Solar roof

Solar roof


Is it possible to have an integrated solar panel on the roof that charges the battery while in the sun?


Brian H | 24 dicembre 2012

Mentioned often. Ridiculously expensive compared to added storage, trivial charge rates, etc. Invest in rooftop solar on your home or garage if you must have solar!

teddyg | 25 dicembre 2012

Granted it is not worth it at the moment but EVENTUALLY I imagine EV's will be coated in Solar paint which is under development currently. Considering most cars spend 90+% of their lives parked it is conceivable that the EV's of the future may not need to be plugged in at all!

Brian H | 25 dicembre 2012

Parked outside? Garages will be obsolete then, I guess. Street parking will be a horror show!

Pungoteague_Dave | 25 dicembre 2012

I have solar panels on our sailboat, and it stays outside all the time, so can it maintain the batteries on a static basis. However, there is no way the panels could actually run anything on the boat on a real time basis, even something as limited as the radio or navigation lights. I also have a 27kw system (84 panels) on my barn that can power about 200% of our home's electical requirements. However, even the most efficient solar panels that would fit on a car surface could not provide enough power for more than a few minutes per day of running these cars. Also, these vehicles will spend 90% of the time garaged and out of the sun. The answer is charging EV's is to add solar panels to a building roof or some other wide open space.

teddyg | 27 dicembre 2012

Well of course that is the only solution right now Dave...that's why I said EVENTUALLY...but one day solar technology will advance so that every building, EV, and home will be painted with solar cells...maybe the garages of the future will have transparent cielings?..still if you have a garage you probably have a driveway to park in as well, and chances are you park your car outside if you park at work/shopping malls/ etc. Building design will adapt over time to accomodate as well, the world is not static. Solar paint might just be an option for your car if you want it or not.

Obviously the cells wouldn't generate enough energy to actually power the car directly but with a 500-1000 mile range battery it would be conceiveable that the car's cells would generate enough energy (by sitting parked 95% of the time) to continuously trickle charge the car's battery so that plugging in would only be required for your long distance trips, where rapid charging times are needed to keep you on the go.

Granted I am talking about in 20-30 years time here...but definately possible longterm.

New nano solar cell developements are actually taking about being able to generate electricity using different wavelengths of light such as Infra-Red so eventually we may even generate solar electricity at night!
Not saying that all this isn't very experimental at this point but if nobody had a dream then companies like Tesla wouldn't exist. Who knows what we can achieve in time.

Brian H | 27 dicembre 2012

You're doing a lot of hand-waving there. The total solar energy falling on a car is a function of its size (not to mention latitude, etc.) There's not enough "there" there. You can't make a silk dress out of a sow's ear.

Runar | 27 dicembre 2012

Brisen h, when efficiency increase on solar panels, it may be feasible.
As an example, central Colorado receives annual 2200 kWh/m² solar energy. This is quit a few charges.

Runar | 27 dicembre 2012

Is should be possible to get at least a couple of m2 in full sun at all times, so with a near 100% efficiency in 20 years, you would get enough energy to charge the car 50x a year. Should be enough for a year driving.

Runar | 27 dicembre 2012

50x full charges i ment..

teddyg | 27 dicembre 2012

Well I guess you can pretty much say anything could be possible in a 20-30 year timespan so I admit I cheated a bit there. But solar might not only be generated eventually from the paint...the glass on the car could be generating electricity as well, from solar windows!:

The possibilities are truly endless.

Pungoteague_Dave | 27 dicembre 2012

Dream on. Even if you could harvest the total energy available from sunlight with 100% efficiency and full conversion, and even if every surface on the car had such collection capability, you could never keep the batteries charged for a real car. This isn't "anything is possible with enough time and technology gain" stuff like the old Dick Tracy wrist communication device that did become reality. That just required new technology. Solar powering car batteries with car mounted solar panels, paint, windows, etc. is against the laws of physics. There simply isn't enough energy available in that envelope to do the job.

