Toyota Motor Corp. is secretly developing

drmike

Uh, yeah. On a sunny day, the intensity of sunlight hitting the Earth's surface is an average (over a sunny day and with consideration for the angle of incidence) of about 500 W/m^2. That means the most power you could hope to collect with a square meter of collection area is 500 Watts, and that's assuming no losses in the solar cells. In fact, even the most advanced solar cells struggle to do better than 30% efficiency, so we have then about 150 Watts per square meter.

Now, let's say we need about 30 horsepower, on average, to use for about 20 minutes one way to work (I'll assume it's a flat place, the car is pretty streamlined, and we're not in a huge hurry). 30 hp is about 22.4 kW, and since we want to produce that power for 40 minutes (to work and back home again) we will need 22.4kW*40minutes*60sec/min=54000kJ of energy.

OK, so we have 150 W/m^2 of generating power, and realistically we should have about eight hours of sunlight that's not at very oblique angles to the solar panels.
For every square meter, we will get 150*8*60*60=4320kJ of energy. Uh oh.

For each one square meter, on a good, sunny day, I will capture 4320kJ of energy, if I can store it in batteries without any conversion or storage losses. But I need 54000kJ. No problem, I just need, er, 54000/4320=12.5 square meters of solar panel on my lightweight, streamlined car.

Now assuming my car can only be two meters wide to fit on public roads, my car will include an uninterrupted solar panel that is about 6.25 meters long sitting on top. And I still won't make it home on an overcast day.

Totally solar-powered car? Better have a solar generating station to plug into somewhere.

Now of course there have been solar-powered cars for races. They can move at 60mph all day on flat ground because they do not need anything like 30hp to do so. But these things are flyweight vehicles that would never, ever be seen as safe or practical, even for the most diehard extremist.

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