Wind energy - Blades

It turns out, there is a stack of energy in the wind. In fact the more I research, the more I see it that way. I'm starting to get some kind of grip on this energy stuff. I'll try to explain what I've understood so far.

Water pumping windmill
Just looking at the traditional windmill for now, (traditional to me) the one that looks like a fan, we see there are a stack of different blade shapes, and some seem to have more blades than others. Some seem to be always used for pumping water, and others seem to be always used for generating electricity. In keeping with 120 things in 20 years tradition, I'll start an explanation of wind energy by talking about cogs.

Connect two different sized gears together. Choose two cogs so that when the small one rotates 100 times, the large one rotates only once. Now give the gears some power by turning them. The same amount of power exists in the big and small gears, but in the small gear, its spread out over 100 turns. This means that you can slow it down by resting a feather on it. It has no grunt. Try the same feather trick with the large gear, and your large gear wont care a bit. 

If you put a set of wheels on the axle of the small gear you will zoom along until you get to a steep hill, or a feather.

If you put a set of wheels on the axle of the large gear, you will drive slowly through a pillow factory with ease.

Having just described this, for the first time in my life I suspect I might be leaning toward some vague understanding of "torque" that I didn't have when I started this post. I think torque might be rotational grunt, where power is what the engine has. If this is true, you can express an engine's power as more grunt or more speed while keeping the same power (the engine). That must be it. Or not. But for now, I'm sticking to "grunt", so now might be a good time to edit your dictionaries and engineering manuals.

A windmill's power comes from the wind. If the wind is fast we get more power. Now, picture a string of air 100 metres long. That's called a string of air. Now move it at 100 kph. That's called wind.

If we slice that 100 metre string of wind 100 times we get 1% of it's power in each slice.
If we slice that 100 metre string of wind 10 times we get 10% of its power in each slice.
That's simple enough.
If we have a 10 blade windmill, it makes 10 slices every time it does one revolution. That means it will make 10 revolutions as that 100 metre string of wind blows past.
If we have a 100 blade windmill, it will make 100 slices for each revolution. That means it will make one revolution as that 100 metre string of wind blows past.

The same amount of power is in that 100 metre string of wind, but we can harvest it in such a way that suits any combination of grunt and speed that we might need for our application.

The 10 blade windmill spins 10 times with stacks of speed, and the 100 blade windmill turns only once, but with more grunt.

It turns out that lifting water from a well requires lots of force, so we use windmills that have a lot of blades, and generating electricity requires a lot of speed, so we tend to use windmills with fewer blades in power generation.

A 100 metre string of air doesn't really get you 100 slices. Actually for all I know it might. But it probably doesn't. I made those numbers up to make the calculations easy to see, but it all works pretty much the way I described.

So anyway, that's the story of where babies come from.

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