Solar PV inverter versus petrol generator - Page 1
Forum section: electronics / general

author: IanJ
author_rank: Unknown
timestamp: February 07, 2022, 07:23:35 pm
content: Hi all,Got a query in regard to my Bosch Solar PV Inverter (model BPT-S 4).I am going to be getting my electrician to hook up a large 100A changeover switch on my incoming mains to the house so that it can select between my new 3kW generator I have and the normal house incoming mains. This is to be used in the event of power cuts. The idea is to have it all plumbed in nicely and just requiring starting the generator and flipping a switch.This is something my electrician does all the time.......BUT the query I have is in relation to the Bosch Inverter. So, with the changeover switch in the 'generator' position the Bosch inverter would see 240VAC from the generator rather than the national grid.Thoughts on this being a problem for the Bosch inverter?.....especially if the sun was out and it was trying to deliver power.......?Or would I be right in thinking the inverter would know it couldn't deliver power back out to a generator and would go to sleep effectively?Perhaps a query for Bosch themselves.....but asking here just incase others have come across this before.PS. Yes, I could flip the MCB for the Inverter BEFORE engaging the generator.......but just incase I forgot I'd like to avoid blowing stuff up!Ian.

author: IanJ
author_rank: Unknown
timestamp: February 07, 2022, 07:36:26 pm
content: Hmmm....just been reading some stuff I found on google and it's a no-no.Video:-Ian.

author: bdunham7
author_rank: Super Contributor
timestamp: February 07, 2022, 07:50:54 pm
content: I would think that with only a 3kW generator you are going to transfer a limited number of circuits to a separate generator sub-panel. There's no real need for a 100A transfer capability with generator that small. That's the way I think is best and typically what is done. The solar remains attached to the main panel. Then when the system is switched over, the main panel + solar remains connected to your mains supply and your generator and its sub-circuits are isolated. Normal grid-tied inverters will quickly trip out if they are energized by a generator, especially one that is small in capacity. You probably won't blow anything up, but it is definitely not how they are supposed to work. Solar backfeeding anything but your mains supply requires specialized equipment, either a battery-mediated system or special inverters that can incrementally curtail their power.

author: IanJ
author_rank: Unknown
timestamp: February 07, 2022, 08:13:03 pm
content: Quote from: bdunham7 on February 07, 2022, 07:50:54 pmI asked my electrician about where they usually hook up the changeover switch to and he says they interrupt the main incoming supply (easiest)......therefore as the existing main incoming fuses, the electricity meter and the main incoming breaker MCBs are all rated at 100A, then anything in series with that needs to be the same rating.3kW will run everything in the house except the electric shower and other such high power devices.If I don't have to worry about the Solar Inverter backfeeding the generator it would simplify things.......otherwise I'd have to find a couple spare contacts on my new switch to disconnect the Solar Inverter when it's in the Generator position.PS. I already have my own electricity meter in series with the existing electricity meter so I can monitor via modbus the import/import/consumption side of things to PVOutput.org........but thats another story!Ian.

author: richard.cs
author_rank: Super Contributor
timestamp: February 08, 2022, 02:39:28 pm
content: The inverter willprobablylockout as the generator frequency is not tightly controlled enough, so that alone may trip its islanding detection, but there are usually other checks as well. If it does try to feed power, either it'll take some load off the generator and save you fuel, or push the voltage and/or frequency up enough that the inverter trips and shuts down. The absolute worst case is that the inverter cuts in and out of export mode but I don't think that'll actually damage anything.It would be nicer to disable the inverter when running on generator unless load is always greater than available PV. Lazy way would be to tweak the governor on the generator up to 52 Hz or so which should be harmless and ensure the inverter island detection is tripped.edit:typo

author: IanJ
author_rank: Unknown
timestamp: February 08, 2022, 03:44:37 pm
content: Thanks all, good info all round.I have contacted Bosch's Solar dept.......will be interesting to see if the respond.Ian.

author: bdunham7
author_rank: Super Contributor
timestamp: February 08, 2022, 04:18:11 pm
content: Quote from: IanJ on February 07, 2022, 08:13:03 pmA transfer panel with breakers for just the circuits you want to have backup power is indeed a bit more work, but if you do it the 'easy' way, then the issues in that video will apply and you'll have to reroute your solar.