During my undergrad days in East Tennessee, I was lucky enough to have a friend whose parents owned a farm about an hour from the city. There weren’t really any buildings on the property, so we would escape for some pseudo-camping that was more like drinking in a field with the car radios blaring. It was awesome, but not for our vehicles. Inevitably, we would awake to find one (if not all) of the batteries dead in the morning.
Apparently Bryan, an electrical engineer from Florida, experienced a similar problem. Especially fond of driving his truck into the middle of nowhere for a day or two, Bryan was looking for a way to keep the electronics (like ventiliation fans, the stereo and lights) operational without keeping the engine on or running down the battery. He decided the answer was a solar panel, so he set about designing and building his own charging circuitry. Two months later, it appears to have been a success. Check it out in action:
On his blog, which details the project, Bryan is very careful to point out that he isn’t interested in using solar power as a substitute for fossil fuels–in fact it would take a solar panel of around 3,000 square feet to even offset 20 percent of the power his truck’s engine normally produces. But as a substitute for battery power, he found that a cheap 50-watt panel worked just fine.
As this review points out, Bryan’s system uses an Arduino, which draws its own power from the panel via a regulator. It senses the voltage level of the battery and the available juice from the panel, connecting or disconnecting it from the electrical system as necessary. The system includes a set of LED indicators, which he installed in the dashboard near the cigarette lighter.