Runar | 28 dicembre 2012

Pungoteague_Dave, how much energy is available then kWh/m2 by your numbers?

I showed above that for Colorado, you get enough sun juice from 2x m2 to fill the battery 50x a year if you get solar panels at 100% effeciency some time in the future.

On which numbers do you base your conclusion on that there isnt enough energy available?

Vawlkus | 30 dicembre 2012

The only way your gonna see a solar powered car is if you reduce the amount of power it takes to run the thing. If you can dream up a way to make a sedan sized car run off a smaller battery, THEN solar becomes an option. Until then, you're just tilting at windmills.

Pungoteague_Dave | 30 dicembre 2012

Vawlkus, you are correct. Moving two tons is more than a self-contained package can handle given the basic laws of physics that no amount of further advancement can overcome. What could happen is better and smaller energy storage technology. We may well see batteries that give 1,000 miles or more range in the same envelope from which we get around 250 miles today.

Brian H | 30 dicembre 2012

Solar-powered cars need an enabling technology. I propose anti-gravity.

Mark22 | 30 dicembre 2012

If you could get 100% efficiency, which you can't. That would be about 1kW/sq meter.
However, the angle would not be ideal for all of the surfaces at is also likely the car wouldn't be in sunlight all day (covered or garage parking).
But in a perfect world, if you had 2 sq meters of area gathering solar energy which was always available while the sun was up you would get about 20 kWh/day.

Of course, in such a world you would have to worry about the life ending drought from never having clouds, much less rain:-P

jat | 30 dicembre 2012

The amount of solar energy at the edge of the earth's atmosphere is about 1361 W/m^2. The average at the earth's surface is about 680 W/m^2 (more on noon at the equator, less at dawn/dusk or further from the equator; peaks to about 1kW/m^2 at noon).

To get maximum efficiency, you have to have the PV cells perpendicular to the incoming light, but you won't be able to do that on a car. Due to the losses from reflection at the front surface and photon energies not being in the range capturable by an electron transition, you get a maximum theoretical efficiency of about 35%. Today's cells get around 15% efficiency, but less assume for the sake of argument you can get to the theoretical maximum efficiency of 35%. That gives an average energy available of about 238W/m^2, assuming you have perfect angle to the sun, no cloud (or tree or other obstruction) blocking it. Let's ignore those and assume the entire planar projection of the Model S can be covered in PV cells (we don't have transparent PV now but maybe we can while we get the theoretical maximum efficiency). That gives us roughly 9.7 m^2, so we can get on average 2.3kW of electricity, so it would take roughly 37 hours to fully charge the 85kWh battery.

Given all that and the deviations from maximum we ignored, it simply isn't practical. Also add to the fact that many cars spend most of their parked time in covered garages, it makes it simply not worth the effort and cost.

For more details about the technical issues about PV cells, see

teddyg | 30 dicembre 2012

Geez guys given that we are talking about 20-30 years time lets allow for a bit of imagination here.
Ok so we thought that by then we might have EV's with a 1000 mile range lets say a 300 kWh battery pack.
Mark22 above thought it might be possible to generate 20 kWh per day given the surface area of paint and windows on a car given advancements in solar lets half that and say 10 kWh/day might be possible.
Assuming the car comes fully charged from the factory and average daily driving statistics stay the same at roughly 40-50 miles per day. You would only on average be using 15 kWh of your total 300 kWh pack each day...but if your car sits outside where you work or live then you could generate 10 kWh back for a TOTAL drain of just 5 kWh per day.
If you did this everyday it would take you 2 months to run the battery to 0% charge. But remember there are days you may not drive at all so could get a 10 kWh gain on those days.

I am not saying that EV's will ever be built without a plug to charge, I am just saying that those plugs could be used much less with solar paint/glass. In fact you would probably only have to plug-in once every two months to top up and besides that only supercharging when going on long distance trips where you are using up a significant amount of range in such a short amount of time that the solar cells could not keep up. But we all know here just how rare long distance car travel is on average.

