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PV cells for battery maintenance electrical draw

How about including some PV cells in the pano roof to cover the battery maintenance electrical draw? That would keep the pack from ever reaching low volt damage. It would also look cool to see the PV cells through the sun roof. PV cells are getting so cheap and their efficency climbing every year, not to mension I think Mr Musk might get a bulk discount . You could leave your car in long term parking for ever and that battery level would never drop. I don't know what the battery climate control draw is, but you might even have a little left over to charge the pack.
What do you think?

This question keeps popping up in these forums. Here are some threads that may be worth reading:

http://www.teslamotors.com/forum/forums/solar-roof-option
http://www.teslamotors.com/forum/forums/rear-spoilerroof-solar-panels
http://www.teslamotors.com/forum/forums/what-potential-solar-panel-model-s
http://www.teslamotors.com/forum/forums/crazy-idea
http://www.teslamotors.com/forum/forums/why-solar-panel-top-great-idea

To summarize: The opinion here in the Tesla forum is that solar panels (as can be found on the Fisker Karma) are merely for coolness and (pseudo) green image. The amount of electricity generated by a photo voltaic area as small as the roof and/or bonnet of a passenger car is so small, that a) it is not really good for anything except maybe running an additional fan while the car is sitting in the sun, and b) if you want to run an additional fan you could as well draw the power from the main battery which would not be affected much. Photo voltaic cells need to be produced, integrated into the car's electricity, and maintained -- at the current state of technology, it does not seem worth the cost and trouble.

That said, using solar merely to counter the batteries self-discharge while the car is sitting, and thus eventually further reduce the risk of "bricking" your Model S, is a novel idea. The more I think about it, the more sense it makes for me. I'd certainly hope that self-discharge within 24 hours is not more than what can be collected by a small solar array during some "average" day.

You might have 10 square feet of usable space, but it would have to be outside the pano roof, since the glass is dark. Then that kind of defeats the purpose of a pano roof because you look up and see the back side of a PV array. But lets say 10 feet at 10 watts per sq ft = 100 watts. Some of the guys here report that their total daily output is 4X the rating of the panel. Total output then of 400 watts in 24 hours, or an hourly average useful energy of 17 watts. That's 0.017 kWh.

It's enough to run a CFL, and it's not negligible, but considering the power consumption of the car, it would only be for show.

Another thought. Power from the grid here is $0.11 per kWh. On a panel that small, adapted for automotive use, payback is very long. Let's say you can get it as an $800 option on your car. At 0.4 kWh per day, you are generating $0.044 of power. For your $800 investment, your breakeven is 50 years.

(Numbers are different on larger installations like houses, which are a good investment)

cadethoerk point is valid and novel idea just like Volker.Berlin above says. If you leave your car in airport or similar place without charging possibility even tiny solar panel would help to maintain battery charge. For that purpose I agree that it would not be such a bad idea, just not very useful outside of sunny regions of the world. Maybe as option for 2013?

jbunn, the point of the original post is not to recharge the batteries or extend the range. It's merely meant to counter the self-discharge when the car is sitting. Could be a fourth roof option (pano, body color, black, solar).

On the other hand, if the car is merely sitting for a couple of days or even two weeks at the airport, a) you may even be able to plug it in there and b) self-discharge is not a big concern, anyway.

If the car is sitting for months on end, you better have it placed under a roof for various reasons. In that case, solar won't be of any use.

Whichever way you turn it, the Model S isn't going to have built-in solar any time soon.

Although the post writer briefy speculates on extra power to charge the pack, I understood that it was not the point of the post, which is why I don't mention range or charging in my calculations. There is only a small amount of energy you can gain and the high cost of a mobile collector makes it prohibitive.

Overall the cost of the panels always appears to outweigh the 'savings' for electricity for the car.

Consider that the panels must be made/installed in a way that keeps the 5-star safety rating. Plus micro-inverter and extra wiring. A lot of fuss for very low benefit.

Brings up the question of whether it's meaningful to characterize self-discharge in wattage equivalence, or even as a percentage of charge level. Offsetting that with car solar is hard to assess without some such figure.


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