Saturday, December 05, 2009

All change on renewables

In my October post, I gave the impression that the case for the wind turbine was all cut and dried. It wasn't, as it turned out, and was a lesson to me on accepting real data as real. I had very much wanted a turbine for two reasons: 1. when the wind blows strongly, it's generally the time you need energy; 2. our location in NW Wales should have been pretty good for windiness. This latter assumption was strongly backed up by the two national databases of wind speed averages and predicted power output. The latter, as it turns out, was wildly optimistic.

NIMBY neighbours do us a favour: We had a tense meeting with our downwind neighbours, arranged to test the waters before formally applying for planning permission. They were implacably opposed to anything visible or audible and I found myself having a little sympathy with their views such that we agreed to go back to the drawing board and see if there were alternative sites or just alternatives. So, Val and I had another look at the results for the average wind speed yielded by the anemometry; the real data. I had previously suspected the anemometer of under-recording wind speeds and, with this in mind, we had checked its calibration by holding it out of the car window at different speeds on a calm day. It was spot on.

And the real average wind speed? I had two results from the anemometer read-outs. One was the average wind speed and the other was the average gust speed. I had - wrongly as it turned out - assumed that the true average would be the average of these two averages (the 5.1m/s figure I quoted in the earlier post). I was always worried about this assumption and had made efforts to find out the correct position, so I posted a question of Green Building Forum and Val phoned an anemometer company and discussed the issue with an expert. The upshot of Val's chat was that we should totally ignore gusts! So that means that the windspeed on my best exposed site in windy north Wales is a paltry 3.58m/s, averaged over almost 12 months! So a wind turbine is out for the best reason of all: there really isn't enough wind on this site. The anemometry and neighbours' complaints saved us from jumping to the conclusion, fostered by the databases I mentioned above, that windpower was for us. So we are saved from acrimonious disputes and almost inevitable planning rejection, from appeals and from building a 25k pound white elephant!

So we're now looking at photovoltaics for which no planning consent is needed. Feed in tariffs of around 36 pence/kWh make this a viable option.

The moral of this story: If you're thinking of putting up a turbine, do the anemometry and believe the results!