[helicon]

Forgive me if this is a silly question but when he talks about "beautiful solar-roof-with-battery", is he talking about car roofs or roofs of buildings?

An electric car with a solar roof that charges all day would be pretty cool.

[maxerickson]

Buildings. A car roof isn't enough area and isn't pointed in the right direction.

[tamersalama]

Not if it's a trailer.

[maxerickson]

I haven't figured it out, but my intuition is that the increased energy requirements of a tractor trailer mean that there isn't enough area there either.

Back of napkin, it looks like you get ~3*15 meters of roof which seems to translate to 10 kW of output under good conditions and then you need something like 150 kW to rumble up the highway.

[mrfusion]

Well trucks still have a lot of low hanging fruit for becoming more aerodynamic.

Plus you could use the sides of the trailer for some power too.

Finally even if 10kw can't power the truck. It could extend its range by some amount. Plus that's still a significant amount of power you don't need to buy. 2-3 rooftops worth?

[maxerickson]

Those improvements are presently not done because of cost. Grid electricity is a lot cheaper than diesel.

I guess electric trucks would still put a lot more effort into avoiding air resistance because of the lower energy per unit mass of batteries (the aerodynamic improvements can be pretty directly traded for either range or cargo capacity).

I think present day solar cells are a combination of too expensive and too heavy to bother with. That could change in the future.

[ams6110]

I have thought the same thing -- that trucks could be more aerodynamic. So why aren't they? The economics of freight are such that any measurable improvement in fuel economy is worth a lot. Why do we not see super streamlined semis? Maybe there's some non-obvious reason? I don't know.

[tamersalama]

That clicked when he talked about Tesla Semi. A roof installation on the trailer would make sense and might generate a 'useful' amount of power.

[mrfusion]

That's a great point. I'd imagine they need 3-4 times the power of a car but have 100 times the surface area. It seems like that could actually work.

[Kliment]

I think that's still two OOM too little.

[BurningFrog]

Buildings.