A hypothetical cheap ~30% efficient solar panel could add something like 40 miles of range per day to a car in ideal conditions. That starts to look actually useful vs a simple gimmick.
A 100 watt solar panel, producing the full 100 watts, would take 80 hours of perfect sunlight to produce enough power for an extra 40 miles of range.
Assuming best case (unrealistic) conditions, if you get 8 hours of perfect sunlight in day, and your solar panels produce 100% of their rating for all 8 hours, it would take 1000 Watts worth of solar panels to produce that extra 40 miles of distance over 8 hours. It seems kind of unrealistic to fit 1000 Watts of solar on top of a car. And that's an absolute minimum, under best case conditions.
If you had, say, maybe a more realistic 300 watts worth of panels on top, and they got 4 hours of full sunglight, you'd be producing an extra ((300W * 4h) / 200Wh/mile) = 6 miles. And that's still assuming best case condition for power consumption per mile.
[Edit] - And like the other commenter stated, those few extra miles get cut down when you consider the weight of hundreds of watts of solar panels added onto the vehicle.
To me it looks like it will never be a meaningful solution, due simply to physics.
> The usable clear area of a Model S glass roof is 42” x 45”
A Model S is actually 195.9” by 77.3 (ex. mirrors). Assuming a reasonable shaped solar car using 75% of that surface is covered in panels that’s 12x the area. But you also gain from panels covering the sides of the vehicle.
Further “Because the vehicle roof is flat, it collects less light than if it was positioned at the optimum angle to the sun.“ as I said your not limited by the roof. “Lastly, we lose at least 10% more due to the safety glass,” we don’t need glass and that’s already part of panel efficiency numbers. “and the inverter/charging is only 81% efficient.” Solar panels and batteries are both DC so you don’t need an inverter, the charge discharge efficiency of lithium ion can be over 90%.
San Francisco 5.34kWh/m * .3 efficiency * 7.33 square meters = 11.7kW/day /.3kW per mile = 35 to 39.14 miles in San Francisco depending on how much your charging the battery with plenty of areas getting more sunlight. Using the highest efficiency panels currently produced that goes up significantly, but cheap 30% efficient panels seems like a more reasonable mid term prediction.
PS: Example of a flexible 1m panel zero glass required at under 300$/m: https://www.amazon.com/dp/B082FCZ4MD/ref=emc_b_5_t?th=1
You'll still need a DC-DC converter, which is just an inverter with a rectification step. The 81% number is low, but there is a loss here.
The maximum daily energy density of sunlight in sunny Los Angeles is about 6.4 kWh / m2 [1] (assuming perfect, moving angle of panels to sun).
If we can turn the entire footprint of a Model X into solar panels, that gives us about 10 m2 (big car!).
The US DoE reports the Model X gets 100 mi / 31 kWh [2]. Or 12.4 kWh for 40 mi.
So those panels would need to get 1.2 kWh / m2 of solar power. Which is about 18% efficiency and pretty reasonable for good consumer panels [3].
But it assumes the car is in sunlight all day at the perfect angle, there is no loss (eg due to weight), in a locale as sunny as LA (eg Seattle gets half of the sunlight as LA), and can be completely coated in efficient panels (the model S solar roof is <1 m2 in comparison). Bumping efficiency to 30% gives some headroom but it still seems pretty impractical.
[1] https://globalsolaratlas.info/detail?c=34.270738,-116.929301...
[2] https://www.fueleconomy.gov/feg/Find.do?action=sbs&id=41196
[3] https://news.energysage.com/what-are-the-most-efficient-sola...
It is true that you lose some energy every time you store or transfer it, but if we install solar panels on every roof (so we get excess energy from solar) and also find a way to store energy cheaply for a long time, that should be enough to completely switch from fossil fuels, (well, mostly)
routinely sells panels for 30 cents/watt.
If you could skip the inverter step, charging your electric car could be very low cost.
5,000 watts of (raw) solar panels for $1500 and would give even the most power-hungry 350wh/mi tesla ~ 70 miles of charge in 5 hours of sun.
(a 200wh/mi car would need ~ $500 of panels for 40 miles)
Does this take into consideration the increased weight of the solar panel and any additional equipment?
Even relatively small solar arrays could keep a car from discharging at an airport parking lot etc. That could extend to running the climate controls when your shopping without concern for draining the battery.
PS: That said, the roof also has many advantages such as allowing you to park in a garage without issue.
I am not really an expert on electricity but there could also be additional equipment involved as well (inverters, transformers, etc).
59.2 by 26.5 inches or ~1 square meter Weight: 6.2 lbs.
If you looking at 12 square meters of space that’s 75 pounds though an integrated system would have plenty of options to save weight.
Solar panels are DC as are batteries so you don’t need an inverter.