Friday, May 8, 2009
Is David MacKay "trying to make wind sound useless"? Let's look at more data
I'm delighted to see that the response to Sustainable Energy - without the hot air so far has been remarkably positive. There's just one or two folks who have become convinced that I am anti-wind, that I am deceitfully making wind sound worse than it really is; and they have been running round leaving comments on blogs (for example, you can find one lurking in the comments on this excellent article about the financial cost of wind power (the oil drum), who asserts "MacKay has made a serious error in his calculations of on-shore wind energy resources. ... Some of the wind farms initially built were in poorer locations but close to electric transmission lines, so his calculations are not good examples of what is possible in UK.")
I've written three blog posts about this topic already, encouraging people to provide real data rather than just spreading poisonous rumours. I've now worked through the ordnance survey maps and ROC register entries for about 15 windfarms around the UK, and included the data and maps in a presentation I made at a wind energy conference in St Andrews this week. I am still working on this; what I have focussed on so far is mainly the newest windfarms for which data is available, with the largest numbers of turbines, with biggest diameters, and mainly on scottish hilltops or welsh hilltops or near to the coast. The new data starts at slide 30 and is summarised on slide 41. These onshore wind farms have powers per unit area between 2 and 4.6 watts per square metre. To indicate the rough scale of windfarms required to deliver large amounts of power, I assumed in the book a power per unit area of 2 watts per square metre. So yes, there are windfarms that have powers bigger than 2 watts per square metre. Was I deliberately "making wind power seem worse than it is"? No. I chose 2 watts per sq metre as an estimate of what we could get if we put up lots of wind farms (with the area of Wales), which is obviously going to be less than the power per unit area of the very best spots. Yes, I willingly agree that if we want wind to make only a small contribution (for example, less than 1 kWh per day per person), then it would be appropriate to assume a higher power per unit area - perhaps 3 or 3.5 W/m2 instead of 2 W/m2, if we keep building in the best spots.
As evidence that I am not deliberately biased against wind, take a look at the data for offshore wind farms.
In my book I assumed a power per unit area of roughly 3 watts per square metre for offshore wind. But the two offshore windfarms in my data have powers per unit area below 2.5 watts per square metre.
There are several other scientists who have used a power per unit area similar to mine when estimating wind resources. For example, Socolow from Princeton uses 2 watts per square metre when discussing his "wedges". On page 234 of my book I cite a study by Elliott et al. (1991) in which windfarms in the best locations in America, covering an area equal to that of California, were estimated to have an average power density of 1.2 W/m2.
While my book is technology-neutral, the truth is that personally I am pro-wind! I think wind farms are brilliant, and I'd be very happy be within eye-shot of one almost anywhere in the ordinary countryside.
Please could the commentors call off the dogs?