# Solar Panels on roof of car for charging



## Eric (Sep 9, 2012)

Charging batteries with solar power is great for home use, campers, garden sheds, etc.
You need large panels, 170x99cm(250Wp) and a good day of sun to fully charge a 200aH battery.
And you wont drive far on that with a medium sized car.

So driving on solar power alone wont be a useable idea for now.


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## Siwastaja (Aug 1, 2012)

Fulgrate said:


> Has anybody tried using solar panels on the roof of their electric car?


Discussed many times; please use the search function. Some have tried. Does not work. Carrying the panels consume more energy than they produce, in most cases. Even in optimal conditions and sunny days, you could recharge at average speed of maybe 1-5 mph.

OTOH, installing them at your _house_ makes perfect sense as you don't need to waste the sunlight when the car is fully charged, you can install a large area of them, their weight and shape don't cause problems as in a car, and they can be directed to optimum direction.

The surface area of the car just isn't enough and it's almost never in optimal position.

The largest problem however is the poor efficiency of solar cells. The flexible cells could be physically usable in car surface, but their efficiency is even worse than that of solid panels.



> I was thinking maybe using two sets of batteries, one that the car uses while driving, and the other that gets charged for later use or when the other runs out. Then switch the batteries and keep driving while the other battery gets charged by solar power. I think it would be a good idea in sunny places.


Multiple battery banks are always a bad idea in every sense. You get effectively the same result with just one larger pack, but with the following benefits

- no expensive switches
- no expensive switching logic
- less cabling, fusing etc
- better efficiency
- better reliability
- higher power output when you need it

The idea of multiple battery banks surfaces every now and then from non-technical people, but believe me, it just doesn't work and doesn't make sense at all. The usual misconception is that you couldn't discharge and charge a single pack at the same time. In fact you can and it's always the best solution; in fact, the electricity kind of "skips" the battery and runs the best way directly from the source to the consumer, and only the excess is taken from / put into the battery. All of this happens automatically without any control systems due to laws of physics. What these people propose is to artificially prevent this mechanism and then do it separately, causing only extra complexity and losses.


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## Roy Von Rogers (Mar 21, 2009)

Fulgrate said:


> Has anybody tried using solar panels on the roof of their electric car?
> 
> I was thinking maybe using two sets of batteries, one that the car uses while driving, and the other that gets charged for later use or when the other runs out. Then switch the batteries and keep driving while the other battery gets charged by solar power. I think it would be a good idea in sunny places.
> 
> *My understanding on the technology is minimal, otherwise I would suggest just having the solar panel connected to the main battery so that it charges even while you drive and perhaps the batteries charge won't go down at all while driving on sunny days?*


 
So why don't you put one of those panels on your roof, and run your house with it ???


Roy


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## dougingraham (Jul 26, 2011)

Yes, discussed often. At my latitude if I cover my hood with cells and park it when I get to work with the hood raised so it is perpendicular to the sun I could charge about 4 miles per day average. Payback in this situation is over 30 years when you count the costs of everything needed. Much better to put the solar cells on your house and sell the power to the power company during the day when they need it and buy it back from them at night to charge your car when you need it.


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## TEV (Nov 25, 2011)

Happy reading 

http://www.diyelectriccar.com/forums/showthread.php/has-anyone-tried-solar-poweri-81111.html


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## Caps18 (Jun 8, 2008)

There are boats that use solar to power them... 

But, I think you would need something like 80 solar panels on a sunny day to continuously power a Chevy S10 at 60 mph.

And that doesn't take into account the 3,200 pounds that would weigh and how much power it takes to move it 1 mile.


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## Ziggythewiz (May 16, 2010)

One solar powered boat I'm aware of used about a billion dollars worth of panels and expandable wings that could be extended when out of port.


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## Caps18 (Jun 8, 2008)

http://dsehybrid.com/

https://www.youtube.com/watch?v=ESC5fE0vd7Y


There are a few other boats too that don't cost quite as much...


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## Siwastaja (Aug 1, 2012)

I'm not an absolute naysayer on this, just that the current solar cell technology is not up to the task for this purpose.

I do believe that at some point in the future, we have lightweight, flexible solar panels that are 30-40% efficient (current technology is about 8% IIRC). Even though they couldn't provide all the electricity needed in normal driving, the contribution would be significant. But the technology needs to be lightweight, shaped to the aerodynamic form of the car, and cheap enough.

As long as solar power is an expensive investment, it's best to be installed somewhere where you can _always_ utilize the power; if nothing else, by selling it out to the grid. It has to be cheap before you can just randomly coat your car with the cells so that most of the investment is wasted (not directed to the sun, or energy wasted while the battery is full)

In addition to the cost, it needs to be efficient to produce relevant power levels; otherwise, it makes no sense to increase the complexity of the car for almost nothing.

In addition to cost and efficiency, it needs to be lightweight and thin film, so that it doesn't hurt the efficiency of the car by increasing the weight or aerodynamic drag.

