"Dow" equation for the power and energy output of a wind farm. "Dow" equation for the power and energy output of a wind farm. "The power and energy of a wind farm is proportional to (the square root of the wind farm area) times the rotor diameter". In his book which was mentioned to me on another forum and so I had a look, David MacKay wrote that the power / energy of a wind farm was independent of rotor size which didn't seem right to me considering the trend to increasing wind turbine size. Now I think the commercial wind-turbine manufacturing companies know better and very possibly someone else has derived this equation independently of me and long ago - in which case by all means step in and tell me whose equation this is. Or if you've not see this wind farm power/energy equation before, then see if you can figure out my derivation!