I’m used to it with generators: our backup generator is rated at 13,000 watts. It’s model number is “XP13000EH.” Yet, it’s really only rated for 10.5 kilowatts continuous output on gasoline and 9,975 watts on propane. Every gas- or diesel-powered generator is the same: the big, advertised number is somewhat more than what the machine can actually deliver continuously. While both numbers can be important, it still feels deceptive.
I didn’t think the same was true of solar inverters. I thought that an inverter advertised as “15 kw” would actually be able to deliver 15,000 watts of power. I even looked at the specs pretty closely. I was surprised, then, when two times the inverter shut down. It spontaneously re-started a minute or two later, but both times the logs showed that the shutdown occurred when it was delivering just over 12,000 watts. Each time, I was charging the car (about 8,000 watts) and we had a couple of heating appliances going (less than 1,500 watts each) plus the baseline current for the house (about 600 watts)… a total of less than 11,600 watts. Then we switched on another induction burner or the microwave oven, an additional 1,500 watts. That’s just a shade over 13,000 watts, but a good ways from 15,000.
I went back to the inverter’s specifications and discovered that it indeed says “Real Power, max continuous…15,000W” but also says “Real Power, max continuous (batteries only, no PV)…12,000W”. Hmmm. I wouldn’t have been charging the car at 32 amps if, in fact, there was no sunshine, but it also implies that there’s a continuity between 15,000 if there’s plenty of sun and 12,000 if there’s no sun. I suspect that a cloud had passed over the compound and dropped the solar input right around the time we switched on the extra appliance.
It’s kind of a drag, as I specced the system pretty carefully and discovering that I have 20% less real capacity than I had planned for means that I really cannot let the automated charging protocol that I’ve created charge the car at full capacity. Oh, it’s not the end of the world, but kind of a disappointment and a reminder to read specifications really carefully and always be skeptical of the large-print advertised capacity of any product.
—2p