At the very beginning, Fenske shows how much energy the sun supplies the earth. At any given point in time, we get 1.36 kW/ m². The engineer multiplied that for the earth’s surface and concluded that the planet is getting 173 trillion kW. If you consider that humanity spends 190 trillion kW per year, it would only take an hour of sunlight for that.
The problem is that things are not that simple. First, because not all of the energy actually hits our surface: 22% is reflected and 23% is absorbed by the atmosphere. We still have 55% of that solar energy to use, but then comes the obstacle to our technology.
Single junction solar modules – the most common ones – have an average conversion efficiency of 33.7%. The earth is also not flat, which causes the rays of the sun that hit each location to vary throughout the day. If you take all these factors together, you get in the best case only 250 W of the original 1.36 kW. In the worst case, if you still have sunlight, the amount of energy drops to 62.5 W.
For example, suppose a Tesla Model 3 has solar panels all over its surface and it has the best sun exposure. In this hypothetical situation, Fenske calculated only 1.5 kW in 24 hours. With his 75 kWh Battery pack, it would take 50 hours to fully charge.
If the Solar Model 3 had to run at the worst number, it would get just 375 W in 24 hours – or 0.375 kW if you prefer. It would then take 200 hours or 8.3 days to recharge. That sums up why no conventional car harvests solar energy with its own body.
For this, the vehicle needs a large area and high energy efficiency. This is how Aptera promises its electric trike. It also promises that the Never Charge system – a standard solar charging strategy – can offer a range of up to 70 kilometers per day with solar power alone.
Fenske checked to see if Aptera’s numbers were correct and there is nothing wrong with that. Now that the theory is backed up, the engineer wants to see what the company can really deliver, and he’s not alone. Check out the entire video below.