As I said the solar paint/glass might just be an option for those who park off street, in driveways, or have outside parking at work. Obviously if you keep your car undercover most of the time then you wouldn't choose solar as an option. But that doesn't mean that it couldn't work well for a lot of people...especially those who park off street without their own designated spot for conventional charging.

Pungoteague_Dave | 31 dicembre 2012

This forum is fun but are we seriously going to waste time theorizing about expanding the laws of physics and making photovoltaics that are transparent enough to be windshields (ridiculous and virtually impossible given the way sun energy is collected)? There's a better theoretical chance that we will be driving levitating vehicles in three dimensions than having a car with significant photovoltaic self-replenishment. I say that as an owner of hundreds of PV panels on two homes and a sailboat. Ain't gonna happen. Let return to reality....

olanmills | 31 dicembre 2012

Obviously, if the glass is transparent, then visile light has to pass through it from the outside in, but that doesn't mean other energy has to pass through the glass. You could also create glass that has some kind of PV film that is transparent until you flip a switch upon leaving the car, which turns the film opaque and enables energy collection. Also, you don't necessarily need glass. The car could be windowless with viewscreens inside.

With that said, that sounds really stupid. As mentioned, there is a fixed ideal amount of energy from the sun hitting a surface per square meter, and that changes depending on the angle of the sun, the position of the car on the earth, local obstructions, time of day and day of the year. You will almost never get ideal conditions.

Further more, even if the car was 100% efficient at collecting energy and driving the wheels, there is a fixed amount of energy necessary to move a certain mass a certain distance. The only way to make the car more "efficient" after it's ideal 100% efficient drive train would be to make it lighter, which of course is always possible, but obviously can't be anywhere near zero mass.

You could increase the car's surface area with some kind of deployable umbrella, but then you'd need a parking lot to yourself.

It's much more feasible to work on better battery capacities and faster charging systems. If solar power is the answer, then you could make a power plant with lots of solar panels out in the desert or on a mountain or in space, or whatever, and we could all plug into it, but we can't carry it around on top of our cars.

Runar | 31 dicembre 2012

The fact is though, that it would be very nice to get 3-4kWh a day... Or even less. So i do think solar panels might be a future with higher efficiency. Not to avoid the plug, but as an extra source of power.

ltd | 31 dicembre 2012

"The fact is though, that it would be very nice to get 3-4kWh a day..."

No chance. You have maybe 2 m2 on the roof of the car. That maybe gives you room for 300W of panels however as others have pointed out, orientation of the panels is not ideal so would probably behave more like a 200W panel if not 150W panel.

Even if you parked in the sun on a cloudless day you'd get maybe 750Wh out of that.
About enough to drive you 2 miles. For 5+ hours.

Park in the shade UNDER solar panels. Far far far better use of resources.

teddyg | 31 dicembre 2012

Wow I wonder if you could have predicted the state of today's technology back in 1985? We didn't even have internet or cell phones then! Back then solar panels were huge heavy things averaging 5% efficiency and costing well over $10 watt...look where we are now!

Point is that we may be producing thin film solar panels/paint/glass so cheaply by then that it might not actually cost that much to just do it even if the gains are only a few kWh per day...might as well take it if you can.
You guys also forgot the developments going on with infrared solar technology that may be able to even generate power at night!
Who knows how far we can go with new materials and discoveries.

NO CHANCE seems a rather odd comment on a forum of a car company who the "experts" gave NO CHANCE of succeeding.

Pungoteague_Dave | 31 dicembre 2012


The physics potential for what we have today and think we might get in the future (1,000 mile+ range) existed in 1985 and were foreseeable. What you are suggesting is beyond physical energy potential and even if possible, would be wasteful not to mention Inadvisable. These cars should be stored inside, with PVC panels restricted to the building roof. Same for any high-value vehicle.

