Off-Grid Electricity on the Cheap

When I decided to build the Secret Lair, I had a series of problems to overcome. They all had to do with Money: Lack Of.

As much as possible of the Lair is built with salvaged material: All the dimensional lumber, windows, wood stove, appliances, most of the plumbing, almost all the electrical. In fact, early plans didn't call for running water or electrical at all, because I didn't think I'd have access to water or enough electrical components. M kindly let me plug into his water supply and a friend with a backhoe trenched all the way down the ridge, so that meant I got a shower and a flush toilet just like a civilized person. But the electrical: Well, there I got lucky with scrounging. My current electrical system is about as simple as a solar electric system can be, so it's a pretty good case study in how a very basic system is constructed.

As you can see, I've still got some carpentry in my future. The panels will soon be mounted on a home-made rack. The process starts with the solar panels. I've got six small panels rated at 48 watts each. They're very old so I doubt they can really crank out that much. But in total, I can probably count on about 250 watts, which is enough for my use. One thing I've learned over the past four years is that I actually use relatively little electricity: Really just lights, my laptop, and an occasional power tool. I don't need power for water pressure, and the well pump has its own power source. But for a normal household, this wouldn't be enough. Needless to say, the Secret Lair does not have electric kitchen appliances in its future. Wired together, the panels produce about 18 volts.

The power from the panels goes to a charge controller. The controller regulates the power that goes to the batteries. The batteries (I'll eventually have four) are wired in parallel, so that the output voltage is roughly 12 volts - actually more like 13-14. Again, carpentry: I've got to get these under cover before it starts to snow.

Power from the batteries goes inside to the inverter. This is a 1500-watt auto/RV inverter, and one day I'll almost certainly replace it with a bigger one because 1500 watts isn't enough to run tools like a circular saw. Bother. But it's more than enough for common household appliances.

The inverter has its own internal protection against short circuits and such, so the breaker panel is probably redundant. But still - izza house. You want a breaker panel. This one's got four breakers, which is ludicrously overspecced for my 200 sq. ft. lair. But it was free. All this stuff will eventually be covered up by the kitchen counter.

One thing Landlady and T learned to their grief: The balance between the power output of the solar panels and the storage capacity of the battery bank is very important. You're actually better off with a battery bank that's too small than one that's too big. Lead-acid batteries must be fully charged much of the time, or they will lose capacity and gradually just stop working. Big storage batteries are tragically expensive, and it's a truism around here that you always kill your first bank of them by making mistakes that in hindsight seem fairly obvious.

When in doubt, go bigger on the solar panel array and/or smaller on the battery bank. If your batteries aren't fully charged by early afternoon on a sunny day, you've got too much battery or not enough solar. Ideally, you should have enough battery capacity to power your needs for two days without sun, and enough solar power to charge the whole bank by early afternoon of a sunny day. With that in hand, you won't go too far wrong.

And that's it, really. Obviously, a proper solar electrical system is rather more complex than this, but not in concept. It's also far, far more expensive. ;^)