PV+battery with change over switch

SodiumCooled

Hi, Just a few questions to help with my understanding on this. My solar installer as an add on option of a change over switch (and its not cheap) to allow off grid use during a power cut. However I have already allowed for a change over switch as part of my electrical installation with a generator hook up so my switch will allow switching between mains and generator.

I asked the rep can I operate off grid using this and he said no that I would need a second change over switch but to me this doesn't make sense. Unless I am mistaken all the PV install would be on the consumer side so once I switched to the generator port then this would switch away from grid and isolate the system making it safe to use the solar? I guess the only possible issue is how does the system know I "changed over".

Alternatively since the PV I assume drops when it no longer senses the grid supply based on a CT clamp? If the CT clamp was placed on the output of the change over switch rather than input wouldn't that allow the generator to trick the system into running which would still be beneficial since the generator would not have to work as hard plus probably a bit better for sensitive electronics. Only issue there would be ensuring no back feeding into the generator I guess.

Any feedback or alternatives would be interesting to help my understanding, thanks.

10-10-20

The issue is that unlike a true fuel powered generator, the inverter's AC input needs to be isolated off the house-supply so that if you were to attach a gen-set or even the output of the inverter's gen port that you wouldn't be back-feeding the inverter with it's own AC waveform. So a rudimentary change-over switch would not suffice, as I understand it you'd need a proper ATS wired up like so:

The inverter will isolate or power off once the voltage or frequency start to slide out of the prescribed limits and this is done at the inverter input side and not at the CT. The inverter would then "know" on the basis of having no valid voltage at the required frequency on the AC in, but would see and be powered-from the battery voltage.

SodiumCooled

Thanks for the explanation. Sorry if I am mixing things up a but wouldn't my change over switch come before that first MCB meaning the inverter would be fed from a generator? Or is that wiring diagram specific to the ATS?

10-10-20

Well my first comment was going to ask for a circuit diagram... that's only how we'll know. Don't want to be assuming at all here.

SodiumCooled

It's a new build so wires are run but nothing terminated yet but my understanding on how the CoS will be wired is that that the main tails from the meter go to the CoS first and then onto the consumer unit. I wouldn't have thought solar installers would have any part in touching the main electrical installation so would only be working on the consumer unit side hence my comment?

To clarify the solar install "first fix" hasn't been done yet.

There is two parts really to my question - the first was if I can run the system the second is there potential issues I could cause by adding the generator to the mix.

10-10-20

Ah, so this isn't in situ already for an existing gen-set - ok understood. Then it's not obvious to me why you'd need an additional change-over switch unless they assumed that you had two independent sources. Might be one to post in the Electrical forum.

SodiumCooled

https://www.boards.ie/discussion/comment/122022083#Comment_122022083

Thanks and apologies I should have clarified its a new build in the opening post.