So, you want to put a solar panel on your car. Or, you don’t.

Something like a solar panel to try and charge an electric heater will simply not work. You can’t get enough power for high wattage applications like that.

Why?

This is a good question:

  • You want to use a lot of car accessories without draining your battery.
    • Perhaps you want to sleep in your car?
  • You think solar is interesting

Equipment:

How long did it take?

Build: 4-6 hours

Research: 8 hours

I spent more time researching than getting the pieces together. That was probably not required, but I enjoyed it. Getting the panel mounted was an afternoon’s worth of work and a run to the hardware store.

I spent more time researching than getting the pieces together

The hardest part to plan ahead of time was figuring out exactly how to attache the panel to the roof. In the end, the Xterra that we’re attaching to provided a fantastic by sliding in right under the stock roof rack. This was really nice for a few reasons:

  • Added stability.
  • Lower wind resistance
  • Still able to use the roofrack

Downsides:

  • The roofrack will always block part of the panel. We operate at a lower efficiency. We decided this was worth it for the pros.

We drilled out holes in the metal framing for the solar panel. The actual panel is very thin, the reason the whole assembled panel is an inch or two thick is the electronics on the back. Also, most panel design is concerned primarily with surface area and not making the panels as thin as possible.

These holes then had eye bolts connected to some metal rings that would go around the car frame.

If you take a close look at the pictures you’ll note that the bolts provide a second layer of security when attaching the panel. Even if all of the connector rings were to fail, the panel would still not become detached from the car.

The wiring to connect the panel to the charge controller could still use some work. I’m a little divided on how to do this. Feedback is welcome.

Still to do:

  • Permanent mounting of the charge controller/battery. These should have some sort of mount/assembly, this can also make connecting accessories more streamlined.
  • Wiring cleanup mentioned above.

Choices

Some choices:

  • Should you use a battery or just plug into the car system?
    • I find this decision to be the most interesting. Since your car already has a battery you can combine that with a solar panel and charge controller and make sure that your battery is always getting topped up. However, the downside is that car batteries are meant to never draw significant power.
    • We opted to get a new battery. This is primarily because of the load curve of car batteries vs deep-cycle batteries. The battery we got is meant to be drawn significantly down and still recharge correctly. Car batteries simply are not. In addition, cold weather already puts a significant wear on car batteries.
  • If you do opt for a battery what type should you get?
    • Get a deep-cycle.
  • 12V or 24V?
    • 12V, all car accessories are meant to be 12V, just stick with that.
  • How big of a panel should you get?
    • The smallest surface area with highest wattage that you can afford. We chose a 100W panel knowing that our expected usage curve is a bit up in the air.
  • What gauge wire should you use?
    • We opted for 10 gauge. This is probably the max you should need for your application.
    • Remember that wire gauge is rated by amperage, not wattage. That is why, in a house you will see higher gauge, smaller wires. 10 gauge for example matches ~30A load, which matches our charge controller and the system as a whole. Note: a 100W panel at 12V is 8.33 Amps, so this is probably overkill. The load however, might exceed 100W at a time, which could justify the higher amperage (it is unlikely that the draw will ever go over 200W/16.67A so, still lots of overhead).

Issues

Very few so far. The system has been running for a couple of months, and has been lightly taxed.

On the panel, one of the MC4 connectors does not clip in to anything well, we might replace that at some point.