Maximum achievable Cp for a two-bladed wind turbine

[Alexander Tangen]

Hi, we have a project where we are trying to design a two-bladed wind turbine from ebaboard with a diameter equal to 1 m. We would like to know what the maximum Cp value we can expect is. From a formula in the book "Wind Energy Explained" by Manwell, McGowan and Rogers, we calculated that maximum is 0.453 for TSR=7 from the calculations of Wilson et al. (1976).

I mean, we have had wind turbines in the lab which had a greater Cp than that. Is it something wrong with the formula, or am I missing something?

Thanks!