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How to choose the best wind turbine for your site.

Posted by Graham Eastwick on 28 June 2011 at 2:40 pm

There are a wide variety of wind turbines on the market today. These split in to two main categories: horizontal axis akin to the old fashion wind mills and vertical axis turbines. Most installations use a horizontal axis, vertical axis turbines are most often found in urban environments.

Below are a number of pointers to the things you will want to consider when selecting a turbine.

Space

You will need space to locate a wind turbine away from buildings and other obstructions. Ideally it should at a distance equivalent to around ten times the height of the obstruction; we have not found mounting turbines on to the sides of buildings that successful.

Planning permission

There was a proposal a few years ago to grant permitted developments rights to small wind turbines, however these have still not been adopted into law so you do still need to apply for planning permission. In addition, you will also need permission from the local electricity distribution company (DNO) if the wind turbine can supply more than 16 amps per phase. In practical terms this means if the generator is around 4kW on a property with a single phase electrical supply or 12 kW if you have a three phase supply.

Wind resource

Obviously the wind speed is the crucial factor and determines how much electricity (and revenue) a wind turbine will generate each year. Whilst make and the NOBAL database can give an indication, the windspeed needs to be measured on site prior to an installation if you want any degree of certainty as to the wind speed. More sophisticated prediction software tools are being developed and may, over the next few years, reduce the requirement for monitoring.

Finance

There are no public grant schemes to provide capital funding for wind projects. The feed-in tariff program provides a payment for all the electricity generated. The rates of return can be attractive and could justify a loan for the project. You will need to carry out a detailed cash flow to ensure that the payments can be afforded.

Things you will want to ask your supplier:

Reliabilty

Wind turbines are mechanical devices and can be placed under a high amount of stress. You will need to confirm with your supplier that the turbine has been used in wind conditions similar to the ones present on your site and has demonstrated reliability over a number of years; I have come across examples of turbines that have suffered major mechanical failures after a few years. This is sometimes blamed on excessive turbulence at the site so you need to discuss this with your installer.

Warranties

Check what warranties will be provided; it is also good to ask what they will do to rectify a persistent problem after a few years. The best thing is to talk to a previous customer who has had a turbine operating for several years and ask them about their experiences.

Turbine size

This is often restricted by the space you have available and planning restrictions. Small turbines can be installed in some circumstances under permitted development.

Generally the larger the rotor the more energy the turbine will capture. However, you will not always want to have the largest generator size (this will be stated as the maximum output in kW). A large generator provides more resistance and can prevent a wind turbine starting in lower wind conditions, so you may actually generate more electricity on a site with lower average  wind speeds.

Wind turbines and FITS

Wind turbines sized under 50kW need to be MCS approved in order to qualify for the feed-in tariff. The list of approved products can be found on the MCS website. For systems with a capacity to generate more than 50kW the choice of turbine is wider as MCS certification does not apply.

Photo by Patrick Finnegan

About the author: Graham Eastwick is a director of Encraft, and manages renewable energy installations for home owners, community organisations and small businesses across the UK.

If you have a question about anything in the above blog, please ask it in the comments section below.

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Comments

1 comments - read them below or add one

Ingleside

InglesideComment left on: 4 October 2011 at 12:21 pm

We have a Windsave 1000 wind turbine, which isn't doing anything as the inverter has failed. Since it was only generating about £50 worth of electricity pa (problems with eddying) there is no point in buying a new inverter for £600. We've explored buying a charge controller, and charging up a leisure battery, and using it to run (say) some lights, but can't find a suitable charge controller - WS output is 1kW max, and it does happen on occasions. Suppose we wired the Windsave directly into an immersion heater, and let all the energy go into heating water, without bothering about an inverter? I don't suppose the heating element cares which way the electricity is going! The snag would be that if we gave a 3kW element designed for 240V only 24V, it would only use 30W - which is neither here nor there! If we could we buy a low voltage immersion heater element, we could install it in a new tank, and use that as a pre-heat for the hot water. But do such things exist? Or has anyone got any other ideas we could try?.

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