12 Oct 2006

Rejected by Windsave

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.

6 comments:

  1. If you had gone ahead (assuming the roof was sturdier) would B&Q guarantee any of the performance claims. i.e. would you have been entitled to a refund or compensation if the output was considerably less than their claims?

    ReplyDelete
  2. Matthew,

    Neither B&Q nor Windsave make any guarantee about the amount of power delivered. And although the Plug & Save unit shows you how much power is being generated, there is no meter facility to tot this up. So no one will have a clue just what the cumultive output actually is.

    So I don't think a refund is on the agenda. You really are buying on a wing and a prayer.

    ReplyDelete
  3. john yorkshireNovember 15, 2006

    hi ive just bought a windsave from b&q the grant is going through too but i am having my doubts now and wish id have waited to see how other people go on with them before commiting myself.We will see if they save 1/3 of an average household bill!!! My average windspeed is 6.5 to 7.5
    A guy i met that works in this field he had heard a windsave that was tested in leicester saved only 46 pence in the year .Im sure some company will invent a larger than 1kw turbine for rooftops soon as Windsave Seems to be one of the first to sell to domestic.I am also a bit unsure what these turbines will do to the structure of my gable end over the next ten years i wonder if windsave would be responsible if cracks started to appear!!!!

    ReplyDelete
  4. Hi, I'm a consultant to windsave, so will try and answer your questions Mark.

    Firstly I'm glad we didn't try to fit a windmill and I hope you see the sense that we didn't. With just 5.1m/s I doubt you would have seen anything close to 1000kWh per annum so payback would have been terrible anyway.
    The Inverter does have a kWh meter on the front so you can always know its total export

    ReplyDelete
  5. Nathan,

    Good to hear from someone on the Windsave side of the debate. And to be corrected about the meter issue.

    My question back to you is this. My average wind speed , 5.1m/s at 10m height, according to the DTI windspeed database, is pretty typical of southern England and in fact is rather higher than most large urban areas. You are candidly admitting that at this windspeed my payback would be "terrible". So why are Windsaves being sold through B&Q across the country with the oft-stated suggestion that they could geerate a third of your household electrcity?

    ReplyDelete
  6. Mark

    Sorry about the delay in responding, your site is probably average wind speed and it may be that many urban sites are unsuitable, but Windsave reckons between 10-20% of households are suitable in terms of payback at current electricity prices, and when prices rise and costs fall...

    ReplyDelete