1. Because the wind is variable, the windmill will not be on all the time. There are a couple of options. You could oversize the windmill to generate excess power and store it in batteries. Or you could just use the power from the windmill when it is available and rely on the grid for the rest of the time. If the windmill generates more electricity than you are using, you can send the power to the grid. But the selling price is much lower than your buying price.

2. If you use 1000 kWh in a month like me, then the average power is 1000kWh / (31*24hours) = 1.344 kW. If your generator is 80% efficient, then you’ll need to supply 1.344/0.80 = 1.68kW worth of mechanical power on average.

Since power is torque times angular frequency, you can see that as the RPM increases, torque decreases. This presents a unique problem. If you put too much of a load on the generator, it will cause the windmill to stall. So, the faster the windmill turns, the less torque required for the same output power. There’s some math involved here. Mechanical power can be in horsepower or watts, and you can convert between the two.

I had to get out my old physics book. This will help you in determining the input mechanical power. One horsepower is equal to 746 watts. Rotational power (in Watts) is torque (in Newton meters) times the angular frequency in radians per second (one full rotation is 2pi radians).

Setting up a home windmill is not cheap. The payback time may be longer than you’re willing to invest in. You’ll need several things besides the windmill and generator. Battery storage is optional, but helpful. You’ll need an inverter to convert the power from the windmill to 60Hz 120V, and synchronize the frequency with the grid’s power.