I'm currently looking at installing a micro wind turbine, and have opted to purchase a Power Predictor from Better Generation after recommendation from the Energy Saving Trust. The device has a built in logger and once you've recorded enough wind speed data, the Power Predictor website analyses it for you and produces a power report. This report shows projected payback times, energy bill savings, and CO2 savings achievable for the main wind turbines and solar panels on the market, which all have their output data stored within the Power Predictor database.

It’s all very clever and in my opinion a vital first step which should prevent you from purchasing the wrong turbine or solar panels. I've decided to setup a blog to review the power predictor and document my results which you can find here: http://www.powerpredictorreview.com