150lb Savonius Wind Turbine

On top of that I realy love the "Mad Max factor" of it.

despite the "low" efficiency and all the negative stuff described here it's an easy to build device, cheap too and it will power your laptop, radio etc.

I'm working at home, have a flat roof and will try to make one to power my office.

what does it do?

it spins

What kind of power output are you getting from this?

:o) nice design.

The problem also has to do with speeds. Your wind turbine there is a stationary object with its wings moving at a certain rate relative to the wind depending on the load. Move too slowly and the air packs up against the wing, which doesn't permit any more air to move in that direction.

And that's precisely what happens when the turbine is making lots of torque in high winds: lots of force against the wind in a small area, which pushes most of the wind around the turbine and not through it.

Using directional baffles, the Savonius is the most efficient design, up to 45% efficiency which is damned closed to the 59.6% hypothetical limit. It will begin turning in as little as 2m/s, will continue turning in turbulant winds even when direction changes, and is able to withstand hurricane winds: HAWTs cannot do this.

Are you sure you haven't mixed up the relative efficiency to the Betz's limit with the total efficiency? I've seen figures of around 30% total for savonius, which is about half of the 59% maximum.

However, it's not a constant figure across the whole scale. If you look at the efficiency curve, it starts to rise at almost zero wind speed and peaks off very early on. The power in the wind is very low until you reach about 6 m/s, but the efficiency by that point is already sloping towards zero.

Which is to say, even if you have top efficiency at, say, 3 m/s wind speed, you will have very little energy generated simply because there is very little energy to be had at those speeds.

That's the reason why commercial windmills are mostly three blade. A five blade one would work well in slower winds, but that's not where the most energy available is.

A savonius rotor still turns in hurricane winds, but it's not making much more energy than in a gentle breeze, because its efficiency drops.