We got an electric car in 2021 — after years of pining for a Tesla (and cringing at the price tag), we picked up a used BMW i3 for a song. Putting a charger in the garage was remarkably cheap, since there was a dryer on the other side of the wall (although the circuit won’t run both the dryer and the car charger!) and we estimate a full charge costs somewhere around $2-3. This is a short range vehicle, and its saved us a bundle on gas so far, but what if there was a way to save even more…

Let me skip to the end: there is not — but it was fun trying!

The idea was that we could build a system for minimal cost, buying extra panels from friends with bigger solar projects underway, and reverse engineer their setups to do the work myself. That part of the plan panned out: panels cost $800, and I fumbled my way through learning the electrical work — without frying myself!

We bought a decent off-grid inverter (not cheap)… then learned it won’t even power up with a battery. Batteries start at around $2000, but when we found one on sale for $1600 shipped, we went for it. After more than a year of piecing together the system, this week it finally powered up…

So between hardware and wiring, all told, the system probably cost about $4000. But does it work?

Kinda…

I’m still a newbie at all the electrical terms, so I won’t try to talk KWh or Amps, but the i3’s battery is roughly 3 times larger than my single solar battery. Now assuming the sun is shining, and the solar battery is being charged at least as fast as the car is pulling out power (limited to 16amps by the charger), in theory it might be possible to keep up. In practice, I don’t have enough panels to keep up the throughput, or enough storage to offset it.

I do have room for another row of panels, and next time I have a spare cash, I could chain another battery into the system. But I think, at least for now, this is as far as this project is going to go. Doubling the capacity of the system still won’t fully charge the car, or run the house. However, even at its current scale, there’s some value here:

1) We can top up the car during the day
The EV (which we call the “tiny car”) is primarily a shuttle to town and back. On a good day, we can do 4 runs on a charge. Now we can do 5 — more, if its sunny enough, and schedules allow for a morning and afternoon top-up.

2) We have another back-up power source
We live in the country, which means we lose power. Its just a fact of life out here, especially in the winter. We have a good sized portable generator, but running on gas is expensive and noisy. For simple needs, or true emergencies, we can use solar power with a little planning.

3) I learned a lot
We really did do almost every ourselves — although not without plenty of advice from friends who have done this before. We mounted the panels, we ran the wires (backwards, at least a couple times), I connected and setup all the system components, and even installed a circuit breaker box and some household wiring in the shed. Most of my tech experience is software, so learning how things are built is always fascinating.

4) I’ll be learning more
The battery and inverter speak an industrial protocol called ModBus. The inverter also has a Cloud API. I fully intend to connect to, and exploit, the data in these systems for learning and professional gain.

So, the direct ROI is not there. Even if we could fully charge the car with this system, at $3 per charge, it would take 1,333 charges for it to pay off. We can’t, so ROI is closer to 7000 charges — that’s 19 years. The car won’t last 19 years!

But as passion projects go, this one was actually a lot of fun. Solar is probably still too costly and complex for the average person right now. But its getting better constantly, and I think having access to, and understanding of, alternative power sources is important for our future. We can’t keep things going the way they are…