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PostPosted: Fri May 22, 2009 3:23 pm 
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Here's a question for you, but first some info....
I have some solar PV with a grid tie inverter. When I'm generating say 800W and using say 1000W I will buy 200W in from the grid. If I use 500W I "sell" 300W back to the grid.
All of this happens automatically.

Right so I now have a wind turbine which I have connected to some batteries. Off the back of this I have an inverter (not grid tie). I can plug in power tools and everything is fine.

Now lets assume the grid fails. My PV system has to disconnect, so I am without power :cb but wait! I have my other supply :thumbright: so I could run an extension lead into the house and use that :wink:

So at long last to the actual question.
If I disconnect from the grid (main breaker off) and connect the battery / inverter into my house supply the PV grid tie would (I Assume) sync up to the new mains supply.

So back to the usage
If I generate 800 and use 1000 would I pull 200 from the battery inverter? and the rest from the grid tie?

However if I only use 500 I would have 300 "spare" so what would happen?
Would the inverter just switch off? But then the PV grid tie would switch off
Would the inverter explode as I was feeding it with 300W?
Would the 300 just vanish (where?)

:?


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PostPosted: Fri May 22, 2009 5:12 pm 
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phill wrote:
However if I only use 500 I would have 300 "spare" so what would happen?
Would the inverter just switch off? But then the PV grid tie would switch off
Would the inverter explode as I was feeding it with 300W?
Would the 300 just vanish (where?)

:?


No one knows.

The performance depends on the controller/invertors. As they were not designed for your intended use, no one knows what will happen. You could try it out, but you may damage one or more invertor/controllers.

I can tell you one thing: the 300W won't just vanish. It'll probably do something nasty somewhere.

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PostPosted: Sun May 24, 2009 9:04 am 
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Thanks,
I'm not intending to be the one to test this, just wondering really.

If the grid fails then I would be best off running an extension lead rather than messing about with switching things off and risking a big fat electrical horror.

Mind you I could put the picture of the burnt out unit on the rouge pages on UHM. Even better if it burn down the whole house.

Phill


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PostPosted: Sun May 24, 2009 7:23 pm 
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I think you will ask for trouble if you parallel up 2 the inverters they especially the wind turbine one could be modified sign wave type and the output transistors/tyristors would be damaged in my opinion.


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PostPosted: Tue May 26, 2009 11:34 am 
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I have 2x inverters, a lumpy modified sinewave which I use for power tools (these are very cheap) , and a nice pure sinewave (much lower output, as they cost a fortune) which I use for battery chargers etc.
So the assumption would be to use the pure sinewave for this "project".


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