"Designing a GTI is a whole new can of worms. You have to match phase, shut off when the grid goes down, meet all kinds of UL and FCC requirements, etc."
My point exactly with regards to over-driving an induction motor. Phase is matched, efficiencies are high, and all the electrical company requires is a switch that shuts charging down should the grid go down. Not to mention that induction motors are readily available off-the-shelf.
Regarding battery life, doesn't that depend on the battery type? If I randomly charge my lithium ions, they are junk in short order. If I run them all the way down and re-charge, they seem to last indefinitley.
The problem with switching the DC to the inverter is it takes a really beefy switch. 280 watts from 12v is 23 amps. That's a good size transistor, or a decent relay. But it's not impossible to find something in that size.
We could also just disconnect the AC side, and that would turn the inverter off. On the AC side the current for 280 watts is only about 2.5 amps.
Ideally an inverter would have a digital enable signal that could be used to turn it on and off then my controller board could do the job of watching the battery voltage. (I guess it could also control the relay with a little extra circuitry to drive the coil.)
I have been doing something similar here, but with a normal GTI. Charge the battery until full. Then run my computers off of the battery until 12.0v, then let it recharge for a day (on solar) and repeat.
I agree that it would be the best approach in feeding the grid via a battery to GTI.
Just to clarify, we don't need to shut off the GTI, just shutoff the supply of DC from the battery. This would be similar to a cloud passing over a solar panel.
I can do this by hand. Hook up the battery to the GTI and see 280 watts pouring into my grid. At the same time I watch the voltage drop steadily to about 11.9 and disconnect. The battery voltage recovers right back to 12 v without the load.
The problem with DC is there is quite an arc when disconnecting with a mechanical switch so it would be nice if the switch was gradual and an electronic circuit that senses the battery voltage. Like a cloud or nightfall on a solar panel.
Off at 11.9 v, on at 12.4 volts
I think the GTI would be a more efficient approach. The trick would be adding some smarts so that the GTI would turn off at 12.0v (or 24 or 48). You wouldn't want to constaly bring a 12v system down to 10 or 11v because the batteries wouldn't last very long.
The other alternative would be to build a GTI meant for wind. The problem with most GTIs if they are made for solar and they just don't accept fast changes in the amount of power coming in.
Designing a GTI is a whole new can of worms. You have to match phase, shut off when the grid goes down, meet all kinds of UL and FCC requirements, etc.
Given the wind turbulence near the ground, how feasible is it to attach a GTI to a VAWT and expect some reliable efficiencies? As Steve has pointed out, the electrical spiking that occurs could best be buffered by a battery bank, or some super-capacitors or similar.
Not being an electronic guy, I tend to speculate along the path of least resistance (pun intended): What if a battery bank was set up to over-drive an induction motor (feeding the grid) when topped up, depleting the batteries to a pre-set level, and then shut off. You would effectively be feeding the grid in "bursts" that cycle according to charge rates.
Or is this just a completly stupid idea because really all you have to do is hook the battery bank up to a GTI? Maybe the real question is, do you gain effeciencies by feeding the grid in bursts? And by bypassing the complex electronics involved in a GTI?