Help please to understand whether my PV system has been correctly installed?

RayWalker · Oct 30, 2021

I have recently had installed an 8 PV panel and inverter on to my roof. This was a local authority initiative which was installed free of charge. The system has been working and reductions in my electrical usage is being assessed. I was so impressed with the reductions that I have had a further 18 panels, another inverter and a storage battery installed. This also seems to be working satisfactorily and can be monitored through an App on my phone. What I can't get my head around is how the 2 systems work together? The App for the second (18 panel) installation shows that electricity is being generated during the day and either used internally to my house or into the battery or to the National grid. But what is happening with the electricity being generated by the first (8 panel) installation? The first (8 panel) installation is connected through a double pole isolator straight to the incoming tails of the main electrical meter and the second (18 panel) installation is wired into an MCB on the main consumer unit. Can someone explain if this is correct and I'm using all 24 panels worth of generated electricity in the most effective manner? Thanks

plugsandsparks · Oct 30, 2021

how did you monitor the first 8 panel install before

Simon47 · Oct 30, 2021

Your new system monitoring is just telling you what your new system is doing - it knows nothing about the older system. Both will generate according to the amount of sun on the panels, and any not used in charging batteries or in your house will be exported.
Provided the meter is correctly set up, then you'll get paid for your net export (i.e. what's left after you've used some).

Connection wise, both are OK as long as they are done correctly. It is OK to connect the solar inverter to an MCB in the CU provided it's done right - but if it's done wrong then it can make your whole installation "less safe". If you post a photo of your CU, then someone can probably spot if one of the common mistakes has been made.

littlespark · Oct 31, 2021

Im maybe overthinking this... but wont the two invertors argue with each other?

In laymens terms:

My understanding is, the inverter reads the voltage coming in from the grid, and produces a little bit more to push it out to the grid.
If inverter #2 reads invertor #1 voltage over the grid... it will push out a little bit more again.... then #1 will read the increase... and push out a little more again... on and on until some preset maximum is reached.
Will the invertor just shut down if it cant push back?

Would that happen?

Simon47 · Oct 31, 2021

Yes, you're over thinking it.
Imagine your neighbours also have solar PV, they will also be pushing into the grid. In effect, you just have less (cable) distance between neighbours.
Also, the grid is very "stiff" - other than the resistive losses in the local cables, your tiny little PV inverter is going to have no effect on a grid that covers the whole country - a few kilowatts vs something in the order of 30 gigawatts. A bit like you pushing on your house wall with your little finger - the house is massive and "stiff" compared to your little finger.