It seems the only way a small wind generator makes sense is if you receive it for free. Even then, it might be more trouble than it's worth.
It's 99.9% of the time not worth it. The only time it makes sense is if you're on wide open plains with lots of high, constant wind.
You're dealing with two fundamental issues:
- The Betz Limit
- The Power in Wind equation
The Betz Limit is basically a theoretical number of the maximum efficiency you can possibly get. At most, only 59.3% of the kinetic wind energy can be used to spin the turbine and generate electricity. Remember this is a theoretical limit; in practice, you're going to be closer to 40%.
The Power in Wind equation is given as:
P = 1/2 x ρ x A x V³
Where:
P = power in Watts
ρ = air density (kg/m³, at about 1.2 at sea level)
A = Swept area of the blades (m²)
V = Velocity of the wind
So, no matter how good your turbine is, you will get in practice at most 40% of the wind energy converted to electricity. To capture the wind energy in the first place, you have two variables to increase (one in your control, the other not): swept area and wind velocity. The smaller you make the turbine, the faster you need to spin to make any meaningful energy. The only variable you control is the swept area, which means making the blades as big as possible. Also notice that the velocity is cubed in that equation, so you'll generate much, much less power at low wind speeds.
In other words, small wind turbines don't work except in ideal situations because physics.
