feel there is a threat to fish, they will insist on a by wash being established to enable fish to bypass the turbine system.

Where there are young salmon likely to migrate down stream, a fine mesh needs to be installed for several months in spring and summer. This will accumulate large volumes of debris which will need to be cleared frequently and an automatic clearer will be essential.

A number of innovative methods for excluding fish from intakes which avoid a fine-meshed physical screen are being trialled. They will be much more beneficial to the system as they will not reduce the flow of water, but are yet to find favour with the environment agency.

Automatic systems an include

• A robotic rake. There are several designs but they usually involve rakes operated by a hydraulic ram. They are very robust but there are slight H and S concerns and the visual presence.

• A rake and chain clearer. This moves the debris into a channel to be flushed away into a side spillway.

• A grab and lift cleaner. This lifts the debris straight into a skip.

• Coanda screen. This is only applicable for high and medium head schemes require no raking because they utilise the Coanda Effect to filter out and flush away debris and silt particles. Precisely positioned, finely spaced horizontal stainless steel wires are built into a carefully profiled screen which is mounted on the downstream face of the intake weir. Clean water is collected in a chamber.

INSTALLERS

Installers will take the project through from specification, procurement, installation to commissioning of the scheme. They may also carry out a full feasibility study if required. A civil contractor may also be needed for the site work.

When choosing an installer, it is worth asking for references or a list of past projects that you could contact.

There is a list of approved installers at the Microgeneration Certification Scheme (MCS) website. This is a UKAS accredited certification scheme for installers and products, offering consumers protection. The feed in tariff consultation document suggested that MCS accreditation (product and/or installer) might be necessary to access the FIT – however for micro hydro this is not yet confirmed. More information should be available from DECC in Q1 2010. A comprehensive list of installers, manufacturers etc. can be found on links page of this site.

A nice guide to this by Alan Robinsin of Gilbert Gilkes and Gordon Ltd. can be found here: http://www.british-hydro.org/uploads/03%20Alan%20Robinson.pdf

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