Rob Beckers
15th July 2009, 07:09
(Edit: I previously posted this on the S-W-H list, then realized it would make a good thread here as well)
The Energy Saving Trust in the UK has just published their report on a field trial of a total of 154 wind turbines in the 400W - 6kW range. A number of turbines was building mounted, and a portion free standing. Of the total, 57 were fully monitored by EST, the rest of the data was provided by owners and the Warwick Wind Trials.
The report is a little light on reported data (I wish there were more numbers in there). Instead, they give a more abstract view of wind turbine performance. From the conclusions: Building mounted turbines uniformly performed very poorly, with some even being net-consumers of electricity! The wind prediction tools generally overpredicted wind speeds, especially for urban and/or rooftop sites. Turbine location (in clean, non-turbulent airflow) is everything when it comes to production.
The best performing turbine was a 6kW Eoltec Scirocco installed in the Orkney Islands, with an energy production of 22,000kWh/year (FULL DISCLOSURE: We are a distributor for the Scirocco wind turbine in North America).
A nice write-up by the BBC of the report can be found here:
http://news.bbc.co.uk/2/hi/science/nature/8139373.stm
For the full report go to this link:
http://server-uk.imrworldwide.com/cgi-bin/b?cg=corporatedocs&ci=energyst&tu=http://www.energysavingtrust.org.uk/content/download/554381/1961689/version/3/file/location
While trials such as these are important, my own opinion is that they dumbed down the results too much to make the report very useful. I would really have liked a more comprehensive listing of sites, pictures, turbines installed, and wind plus performance data for the sites. The conclusions as drawn by the report are rather obvious, and while it is a good thing that they went through the trouble of confirming them, they should be no surprise for anyone in the wind business.
Trying to link wind prediction models to actual wind speed measurements for building-mounted turbine sites is very much comparing apples to oranges: It is clear that buildings obstruct the airflow and cause turbulence, something that is simply outside the scope of wind prediction models (both in how they work internally, as well as how they are intended to be used). I am not sure how the writes of the report see this as a shortcoming of the models, while it rather is a shortcoming of turbine siting. I can install a wind turbine in my basement; should there be a wind model that properly predicts production for that?
While the free standing turbines do better, the report concludes also for them that sites with adequate wind are few. Given the European love affair with very short towers that, again, is no surprise. It is rare to see a small wind turbine (ie. 10kW and under) mounted on anything higher than 15 meters (50ft) over there, with most well below that number. Their best performing turbine, the Scirocco on Orkney, is mounted on a 12 meter tower (40ft). What do they expect? Except for a few lucky locations, anything under 18m (60ft) is bound to be well within turbulent air, and most locations will need a substantially higher tower to get into clear, non-turbulent air (let alone that wind speed and energy production also increase with height). Possibly the focus should be on advising about more realistic tower heights and wind turbine locations.
For anyone interested, I wrote a web page that tries to present an overview of wind turbine site selection:
http://www.solacity.com/SiteSelection.htm
Enough of my rants. It is a good thing that this reports once again underlines the importance of proper turbine siting. Now let us hope people learn from it.
-RoB-
The Energy Saving Trust in the UK has just published their report on a field trial of a total of 154 wind turbines in the 400W - 6kW range. A number of turbines was building mounted, and a portion free standing. Of the total, 57 were fully monitored by EST, the rest of the data was provided by owners and the Warwick Wind Trials.
The report is a little light on reported data (I wish there were more numbers in there). Instead, they give a more abstract view of wind turbine performance. From the conclusions: Building mounted turbines uniformly performed very poorly, with some even being net-consumers of electricity! The wind prediction tools generally overpredicted wind speeds, especially for urban and/or rooftop sites. Turbine location (in clean, non-turbulent airflow) is everything when it comes to production.
The best performing turbine was a 6kW Eoltec Scirocco installed in the Orkney Islands, with an energy production of 22,000kWh/year (FULL DISCLOSURE: We are a distributor for the Scirocco wind turbine in North America).
A nice write-up by the BBC of the report can be found here:
http://news.bbc.co.uk/2/hi/science/nature/8139373.stm
For the full report go to this link:
http://server-uk.imrworldwide.com/cgi-bin/b?cg=corporatedocs&ci=energyst&tu=http://www.energysavingtrust.org.uk/content/download/554381/1961689/version/3/file/location
While trials such as these are important, my own opinion is that they dumbed down the results too much to make the report very useful. I would really have liked a more comprehensive listing of sites, pictures, turbines installed, and wind plus performance data for the sites. The conclusions as drawn by the report are rather obvious, and while it is a good thing that they went through the trouble of confirming them, they should be no surprise for anyone in the wind business.
Trying to link wind prediction models to actual wind speed measurements for building-mounted turbine sites is very much comparing apples to oranges: It is clear that buildings obstruct the airflow and cause turbulence, something that is simply outside the scope of wind prediction models (both in how they work internally, as well as how they are intended to be used). I am not sure how the writes of the report see this as a shortcoming of the models, while it rather is a shortcoming of turbine siting. I can install a wind turbine in my basement; should there be a wind model that properly predicts production for that?
While the free standing turbines do better, the report concludes also for them that sites with adequate wind are few. Given the European love affair with very short towers that, again, is no surprise. It is rare to see a small wind turbine (ie. 10kW and under) mounted on anything higher than 15 meters (50ft) over there, with most well below that number. Their best performing turbine, the Scirocco on Orkney, is mounted on a 12 meter tower (40ft). What do they expect? Except for a few lucky locations, anything under 18m (60ft) is bound to be well within turbulent air, and most locations will need a substantially higher tower to get into clear, non-turbulent air (let alone that wind speed and energy production also increase with height). Possibly the focus should be on advising about more realistic tower heights and wind turbine locations.
For anyone interested, I wrote a web page that tries to present an overview of wind turbine site selection:
http://www.solacity.com/SiteSelection.htm
Enough of my rants. It is a good thing that this reports once again underlines the importance of proper turbine siting. Now let us hope people learn from it.
-RoB-