My plan to use a commodity inverter generator instead of a larger, more expensive generator has mostly worked out well. I only tap the generator for about 2,000 watts which is enough to charge up the house batteries over a period of time, yet the generator is quiet, efficient, and most importantly easily replaced. There are, however, a couple of places where it fails. I think the blame belongs with both the generator and the inverter, but the bottom line is that this particular generator is not fit for purpose. I’m not sure how different generators in the same class would perform.
Here’s the problem: when we’re running the generator and bring a big load online — in this case the electric clothes dryer that draws 5,000 watts — the generator’s internal inverter will shut down, but leave the engine running. This is the worst of both worlds: we’re burning gasoline but not generating any power. That entails a trip down to the generator, which is a bit of a walk that’s pleasant enough when the sun is shining but can get pretty wet and muddy in the rain. And it has rained all but a small handful of days since April.
What I believe is happening is this: our total electrical load is rarely over a couple of kilowatts. When the inverter sees that 2kW of generator power is available, rather than add that to the existing solar+battery power, it passes through the generator power to the house. That’s all well-and-good until a big load (like the dryer) comes on line, at which point the generator sees the full load momentarily until the inverter can transfer over to solar+battery power. That’s enough time to cause the generator to enter into its unfortunate persistent “I’m burning gasoline but not going to give you any power” mode.
Now, sharp-eyed readers might have noticed that the generator is rated to produce 5,200 watts of burst (“starting”) power, and I’m only asking it for 5,000. Just don’t believe generator specs. In my experience, they’re always over-rated.
This particular problem is easily avoided. We simply don’t run the dryer when we’re running on generator power. We can always wait for the sun to come out or for the generator to charge the batteries, then kill the generator and run the dryer.
The other big demand we put on the system is charging the car. That’s not a problem, because Tesla engineers were smart enough to always ramp up the charging current over time, giving the inverter a chance to switch from generator pass-through to solar+battery+generator power. It all goes smoothly.
The glitch happens with my beloved hot tub. When the generator is running and the hot tub tries to start (either due to low temperature or because I’ve pushed the button to start the jets), the panel lights flash and the tub resets to default temperature (100°F) and shuts down. Sometimes, after a large number of tries (which feels harmful to the pump motor) it will start, but generally it won’t. What seems to be happening is that starting the motor (I think it’s a 1½ HP pump) causes a huge inrush current, which is more than the generator can handle (but 5,200 watts??). The power glitches, and the hot tub resets. Fortunately, the tub resets before the generator’s gas-wasting mode kicks in, but I’m still left without my tub.
Today, I really needed to start the tub. It needed chlorinator added and that means it needs the pump running. I wasn’t excited about slogging down to the generator in the rain, turning it off, slogging back, starting the tub, then slogging back down to start the generator again. So I set the car to charge at 8 amps (about 2 kW) on the theory that this would force the inverter to switch out of generator pass-through mode so I could get the tub started, then I could shut down the car charging and life would be good. It worked!
—2p