Hello all. Having read some posts here I see there is a wealth of experience. I hope that some can come to bear on generating a possible solution to my problem.
I have 4kWp of solar pv on my roof via 16 off 250W panels, with 16 x Enphase M215 micro-inverters. As luck goes, one of the inverters croaked a few weeks ago, and I bought 2 secondhand replacements, one of which is up there doing the job of the dead one. Enphase have had no qualms about replacing the duff one, so now I will soon have 2 spare inverters with connections via Enphase’s Engage cable.
My proposal is to hook up the two spare inverters to the mains, and supply them with battery power to supplement my overnight electricity use, ie power the fridge and a few lights while the batteries last.
It seems that the primary problem will be to stop the inverters sucking all the power out of the (rather meagre 10Ah @36vdc) batteries as soon as they are connected, and squirting it straight into the arms of the big bag Grid, that is being of no benefit to my lights or fridge after dark.
Clearly I need a smart controller that measures the export current and controls the inverters’ output (2 x 215 = 430 Watt) to give nothing away to the Grid, and this is where I seek your suggestions. How best to achieve this, short of spending big bucks/pounds?
I have built one of Robin Emley’s Mk2 PV diverters from his kit.
I have an un-used, but not new, EmonPi.
I have two spare Raspberry Pis.
I have an EmonTx v3 with two CTs.
I have some small amount of experience with Arduino, but next to nowt on RPi.
I have a willingness to learn, so pointers to others’ similar projects would be welcomed.
My own thoughts are that a philosophy close to that which Robin applied to his Mk2 PVdiverter could work on measuring the exported power after dark, though I am a little ‘in the dark’ regarding the possible techniques to control the inverters’ output, in that they must be connected to the mains in order to synchronise phase and frequency with it, and that they will take about a minute to do this if disconnected from the mains for just a short time (anti-islanding?).
Regards, Phil J