Re:Solar panels on cars make no sense
by mikem170 on Monday January 30, 2023 @12:24PM
(#34583113)
> So, assuming 4miles per kWh that Prius was expected to hit over 6kWh per day
I checked your link after reading your math, above. Coming from the RV solar world I found these numbers surprising. I think your comment about the 100 kWh battery pack threw me off. The normal battery in a Prius is 8.8 kWh with a 25 mile all-electric range [0].
Toyota is saying that the panels they used generate approximately 860 watts of power. The normal rule of thumb in the RV world (which I am familiar with) is to multiply panel wattage by 5 for kilowatt hours per day in good sun, so I would assume 5 kWh total per day for 860 watts of panels, in real life. So their numbers look optimistic to me, but aren't crazy - I would have said 15 miles under ideal conditions (5 kWh of their 8.8 kWh 25 mile battery), they said 44.5 km. They used a 34% efficient panel to get these numbers, something normally only available to the likes of NASA at this time.
Only people in places like Arizona and Texas would get most of that power output, others not so much. I don't think people realize how much impact clouds, shade (even partial shade, even a bunch of bird crap), and optimal panel angle towards the sun have on solar power output. For example, in 2021 Germany had 58728 MW of solar panels generating 49011 GW of power per year [1], which is 134.2 GW per day, which is only 2.3 times their panel capacity, and this is due to clouds. So instead of 25 miles or 15 miles that car in Germany may only get 7-12 miles of extra solar powered range, and perhaps a good bit less because the car panels are not oriented towards the sun like fixed panel installations usually are, and people park in shade under trees or next to buildings sometimes, winter when it's below freezing and cloudy and the battery needs to warm itself to safely be charged, etc.
The only other thing I would add to this discussion is that panels fixed to the surface of a car may have problems with heat. Normal rigid solar panels are in frames and elevated, allowing air to flow under the panels and cool them. Panels loose efficiency with heat. Flexible solar panels, which don't need a frame and can be attached to curved surfaces, typically fail in a year or three, they are nowhere near as reliable as rigid panels. There's a lot of discussion about this in the RV and boat communities.
If the numbers work out on this idea, then that's great. Reliability would be my biggest concern, these panels need to last to pay for themselves.
I checked your link after reading your math, above. Coming from the RV solar world I found these numbers surprising. I think your comment about the 100 kWh battery pack threw me off. The normal battery in a Prius is 8.8 kWh with a 25 mile all-electric range [0].
Toyota is saying that the panels they used generate approximately 860 watts of power. The normal rule of thumb in the RV world (which I am familiar with) is to multiply panel wattage by 5 for kilowatt hours per day in good sun, so I would assume 5 kWh total per day for 860 watts of panels, in real life. So their numbers look optimistic to me, but aren't crazy - I would have said 15 miles under ideal conditions (5 kWh of their 8.8 kWh 25 mile battery), they said 44.5 km. They used a 34% efficient panel to get these numbers, something normally only available to the likes of NASA at this time.
Only people in places like Arizona and Texas would get most of that power output, others not so much. I don't think people realize how much impact clouds, shade (even partial shade, even a bunch of bird crap), and optimal panel angle towards the sun have on solar power output. For example, in 2021 Germany had 58728 MW of solar panels generating 49011 GW of power per year [1], which is 134.2 GW per day, which is only 2.3 times their panel capacity, and this is due to clouds. So instead of 25 miles or 15 miles that car in Germany may only get 7-12 miles of extra solar powered range, and perhaps a good bit less because the car panels are not oriented towards the sun like fixed panel installations usually are, and people park in shade under trees or next to buildings sometimes, winter when it's below freezing and cloudy and the battery needs to warm itself to safely be charged, etc.
The only other thing I would add to this discussion is that panels fixed to the surface of a car may have problems with heat. Normal rigid solar panels are in frames and elevated, allowing air to flow under the panels and cool them. Panels loose efficiency with heat. Flexible solar panels, which don't need a frame and can be attached to curved surfaces, typically fail in a year or three, they are nowhere near as reliable as rigid panels. There's a lot of discussion about this in the RV and boat communities.
If the numbers work out on this idea, then that's great. Reliability would be my biggest concern, these panels need to last to pay for themselves.
[0] https://getjerry.com/car-repair/toyota-prius-plug-in-hybrid-...
[1] https://en.wikipedia.org/wiki/Solar_power_in_Germany#Generat...