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Solar panels on the top of a vehicle

  1. Sep 11, 2014 #1
    I have project in which I have to come up with the ideas of improving the efficiency of a car (electric). For now I'm considering a hybrid electric car that has more than one power sources to run a vehicle. I came up with an idea that building solar panels on the roof of a vehicle can be one of the efficient ways. Solar panel will actually absorb the sun rays during the daylight and their maybe a motor inside a car that converts thermal to mechanical energy and thus becomes a source of power to run a car.

    That's what I thought of but I want to confirm if that idea is applicable in real life or as far as engineering principles are concerned.

    Look forward to receiving responses
    Regards
     
  2. jcsd
  3. Sep 12, 2014 #2

    billy_joule

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    Possible, yes. vehicles can be solely powered by solar panels on their roofs:

    http://en.wikipedia.org/wiki/Solar_car_racing

    But they are not practical vehicles for day to day use..No stereo, or AC, or passengers and most importantly; no movement on cloudy days.

    As for putting them on practical vehicles (eg a family saloon), you are better off putting them on the roof of your garage, in full sun all day, correctly oriented. Many cars spend most of their time in shade (in parking buildings while the driver is at work or in the garage when they're at home) so putting panels on the car is a waste. It is done, but it's a gimmick. Even if the car is parked in the sun, the panels aren't oriented for max efficiency,

    I would guess the overall energy cost of lugging the extra weight of panels and associated components would give a net loss in energy in many cases.
     
  4. Sep 12, 2014 #3

    NascentOxygen

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    I believe huzzi.123 has solar thermal in mind.

    Thermal energy is probably nowhere as easy to store, currently, compared with that from photovoltaic cells. Given that you already have rechargeable batteries fitted, it would seem that PV cells should be the obvious choice.

    Would there be any attraction in using the thermal energy immediately it is collected to power some sort of small heat engine which drives a generator to help charge the batteries?
     
  5. Sep 12, 2014 #4
    Yeah that can be one challenge. However since I'm considering a hybrid car I can think of more alternative ways than only taking solar energy into consideration. Like when the weather is too cloudy or there's no sun outside the car can run on either through charged batteries or by combustion engine but again combustion engine would emit several gases which will eventually contaminate the environment.

    What say?
     
  6. Sep 12, 2014 #5

    Okay so you're saying that thermal energy obtained from sun rays can be used to drive a generator which charges the electric batteries? Or in other words, converting thermal to electrical energy?
     
  7. Sep 12, 2014 #6

    NascentOxygen

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    In principle, yes. In practice, I think you'll be struggling. Experimental solar stations are being designed to generate steam for powering a steam engine. When all you'll have on the top of your car is hot water, doing much with it will be difficult―and inefficient. You could consider the Seebeck effect, at least there are no moving parts in the thermocouple.
     
  8. Sep 12, 2014 #7
    I haven't really studied much about solar energy and it leads me to wonder as to why the solar panel will generate steam? I think of it as solar panel on the top of the car absorbing heat rays and then those heat rays are used to run a generator (inside a car) that charges up the batteries and in turn the energy is supplied and the vehicle starts running..
     
  9. Sep 12, 2014 #8

    NascentOxygen

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    If you need to demonstrate experimental flair you could try one of these Peltier plates. They are reversible, in that if you heat one side (while keeping the other cool) it will generate electricity. http://www.dx.com/s/thermoelectric

    Not highly efficient, but efficiency can always be improved later. :wink:

    Probably go for the cheapest, it has good reviews. Note its specifications; respect its limitations. Treat it with care.
     
    Last edited: Sep 12, 2014
  10. Sep 12, 2014 #9

    billy_joule

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    Steam is being mentioned because it is the most common working fluid in a heat engine (a device which transforms heat into work, which in your case would spin the generator)

    A solar powered heat engine on the roof of a car is not sensible at all. There are much better ways eg: PV cells.

    http://en.wikipedia.org/wiki/Solar_cell

    If you want a solar powered heat engine this is generally the path taken:

    http://en.wikipedia.org/wiki/Concentrated_solar_power


    How ever you propose to do it, if you consider energy flows you'll soon see it's generally a waste of resources.

