I hope you find this wind turbine power calculator useful. Most of the results should be reasonably accurate. I could not find any way to determin the cut-in speed for the vertical axis turbine, and having not built one, it's hard to even take a wild guess at a formula. Turbine efficiency is the result of multiplying the alternators electrical efficiency with the turbine mechanical efficiency, 0.35 should be about right for a well built DIY machine. Most of the input fields should be self explanitory. Air density is set as that at sea level, you can pretty much leave that field as it is. The VAWT calculator has the air density hard coded in at 1.23 Kg/cm^3. Happy building :)