One for Adam maybe; what has to happen in the event of a power cut when a 13kVA genset automatically starts up and triggers a changeover switch between the mains meter and the consumer unit when a 4kW grid interconnected array and 6.5kWh battery are on the consumer side?
Does the PV still work by sensing the AC from the genset or does it have to be isolated with its battery during the time the genset is running?
If you consider the solar+battery+inverter as a glirified inverter, I've known several [decent] UPSes that aren't very happy when running from a genny.
Or even as a glorified UPS
You can't feed power into the generator, so the grid output of the solar would need to be isolated.
In normal times the solar is used to top up supply or demand - say if the battery is offline, the solar outputs 2kW and the house demand is 10kW, the remaining 8kW will be supplied from the grid. In that case things are OK. But if you turned off the 9kW electric shower then the demand would fall to
1kW - normally this is fine as the solar pushes the remaining 1kW into the grid, but the generator can't take that.Unless the solar inverter has a mode by which it will disable grid upload but still provide to local loads, which would need to be activated any time the generator is connected. But as mentioned the generator might not like even that if the waveforms don't match.
Theo
That was my guess but the generator would still charge the batterry as long as its charger is AC and not DC straight from the panels. Easily done with a tandem changeover switch I think.
In fact as long as the solar inverter accepted the near sinewave from the generator was clean enough, thanks Andy Burns, why should the PV inverter not backfeed the generator, surely it would just take load off the generator? It's moot though as I agree the PV should not be connected when the generator is on.
It's just that a PV installer I spoke to said it just could not be done and in this situation the prospective PV buyers will not proceed.
No but the battery charger could.
Yes as I said I think the changeover switch will have to isolate the PV but I'll await further input.
I'd tend to think the battery *is* charged by the DC output of the panels (MPPT/MPPC?)
Surely you expect the generator to run so infrequently, that costs of genny fuel vs maximising battery are the least of your worries? Wire the solar before the changeover switch so it "anti-islands" when you're not on mains?
It sounds like what you need is a control system with the following inputs:
Grid Solar inverter Battery inverter Generator
and the ability to both disconnect and crossfeed between the power sources.
I'm sure that must exist, but it's not necessarily a feature of a particular product that the installer might be familiar with. So 'can't be done' is only because they only know brand X and that doesn't offer the feature.
I'd guess it can be done with a solar inverter that supports a generator input, which is where most of the logic goes. And ideally one that can have a battery hung off.
Theo
I fear that the problem is that such an inverter is not permitted to be connected to the grid.
Chris
It would be fool hardy to connect your solar panel inverter to your generator. Keep it connected to mains side.
If you want a combination of a solar, battery and generator then it's not trivial. I would suggest you look at boat or RV power installations.
If you have access to your solar panels you will need to switch over to your own MAPPT converter to charge your batteries, either 12V if you can keep the LV cables very short but would recommend 24V or 48V batteries. Then use an inverter to supply the mains power you need. Again 12V and
24V inverters are common. I recommend pure sine wave and avoid anything lessIf you do want to use a generator then it's probably best to use this to charge your batteries, as you won't be able to connect the output of your inverter to any generator.
This is vastly more complex than I suspect you can imagine. 6.5kW batteries is respectable 12V @ 550Ah or 24V @ 270Ah. But assuming these are Lead Acid then at high loads not all capacity will be available.
The question you need to ask yourself, is what sort of load and for what duration. A good 1kW panel will produce 800kWhr per year, Your 4kW panels will produce very different amounts according to season, as this indicates:
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