Generators just have to be one of the best inventions ever — power when and where you need it.
I’m not any kind of generator expert; I’m just a user and a big fan of what these machines have allowed us to do over the years. In the past, I’ve owned several types and sizes of generators in my commercial construction company. We were able to work way up in the mountains or anywhere else that power wasn’t available. We’ve built everything from buildings to bridges with nothing more than a generator to power our tools.
Right now, living off the grid, I own two generators. One is an inexpensive, 3,500-watt portable generator. The other is a more expensive, 12-kw home standby generator.
I use the small one for all kinds of things. If I have to install a new entry gate, I just load my tools, materials, and the generator up in a vehicle, drive it to the work spot and get to work. When we camped on our property, I used it to pump water into a holding tank. I've also used it to charge my trailer batteries. Sometimes I may have to load it up along with the air compressor and drive to a remote spot on the property and air up a flat tire. There is almost no limit to the usefulness of a small portable generator.
The only thing I would recommend in a small one is that you go for one that has a 220-volt option. I still use mine to pump water on occasion. I also use it sometimes to charge my solar batteries and that is done on 220-volt because of the way my system is wired. You may never use the 220-volt option, but it sure is nice to have when you do need it.
Most of us who live off-grid and use an alternative power source such as solar, wind or hydro, also have a battery-backup power storage system. That is where my power comes from at night or anytime the sun isn’t shining and the solar panels aren’t producing power.
I can go about 3 to 4 days living off my batteries until they need to be charged again. If the sun still isn’t shining then I use one of my two generators. When the batteries are very low, I use my Kohler 12-kw (12,000-watt) propane generator. It produces about 125 amps at 90 percent capacity, and in my case, that brings the batteries up about 10 percent per hour. So if the batteries are at 60 percent capacity, I can run my big generator for one hour and they will be charged to 70 percent capacity, an increase of 10 percent.
Mathematically that would mean if you started charging when the batteries were at 60 percent capacity, then you would have to charge for four hours to get them to 100 percent — but unfortunately that isn’t quite how it works. All of our systems are different, but for mine, as you get close to 85 percent to 90 percent capacity, the (ever so smart) inverter will slow the charging down. It’s not good to throw that much charging power at your batteries as they get closer to full charge.
The inverter will slow the charging capacity down from 125 charging amps to 60 and then 30 and so on, so that by the time you get to 100 percent, the charge will be very small. My small generator will charge the system as high as 60 amps although that is pushing its capacity.
Bottom line, when the batteries are way low, I use the big generator up to about 90 percent capacity and after that, I may switch over to the smaller generator. Why run the big one when the inverter won’t let it charge at its total capacity? I think it’s more efficient to use the small generator to charge that last 10 percent or so.
I like the 12-kw Kohler but be forewarned that if you are using it like I am for off-grid purposes, Kohler will not honor the warranty. They claim the generator just isn’t built for long-term use. It has an aluminum block, is not water-cooled, etc. It was created to come on a couple of times a year when the power goes out in an urban residence. That’s why it is called a “Standby Generator." They say it is not intended for the type of regular use it would get in an off-grid situation. I run mine about 100 hours per year.
It is my understanding that Generac now has a 6,000-watt generator that is made for off-grid use and that size would be adequate for us. I’m not promoting products, just trying to make you aware of some of the pitfalls of backup generators in the off-grid world and what options you might have to overcome that. Backwoods Solar used to sell a propane fueled, water cooled, name brand generator but it was very expensive and not UL listed so in this state you couldn’t use it anyway.
Like I said, I’m not an expert. Like anything else involving off-grid living, do your homework and you will be okay. Just be aware that warranties can be an issue and you always want to be careful you get the right size generator. Too small and you will wear it out before its time. Too large and excess power may be wasted.