My older brother sent me an email with a thought I hadn’t considered…
In the alternative energy world, it’s important to “right size” every part of your system. I think you are going to find that your new little inverter saves you a noticeable amount of power compared to the old one. — Why not call that new one your regular inverter, but also find a cheap (but heavy duty) inverter just for occasional use with power tools?
I never considered whether I was wasting a lot of energy by the constant use of a 4000W inverter, or would save energy by running a smaller one. So I went to the Wizard and asked the question, and had no trouble finding a corroborative answer…
As a general rule you can figure 15% of maximum. If your inverter is 2000 watts max, a typical loss might be 300 watts. It doesn’t matter how much or even if you are using equipment that’s plugged in. If the inverter is turned on, it’s using 300 watts and is “lost”.
There’s more at the link. 15% of 4000 watts, which is the max rating of my old inverter, is 600 watts lost just running the inverter. 15% of 600 watts, the rating of my new inverter, is 90 watts.
Since a 600 watt inverter handily meets all the day-to-day needs of the Secret Lair, falling short only in the matter of power tools, it appears my brother may have a seriously good point – which I have overlooked for years. I’ve always known I was losing power overnight for no good reason, but most of the time it isn’t enough to worry about. It only becomes a matter of concern during rare times of extended overcast or snow, when I can’t keep the solar panels uncovered and so spend more time leaning on my batteries.
In the next few days I’m going to do a more careful study of morning voltage with the new inverter, comparing it to figures I’ve kept daily over the past several months. Unfortunately I’ve only recorded that data to a single decimal point, so the historical data may not prove of use. But I’ll see if I can learn anything.
Which leads to the obvious question of “what if you didn’t use the inverter at all”? How much of the Lair could run on 12 volts, allowing an even smaller daily-use inverter ? Distance runs of DC suffer high losses, and I’m not well versed in high efficiency 12V stuff, but distance & efficiency losses with some 12V equipment might be less than inverter loss.
The 15% loss in inverters is high-test BS; inverters have been better than that for 40 years. 5% is a closer number, but the principle is correct, and it is not limited to the alternative energy world.
Inverter wastage is not a problem so much as the time is. Is that inverter on 24 hours a day? Just turning it on when you need a particular appliance sounds like a good idea if you can do it. Are we talking refrigeration here?
Back when I was doing some reading, the other thing about inverters is that the efficiency varies depending on load. Should be possible, for good brands, to get an efficiency/load plot from the manufacturer. IIRC, highest efficiency is around 50% load, but don’t quote me. So that’s yet another reason for “right sizing”. I suspect you’ll see noticeable improvment.
I have read the same thing about inverters as for generators. Have more than one, and use the 2nd only when you need the capacity.
In some ways, that helps me with my own emergency solar system. To some extent, I can start small, and add on later. Charge controllers, particularly good ones, can be paralleled, and one can always add another PV panel and battery. My main hangup, other than money, is figuring out how much MPPT controller to buy as a start.
If you can run 12v trailer LED lighting, you may drop your power consumption even more.