Cramming a panel on every bit of usable space, using the best panels my money could buy me, got us 410W (26' RV, kinda small). That'll almost run half a microwave under perfect conditions at noon on the summer solstice. It is a long enough way from running a car that I'll use the napkin to wipe burrito sauce away.
That being said, 780 miles (1300km) of free range by just parking outside is pretty cool!
1. Complement audience
2. Establish credibility
3. Set up punchline ("I needed no napkin")
4. Explain first hand experience to make point
5. Deliver punchline ("Wipe burrito sauce")
EDIT: And now that you make me think about it more, it's just dumb; or maybe an interim solution at best. Because solar panels on the roof of my house is much more scalable, efficient, and for the same power output, less expensive (no one does crash-tests on my house roof). The "interim" part comes from admitting that residential roof solar is quite uncommon, but hopefully not forever.
Let me edit some more with an extreme example: my electric scooter that I ride work every day. I could squeeze some panel on there somewhere, and add a teensy bit of extra mileage. But I won't, because remember that RV solar I talked about? Most of the time it's just sitting there doing nothing, so I ran an extension cord from the inverter to the scooter and electric bicycles. Now our Personal Electric Vehicles are solar-powered, and all I did was run an extension cord. (Tiny though it might be, the RV solar can easily handle a scooter and some bikes.)
But none of these are really going to move the car much more than pushing it.
Reality is that most of the time the car isn't doing anything. So if solar can give your car a few extra miles everyday you commute, it seems potentially worth it then.
So is there any more than PR value to this?
A Toyota Camry is 4.9 meters long and 1.8 meters wide. That’s almost 9m2, if they can cover ~2/3 of that with panels you’re talking around 6m2. You don’t get to tilt the panels, but you can put them on the sides which makes up for it.
Space is limited so using 30+% efficient panels is reasonable. That’s 1.8+ kw in full sun which is about 5.4 miles of range per hour. These numbers are appropriate, but when you start talking 40+ miles extra range per day that’s not worthless.
Use fewer lower efficiency panels and 20 miles per day should be cheap. This is well below that.
On space: the car may be that size but the roof is smaller. The car tends to get dirty, be in absurd orientations, etc. Plus don't you want to park in the shade if possible? Ever driven in a city?
You're suggesting multi-junction cells which cost an order of magnitude more than mass production polysilicon cells. For a vehicle where they are trying to trim the BOM by pennies (e.g. resorting to 8-bit CPUs in the ECU).
I mean, great, more power (ahem) to them, but I can't make the math work.
It's like the BIPV roof that musk keeps promising for delivery by 2016 or sooner: people have been making them for years and year and yet somehow they don't get deployed. Why? Well physics and economic factors like labor to start, as well as safety (which is the killer issue for me) and, quite significantly, aesthetics, which a lot of people seem to care about (I don't). Having the idea, and even making them, is the easiest part of getting them deployed.
as for my 2¢, regardless of the technical merits, i'm all for more solar. it's earth's ultimate energy source. let's cut out the intermediaries, particularly the unrenewable ones.
regarding economics, it may not make a lot of sense on a cost basis, but as others have noted, it may make sense from a value basis (i.e., higher profit margins).
I suspect when a ~2,500$ option lets people keep the AC running when forced to park in the sun people will seriously consider it. And at that point we are talking about significant power over time. The use case is different, but Solar conversion kits are quite popular for RV’s even if it’s not enough power to run the engine.
The difference is quite noticeable. Especially on days/mornings/etc where it's relatively cool but the sun is hot. The air circulation really does wonders.
Then again, the battery pack in the Prius (not Prime) is so small, perhaps it wasn't worth trying to connect the two.
One of the things I do to keep myself accountable for all the subscriptions in modern life is to annualize them, so it's not "just $10/month!" but "$120". But in this case, I think we want to flip it around; at 6 hours of charging you're going to get... approximately two miles per day. Three if you're inclined to round up through the pile of lossy conversions I'm pushing that number through. And that's only going to be in play when the battery is not already full, and it probably won't work while you're charging, either, because the charger will be saturating the battery's incoming charge rate.
I don't find anything particularly unbelievable about that, but it's a marketing stunt, not a good engineering idea, as evidenced by trying to present this in terms of "km per year". That's worthless, swamped in the noise of how your driving style will affect your mileage on an electric car (or any car).