    Solar energy is about 1 kW/m^2.

    http://en.wikipedia.org/wiki/Sunlight#Summary


    Lets say the roof of your car is 2 m x 3 m = 6 m^2

    High tech solar panels are around 30% efficient, so;

    Power = power/area * area * efficiency
    W = 1 kW/m^2 * 6 m^2 * 30% = 1.8 kW

    This is the upper limit, once other conversion/storage losses are considered you'd be lucky to get 1kW

    A modern car may have a 100kW engine (and around 30% efficient so 300 kW petrol consumption, it's better for EV cars around 90%).

    So in the whole scheme of things generating .3 - 1% of total power at noon in summer is pitiful.
    Over the life time of the car the extra weight and resource cost of the panels and associated parts will probably result in a net loss of energy.

    Mostly it comes down to this:
    A car is not a wise place to put solar panels because:

    Put them where they work best, have two batteries, one charging at home while you are at work.
     
  11. Sep 12, 2014 #10

    NascentOxygen

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    Many cars spend 5 days a week parked in full sun on the street, too, including parking stations near a bus or railway route. It's an opportunity to recharge the batteries, if solar cells were cheap and integrated into the vehicle. Many city dwellers take their car only short distances, and few rental apartments have a suitable location for a PV array.

    It's a case of horses for courses.
     
  12. Sep 15, 2014 #11
    isn't 30% pretty lenient on the energy efficiency of your solar panel? I think those are the high dollar ones that they would use on a satellite or something, and even those have less than 30% I think.

    Most solar panels are in the 15-17% for silicon based, and at most 11% for the cheap organic ones (don't quote me, my knowledge on this is fuzzy).

    I used to be interested in solar panels, but those won't take off unless the efficiency increases dramatically (doubt it will), costs falls dramatically (at a cost to efficiency), or somebody builds a super battery with high energy density so that we can actually store the power and use them at night when it's actually needed.

    but I digress. I don't think it would be a bad idea. But practically, I don't know. like already mentioned, You'll have to think about the actual energy generated, cost of implementation, maintenance, all that good stuff.
     
  13. Sep 15, 2014 #12
    btw.

    I'm not very familiar with solar thermal energy, but I highly doubt you would be able to efficiently run a steam/condensate system through your car...
     
  14. Sep 15, 2014 #13

    CWatters

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    Interesting thread but I'm curious as to how any of this improves the "efficiency" of an electric car? What does the OP mean by that term?
     
  15. Sep 15, 2014 #14
    it increases your output without increasing the input (assuming cost of operation is zero). It counts in my opinion.
     
  16. Sep 15, 2014 #15
    Does the aerodynamics of the car also affect the performance of a solar-powered car?
     
  17. Sep 15, 2014 #16
    And what principles are being used to illustrate the processes happening inside? Like the conversion of thermal to electrical energy and all?
     
  18. Sep 15, 2014 #17

    russ_watters

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    The aerodynamics of any car affects its performance. To put a finer point on it, at cruising speed, aerodynamic drag is the primary force the engine has to counter.
    I'm not following: inside what?
     
  19. Sep 16, 2014 #18

    CWatters

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    Lets say you drive your car for 10% of the day. That implies most (90%) of the electricity from the PV array is generated while the car is stationary and has to be stored in the battery (or extra batteries if you want increased output).

    Taking the PV out of the car and putting it on the roof of your house/office instead saves all the weight of the PV array (and the increased drag due to rolling resistance) for only a 10% reduction in energy/output. So not clear that putting them in the car increases overall efficiency.

    Edit: Looking back I see billy_joule has explained the issue better.
     
  20. Sep 16, 2014 #19

    Sorry I didn't quite get your point. Putting the PV array on the roof of the house/office saves the weight of pV array for a 10% reduction in energy?
     
  21. Sep 16, 2014 #20
    or you mean putting the PV arrays on the roof of your house to charge them fully and then put them back onto the roof of the car?
     
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