Pungoteague_Dave | 31 dicembre 2012

Sorry, PV

Brian H | 1 gennaio 2013

Of course, if you supplemented it with zero-point energy from the Void ... <;p

ltd | 1 gennaio 2013


Yes it may be possible in future and worthwhile.

But with technology where it currently is, there is little point to suggesting it. Any 'car' that does today today is simply 'greenwashing' the clueless who don't know any better.

The OP was asking if it was possible. Yes, its possible today. Just fundamentally flawed as an idea at this stage.

Brian H | 2 gennaio 2013

At any stage. To get enough energy delivered, you'd have to track the car from above with a large transparent blimp that acted like a magnifying glass. Which would have the effect of roasting the occupants in short order. A rather extreme Unintended Consequence.

ltd | 2 gennaio 2013

Right, there is no magical way to increase the W/m^2 solar irradiation and the limited surface area on the car means its always going to be a non-starter.

Even if PV solar jumped from its ~12-15% efficiency today to 100% -- or even with solar magnification (mirrors, blimp, whatever), reality is that its not going to achieve much except cost & weight (panels, glass, MPPT rectifier electronics)

olanmills | 2 gennaio 2013

teddy, maybe you're not understanding. It's not a matter of technology.

In a certain square meter on the ground, there is only a certain amount of energy from the sun hitting that square meter. A car's roof is not very big. Even if you captured all of the solar energy hitting the roof using the best, highest-tech solar panels that the brightest minds of the future will invent, it simply won't generate that much electricity. There just isn't much solar energy to be had in a small area.

If we want to use solar power for ecological or econmical reasons, it makes more sense to build big solar energy power plants that can collect solar energy at a large scale.

DTsea | 3 gennaio 2013

olanmills: +1!!!

Even if the whole car were covered in magic solar paint (good luck with body work) there just isnt enough energy there shining out of Mr. Sun. Cars are too small and too heavy to move by solar power.

Now... if we invent magic super light materials that could make a safe car that weighs next to nothing (don't forget still needs seats, displays, computers, brakes, AC, motor, inverter, wire harnesses, tires, wheels.......) then it would not need so much power. Even then, the body of a modern car doesnt weigh much. For example a Subaru Outback body weighs only 700 lb and it is STEEL

techmaven | 6 gennaio 2013

I know that there isn't enough solar energy to meaningfully charge the battery for additional range. However, I would be interested in a solar roof option (say, 300w nominal) for maintaining the battery, especially to cover the drain of the on-board computers and communications electronics, interior cabin climate control, and for battery temperature maintenance (cold or hot). If you leave your car at the airport for a week, it would be nice to come back to a car that hasn't lost any charge over that period of time. If you park outside at the mall, it would nice to have climate control kick in using solar on hot days, or have the heat on in the cold. Finally, in the very cold or very hot, the car must act to protect the batteries, potentially increasing the longevity of the batteries.

Brian H | 6 gennaio 2013

Assumes a)outdoor parking in b) enough sunlight. Probably irrelevant to airports. For the $5K or so a trivial panel costs on a car, you could probably boost the battery capacity by 15-20kWh. Much better use of $$.

Timo | 7 gennaio 2013

Solution to too little Solar irradiation: Move Earth closer to Sun. That has some tiny negative effects on life on Earth, but who cares, at least we could then drive cars powered only by Sun.

More seriously, we can get a lot more solar energy from fixed structures, even from roads and parking lots with proper tech, then use that with wireless charger to charge cars. Something like large airport parking lot and big parts of the runway could be turned to rather large solar power plants if we ignore the costs (=assume costs of manufacturing such installments goes down to feasible numbers in future).

You don't need to use solar paint for cars if you have wireless charger infrastructure with solar power plants (or any other kind of power plants) feeding those wireless chargers.

