I posted a situation in the New to grid tend solar section about having no solar power when our power was shut off last Thursday, the third, and am trying to find a way to not just lose a days production. A utility worker I asked said that the solar needs a.c. power to make it work like an exciter I guess. He said that if you have a battery system like the Tesla power wall or just use a portable generator properly wired into the system it would work. I have a new old stock 6000 watt gen.set that I plan to have set up as soon as the local electricians can catch up but am wondering how this can work. How can it handle the excess electricity without sending it back to the grid and possibly killing a line man. Following your adventures I think you or David are the only people I know of that can explain this. Any help would be greatly appreciated.
I'll defer to David, other than to explain how my system works, as he has far more experience than I do.
The system here is battery based, designed to operate independent of the grid. Power collected from the sun by the solar panels is DC electricity, and goes to charge a battery bank via a pair of charge controllers. When I use AC electricity, the battery bank is tapped by inverters that convert the DC in the battery bank to AC that powers all of the loads in the home. But since I still retain a grid connection, once the batteries are fully charged, any solar power left over is also converted to AC and sold back to the power company. When the grid goes down here, I depend on the battery to keep things going when the sun goes down. My battery bank isn't very large, it was sized so it would last for a couple of hours powering my well pumps so I could fight a wildfire. As such, I try to get as much of my electrically intensive activities done during the day as possible. During this past summer's fires, the smoke was often so thick that very little sunlight was reaching the panels. That meant that the batteries weren't being fully recharged, and when the voltage level fell low enough, the system started the generator to bring them back up to full charge. At that point, it turned the generator off. Since all the household loads are powered by the battery, there were no power interruptions as the source of energy for battery recharging switched from the sun to the generator. Indeed, when the grid is being used to power household loads, which is most of the night, I don't notice any flickering lights when the charging source changes.
In a typical grid tied system, there is no battery bank. There are still solar panels and inverters, but my understanding is that the inverters commonly in use, for reasons I don't understand, aren't capable of supplying household loads directly unless they are connected to the grid. A few years ago, some manufacturers started offering inverters that could supply small loads via a couple AC outlets, but these were intended for such things as charging cell phones and the like, and aren't up to running large inductive loads like washing machines and air conditioners. I suspect, but don't know for a fact, that switching household loads from grid to solar to generator power directly is something not easily accomplished. At some point, power from one source would have to be stopped, creating a power outage, before power could start flowing from an alternate source. Last year, before my solar power system was installed, I had to break the connection with the grid before I could start the generator. Every time I went through that, everything in the house that wasn't on a UPS was turned off. Modern electronics really don't like that, so I have a large number of UPS units installed now. It was better than not having any electricity at all, but it was still a major inconvenience, as well as a continual reminder that the grid is something that I can no longer depend on for my energy needs.
Technology evolves rapidly, and things may have changed, especially after all of the hurricane and fire induced grid outages of the past few years. I suggest you call a few solar energy installers and ask them if a batteryless system can be built that does not need the grid.
