Tesla To Make Car Roofs Useful?



Criswell predicts TeslaMondoTo date, no automaker has figured out how to utilize a car’s roof for anything besides holding cargo, intermittently letting in light, and temporarily holding your coffee until you make your first turn. Any solar effort “up there” has amounted to gimmickry. The limited surface area and the sheer porkiness of solar equipment negate any meaningful utility — so far, at least.

Criswell thinks that Tesla is going to solve this puzzle, and soon. Tesla and glass are becoming a thing, ‘case you haven’t noticed. Witness the household solar roof products, and the newish in-house glass division, and the big-sky Model X windshield/moonroof, and the new Model S glass roof option.

It won’t be long before Tesla’s automotive roofs perform meaningful functions. At first, they might generate enough energy to nix vampire draw. With time, they’ll extend range a bit, and so on until they become a vital part of the vehicle’s powertrain. Yes, vehicles are lagging behind buildings in solar harnessing, but all indicators point to Tesla closing that gap very soon. Technology, some of it pioneered by Tesla, will make smaller and smaller surfaces usefully photovoltaic. If solar-plus-battery go together like peanut butter and jelly in buildings, the same combo will soon work in vehicles. So says Criswell.

Recently Karma announced that the Revero's solar roof can now also charge the car's HV battery as well as the 12V

Recently Karma announced that the Revero’s solar roof can now also charge the car’s HV battery as well as the 12V

Not to be outdone, Toyota is making a solar roof optional on the upcoming Prius Prime in some markets

Not to be outdone, Toyota is making a solar roof optional on the upcoming Prius Prime in some markets

*Editor’s Note: This and other Tesla-related posts appear on TeslaMondo. Check it out here.

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51 Comments on "Tesla To Make Car Roofs Useful?"

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Sorry but the solar roof on my 2010 Prius worked GREAT at keeping the cars’ interior cooler during our Texas summers and was not a gimmick. Cooler interior temps keep the battery cooler too which aids in both power and longevity.

Sure, a small solar panel provides sufficient energy to run a small ventilation fan, which is all you need to keep heat from building up too much inside a car on a hot sunny day.

But the roof of a car is too small to gather enough energy to provide anything more than auxiliary power to a street-legal, highway-capable BEV passenger vehicle.

I agree with you, but A LOT of Prius owners that Ive talked to loved their solar roof and I think Tesla owners will like it too, especially when the glass roof is much larger on the MS.

What About The Hood & Drunk Lid ..shouldn’t they Also Be Photovoltaic as well?

Why can’t the internal tyres & suspension also generate electricity.

Springs/suspension = generate electricity through vibrations on the road.

Tyres = when driven are compressed against the road surface should also generate electricity.

Just my 2 cents.

Sir would like Fast Charge Optional w/the Regen-Suspension?

Why yes actually I would 🙂

The energy u can harvest from springs is so tiny, that it’s not worth the effort. This is a marketing gag, but it will probably make it in series.


There are other advantage offered by this technology: It allowing active suspension which means better comfort.

The cost benefit is not a compelling factor when you spend $ 1500.+ for a hand full of extra miles every day. Plus your vehicles hood, etc… paint gets a good UV workout while parked in the sun. This could change, if panels on the roof glass can have decent efficiency. Tesla might be the one to make this less of a EV gimmick.

Why would you assume it costs $1500? That is MUCH more a few solar PV cells cost. And I don’t think the charging electronics would be very expensive either.

Jipiieeyaheee juchee !!!

Oh sunny ooh sunny day!

It is unclear how Tesla would solve the problem of car roofs being at poor angles to capture solar energy.

The efficiency of roof-mounted solar is affected greatly by the positioning of the panels. The solar power generation of an automobile with solar panels on its (fixed) roof is greatly compromised by this factor.

There’s no evidence that car-roof-mounted solar panels will be a cost-effective solution any time soon.

There isn’t any magic formula here. The physics and the practical aspects are unfavorable to solar panels on the roof of a car, and that’s not going to change. Anything beyond a small panel to provide a small amount of auxiliary power is a foolish waste of money.

Nobody in his right mind is going to choose to park an expensive car in the sun, instead of in the shade, just to provide a bit more solar power to the car.

I don’t know about anybody else here but I actively look for shade or garage parking when around and about in my MS. It seems a solar roof is more of a gimmick than anything else.

