In the context of home electricity, solar is fine. Germany has a lot of solar acceptance, and it’s much further north than the PNW.
But in terms of powering automobiles, solar is not practical/effective for a number of reasons given above, some of which are exacerbated by geography.
Notes:
If you want to brag about your solar house, whatever. But we’re talking about cars here. Small area. Weight limitations. Variable orientation. Throw in some clouds and the numbers get even worse. Etc.
There’s also the e.home concept RV. Though the range is only 100 miles, and it doesn’t say how many days it takes to fully recharge the battery with the solar panel. It may still be practical for a relaxed RV lifestyle.
Fair enough. I suppose it’d make parking garages rooftops cool again 
I’d love to have a solar-powered car, but…
To be universally practical, a solar-powered car needs to be:
[ol][]Able to cruise at highway speeds continuously from solar input and/or battery[]Able to supply a charge to the power train continuously during daylight hours, even in cloudy weatherAble to supply enough charge to a battery or other storage device that will power the car without sunlight for 16 hours, the amount of a winter night at temperate northern latitudes.[/ol]Until that happens, I will be driving my cheap, gasoline-powered jalopy at a considerable saving, without worry about the time of day and/or night.
I don’t know how many of you have picked up a 2’x4’ solar panel but they are not that heavy. I don’t recall them being 20 pounds when I had two on a shed. Also, the panel on a car roof would be just the panel, could readily place the inverter elsewhere.
Also, many boats use them and the panels they use are rated for salt, high wind, and hail. Again, not that heavy.
I can see this making sense only if you happen to regularly drive to an area that doesn’t have a charging station to help maintain the battery. But, if there’s a plug somewhere possibly a portable charger could be used. Which would probably have better ROI over the life of the vehicle compared to panels.
Maybe, if you had them on a roof rack and they opened up and you had the entire footprint of the car to work with.
I just re-read The Martian and noticed something. When Watney’s driving across country in the rover, he has a couple stacks of solar panels[sup]1[/sup] on his roof. Why didn’t he plug the topmost ones into the rover? Also should have plugged the RTG that he has for heat into the rover too. The RTG was used to help recharge the batteries, so why not use it during driving? He could have gotten 15 or 20 more minutes fo driving each day.
[sup]1[/sup] The panels are only 10.2% efficient, which at the time he wrote it (published in 2011, so written some time before that) may have been better than what you could get for your roof. But NASA had already launched Dawn in 2007 (panels probably built around 2005) and that had triple-junction InGaP/InGaAs/Ge photovoltaic panels that had 27.6% efficiency. Weir didn’t do his homework on that.
Interesting news of a Toyota trial of cars that get a significant range boost from car mounted solar cells:
Interesting numbers in that news relase:
Maximum charge to the driving battery while the vehicle is parked (per day):* 44.5 km
Maximum charge and power supply to the drivng and auxiliary battery while the vehicle is being driven (per day):* 56.3 km
*according to the JC08 Japan test cycle
I would prefer to see kWh numbers but I guesstimate those numbers are roughly 4.5 and 5.5kWh (JC08 is hopelessly optimistic)
And they seem to be using triple junction cells which are impossibly expensive (I wonder if that is ever going to change).
Yet another example from the marketing gimmick world: Hyundai adds solar panel to a hybrid
Bumping this thread topic to report on the latest solar-paneled vehicle:
It’s basically what you’d get if you converted one of those World Solar Challege vehicles to be street legal. Because that’s basically what they did. OK, it does have a battery, which the WSC vehicles do not, or at least I don’t think they do. They claim you can get 1000 miles with the 100 KWh battery.
It is really a great idea. but what about the third world countries especially in Asia and Africa.? they even don’t have electricity. they are facing loadshedding everyday for 4 to 5 hours. However the idea is great and where it can be implemented . it must be used.
If you lived in Phoenix AZ, in a small apartment so you have no place to put solar panels except on the roof of your car, and you only travel a couple of miles a day on average, then solar panels on the roof could provide up to 50% of your power. It’s not all that much to begin with, in a conventional car you might be using 1 gallon of gas a week in that scenario. From that low usage point upward the power provided by the rooftop solar panel rapidly becomes insignificant, and if you have a house or a yard you can use many more fixed solar panels to charge your car or an external battery.
So the upshot, good for low usage with no other place to put solar panels, in high sunlight zones.
Though it would still be better to just put the solar panels on stilts over the driveway/parking spot. The stilts would cost less than fitting the panel to the car, and it would be more reliable.
Would it be enough to run the AC or the fan in the summer so the car is more comfortable to to return to?
Yes, it’s a very limited set of circumstances where the car top panels are a true benefit, perhaps if you can’t put up a car port with solar panels on the top because you don’t even have a fixed parking spot. There have to be upwards of 10-12 people in the American Southwest who would meet these criteria. I’m sure the car manufactures are refitting their plants as we speak to take advantage of that market.
Not the A/C. Typical automotive A/C compressor needs a few kilowatts of mechanical power, whereas we’re talking about maybe getting a couple hundred watts from a rooftop pane.
Maybach (ultra-luxury Mercedes brand) vehicles had the option of solar panels to run a ventilation system when the car was off. Not sure how well it worked.
You can do that today. But apparently there’s not much call for either to be integrated into the car as a factory-standard accessory.
In the “boondocking” community (basically RVing, usually with aftermarket commercial vans converted for the purpose, specifically done away from established campsites with hookups), solar panels on the vehicle roof are becoming quite common. However they’re largely there because people deliberately trying to do RVing without any hookups are trying to find anything they can to lengthen their “tether.” The typical setup will have a battery bank of deep cycle style RV batteries, these batteries will often be setup so they can be charged by either the solar panel (generally the preference if conditions are right) or the vehicle’s engine. An inverter is used to power common electronics from the batteries. This setup is often quite sufficient for things like laptops, lighting, TV, and some other light appliances.
Cooking and heating are often done by propane and sometimes wood stoves (there are boondocking wood stoves some people install where they vent it through a cut-out in the roof of the van), as it would be difficulty to heat a vehicle in cold weather or cook from the amount of electricity you can get from van rooftop solar. If an air conditioner is needed it’s almost always going to be powered by a dedicated generator as there aren’t a lot of great options otherwise.
It may seem like solar isn’t doing much, but if you’re boondocking in weather where you don’t really need cooling or heating, and you’re cooking on a propane or charcoal grill outside the vehicle, the solar panels and batteries can keep a lot of your creature comforts like TV / internet / laptop going indefinitely.