Making wind work in Cities: you canít convert energy that isnít there!

Posted Monday 18th of August 2014 at 14:32

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We are often asked whether our turbines can be mounted on buildings and whilst we say 'yes' we add the caveat that this is probably not ideal. A better option is to have the wind turbine freestanding on a pole or mast well away from obstructions.

The turbulence experienced around buildings reduces the performance of wind turbines as they 'hunt' the wind. In contrast open sites away from buildings and trees where airflows are constant result in much higher power generation.

As anyone in the wind industry will confirm urban environments and building mounting is probably the most challenging context in which to try to make wind power work.

Warwick Wind Trials

Tubines on the top of the Ashton Court flats performed well

This is borne out of research carried out by the Encraft Warwick Wind Trials Project covering 168950 hours of operation of 26 building mounted wind turbines across the UK during 2007-2008. The objectives of this study were to see how grid connected microwind turbines perform on a variety of building types - ranging from theoretically poor (single storey urban buildings) through to theoretically excellent (45m tall exposed flats in isolated settings on hilltops).

The average energy generated per turbine per day across the sample set was 214 Wh (including times when turbines were switched off for maintenance or due to failures). This is equivalent to an average of 78 kWh of energy produced per site per year.

If the results are adjusted to exclude data from periods when turbines were switched off or broken the average energy generated per turbine per day rises to 628 Wh (230kWh per year equivalent). Of particular note is that turbines on the high rise sites (Eden Ashton photographed here and Southorn Court) were able generate as much energy in one month as other turbines in the trial did in one year.

The best performing turbine in the trial generated an average of 2.382 kWh per day when in operation equivalent to 869 kWh in a full year. The poorest site generated an average of 41Wh per day when in operation or 15 kWh per year which is less than the energy it consumed to run the turbine's electronics.

Recommendations

A key recommendation from the study was that great care should be taken in selecting suitable sites for building-mounted turbines. There was no doubt that some locations performed well.

Wind speeds need to be measured at the exact location where the turbines are to be mounted - and ideally for a full year - as predictions were not found to be accurate. Average wind speeds measured at all sites are lower than the UK NOABL prediction - wind speeds at 16 out of 26 sites were over 40% lower than NOABL.

Small wind turbines work well where the average annual wind speed is more than 4m/s but in urban developments wind speeds tend to be lower than this. However on top of tall buildings wind speeds are often high enough to generate useful amounts of energy. As they say 'Location is everything'

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