Pairing up a battery inverter with a grid tie inverter...

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jonescg
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Pairing up a battery inverter with a grid tie inverter...

Post by jonescg » Thu, 16 Nov 2017, 12:28

Here's a quirky (and probably dumb) idea suggested by someone on the internet:

Take a grid tie inverter and power it with a 2 kW array, for example.

Take a 3 kW DC-AC inverter powered by a 10 kWh battery.

Parallel the AC outputs of both inverters, protected and switched, of course.

Turn on the Battery inverter and start supplying a load.

Turn on the grid feed inverter.

Presumably if the PV/Gridtie inverter voltage exceeds that of the DC/AC inverter, current will flow back to the battery?

I can see a few problems with overcharge...
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Richo
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Re: Pairing up a battery inverter with a grid tie inverter...

Post by Richo » Thu, 16 Nov 2017, 15:38

The DC/AC inverter probably has polarity protection on the battery side preventing the grid tie from feeding power into the 10kWh battery.
My guess is the grid tie will bump up the AC voltage until it hits it's maximum AC output threshold, shuts down and reports an error.
Likely will happen within a few secs.
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Re: Pairing up a battery inverter with a grid tie inverter...

Post by jonescg » Thu, 16 Nov 2017, 16:49

https://www.youtube.com/watch?v=F1q5uIzjj_M&t=391s

This is where he's coming from I think. Perhaps he didn't specify that the inverter needed to be an inverter / charger? Presumably the one with the transformer built in?
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Re: Pairing up a battery inverter with a grid tie inverter...

Post by weber » Fri, 17 Nov 2017, 08:00

This can be done, and is referred to as "AC-coupling" your PV array (Google it). And yes, the battery inverter certainly has to have been designed as an inverter/charger. Whether it works or not depends strongly on details of the implementation of the two inverters -- details which are not usually given in their specs and are not easy to find out, unless the manufacturers specifically say that they have been tested or designed to work together in this manner, and it usually requires a communications link between the two inverters to do it properly. An example is the Kaco grid-feed inverter and the Selectronic SP PRO battery inverter.
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