But it's not just about range. Long-term parking of EVs is problematic because if a lead-acid goes kaput after sitting unattended for a year, you're only out $100. But if that's your traction pack, it totals the car. Solar charge makes long-term parking feasible, and enables telematics modems to stay awake, etc.
I didn't say it was nothing, I said it was below the noise floor, which is a much more interesting way of putting it. It's not worth putting a big solar panel on the car and pretending it's going to do anything if the effect of the solar panel is literally swamped by whether or not you had coffee this morning and its effects on whether or not you have a lead foot this morning. Since "literally" has been devalued, let me highlight that I mean it in its original sense; it doesn't take that much of a commute before that will be the case. Or any number of other things that will just swamp this signal, like whether you had to use the electric heater or AC and how much of it you needed, whether you got stuck behind a semi doing 65 for a good portion of your commute or were cruising by yourself at 80 in the left lane, whether the wind was blowing against or with you today, and so on. It's not zero, but it's lost in the noise.
"Solar charge makes long-term parking feasible, and enables telematics modems to stay awake, etc."
https://forums.tesla.com/forum/forums/how-much-battery-charg... suggests drain can vary in the 1-10 mile/day range just sitting there. This wouldn't even cover that entire range, with the optimistic assumptions on how much solar this is producing. YMMV depending on a lot of exact conditions, but it's certainly not the obvious win you'd hope where the solar can overpower normal drain by a clear order of magnitude. (I'm not loving trying to compare two amounts of energy loss in terms of "miles" here, though they're probably roughly comparable.)
It makes me wonder if they've got some other optimistic assumptions in there we weren't thinking of in terms of the car not draining very fast, or even if the number was generated simply by dividing the amount of power it generates by how much power/mile is necessary. Arguing in favor of the latter is that marketers like the bigger numbers, and especially the positive numbers rather than negatives. That post suggests it is likely to be the case that many real customers will at best notice that this solar panel slows down battery drain from just sitting there, but due to cloudy days, winter sun, etc. is not actually capable of overcoming it!
I read those as charging 30-60% of the battery with six hours of charge per day, but I see now that it's six hours a day for 3.5 kilometers per day, and that 30-60% of the battery totally can be charged. Meaning that a car left in the sun for a long period of time can never exceed 30-60% charge.
My bad. Your breakdown makes it more clear that this car is in the same range as my Prius, just marketing the result differently.
This will cut your energy usage by wildly more than anything this solar panel can do.
However, please let me re-iterate, don't do anything stupid. That term will lead you to some stupid things to save trivial amounts of energy.
If you want to save gas go into neutral and go as fast as everyone else or don't do it unless you're alone.
By the way, the best book and/or course I've read for building intuition for these kinds of questions is "Physics for Future Presidents" by Richard Muller. He used to teach it as a course at CMU and I believe the lecture series is still available to watch or listen to online. Very worthwhile.
Even if it doesn't power the motor, a van can have appliances, tools that can be powered by a .9kW setup (I think that could fit on an average van roof)
Also, they have more flat surface for batteries at the bottom too.
I imagine vans use the battery for more than propulsion, so PVs on the roof might be welcome. Charging from a generator is probably still more cost-effective, except for some niches (e.g. boon-docking). Lots of van-dwellers have PVs on their roof.
Saved me the cost of a tow and expensive repair wherever the tow truck took me to. Instead I was able to drive back to civilization proper and have the alternator rebuilt locally for $75.
So I think having solar panels for assisting the alternator on an otherwise conventional econobox could at least be useful in terms of redundancy. It would improve the MPG slightly in the daytime as well, offloading the alternator.
In a hybrid that can operate entirely off batteries, a rooftop solar system could get you out of an out of gas in the middle of nowhere bind if you've got plenty of time, food, and water on your hands.
So a six hours charge adds 3.56 km. This does not seem very useful to me if one uses the car to commute and charges every night anyway.
At 12 cents per kWh, that means if you get six hours of solar every day (365 days), you'll save about $44 per year in electricity costs.
The average person has a car for 6.6 years , so that adds up to a whopping $289 in savings (assuming constant electricity prices, anyway). I wonder how much extra the solar panel costs?
I wonder if that range number includes or excludes self-discharge rate? How about reduced AC usage on hot days? That number may be more significant than the charging capacity (didn't Toyota do a vent-only solar roof for this reason?)
Certain battery chemistries degrade more when they reach a low state of charge, so this trickle charge might end up protecting long-term range retention as the batteries age, maybe?
Friend had to have his Prius towed because they stopped driving it for a while.
/Yes, its a tax on stupid.