If you go to place where you don't have any charger infrastructure you are in no worse situation than with gas cars without gas stations nearby, and if there is enough Sun in that middle-of-nowhere place you could always get some large canvas solar panel folded in your trunk like large tent in future (cheap and large, not necessarily efficient panel).

techmaven | 7 gennaio 2013

Again, the issue here for me isn't about usable range out of a solar panel roof. For me, the primary risk with Tesla's cars have to do with the battery. There are all the risks wrt Tesla being a young and unproven company as well as the design and manufacturing of a new product. If Tesla was making ICE cars, that would all be there too. But the big additional risk is the very real potential for some sort of significant damage to a part of the car that costs as much or more than a full ICE replacement. The replacement costs given by Tesla Motors are after 8 years and are presumably very much subsidized. I also buy cars to keep for a very long time. So for me, the solar panel roof is about extending the potential lifespan of the battery by providing maintenance charge, reducing the effect of on-board electronics that are running when the car isn't, and maintaining the battery's temperature. The significant risk is parking the car for extended periods of time where an outlet isn't available. There should be enough solar energy falling on the roof for 200-300 watt nominal rating with actual energy produced is 70% of that for 5 hours a day. The cost of the panels should be $400-600, the additional charger and wiring is probably $500, the glass roof is already $1500, so $3500-4000 seems about right. Putting that towards the main batteries increases the weight of the car significantly.

Brian H | 7 gennaio 2013

Off the rails 3X! You're persistent, anyway.
1)subsidized? By whom, pray tell? Elon isn't fooling when he targets 30% gross margin (by getting into economies of scale, and vertical integration to "capture" the markups that normally sit between each step).
2)Extending the lifespan with trivial hard-to-integrate DC current from a tiny solar array? Dream on. The cost is $000s btw, not $00s, in the real world. All in, you'd be lucky to get much under $20/W capacity installed.
3)Significant risk? Taken only by choice, and normally in places where the sun don't shine much. Neither the problem nor the solution make sense.

Timo | 7 gennaio 2013

Batteries are not subsidized, solar panels might be.

Cost of the solar panel depends greatly of quality of the panel. Low conversion rate panels don't cost much, but obviously require larger area to get same power. For just maintenance charge you don't need much power so low cost panel (solar paint) could be enough. IMO creating maintenance charge to prevent total battery depletion while parked is the only reasonable way to use solar panel in a car.

As option to places where Sun shines and to people that park outside. Not for everyone for sure.

FLsportscarenth... | 7 gennaio 2013

The solar panel (or in the future solar paint-like surface laminate) may not be a major charging source but would be a nice auxiliary and anti-bricking device - well worth it option if it saves a $24,000 battery pack - not a simple greenwash. Worth developing as an package and some early adopters will pay for it...

teddyg | 8 gennaio 2013

No OlanMills your clearly "not getting it".
Did you even read any of my posts?
I never said that the solar paint/glass would provide enough energy to power the entire car all the time so that it could be built without a plug.
I was saying that maybe in 20-30 years solar cells/glass/paint might be being made so cheaply that it might be worth it (as an option for those who park outside/off street/ or place of work has outdoor parking)
Did you read my example?
If we had 300 kWh battery packs by then and you are only using on average 15 kWh per day and the car could generate 10 kWh of solar power for the pack when parked outside then you are only USING 5 kWh per day...carry that forward and you would only have to plug in once every two months! In this respect it might be worth it, again after 20-30 years of deveopment and as an option for people to choose if it makes sense for them in terms of where they park.

It's really not that difficult a concept.

Timo | 8 gennaio 2013

@teddyg, your mistake is to estimate that you could get 10kWh / day from Solar. You can't. 1kWh is more like it. There just isn't enough energy coming from the Sun and car doesn't have enough surface to give you more, no matter how good tech you could get.

teddyg | 8 gennaio 2013

Just to add if the solar cells are cheap enough it might still make sense if you could only get a few kWh per day...might as well take it if you has been mentioned here it would be a great "anti-bricking" or maintainence charge.
Wouldn't it be great if you could park your Tesla at the airport and it maintained its state of charge when you got back in 2/3 weeks?
The point is at some point it may be very reasonable to put solar paint/glass on a car...but it really all depends on the price of the solar cells...I figure if the trend is anything to go by solar on cars in 20-30 years is certainly not science fiction. It may happen much sooner than that for the maintainence charge alone...people who travel a lot might really like coming back to a Tesla with the same range that they left it with and the comfort of knowing that it would be impossible to brick...I could see those people paying $3500 for that security as an option right now...let alone in 20-30 years.

