Payback times are difficult to predict as it depends on your guess of future energy prices. That said, most people expect electricity to get more expensive, so predictions at today's prices are likely to be worst case senarios.

If you want to get a better handle on your wind speeds we can supply also an anemometer and correlate your data against long term met station data, I have seen the online database be out by +_50%.

Please have a look at our website for more info and let me know if you'd like to discuss further. We are based in Bristol.
www.the-green-company.com

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Ben Cosh