Solar roof

edited November -1 in General

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



  • edited November -1
    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!
  • edited November -1
    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!
  • edited November -1
    Parked outside? Garages will be obsolete then, I guess. Street parking will be a horror show!
  • edited November -1
    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.
  • edited November -1
    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.
  • edited November -1
    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.
  • edited November -1
    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.
  • edited November -1
    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.
  • edited November -1
    50x full charges i ment..
  • edited November -1
    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.
  • edited November -1
    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.
  • edited November -1
    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?
  • edited November -1
    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.
  • edited November -1
    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.
  • edited November -1
    Solar-powered cars need an enabling technology. I propose anti-gravity.
  • edited November -1
    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
  • edited November -1
    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
  • edited November -1
    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.
  • edited November -1
    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....
  • edited November -1
    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.
  • edited November -1
    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.
  • ltdltd
    edited November -1
    "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.
  • edited November -1
    NO CHANCE???
    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.
  • edited November -1

    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.
  • edited November -1
    Sorry, PV
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