New member, I apologize if I sound stoopid, this is a little long. I am all electric, in Phoenix AZ. I have two EV's a Kona, and a Niro. Last year, in preparation for a solar install, replacing some aluminum wiring, and setting up a charging pedestal outside), I moved all my loads inside to a utility room on a 100A (125A w/downsized breaker) load center, behind another 100A breaker from the outside 150A panel connected to the secondary of a 100A transfer switch with the primary on a 150A bus bar for the inverter(s) AC bus. I put in a couple of amperage sensors (modbus) on the legs in the panel, and wrote some software (using modbus libraries and C) for an SBC to monitor the loads. Further, to limit demand, I put my HWH behind an EV switch in front of the dryer line, so only one can run at a time, priority to the dryer. The range circuit is connected to another transfer switch controlled by my software and the SBC, allows me to cut the load back to the outside panel based on load. A third transfer switch controls a 50A service from the panel out to a pedestal outside for EV charging, and a fourth transfer switch is connected to the 30A circuit running an EV charger in the garage, being used as a simple on/off relay (for time of use), both controlled by my SBC and a relay board.
I had 5 inexpensive "parallel capable" 5.6K units that literally fell over during a stress test, ... as in turned off dead displays, no thrown breakers, power switch on-off to reset, no recorded errors pulling about 30 amps when the AC turned on poof. So I threw caution to the wind, purchased and just this week mounted two (2) of these 18K units in my utility room on the cement board. My problem is everyone has great instructions and stuff for a single unit, but the minute you go parallel, things get kind of quiet, and I want to be sure of handling a peak 100A of service to my panel that doesn't fall over when the AC cuts on. I note the highest single leg current I have recorded was around 87 amps, and I'm polling at 5s intervals. (I have grafana running with pretty load graphs and stuff).
My questions are about general wiring and parallel operation, maybe someone here has insight, and maybe I'm asking in the wrong place, if so sorry. The original idea was to run the inverters all the time, no feeds or taps against the grid. The batteries should charge from PV during the day (14KW, 4 strings) then drop to batteries (Full Rack of 6 EG4 30KW) as the sun goes down. Average nitetime draw is < 2KW (might go up a bit in Jul/Aug) so if the the batteries fall below say 15% SOC, overnight, I wanted to feed 40A from my grid panel to charge them. I had purchased an EG4 charge controller I was going to wire to the SBC and use modbus to monitor the batteries flipping on a relay with the SBC based on time of day and SOC. I think this unit will do this, perhaps using generator inputs? I think I can allow that feed to keep the batteries at some minimal SOC (maybe between 15 and 20%) until the sun shines again. Or ... should I be tying to the grid inputs and set the inverter to not feed the grid, and limit the charge current there? Does it matter? Can this work as indended?
The next question revolves around grounds and grounding the neutral. The transfer switch is switching L1,L2 and N, it has an empty 4th pole. In the electronics and server room world I'm from grounds are always as short as possible to the nearest ground. However the instructions from SS seem fuzzy on where/how to ground neutral. My best guess is to leave the N-G tie back at the outside panel (It's 3ish wire feet, or less on the other side of a wall from the new load panel), let the 3 pole transfer do it's thing, and just ground everything as close as possible from the inverters. I've been doing a lot of reading on this one and it seems the relevant ieee 1547? is kind of fuzzy. IMHSHO opinion you should not really ever switch a ground, but I could use the dry contacts on the transfer switch to activate a N-G at the 100A panel when the inverters are supplying power. The extra parallel inverter makes it more fun, that configuration gets an honorable mention in the SigSolar video's.
Finally 'RSD' & PV. My solar PV junction box is on the outside near the panel. It is wired for 6 independent strings each individually breakered and surge grounded. I only have 4 strings connected at present (400voc,11a) but I will wire all 6 as 3+3 to the MPPT's 1,3&4 inputs with input 4 on both as N/C for now. on the ground front should I drive a seperate ground rod in below the box and tie to that for the surge blocks? AZ does not require RSD, so I had no plan for it, in the original configuration. OTOH I'm all for safety. One can just open the panel and flip the breakers from the outside, but how would the folks here handle this? Apparently we have wires and wireless something that isn't real clear to me that will drop the draw inside the inverters when you press the/a button, send a wireless signal, do a dance near a box? The concept seems odd. If the house catches fire, the inverters have redundant inputs, and the panels on the roof are going to be in the process of getting destroyed. The rack of lithum batteries on the other hand. . .
I'm committed at this point. Any insights appreciated. Thank you.
