Electric Generators for Wind Turbines 1

[Sparweb]

I have a wind turbine on the drawing boards that I want to prototype this summer. It is a Vertical Axis WT, sized to produce about 1kW (I hope). I expect it to turn more slowly than typical VAWT's (just based on some analysis at this point), something like 60 RPM, with lots of torque instead (lots and lots of torque).

Does anyone have suggestions about selecting generators for it? I'm a bit out of my expertise on the electrical side.

On the safety side, I'm thinking of using an old disc brake from my car to stop it when necessary. Can this be done electrically instead? (or does that just cause a safety problem of its own?)

Thanks, in advance, for any help you can offer.


Steven Fahey, CET

 

[Sparweb]

Thanks jraef, I was picturing taking apart something like a golf cart (a big one), but I've read into it, too - the regenerative braking features on these controllers aren't designed for this.

Maybe I should slap a savonius type of turbine together, just for the sake of getting the electrical system working, and then go on to my other ideas. That would avoid side-tracking on problem "B" in the middle of Project "A".

Like I said - electricity isn't my strong suit.

Thanks so far everybody!



Steven Fahey, CET

 

[Sparweb]

Update:

Shortly after these postings, I started building. I now have two rotors running, though not yet producing electricity. My focus has been on the machinery, as there were lessons to be learned about bearing losses, vibration, and aerodynamic performance first.

I built a 2-foot high model in my garage over a weekend to start, and played around with it for a month. Actually, it's still running, but I'm now working on the third machine.

Again, thanks for the ideas, folks.


Steven Fahey, CET

 

[Warpspeed]

Please keep us posted on progress.

 

[LionelHutz]

Just out of curiousity, what's the average windspeed in your area??

I built a HAWT machine last year. We average around 4m/s wind speed in this area so one goal was to build an efficient machine. Even though the wind is free you have to build a less efficient machine with a larger swept area to get the same output as a machine with a better efficiency.

One big advantage for a HAWT that doesn't seem to get mentioned is the fact that the height of the machine can make or break it. Your machine should be about 30' above any ground obstacles for best wind coverage. To me, putting a HAWT on a 50' to 100' guyed tower seems simpler than doing the same with a VAWT. If I was looking at putting an equivalent output Savonius VAWT on my tower I'd have to put up a much heavier tower.

The best generators for a wind machine are permanent magnet 3-phase types. Driving the field of a car alternator could use up a fair bit of the power you're gathering, especially in low wind conditions.

 

[Warpspeed]

Lionel, all you say is true, but vertical axis wind turbines (VAWT) do not always need to be mounted high up on a tower.

The trick here is to find smoothly rising ground for perhaps a mile upwind. The wind speed will then be fairly high right down at ground level. I have seen some wonderful Savoinus systems mounted only just off the ground in coastal areas where a steady onshore breeze blows up a smoothly rising grassy slope right from the beach.

Another ideal location is the dip in a "saddle" between two smooth grassy hills. The wind blows around the hills as well as over the top. The dip between two large hills can make a terrific wind site, and the wind speed can be high right down at ground level.

Conditions are not always that fortunate, and if there are a lot of large trees and other significant ground objects up wind, a high tower may be required to get above all the slow turbulent air near the ground.

I agree that a permanent magnet high voltage alternator will definitely be more efficient, but how would you control the output voltage ? I suppose a three phase rectifier and a PWM buck regulator to bring the voltage back down would be the simplest and most obvious way to control the output. A rather interesting idea.

 

[LionelHutz]

Warpspeed,

You're right about the possible site locations but I'm not that lucky here. There's just enough wind to run a mill in this area so I wanted to build a good machine to take advantage of the little wind there is.

I believe a Savonius type blade design has a max theoretical efficiency of about 31% while a HAWT propeller type blade design has a max theoretical efficiency of about 59%. If you've got the wind it doesn' matter but since my wind was limited I wanted to start with the most efficient design possible.

You control the output of a permanent magnet generator by two possible means;

On a smaller machine you just charge batteries. Then, you use an actual load, such as a grid tied inverter, or a dump load to control the battery voltage.

On a larger machine, from what I've read, it seems that the output is being rectified into a DC buss and then a grid tied inverter is used for the utility connection. I'd imagine the inverter is used to control the DC buss voltage much like a VFD with an active front end can control the buss voltage.

I believe every windmill smaller than about 10kW (and many larger ones too) presently being sold uses a permanent magnet generator so the permanent magnet generator is definately the most popular.

If you guys want some interesting reading check out the site

http://www.otherpower.com

or the magazine at

http://www.homepower.com

 

[Sparweb]

My location is an issue unto itself. Winds are usually from the north, my house is on the south side of the lot, and there are lots of trees in between. To get good winds, I have to set up a looong way from the house. Any time the wind is from the south, forget it. The Environment Canada average wind speed in my area is 4 m/sec (15 kph or 9 mph), but I find it's either windier than that, or not windy at all. Treated statistically, the weibull distribution comes to mind, with two peaks.

Given the distance to the house, I've been thinking (idly, it's a long way in the future) that I could step-up AC to a transmission line strung on the nearby utility poles already going that way, and then stepping down again at the garage. Then put in the rectifier/inverter/whatever, as necessary.

I'm building something to fiddle with, at this point, so I don't want it up on a tower. If this homebrewed contraption evolves to the point that it produces useful work, it may be triumphantly raised aloft.

A few more months of research has led me to conclude that adapting automotive technology risks being extremely wasteful. Renewable energy fanatics like to wind their own motor/generators, and many favour 3-phase, and let the voltage drift with RPM, usually because they're converting it to DC to charge batteries anyway. I may go the same way, if I get to the point of putting the VAWT to practical use. Since all I want to do at this point is to collect comparative data which I can use to make performance calculations, a simple DC motor, a multimeter, and a few 12V light bulbs will do nicely.

Here's video of what I've produced so far:

http://www.otherpower.com/images/scimages/4378/DSCN2504_short.mpg

The white one on the right is a double cup "savonius", while the one on the left is a two-blade "darrieus". I made the Darrieus blades by sawing vertically down a piece of plywood, at a steep angle to produce a bevelled edge on both, and rounded the LE. So far, it only runs at a TSR of 0.7, not 1.5 or 2, like other VAWTs, and definitely not 5 or 6, like typical HAWTs, but it's pretty crude, after all. It's taught me a lot, in spite of all that.

Great input, so far, guys, thanks.



Steven Fahey, CET

 

[itsmoked]

Pretty cool! Thanks for the movie. Would like to see higher res pics.