openspaceman wrote: ↑Sat Nov 26, 2022 10:45 pm
Oldgreybeard wrote: ↑Thu Nov 24, 2022 10:40 pm
Things get trickier with some other kit that doesn't have such a well coordinated ecosystem.
Yes as I am finding with my growatt ac coupled inverter, the supplier has told me the warranty will be negated should I charge the battery from a standalone array and MPPT solar charger, whereas this is an advertised method with the victron multiplus ESS.
I shall probably risk it because it will cost me five grand to replace the battery and inverter with victron kit anyway.
This is similar to the position I'm in with the Sofar AC inverter. I'm part way through adding another 2kWp of PV and did think at first of just using it with an MPPT charger to charge the batteries, in parallel with the Sofar. I think this could work OK as long as the second DC charger was set to cut off at a slightly lower voltage than the Sofar.
It is a bit of a compromise though, as it would mean that the reported data from the Sofar would be wrong, there would be more charge than it would know about. There are probably ways around that, by adding charge measurement from the new DC charging side, but it all seemed a bit messy.
What I've opted to do instead is add another inverter, so the second PV system is only AC coupled to the house. I can still use the Sofar PV monitoring, as that uses a CT around the live from the existing inverter and it's easy to run the live from the second inverter through the same CT. That will automatically sum the two currents that the Sofar measures.
The only other problem I've had to solve is to find a way to limit the total PV export to no more than the 6kW that I have G59 approval for (now G99). Because the new array faces more or less east, and the existing one more or less south, they most probably aren't ever both going to exceed 6kWp. The new array will mostly just provide early morning power, useful at this time of year when the south-facing array doesn't really wake up until mid-morning.
The solution I've come up with to make a G100 limiting device is to use another current sensor, that has an adjustable current switch, around the live wires from both PV systems and use switch signal to operate a timer relay. This timer relay will disconnect the second inverter for an adjustable time if the combined output of both PV systems exceeds 6kW. I very much doubt this will ever happen, but it will keep the DNO happy as nothing has changed as far as the grid is concerned. The timer function is needed just to try and prevent the tiny risk of the thing switching off and then back on again too quickly. I've bench tested this and it seems to work just fine. Not perfect, as it's restricting generation, rather than export, but fairly simple (and cheap) to do.
25 off 250W Perlight solar panels, installed 2014, with a 6kW PowerOne inverter, about 6,000kWh/year generated
6 off Pylontech US3000C batteries, with a Sofar ME3000SP inverter