I have been using a Power Predictor from Better Generation on a 12m mast for about a year- one got damp in the logger but they sent me a new one- also cows knocked the mast down- so you need to keep stock out!

I am really glad I did measure my windspeed as NOABL and other desk top systems are wildly off most of the time- I have just researched 35 sites around the UK for a Msc thesis and I would never consider spending £20-50k on a wind turbine without measuring the wind for a minimum 18 months.

My own site is predicted at 6.8m/s windspeed but has only measured 3.2 (but Power Predictor estimates 5m/s) over the last 16 months- this makes a huge difference on FITs incomes and pay back times.
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dannyfrost