# How much power from a solar panel on every vehicle?

Assume solar film has advanced to the point that the costs are more or less pedestrian. Every new car put on the road must display at least 1 square meter of solar film. (Exceptions might be granted to very small vehicles).

How much power would that generate? It must be a quantity that increases over time, as the mandate takes hold over a number of years.

Why on a car as opposed on a building where the placement can be optimized? 1 sq meter may produce 100 watts or so in direct sunlight at the proper angle.

To power the electric motor of course.

How many hours at 100 watts = 1 gallon of gasoline?

Going with wikipedias estimate of 125,000 BTUs per gallon, I get 366 hours at 100 Watts.

I double checked nothing, and used a cheap unit converter.

It may be enough to power the electric motor to open and close the power windows on a car. Though the martian rovers are powered by solar, so it’s not entirely out of the question.

Perhaps a better practical use for now would be to eliminate the alternator on a conventional car and replace it with a combo solar panel and thermal generator used off the exhaust heat.

based on a harbor freight cellof 12.40" x 36.42" (45 watts) it would take 3.43218 of these units to equal a square meter. at 45 watts per panel that would be 154 watts. converting that to hp would equal .2065 hp.

It would power a fan on a hot day to make a sitting car cooler. Not sure where you’re going with this.

Let’s just assume that a 1 square meter solar panel will produce about 1 kilowatt-hour each day. That’s a generous assumption, as the 1 kwh/day figure comes from fixed solar panel installations, and some cars will be parked under trees, in garages, etc, and the solar panel will not be perfectly aligned with the sun. In any case though, we’ll go with it. That corresponds to an average power of about 40 W, spread over the entire day.

We’ll also assume that US auto sales total about 1 million per month, which is approximately correct (it used to be more than a million, has recently dropped to less than a million). And for the first few months/years, we’ll pretend that everyone who is buying a new car is replacing a non-solar-equipped car.

So, in the first month, the total energy production from all solar-equipped automobiles will total 40 MW. In the second month, 80 MW. After the first year, 480 MW.

If all automobiles in the US (about 250M) were so equipped, as might happen after 10 years or so, their total energy production would be about 10 GW. Of course, this number is too high, as the solar panels on older vehicles will become damaged/dirty over time.

For comparison, a medium-size power plant produces about 1 GW. Additionally, the total power consumed (on average) by all vehicles in the US is about 600 GW (based on 400 millions of gallons used per day and 0.13 gigajoules / gallon).

A single 1-square-meter solar panel therefore appears approximately 1/60th too small to power the average vehicle, even given all the optimistic assumptions above, and assuming 100% battery efficiency. This assumed a solar panel efficiency of 15% or so, so even a perfect 100% efficient solar panel (impossible) would still be about 10 times too small.

Solar sucks.

there are solar auto (electric auto with batteries and solar panels) races that go cross continents done by university and college teams.

Yes, in cars like this.

Totally useless for practical transportation. And even if the solar cells were 100% efficient (meaning they produced 5x more energy), it would still be useless and impractical. Just look at it.

which, incidentally, is what the solar roof option on the Prius does. puts out a whole 50 watts.

Well, a vehicle with 1m^2 (how do you do those superscript numbers on here anyway?) would at least charge its battery to some degree. Remember, the costs are pedestrian, so you might as well.

Start at 1/60th of the load. Ok, increase the efficiency, increase the surface area, and, you know, plug the thing in at night.

At Earth’s distance from the sun, a maximum of about 1,400 W/m^2 can be had. This energy is greatly reduced due to the atmosphere. For the US, about 230 W/m^2/day could be assumed. For 100% efficient cells, this would provide around 2,000 kWh per square meter per year, or in this case per car. Since the efficiency of current solar tech is less than 29%, and the maximum theoretical limit for the photons from Sol is about 89%, assume a future tech efficiency of 50%, which is generous. Somewhere north of 15 million new cars are sold each year, at least according to the sites I quickly browsed.

This would yield 15,000,000 cars x 230 W/car x 365 day/yr x 0.50 = 629,625,000,000 W/year I believe. This could be written as 629 gigawatts/year. For comparison, the energy output of the world was roughly 15 terawatts in 2008. If we assume that each car stays on the road for 8 yrs on average, and that solar efficiency never declines, 9 years down the road the maximum amount of solar cells would be on the road, neglecting the growth of the new car market.

This number of cars would produce about 5 terawatts of power each year.

I probably miscalculated somewhere along the way, and I’m sure someone will point it out. Some of the bigger assumptions are that each solar cell is in full sun year round, never gets dirty, and has future tech worthy efficiency.

A little off topic but isn’t a solar cell really a kind of nuclear battery? Photons knock an electron loose eventually depleting the material.

No, the electrons come right back in through the positive lead.

The electrons are not consumed, they are “knocked loose” and allowed to flow through the material. The construction of the cell allows them to only flow in one direction. The electrons which are “knocked loose” are replaced by new electrons coming from the other direction.

Imagine an electrical circuit as a big, circular, sealed water pipe. There is a pump that moves water through the pipe, and a turbine that is driven by the movement of the water. The water is not consumed, it simply flows around in the circle.

In an electrical system, the solar cell is like the pump, and the electrical device (motor, LED, whatever) is like the turbine.

If electrons are not used up then why doesn’t a solar cell last forever? There are no moving parts.

Sunlight breaks down the chemical bonds inside of the semiconductor material. Instead of re-forming, these bonds instead trap electrons, leaving fewer electrons available for electricity generation. As you end up with more and more “dangling bonds” the solar cell gets less and less efficient.