How do I convert the RPMs of a simple turbine (e. g. a windmill) into the power it generates? Let's say that I want to know if a single windmill of a certain size can power a refrigerator. Assume that I already know how long the blades have to be to produce the RPMs, and I know the energy requirements of the refrigerator. I am only looking for a basic equation of RPMs to power (watts or joules). Thank you.