Image is a graph from the electric company showing my usage for a day this week. From 6:30 AM to 8:30 PM we used absolutely no utility power.
I'm almost at the three week mark for having this system up and running. The first two weeks I only had 3 KW of PV input but I added another 5 panels to bring it up to 4 KW last week. It's also still running from a transfer switch in "off grid" mode because I don't yet have the prep work done to move my breaker box and start moving circuits to it. (That means I'm either on full solar+battery or utility, no mixing or load sharing).
Once I get it wired in fully, I'm probably going to switch to time-of-use billing. Unfortunately, I can't do that ahead of time because rather than just making off-peak use cheaper, it makes peak usage (M-F 7am to 9pm) extremely expensive while off peak dirt cheap. I wish there was a middle option, but it is what it is.
I'm also being very conservative with my battery usage since I want to have at least 50% in "reserve" to cover power outages. That's especially important during these heat waves. We could easily run 24/7 but would have to take a day off every so often to just let it charge back up since my system is a bit too small to cover all our usage indefinitely (at least if we want to run the A/C for comfort, that is).
Already checked, and we only have to involve the power company if any of the following:
As is, this system doesn't touch the grid at all since it's using a "break-before-make" transfer switch from an old Generac system - it completely disconnects the utility input before connecting the generator/PV's output into the home wiring. I'm also fine once I have it fully installed because it cannot feed power out of the utility input connection, so it remains isolated (unless I would just happen to hook it up backwards which would be a whole other set of problems lol).
Good to know you checked! Excellent job!
I'm curious how you are doing this without losing power momentarily on switchover? Are you always drawing from the battery, and then just changing charging source from grid to solar? Or do you have two stages of switching so you can use the battery as a quick-throw buffer before you detch from the grid?
We do lose power during the switchover. Same as if a backup generator were kicking in (a backup generator is pretty analogous to how I have this wired up currently)
My WFH office, homelab servers, 3D printer, and the fridge are all on UPSs. Fridge is a long story, but a UPS has proven beneficial to deal with its Samsung-ness. Everything else doesn't really care since it's only a literal split second to make the switch.
The only drawback to this manual switchover is the oven and microwave clocks are never right. But to be honest, even before we started switching over to solar every day, the power would flash almost as soon as we set them so we largely just ignore them. Side effect now is they're both timers showing how long we've been on solar that day.
Once I get it installed fully, there will be no cutover. It acts as an on-line UPS, essentially, and the only thing that changes is where the inverter is drawing it's power (PV, battery, utility, or a combo of any of those). It also, supposedly, has a 10ms switchover time if it has to go into "bypass" mode to feed the load directly from utility input. 10ms is comparable if not the same as the switchover time on my other UPSs.