This Is Why We Don’t Have Solar-Powered Cars

Written by roadandtrack.com on June 14, 2021. Posted in Current News

The idea of buzzing about on pure sunlight sounds compelling. The sun certainly gives off enough energy, but math reveals that it’s less practical than it sounds.

The sun is the closest thing we’ve found to a limitless source of energy. It bombards the Earth with enough energy to power a year’s worth of human electric activity in just over an hour. It won’t run out for billions of years, it doesn’t pollute our atmosphere, and it can be accessed from anywhere. You’d be forgiven for thinking it’s the perfect solution to powering our cars.

Despite that, as companies pour billions into electrification and hydrogen, none have introduced a solar-powered car. The reason is simple math. As Engineering Explained spells out in his new video, there are limits to how much energy can be captured by a car-sized solar panel.

Taking the total amount of energy the Earth receives from the sun, you can find an average per square meter. Using that average, you’ll find that a Tesla-Model-3-sized solar panel could theoretically receive 12 kW—equivalent to 16 hp—directly from the sun. That’s enough power to keep a Model 3 humming along at 62 mph without ever needing to charge.

But the real world isn’t that rosy. Between the sunlight reflected by and absorbed by the atmosphere, only about 55 percent of the energy received by the Earth makes it to the ground. Plus, that only happens during the day. Peak energy is only available at local noon, with off-angle sunlight limiting your power harvesting in the morning and evening.

Then there are the technological limits. Even if we could make a single-panel solar capable of harvesting energy with the maximum efficiency theoretically possible, it’d still only turn about 33.7 percent of the captured solar energy into usable electricity.

The car, too, needs windows and other non-solar surfaces that reduce total energy input. Combined with the losses in charge efficiency and motor efficiency, you end up only getting enough energy to constantly run at 12 mph (not including the energy required to accelerate, which is more than maintaining a constant speed.)

Leave the car sitting still and you can build up that energy reserve. It just won’t happen quickly. With cloudless skies, it’d take 200 hours (8.3 days) to fully charge a Tesla Model 3‘s 75-kWh battery. With perfect solar panels and perfect weather, that’s still a pretty imperfect result.

See more here: roadandtrack.com

Header image: Business Insider

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