A flat mounted panel looses about 5%

Show me your math and your assumptions. Because I suspect you didn’t even try to calculate it.

Clearly when the sun is low in the sky, as is the case most of the time far from the equator and half the time even on the equator, a horizontal orientation means a loss.

The intensity factor is the square of the sine of the angle. So at 45 degrees it’s already down to 0.49, with a loss of 51%.

And the sun barely goes any higher than that in northern US or Europe.

For a loss of only five percent sure to the panel not directly facing the sun, the sun must be at least 77 degrees over the horizon (the panel plane), which only ever happens around noon at less than 23 degrees latitude north or south of the equator.

With the astonishing decline in panel prices and the slight increase in efficiency we can still expect to see, I’m not prepared to say panel roofs are a bad idea. Over the life of the car they may be self financing or better. But to speak of them as driveling components is and will remain idiocy of a high order.

Some is better than none, and don’t let the perfect be the enemy of the good.

“At first, they might generate enough energy to nix vampire draw. With time, they’ll extend range a bit, and so on until they become a vital part of the vehicle’s powertrain.”

Never will solar become a vital part of the powertrain.

Under typical conditions, the sun provides 1000w/m^2 about an hour after sunrise to an hour before sunset. Now given that the roof of a car mostly flat, not perpendicular to the sun, its effective irradiance is 40% lower based on my years of experience managing a solar power plant with a mix of tilt and single-axis tracking panels. The best single-junction solar cells are 25% efficient. Multi-junction that they use on satellites are around 42%. Even if you assume a 3m^2 area, it’ll generate around 450-500W.

Thats enough to run the fan and heater/compressor on low.

In addition they increase the weight of the car.

I suppose you could also put it another way:

If solar panel technology advanced to the point where car-roof-mounted solar was powerful enough to generate significant energy, building-roof-mounted solar would be so overwhelmingly powerful that power plants would become nearly obsolete.

The limitation isn’t the technology; the limitation is the energy available per square foot/meter from solar power. Even if you capture 100% of that, it’s just not enough to do much.

The only way around that limitation would be to put some sort of fold-out panels on the roof, which would make it too fragile to survive a strong wind, and would also be impractical in a parking lot where unfolding panels would put them above other vehicles.

There’s a whole science and mathematics dedicated to folding and unfolding (especially solar panels for satellites and spacecrafts; see Miura map fold). Maybe the engineers at SpaceX and Tesla have been collaborating on some sort of lightweight, durable and auto-opening and closing canopy?!

I agree. I would spend the money on a bigger battery instead. Solar power makes sense with large surface, which a car roof doesn’t have.

Deployable solar sail would still be interesting for further research.

Of course they will.

I read it would take only half of roofs covered with solar to power the entire world.

Or it would take 0.6% of the land.


Maybe you shouldn’t believe everything you read, and read stuff that shows you how to do the calculation rather than just the conclusions of someone out to make a headline but less keen to explain their assumptions.

Read Sustainable Energy Without the Hot Air. It shows both how to do the calculation and then uses that to show why rooftop solar is a contribution but nowhere near enough.

So based on your math, a 10 hour sunny day can add about 20 miles of range. For some, that will cover their daily commute.

“Criswell predicts”?

Does anyone under 60 actually get that reference?

Criswell was known — to the limited extent that he was — for making predictions which were not merely wrong, they were ludicrous. Is TeslaMondo perhaps subtly suggesting that any predictions for Tesla putting solar cells on the roof of there cars are just as ridiculous?

Well, Elon did not long ago state rather firmly that solar cells belong on the roof of your house, not your car. On the other hand, as the article notes, there would be some utility in providing enough solar power to eliminate vampire drain for Tesla cars parked outdoors long-term.

Beyond that, I agree with Elon: It would be a waste of money. The roof of a car simply doesn’t have enough surface area to gather enough solar energy to add many miles of range per day.

I really don’t get that argument that something can be waste of money… Maybe leather seats ok. Or fwd…

But a solar solar roof? (I call it solar solar because it will be a solar roof with solar cells…)

A semi transparent solar^2 roof with maybe even automatic dimming will be a money milking cowbell gimmick for TSLA. It will be fancy! To my best knowledge Tesla products are not about η at this point of development. They are about money. One more expensive option means more money to get the EV train rolling. So it would be a waste of money to not offer it… If people want to pay an unpredictable amount of money for an unpredictable amount of miles just let them do so. Those people who paid will most likely not complain later on that they made the wrong decision so there is low risk of negative perception… Fwd on the other hand…

All this speculation originates from a couple of cryptic Tweets by Musk recently that hint here has something innovative in the works on this front.

