Sunday, May 17, 2009

Wind farm power-per-unit-area data complete

I have updated my data on windfarms.
I've gone through roughly 75 farms, finding the power per unit area. You can see the results here.
The conclusion is that many Scottish wind farms, located on hilltops, have powers per unit area of about 4 W/m2. English and Welsh wind farms are in the range 2-3 W/m2 for the most part, though there are a few in England below 2 W/m2.
Incidentally, while looking at the windfarms, I had a think about the Braes of Doune photo above, which shows a windfarm ruining the view of Stirling castle. The distance from Stirling Castle to the wind farm is actually about 15km. The photograph subtends an angle of about 3 degrees. It is the sort of view you get through a 670-mm zoom lens.
The two summary figures from my wind farm survey are shown below. The top one shows power per unit area versus turbine diameter; the lower one shows it versus wind farm size. The point style indicates the type of windfarm location.

Thanks to Oswald Consultancy and the Renewable Energy Foundation for collating most of the power generation data and turbine specifications. All the original data can be found at OFGEM. Thanks to Ordnance Survey for their getamap service.


Alex Terrell said...

Are our current wind farms too small to draw conclusions about W/m2? On most wind farms, there might be one or two turbines obstructing each other.

Can you extrapolate to multi GW offshore farms?

Wind turbines have an effect on their neighbours which means above a certain density, the economic case falls, but you can still get more power by infilling up to a point.

I suspect current wind farms could get more power / m2, but there would be an economic argument against it.

Brian O' Hanlon said...

I noticed this in yahoo green blog today. A turbine the size of a tennis racket is going to supply 20% of a dwellings energy supply? ? ?

Brian O' Hanlon said...

But curiously enough, the next blog entry after it was more like the real deal.

It talks about 2020 being an achieveable timeline for delivery, with audacious investment and infrastructural work. This is the curious thing about the blog medium I guess. Being able to see two ends of a spectrum along side each other.

Unknown said...


A graph of W/m^2 vs hub height would also be handy.

W/m^2 doesn't change too much directly with rotor diameter (though bigger rotors usually means taller towers).

But W/m^2 should be sensitive to hub height.

Note that a typical modern turbine has a hub height of 80 to 100 m.

Unknown said...


A minimum turbine spacing is typically 5 rotor diameters in the direction of the prevailing winds and 3 rotor diameters in the other direction.

You could look at what sort of rotor spacing typical UK turbines use, e.g. using google earth.

Whilst wake losses are very important, the minimum spacing is more to do with minimizing turbine loads due to the wake.

The other issue is hub height which i mentioned before. Due to wind shear, wind speeds, and hence energy, increases with height. Hence a modern turbine with a 80 - 100 m hub height will have higher energy density at the same location as a turbine with a hub height of 30 m.

e.g. if at 30m the mean wind speed is 7m/s the wind speed at 80m may be 8.5m/s and hence if you replace a 30m hub height turbine with an 80m hub height turbine you should get an 80% increase in Energy density (all other things equal).

Col said...

I can confirm your conclusion about the Stirling castle/braes of Doune photo, as I live in the area. The castle is actually one of the highest things in the area - if you are nearby, you look up at the castle, and can't see the braes of Doune at all. In fact, I can't think where this picture was taken from, unless it was from a helicopter or the top of the nearby Wallace monument (but the direction seems wrong). Even so, the turbines look magnified here, supporting your lens theory. The windfarm is surprisingly visible from lots of locations in the area, but at a far less obtrusive scale than the photo suggests. And the site is actually a fairly dull, rolling hump - the turbines improve the view in my opinion. I'm against building them in genuinely scenic highland locations, but these ones are fine.

N.S.C Dalton said...

Interesting, If I told you I could get 10w/m2 or even 5-12 times more power per square meter more economically than present would you be bothered enough to contact me ? I'm looking for seed funding to prototype an idea which isn't against the laws a physics!

Love the book and the attention to the facts for once !