Powering Stuff *Directly* From Solar Panels Feels Like Magic

Alright, I’ll give you that a solar powered LED lamp with no energy storage is pointless. Still, witnessing light turned into electricity and then back into light is pretty fuckin neato. There’s something about the immediacy of catching sunshine and turning it directly into useful work that thrills me.

The framerate of the camera on my phone makes this fan look like it’s spinning slowly. Rest assured it was in fact running at full speed. It’s a testament to the miraculous efficiency of electric motors that they can do so much with so little. The panel is advertised as 7 watt after all, but only reliably outputs about 1 watt.

Plenty of power for this fly trap, which consumes only 40ma at 5 volts. The panel produces ~280 ma at 5 volts, or 7 times as much as the trap requires. The set of USB appliances which consume sufficiently little energy to be powered this way isn’t very diverse, but you’d be surprised what it includes.

As it turns out, there’s a few vehicular applications where direct solar power works fine. Boats are one example as they use little energy to move, relative to their mass. Their surface area is also often ample, so there’s plenty of room for panels:

Airships have many of the same qualities: They need a fairly small amount of energy to move through the air relative to their mass. This makes them suitable for direct solar power as well:

There’s also been a directly solar powered RC car, the Tamiya Solar Eagle. It does have a single capacitor to keep it going through shadows, or if a cloud crosses the sun, but besides that it runs directly off the panels:

Why isn’t this more common? Sunlight has a fixed energy density of 1 kilowatt per square meter of surface that it strikes. That’s how much energy we could get from a 1 meter by 1 meter solar panel if it was 100% efficient. However the solar panels available to the public today max out at 22.5%, though the cheap ones can be as little as 15–17% efficient.

So, that’s 225 watts for every square meter of solar panel, best case scenario. That’s about 25 watts short of being able to power the weakest electric bicycle motors available today. As you might imagine, powering a car this way is pretty difficult unless the car is extraordinarily lightweight and aerodynamic, as well as being totally covered in the most efficient solar cells on the market.

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