Actual solar charged, battery electric cars are possible, but a revolution is required in people’s thinking about what they “need” in a car.


Sure. If you’re willing to settle for a three-wheeled bicycle with a “cabin” barely big enough for one small skinny person to crawl into, with no cargo capacity, and no “luxury” touches such as a windshield wiper — never mind an air conditioner! — then you can have a car which runs on solar power… so long as the sun is shining directly on it!

Very few people mean that sort of vehicle when they say “car”.

I guess you didn’t look at the link. This cruiser class has four wheels, seats four, and runs off battery power for 400 miles at night. But hey, don’t let the facts get in the way.

You are not alone in your view. Believers in the rational choice theory of economics make this argument.


Some don’t think the world is that simple, or rational.


The guys passing me every day, rolling coal in the monster trucks they are deeply in debt for, tend to support the second view of economics.

When they start building a campervan / RV…

Eliminating vampire drain is useful. Not sure it’s worth the cost, especially since the drain is eliminated only when you park outside. Not so useful for airport parking garages.

My hope is that it’s enough for aggressive A/C on sunny days.

Agressive ac… Nope.

It would be better to offset vampire drain and maybe add to the battery. Ac has high power draw. No way it can keep the car cool. Better use simple ventilation to keep the temp close to ambient temperature.

Who is this Criswell joker?

The author/creator of TeslaMondo’s alter ego/nom de plume/”avatar”.

Well, it’s good that TeslaMondo has a self-deprecatory sense of humor.

I think Criswell is best known for his narration of Ed Wood movies. In particular, he is seen onscreen introducing “Plan 9 from Outer Space”.

Pretty sure Fisker Karma had/has a solar roof. Not sure why this is painted as such a revolution in thinking. Oh, yeah, Tesla.

Mazda had Solar on their 626 20 years ago to cool the inside of the car while parked. So correct you are, nothing new here. Just something that being reclaimed because it has a purpose now more than ever.

Did they have a scene later about the carburetor that gets a car up to 250 mpg, but GM bought the patents and hid them? I think I have heard about that one at least a hundred times over the years.

I’m still waiting for electrochromic windows on cars. Clear when you want it, opaque when not.

Reject all solar heat while parked and you don’t even need cooling when you return.
With slight solar generation, the power required to change/sustain the electrochromic process could be self-generated by the glass.

Forget Solar, what they should be doing is putting wind turbines up there to recharge the battery! 😉

Solar roof reminds me of Solar Freaking Roadways. Both will suffer the same efficiency drawback, tiny amount of energy, cost, etc.

If you assume average of 200 watts (using 600 W peak) and 8 hours of daylight, that’s 1.6 kWh per sunny day. Inverter to boost voltage might be 90% efficient, battery 90%, usable would be 1.3 kWh per day. Add in cloudy days, shade parking, poor angle, and it could average far less, maybe even 0.5 kWh per day average, and I’m being generous with even that figure.

Cost isn’t clear, but going by 5 years ownership period and 0.55 kWh per day as a guess, that’s about 1 MWh entire duration period. SDGE cost $0.2/kWh, so solar roof would have to cost less than $200 to be cost effective. If your electric bill is $0.1/kWh, it would have to cost less than $100. That isn’t likely.

If you want cooler car, just use battery power. It’d be far more effective and cheaper. It’s not like gas car where you’re running the noisy engine making poison gas.

I am ALL FOR THIS. And I fully realize that it will not appreciably collect much electricity and thus will not help your range.

Why is it good? To reduce the vampire drain and to prevent your battery from being “bricked” if you park it somewhere outdoors for a few months. If it provides enough energy to power all the stuff that still operate when the car is not being used (like security systems, communication systems, etc.) then it will be very useful.

This is all a distraction for what the real motivation is for Tesla going glass in the roof – to squeeze out another inch or so of headroom inside. Battery underfloor combined with stylishly low roofline run counter to each other in terms of interior headroom.

I find my car’s roof to be very useful even without solar cells on it. Especially when it’s raining or cold outside…