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Maintaining a stable voltage on a wind turbine? Answered

Every couple weeks a new instructable comes up on some green energy thing or another, but one I am really interested in is wind.  The problem I see is that with wind ranges from 5 - 25 mph, the voltage change is extremely problematic.  When I see people putting permanent magnets on alternators for use with wind, it seems ridiculous.  Even if you are using an inefficient battery-storage off-grid system, you still need to maintain 12-15 volts to charge your battery, and an alternator is made to do that by varying the magnetic power.  Now I understand the extremes of a alternator's voltage regulator are likely fairly narrow, but still quite useful in generating wind energy.  What I am looking at is 3-5kw of grid-tied power.  This is great and all, and possible in for me, but I don't see how I could maintain a stable enough input for it to work.  Most inverters are for solar power and aren't grid tied. The next most common are grid tied solar which take 12v DC and scale it to 115 ac across three phases.  Finding a grid-tie 5kw 3 phase in and out ac grid tie inverter is extremely hard, but not impossible.  The only thing that is impossible is finding one that can handle highly unstable voltages.  So the options I am left with are using a variable transformer to bring the wind power down to 12v and then rectifying it, then pumping it through an inverter which leaves me with 70 - 80 % of the original power.  My other option is to, like a car alternator vary the rotor voltage to maintain the desired end voltage.  The one problem I see with this is that there is a large amount of potential energy not tapped.  For example lets use 1 as the relative output as well as the input to generate a magnetic field.  If the speed is 1 then both in and out are 1.  If the speed is 2 then the in will be .5 now the out should stay at 1.  But if the in had remained at 1, then the out would be 2 so essentially you are losing half of your potential energy.  This isn't a problem in cars because they aren't tapping the maximum power possible. All the time, they don't need it.  This is a problem with wind turbines, so is there a way around this?  What wold you recommend to do for grid-tied wind power.

7 Replies

liquidhandwash (author)2013-11-16

You may be able to use an induction motor as a generator and it will solve your voltage and frequency issues, but Ive never attempted to put one on a wind turbine. In theory it should work, In practice Im not so sure. have a look at http://en.wikipedia.org/wiki/Induction_generator
and http://www.redrok.com/cimtext.pdf

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iceng (author)liquidhandwash2013-11-16

Nice induction generator PDF.

For the record I don't advocate putting the induction machine across the mains.
Otherwise your generator turns into a motor when the wind slows down !!!
You should rectify the output to DC and run an inverter to feed the AC power lines.

In the US there is a protection requirement worth elaborating.
A US line worker is not expecting a downed power line to have any voltage on it.
You must have an approved automatic power loss disconnect relay to prevent killing a lineman !
Even if the wind is furiously blowing you must not ...  ever apply power to a dead line.

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jj.inc (author)liquidhandwash2013-11-16

How interesting thanks for this.

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iceng (author)2013-11-16
A friend of mine actually did this and used every bit of wind power  !

As can be seen in the first graphic the principal is straight forward.
  • At low wind the incandescent bulbs have a warming glow and the home heating system has to provide 90% of the house heat .
  • At Steady winds the incandescent bulbs are dimly lit generating some more heat and the home heating system has to only provide 60% of the house heat
  • At High Winds the incandescent bulbs are almost fully lit generating substantial IR energy and the home heating system is providing only 20% of the house heat.
BTW the generator was an ordinary 3-phase motor self excited with three AC capacitors
wired across the motor power terminal and hanging mechanically attached to
a junked car differential with the propeller mounted on a wheel side
using the existing bearings and mounts.  The other wheel side is locked-up.
Never implemented, a brake could be a mechanical safety release mechanism.
Then if you are into powering the grid by up-verting to AC mains and have
the dropped line protection protocol for the power company linemen,
you could use a GE four quadrant supply or a variation
of the second diagram provided here..

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mpilchfamily (author)2013-11-16

Your not going to get a home made wind turbine to effectively feed directly into the grid. Your best bet is to charge a bank of batteries then use the power from the batteries to feed into your inverter and into the grid.

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jj.inc (author)mpilchfamily2013-11-16

I was worried that would be the answer, especially after remembering the frequency issue. Thanks!

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jj.inc (author)2013-11-16

Any I completely space frequency. There is no way you can maintain 60hz across a wide range of speeds is there.

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