Solar car

From Silent Revolution

Topic: Solar cars are not a realistic mode of transportation.

So -- electric vehicles are set to take off. Solar power is also set to take off. Well, let's combine them: solar cars are set to take off, right?

Wrong.

It all comes down to surface area. A house, commercial building, or large expanse of desert all have proportionally large amounts of surface area. This means a lot of light striking the surface, which means a lot of power. A car does not have this. Let's give a car a best-case scenario. You have a car plastered in a bunch of traditional solar cells. Let's say they're the more expensive silicon cells, at ~20% efficiency, rather than the lower efficiency (but much cheaper) thin films. Let's say that you're out in the middle of the desert, having beautiful sunny days (1000W/m^2), with the sun passing straight over you at high noon. Let's say that after angles are taken into account, 20% of the sun's energy will be harnessed; that's a bit generous, let's go with it. Let's also say that the car has about 2 square meters of surface area to plate with solar panels (6 1/4 feet long plus length for the windshields, 3 feet wide). The math is 1000 * 0.2 * 0.2 * 2 = 80W average power input to the vehicle. A typical, efficient electric vehicle may get 200Wh/mi at highway speeds. Consequently, this "solar car", if it stored up its electricity for an entire day, could go a mere 14 1/2 miles in this optimal day. Go to a more realistic situation for a more typical driver, and that number goes way down.

Not a realistic mode of transportation. Hardly even a supplement for a plug-in electric.

Now, there is a possibility that may, in the future, make solar cars partially realistic. Nanoantenna solar cells may, after rectifying diodes are added, provide perhaps 70% efficiency. And, since they can capture infrared, too, let's say that they can gather 25% of the solar energy on an optimal day. The math then becomes 1000 * 0.7 * 0.25 * 2 = 350W -- thus, in a day, 8.4 kWh. With a 200Wh/mi car, this becomes 42 miles -- a typical commute. So, on an optimal day in an optimal location, these extreme efficiency solar cells, plastered over the whole car, may be able to provide enough energy for a commute. In less optimal conditions, they could at least supplement the daily commute. Never, however, will they be sufficient for long distance driving. Even with an Aptera's ridiculously low 120Wh/mi highway performance, that's still only 70 mi in optimal conditions (not like an Aptera has a spare 2 square meters of solar panel area) -- a bit over an hour of drivetime per day.