Almost two years ago I wrote a post called “Are there limits to large scale wind power?” The post looked briefly at a paper by Adams and Keith which suggested that large scale wind farms will produce less electricity than expected.
From the paper’s abstract: ” New results from a mesoscale model suggest that wind power production is limited to about 1 W m−2 at wind farm scales larger than about 100 km2. ”
At the time I suggested a possible test of this would be the output of the London Array wind farm, which is 100 square kilometres in size. At the time it wasn’t open. But it has now been running for over a year.
What has happened? The wind farm was expected to have a capacity factor of 39%, if my memory serves me correctly. Capacity factors for UK wind farms are calculated by the Renewable Energy Foundation, using Ofgem data. While it is true that REF is itself an anti-wind farm organisation, their data and capacity factor calculations have never been shown to be wrong, and are thought to be reliable.
They tell us that the capacity factor of the London Array has been 40.2% since it opened, which is pretty much in line with expectations. It’s total capacity is 630 MW, therefore its average output is currently 253.6 MW. In other words it is delivering a power density of 2.53 W m−2 , much more than 1 W m−2 .
Now, this does not prove that the work of Adams and Keith is incorrect, or that the saturation effects they discuss will not prove serious issues; it only shows that it has not come into play at the London Array.
The London Array itself was supposed to see a further expansion, which would have provided additional evidence to test these saturation effects. However, the supposed threat of the turbines to migrating birds put an end to that. So, we may need to wait a while yet to see a wind farm much bigger than 100 square kilometres.
Power density is a topic I continue to return to. Unfortunately many researchers, policy makers and environmentalists pay too little attention to it. Hopefully this will change next year with the publication of Vaclav Smil’s book on the subject, which is certain to be provocative and informative.