Following on from my last post, the Windsave surveyor came today, took one look around the house and said “Sorry, no can do.” The reason our house fails the Windsave test is that the upper storey is covered in timber clapboarding and that isn’t felt to be strong enough to hold onto a windturbine. I can get a full refund but I have to go back into B&Q in person to collect.
There were lots of questions I wanted to ask this guy but there didn’t seem to be a lot of point. “Will it be noisy?” or “Will it attract lightning?” seem a bit pointless if you aren’t going to have one. And, to be honest, I am not sure this guy would have known the answer in any event. He was just there to make an assessment. I don’t think he had been working for them for too long and I suspect he wouldn’t have known the answers.
But I did manage a couple of questions. One was “Do they need planning permission?” He reckoned not, unless the house was listed or in a conservation area. This conflicts with my local council: I phoned them earlier in the week and they didn’t sound very sure but advised me that it would fall outside the normal permitted development rights and would therefore require a planning application.
I also asked him how busy he was. The answer was very busy. He has done 30 visits in the last two weeks. He also said there have been 28,000 enquiries logged via the Windsave website.
Finally, I asked him how much electricity I could hope to generate. “They reckon that you could save up to a third of your electricity bill with one of these.”
Now I haven’t been entirely somnolent since my visit to B&Q last week. And I expect that this casual claim is the reason that Windsave is attracting so much attention. The payback suddenly looks pretty attractive, especially when installtion grants are taken into account. But is it accurate? Just how much power can something like this produce?
There doesn’t seem to be a simple answer to this. The biggest factor affecting it is the amount of wind you get. The power output increases exponentially with windspeed:
• at a windspeed below 3metres/second, it doesn’t produce any output at all
• at a windspeed of 6m/s, you get about 100 watts
• at a windspeed of 12m/s, you get 1,000 watts
So you go scurrying around looking for average wind speed data. It’s there, on the DTI website, if you can handle converting a postcode into a Landranger co-ordinate. Ours is just 5.1m/s, on the low side but pretty typical for lowland England. The likely output is calculated from the average wind speed — Windsave seem to suggest you get a little bit more than you might expect. Their website is fairly helpful in this respect. But there can be no guarantee that you will get what it says on the tin and thus, even with the most sophisticated calcs, you can really only make a rough approximation of likely output.
Nevertheless, you can see that at an average windspeed of just 5.1m/s, we were never going to get that much power out. Possibly 1,000kWh per annum, if we were lucky. Probably rather less. Enough to power the proverbial 60w light bulb but not much more. Having said that, if we lived somewhere where the windspeed was higher, even by just 1m/s, we could be getting three or even five times more power out of it over the course of a year. But I suspect that such locations are few and far between. I hadn't realised just how crucial the average windspeed data is in analysing the cost effectiveness of a wind turbine, but it is the No 1 critical factor. It's something that Windsave don't highlight, but arguably should.