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