The technology improves all the time, but given all those requirements and the current rate of improvement, it may take 100 years until the technology is ready. So, what we should hope for is some kind of breakthrough technology. It is possible due to increased funding in research. Some of those everyday news stories of "new technology" may actually become reality even though they are mostly scams or misinformed media stories.


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## Caps18 (Jun 8, 2008)

The solar panels on my roof are 15% efficient, the inverters bring that down to 14.7% or so (97% of 15%). The direction solar panels are facing does matter too.

Physics is the next problem. Even if you have 100% efficient panels, there just isn't enough sunlight hitting the Earth to power normal cars at highway speeds, let alone down shaded roads or when there are overcast conditions. Best case is 1400 *W/m*^*2* . That isn't much power to begin with, but a 15' by 6' (5m x 2m) array would produce 14kWh in 1 hour of bright sunlight and if it was pointed at the Sun, with those 100% efficient panels.

Now, a lightweight RV where you travel only during the best times of day and have short distances to go...maybe. Same with a boat. And if you have batteries that can charge while at a location and not moving, it would work ok.

Now, what might be interesting is if someone came up with a portable trailer that had a level 2 charger hooked up to it with an array of 10 long by 2 high solar panels.











It is amazing how good those solar cars in Australia can perform when you consider it takes about a full day to generate 1 kWh with one of those panels. And takes about 6 of those panels to make a real life 1 kWh every hour during a sunny day. And you go through a 14 (+/-) kWh battery when driving a normal diy EV every hour at 65 mph...


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## PStechPaul (May 1, 2012)

A solar powered low-speed tractor, tram, or golf cart might be a possibility, since they can run on as little as 500-1000W, and might be used only 10% of the time. So if you can count on half the maximum possible, you might have 700W/m^2 and at 15% efficiency and 15% duty cycle a 3 ft x 3 ft panel might work. But the laws of physics show that even a small EV needs about 5 kW for highway speeds, and a full size car is 10-15 kW, and more on a hill. And the higher the speed, the more difficult it is to deal with the aerodynamics of a solar panel, especially one that is aligned for optimum insolation.


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## Ziggythewiz (May 16, 2010)

Caps18 said:


> It is amazing how good those solar cars in Australia can perform when you consider it takes about a full day to generate 1 kWh with one of those panels. And takes about 6 of those panels to make a real life 1 kWh every hour during a sunny day. And you go through a 14 (+/-) kWh battery when driving a normal diy EV every hour at 65 mph...


If all cars would drive themselves we could have commuter vehicles that consist of bike tires and solar panels.


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## Red Neck (Feb 1, 2013)

You can use a panel to charge a 12v battery and unload the lights, vents, etc. from the main pack. It actually makes a difference. And you should of course also go LED for at least daylights, license plate and cabin lights, etc..

But to actually power a car, no way..


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## Karter2 (Nov 17, 2011)

Red Neck said:


> But to actually power a car, no way..


 Well the solar Racers seem to do it.. 100km/hr average all day too !
http://www.worldsolarchallenge.org/about_wsc_2013/overview


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## Ampster (Oct 6, 2012)

Karter2 said:


> Well the solar Racers seem to do it.. 100km/hr average all day too !


They sure do, but at the end of the day what do you think they do? I mean that literally and figuratively. I don't see any of them going to the grocery store or sitting in stop and go traffic like I can do with my Lithiums. I can't imagine one of them trying to park. Oh, thats right they don't have reverse, but they are really great for cruising in the middle of nowhere on a cloudless day.


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## Karter2 (Nov 17, 2011)

Sure, and it wont win NASCAR races or haul 40 ton freight trucks either...
But the point was ..
.


> But to actually power a car, no way..


 Well,.. there obviously is a way..the technology exists..
It just needs to be developed and applied to a suitable vehicle.


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## Ampster (Oct 6, 2012)

Karter2 said:


> ....the technology exists..
> It just needs to be developed and applied to a suitable vehicle.


While we are waiting, lots of money is being invested to try and develope that technology and figure out what a "suitable" vehicle is.
It is not ready yet so I am happy to settle for PV panels on my roof and a couple of battery powered cars.


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## dougingraham (Jul 26, 2011)

Karter2 said:


> Well,.. there obviously is a way..the technology exists..
> It just needs to be developed and applied to a suitable vehicle.


The only suitable vehicle is the sun racers and the only use is in those races.

To drive my conversion at 65mph (which many people tell me is not a practical car because you cant carry anything in it) would require the equivalent of about 8 sheets of plywood (4' x 8') worth of solar cells all facing the sun. At my latitude it could do this about 3 hours per day on the average. Less in the winter, and more in the summer. But never at night. Never in the rain. Actually never because my car could not tow the trailer it would take to carry 8 sheets of plywood worth of solar panels. And this is a pretty small car. For a more "practical" vehicle it only gets worse.

If we had 100% efficient solar cells it still would not be practical. There just is not enough energy in the sunlight to charge the batteries up to what an average driver needs for a daily commute with the surface area of a car. Increasing the surface area of the car just makes things worse because it would kill the efficiency of the car by adding drag.


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