teddyg | 8 gennaio 2013

Uggghhh Timo you are killing me...its about the price of the solar cells...who cares if you only got 1 or 2 kWh per day if the cells are cheap enough its worth it...and I think they just might be in 20-30 years...jeeez.
And I think if you look at the TOTAL surface area of the car (paint AND glass - see my link to solar window technology above) then I bet 5 kWh could be possible eventually...someone else actually said 20 kWh could theoretically be possible but let's say 25% of that by 2035...all depends on price though.

There is even research going on for infra-red solar technology...that could potentially create solar energy at NIGHT...again way way off but who knows what is possible.

Timo | 8 gennaio 2013

20kWh ignoring all the realities, like the car orientation to the Sun and the fact that you don't get Sun max energy entire day including the night. About 1kWh/day is pretty close to max you could get in very sunny spot in reality. With max realistic efficiency and with entire car covered by solar paint.

teddyg | 8 gennaio 2013

Article discussing Infra-Red Solar possibilities...again before you attack me I realize this is brand new stuff and output is very low...but you have to start somewhere and it seems that the scope for improvement is there. Remember 20-30 years guys.

teddyg | 8 gennaio 2013

And solar glass Timo not just the paint...I really love how you seem to be so sure of your technology predicitions in 20-30 years some point in the future people might be laughing at those predicitons...time will tell.

teddyg | 8 gennaio 2013

Someone also mentioned breakthroughs in strong lightweight materials and lighter batteries in the future that would mean more range for less kWh's...another thing to remember in terms of miles of range that could be generated via onboard solar cells. 1 kWh generated in 2035 might mean 6-8 miles of range compared to just 3.5 miles today.

Timo | 8 gennaio 2013

You are missing the point. There just isn't enough energy coming from the Sun. You can't get better than 100% efficient and Sun doesn't shine every direction at once so only part of the car is pointing anywhere near the Sun at any given time.

It doesn't matter how good the tech gets, you still are not getting anywhere near 10kWh / day in real world. This is not "technology prediction" it is prediction that Sun doesn't get any brighter and cars still look like cars do after 20-30 years time.

1kW/m^2 is maximum you get from Sun directly overhead facing directly at the Sun. Average is a lot less and there is no such thing as perfect conversion of energy.

Pungoteague_Dave | 9 gennaio 2013

teddyg won't or can't listen to reality. He's all balled up in concept so ignores the reality of energy potential and basic physics. Let him live in his little fantasy. Some of his comments are beyond laughable. For example, who would leave a car like this out in the sun for weeks at a time while on a trip as he suggests? I live in Virginia so don't leave cars at LAX often, but when I needed to leave my F-150 there for three weeks in 2011, it was parked in a covered, secure location.

I have one of the few Tesla ownership situations where I will drive 100% free most of the time - the 84 solar panels on my barn roof provide 27kw, double our current usage, so we have excess energy to burn in our car. But those panels take up an area that is about 30 feet by 70 feet... which is the practical issue - they are oriented correctly, within a few degrees of both vertical and horizontal perfection for solar collection - a function which would be impossible within the limitations of a car envelope. The panel designer/installer refused to install a couple panels where I would have even minimal shading for a few hours at the end of the day due to nearby trees, as even a short loss of sun gain would destroy the cost/benefit for those few panels.

The solar panels on my saliboat can maintain the house batteries when it is idle, but even they must be aimed for maximum efficiency to do anything. Large, flat panels on a building roof or in a field with permanent orientation and fixed installation relative to the sun will always be more effective than curved panels/paint/glass on a car, with all the vagaries of shade, orientation, etc.