At the Cybertruck announcement, Elon said that there may be a solar-roof option that could add “up to 15 miles per day” of range. This study is one quick check to see if that is possible.
First, we need to decide what “up to” means. According to the Guinness Book of World Records, Yuma Arizona is the sunniest city on Earth with 11 hours of sunlight each day. Elon doesn’t tend to make claims that are only obtainable in rare conditions, so for the purposes of this study, I will pick Los Angeles, CA – as it both gets a lot of sunlight and has a lot of Teslas. Further, rather than go by “daylight hours,” we need to use “peak solar hours,” as they a standard used to calculate PV cell output. This chart lists 5.62 per day on average for LA.
As per standard solar calculations, each solar hour results in 1000 Watts per square meter of light energy hitting the PV cells. While most home solar modules are 15-20 percent efficient, the cells could be 22% efficient – especially by the time this is available – so that is 220 watts per square meter per hour, or 1.236 kWh per square meter.
Now we need to know the size of the solar array. The best source that I could find was this CAD drawing. According to scale and from making my own 3D models using measurements from it, the door would be 1.3 meters wide. The length would come out to 1.8 meters, or about 1.815 meters factoring in a 7.5 degree angle for the roof. For the purposes of this study, we will assume no gaps in the cells to account for the way that the cover has slats with hinges, so the area is therefore 2.34 meters.
Now for the top portion. It is 1.3 meters wide at the top, 1.5 meters wide at the bottom, and 1.26mm long, including factoring in the 7.5 degree angle. That is 1.764 square meters. So combined, we have 4.1 square meters of space. I am going right up to the edge, and that is not really possible in the real world, so we could easily call this 4 square meters – but let’s give every benefit of the doubt and stick with 4.1 – and we already skipped counting gaps between roller-shutter slats as well. Now we can say that 4.1 square meters times 1.236 kWh per square meter is 5.07 kWh per day for an average day in LA.
How many miles per day is that? Well, a Model-3 Performance that has a 75 kWh battery and a 310 mile EPA range goes 4.13 miles per kWh – so it could run for 21 miles on that. But how much more energy would a Cybertruck use over a Model-3? It is not enough to just compare coefficients of drag because you also need to factor in the frontal area and tire rolling resistance. George Bower did a detailed power analysis and believes that the tri-motor truck will have a 250 kWh battery. For a 500 mile EPA range, that is 2.0 miles per kWh.
5.07 * 2.0 is 10.14 EPA miles per day in LA, a rather nice solar environment. So, it looks like a solar roof that is both on the roller door and roof-top would provide up to 10 EPA miles per day of range. A peak summer day in AZ is 7.9 solar hours, and could hit 14-15 EPA miles. So, Elon’s claim of “up to 15 miles per day” is possible for a bright summer day in Arizona, but expect more like 10 miles per average day in CA. Boston, by the way, would be 6.9 EPA miles on average – and 5.4 in the winter. So not bad! Note that these calculations assume that you are facing North and have no shadows on the vehicle. If you face South or have shadows, then there would be less sun.
Also I wanted to mention that I sell Tesla J1172 charge-lock adaptors that are SLA resin printed and then painted black for UV resistance. While not injection molded, they are a lot nicer than parts printed on home-level FDM (filament) machines.