wheisenburg
Independent Solar Consultant
Did you find this?I've gone through the IQ8 commissioning training (had to do that to bring up the current system), and I'm about halfway through the power stuff (mainly for fun).
In theory, you if you don't care about backup power, you can run their IQ Battery 5P without the system controller. But, you'd lose the generator input though, which is the main goal of that solution.
I guess I could set up the "off grid side" just connected to an outlet or something, get the AHJ to signoff, get PG&E to signoff on the battery + system controller, then after that wire up the Gen to the off grid output.
The downside is that I'd still technically be violating the NEM agreement. However, I could at the very least use one of the grid profiles that limits export to a certain amount (or use the PCS function?)
So, benefits of this would be:
+ Actual power-down backup if grid goes down.
+ Other TOU / power shifting / Limiting sellback to profitable times.
+ No wasted solar -- it can get dumped directly into the house grid and used by all appliances, not just the off-grid loads panel
Downsides:
- Expensive-ish (+$5k adder for battery + MID, in addition to off-grid stuff)
- Requires calling out PG&E to inspect it (well, at least he MID + battery install....)
- Not sure of limitations / definitely not a supported mode
- Actually violates NEM agreement
Edit:
Reading some of their documentation:
"• Allows the generator to charge batteries and serve loads.
• Ensures back-feed protection for the generator."
So yeah, either way, it seems like it would "work"... Hmm.
Enphase-Generator-Support-Technical-Brief.pdf
I actually read up on this. You can't run the "Generator" in parallel with the gird. So some kind of contactor would be needed to disconnect the grid off before connecting the generator. This "System Controller" apparently has some voodoo magic in it that coordinates the inverters in the battery with the ones on the panels. There is both Power Line Communication (PLC) and a reference to "Wireless" communication. You also need to have CTs that measure the current flow between all the different parts of the system. They can then manage the power flow with the generator, and panels to charge the batteries.
I'm not sure how much you know about the issue of trying to run grid tied inverters off grid, but here is a quick summary. Grid tied PV inverters are designed to basically output as much power as possible into the grid. There is a mechanism called frequency shifting, that allows a connected Hybrid inverter to raise the frequency when it determines too much power is being produced. This will cause the micro inverters to ramp down the power production in response. The problem is that it doesn't happen instantly and it works in increments of 10%. So when a large load switches off and the panels are cranking out power, it can take a few seconds for the micro inverters to respond and ramp the power down. During that time the power needs to go some where, so the inverter needs to be able to store that power into the batteries. When the batteries are full or nearly full, it may not be possible to do that. This could lead to a voltage spike that could knock the system off line or even damage the equipment. Apparently Low Frequency inverters are able to more quickly switch directions of the current flow because their design is inherently bi-directional. In a High Frequency inverter they need to store the power in capacitors on the High Voltage DC bus while the inverter switches modes.
In order to best manage the micro grid, there are ratios that need to be respected when building an AC coupled system. Generally you need for the Hybrid Inverter to be at least as large as 100% of the micro inverter power rating. That's why I have 2 Schneider inverters for my 35 panel system. Enphase is saying that the "Generator" needs to be 143% of the power of the batteries (in watts not KWHs) or 100% the size of the PV which ever is larger. You also need batteries that can handle the charge current from the inverters. The max charge current from the Schneiders is 240 amps and I have 3 100 amp batteries. Of course you can only push 100 amps into them when they aren't nearly full. I probably should have 6 batteries and I plan to upgrade when possible. I am building a custom electrical box now that will incrementally shed the PV strings when I am off grid due to an outage and SOC in the batteries is high.
Most other AC coupled Hybrid Inverter / PV inverter solutions require that you shut down the PV inverters before you connect a generator to the Hybrid inverter in order to avoid having the micro inverters trying to back feed into the generator. I have to do that on my system. When running off grid, the AC coupled hybrid inverters can use frequency shifting to control the output of the micro inverters, but that is not possible when running off a "generator". So they apparently built a parallel control system into the IQ8s that allows them to more precisely and more quickly modulate the PV output from the micro inverters and the rate of charging of the batteries.
In your case, it seem like it should be possible to run "On-grid" during the day. Export the excess power and also discharge your battery in the evening at peak rates.
Then at night you could disconnect and run off grid. Your off grid system would run all the loads (and possibly recharge the Enphase battery). In the morning your battery would be all charged up so you could just start exporting power as soon as there was any excess. You wouldn't be buying "Dirty" power from the grid and selling the dirty power back as NEM green power.
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