The findings have been contested by the British Wind Energy Association (BWEA) which argues improviing industry practice is ensuring turbines are installed, sited and operated more effectively.
The Warwick Wind Trials Project – funded by Pilkington Energy Efficiency Trust and BRE Trust – was undertaken by renewables consultancy Encraft which analysed 168,950 hours of operation of 26 building mounted wind turbines between 2007 and 2008.
Researchers said that microwind facilities could perform effectively on exposed sites and on some tall buildings, but on other sites they performed well below expectations.
'Poorest' site barely covers energy consumed
The best site in the trial generated an average of 2.382 kWh per day when in operation, but the poorest site only generated an average of 41Wh per day which is only enough to cover half the energy consumed by the turbines electronics.
The report said: “Overall the trial has painted a picture of an industry and technology that is still at development stage and is likely to make a tangible contribution to energy and carbon saving only on the most exposed sites and tallest buildings.
“The combination of this reality, aggressive and over optimistic marketing by some suppliers and the enthusiasm and credulity of the market (and regulators) has potentially led to an unfortunate outcome where the wind industry as a whole is in danger of suffering from a setback in credibility.”
Wind data needs to be more accurate
Encraft said wind speed and power curve data available to predict performance was “not very accurate”.
The report said: “Using unmodified wind speed data by postcode from the NOABL model and manufacturer power curves for turbines can lead to overestimating likely energy output by factors of between 15 and 17. Buyers should beware.”
Encraft has been careful to note that the findings cannot be extended to large scale trubines and freestanding wind turbines of any size where 'all the evidene is that wind power is an excellent and highly effective choice'.
Micro wind can deliver if placed at sites with 'good wind speed'
BWEA argues the survey was weighted towards sites the industry would normally view as inappropriate.
It said only four of the 26 sites where test turbines were placed had an annual average wind speed of over 5 m/s which it said is ”considered a lower limit of commercial viability”.
It also stressed that industry standards were improving.
Alex Murley, BWEA Small Systems Manager said: “The results show that turbines need to be placed in environments that offer good wind speeds.
“The UK is the windiest country in Europe and there are thousands of such sites, many of which have been utilized to good effect and offer owners of small wind systems not just savings on their electricity bills, but an opportunity to export surplus energy to the grid.”
BWEA said wind system installers and small wind system suppliers recommend that on-site wind speed data and careful measurements are taken over a period of time prior to installation.
'Robust standards' now in place for microwind
Mr Murley said: 'BWEA and the industry has over the last three years developed robust industry standards for both products and installers, to better educate would-be consumers on what the technology can achieve, if sited and installed correctly.
'The overwhelming majority of small wind system installations are a success in terms of commercial viability and we have seen annual sector growth of 80 per cent, projected to carry on into 2009 and 2010.
'The Warwick trials should not be interpreted as demonstrating that wind is not viable. We know that it is, and the experience of thousands of UK users bears this out. '
To read the full Encraft report click here