chain driven transmissions

[bvan1941]

Chris,
with what gains you have demonstrated with your type of transmission, it would seem the concept lends itself to scale itself down to make marginal generators (high rpm/v type generators) become much more productive. This would enable the marginal generators to enter their useful power band better than trying to go with higher tsr rotors. This would be especially important in "low wind" and seasonal wind areas. My thoughts are to minimize the requirements for high speed rotors and produce more average output  in between higher gusts of sporadic wind, normally required to produce power from marginal generators.

what's your take on this idea?
Bill

[ChrisOlson]

There has to be gains in generator efficiency that outweigh losses in the drivetrain to make it worthwhile.  You're trading torque for speed and it really takes a generator designed for the high speed to make it work.  Trying to use "marginal" generators, such as automotive alternators which take a lot of speed but are still only about 55-60% efficient won't work all that well.

With my latest turbine design that uses a geared drive, I got 86% power efficiency from the generator at 2.8 kW output, using ferrite magnets.  Those are the kind of numbers you have to shoot for in your design to make it viable.
--
Chris

[bvan1941]

Chris,
My concept was to use a potential generator like a 1500-3000 RPM, 3 phase motor, was what I was driving at. Some of these units are very capable of providing 2-4kw of power when operated in their proper speed range. That would definitely make these motors much more efficient and keep rotor speeds under 400-500 RPMs.  This would be I think, be better than having the rotor requiring wind speeds of over 20 knots for excellent outputs. Some of us are really in very marginal wind belts and only have decent wind for less than 2-3 moths out of the year. With your type transmission suitably sized I think this would be a measurable improvement.
Hope I've cleared up the thought of using any auto type alternator.
Bill

[ChrisOlson]

Just to be clear, using a transmission is not the magic formula for getting more power out of marginal wind sites.  It can be if you use a very large rotor with a geared generator.  No matter what you do, getting power from wind still depends on two things - swept area and wind   
--
Chris

[Wolvenar]

What are the drawbacks to using a larger blade with gear up in lower but usable wind speeds (over 10mph)

I am looking into this possibility for an alternator (zubbly style conversion) that has a slightly higher than I hoped for cut in. Id rather not rewire this beast if I don't have to there is a lot of copper in this thing. I'd be happy to get a higher consistent output and early furl than trying to go for the bigger winds

[ChrisOlson]

What are the drawbacks to using a larger blade with gear up in lower but usable wind speeds (over 10mph)

Power control is the biggie.  You can get more power in marginal winds from a big rotor overdriving a generator that is ultimately under-rated for the amount of shaft power the rotor can make.  But you have to control it when the wind picks up.  Turn-it-to-the-side-of-the-tower furling is not a reliable method to control power to a set level to save your generator in high winds.  A rotor that goes into over-speed in high winds will come out of furl because the point of thrust on the rotor shifts to the inside towards the yaw.

I have seen one of my 4.0 meter turbines that otherwise furled fine come out of furl at 60 mph wind speed and suddenly go to 50+ kW at the shaft.  The only thing that saved that turbine was the fact that the tower mast broke and I just about lost the turbine off the tower.  The bigger the rotor, the more pronounced the problem becomes.
--
Chris

[bvan1941]

Chris,
All your points are well taken, and I have realized that your talent and skill building robust systems is a must to contend with those wind periods 50-90 (+) mph. I think you and all the people that are lucky enough to have average winds 10-15mph (because you all live in the jet-stream geographical areas, for the most part) also must consider these extreme furling and equipment damaging issues.  On the other hand, there are those of us that haven't seen 45(+) mph winds since the last Hurricane!

What I described as our conditions for this discussion, are consistant enough that our generators are lucky if they produce acceptable power 10-20% of the time-- when we are lucky enough to get winds! I think we would be taking precautions (including lowering our rigs if necessary) if winds exceeding hurricane force is headed our way.

So with all that said, we are just looking for another way of increasing our average power production periods. In my case leveraging your idea of the chain driven transmission to bring the generator I have, into its powerband more of the time.
Hope I haven't offended you. I just got the feeling you weren't envisioning our realistic wind situation.
Bill

[ChrisOlson]

I'm never offended!   

Most definitely, if you have a marginal wind site and can throw a big enough rotor in the air, then use it to drive a generator with a gearing system to get the voltage up, it will work.  High torque rotors with more than 3 blades seem to work well with that sort of situation.  Using 5 or 7 blades self limits how fast the rotor can get going in higher winds and they don't have to turn as fast in lower winds to get decent torque to drive the generator.

The losses due to gearing are actually very small.  About 3 % at lower speeds and up to about 6% at higher speeds.  So if you can use it to get a 10% gain in generator efficiency, then the gearing will put you further ahead than using a direct drive configuration.
--
Chris