moneythat
Posts: 8
Joined: Sat Jul 14, 2012 10:50 am

solar on the car roof

Sun Jul 15, 2012 9:36 am

I'd like to put solar panels on the car roof and anywhere else to charge it during the day while it's parked outside.

Anyone know how I can do this?

Don
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Re: solar on the car roof

Sun Jul 15, 2012 3:20 pm

It's a 330 volt battery, so you'd need enough 12 or 24 volt panels to string together in series to provide about 350 volts - It would probably be a tight squeeze to fit them on the roof of your garage, let alone on the roof of the car

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1994 Miata 60K miles - Soon to be sold
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NeilBlanchard
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Re: solar on the car roof

Sun Jul 15, 2012 7:17 pm

Right -- there are a couple of solar cars; but they are far more efficient than the i MiEV. There is one that is driving around the world right now on it's own power, called the SolarWorld GT built at Bochum University. The panels are very high efficiency (read: very expensive) and they provide a little over 800w, it weighs very little (under 1,000 pounds I think?) and the car has a Cd of just 0.14. It does seat two people, but with no creature comforts, and it can drive along at 30-60mph pretty much all day when the sun is out.

I think that more typical solar panels that you or I could get might power a couple of fans to help cool the inside of the car on a sunny day. To charge the car appreciably, it would take at least 2kW of panels, or so? That is about 8 or 10 panels that are ~3' x ~5 ' each.
Sincerely, Neil

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leec
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Re: solar on the car roof

Mon Jul 16, 2012 12:32 am

A DC-DC converter could step up the voltage from a smaller array of panels to charge the car via the CHAdeMO plug, but I imagine that such a circuit would be expensive to design. It would also be possible to charge a storage battery and then use that to charge the car via the inverter. There would be some conversion losses and an intermediate storage battery might also be necessary, but that would be easier than trying a direct charge of the battery.

Running the 12v systems of the car with a solar panel sounds more reasonable than trying to recharge the traction battery.

moneythat
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Re: solar on the car roof

Mon Jul 16, 2012 2:05 am

how much power would I need to charge the car for 1 mile?

i'm looking to add more range to the car and not necesarrily charge it fully.

i know one company puts solar on the prius roof. so why can't miev do it.


NeilBlanchard wrote:Right -- there are a couple of solar cars; but they are far more efficient than the i MiEV. There is one that is driving around the world right now on it's own power, called the SolarWorld GT built at Bochum University. The panels are very high efficiency (read: very expensive) and they provide a little over 800w, it weighs very little (under 1,000 pounds I think?) and the car has a Cd of just 0.14. It does seat two people, but with no creature comforts, and it can drive along at 30-60mph pretty much all day when the sun is out.

I think that more typical solar panels that you or I could get might power a couple of fans to help cool the inside of the car on a sunny day. To charge the car appreciably, it would take at least 2kW of panels, or so? That is about 8 or 10 panels that are ~3' x ~5 ' each.

Don
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Re: solar on the car roof

Mon Jul 16, 2012 4:45 am

Our car goes about 4 miles on a kilowatt hour of electricity - A little less if you park it in the sun and must run the A/C to remove the added heat from the car. It's *possible* to do all sorts of things, but the cost/benefit ratio makes many of them impractical

The Fisker Karma comes with a $5,000 solar roof and it can generate about half a kilowatt hour during an optimal day parked in the sun. This translates to about 4 to 5 miles of extra range per week (for that car) assuming it's parked in full sun for a week. In actuality though, instead of charging the battery pack with that power, much of it is used by a ventilation system which removes excess heat from inside the car. "Featuring the largest solar glass roof ever designed for a production vehicle, the Fisker Karma harnesses energy from the sun to extend the driving range for up to an additional 200 miles/322 km annually. Custom designed to be a wonder of both art and engineering, the roof visually conveys the Karma’s advanced technology and environmental purpose."

Some things are (evidently) a lot more practical on paper than they are in actuality. If you actually got ALL of that theoretical 200 miles per year (the sun isn't going to shine everyday) and you added it up over 20 years, that 4,000 miles worth of electicity would be worth less than $250 - Not a great return from your $5,000 roof

When you do the math on the range you could expect to gain from parking in the sun with whatever solar panels would fit on the tiny roof of our iMiEV, I think it would turn out that you would actually get more of a range gain if you parked it in the shade, since your A/C system is going to have to cool down the inside of the very hot car once you get in and start driving. It would probably be more cost effective to use 15 or 20 solar panels to make a carport roof, park the car under it and recharge while the car sits in the shade below. You could then use 5X or 6X as many panels as would actually fit on the roof of the car and then you'd begin to see some actual range gains . . . . and you wouldn't need to use the A/C as much

Don
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1994 Miata 60K miles - Soon to be sold
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PV1
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Re: solar on the car roof

Sat Jul 21, 2012 7:59 pm

While cost effectiveness is important, I think what Moneythat is getting at is putting solar on the roof of the car to charge it while you're out and about. I had the same idea because most of the time, you can't find shade to park in. This would be helpful to extend your range if you can't find a plug. Have a few panels on the roof (with some aero work) charge a small LiFePO4 battery bank, and then using an inverter and charge the car with the level 1 cord. This would require more technical work and I think I touched on this before. I was thinking of doing this if I got an I and the apprenticeship I applied for. The parking lot has no shade and no plugs and round-trip range would push the car to its limits. Using this setup would allow the I to charge from the added battery and solar panels while it's sitting. While you're driving around, the solar is charging the added battery. This way, you plug your car in when you park, even if there is no plug available because the plug is in the trunk. The best part is the car is totally autonomous and emissions free, including the power generation. It's a great idea, but is it worth it? Depends, but the extra battery capacity would be nice at times, with a little solar coming in to charge this battery. I'll follow up with the math. Let me know of any circumstances where you would find a solar roof helpful.
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JoeS
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Re: solar on the car roof

Sun Jul 22, 2012 8:39 am

PV1 wrote:... I'll follow up with the math...
Yes, PV1, please do that and share your results. Thanks.
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
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Don
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Re: solar on the car roof

Sun Jul 22, 2012 3:48 pm

It's a neat idea . . . . I really wish it was more practical

Not really trying to pop anyone's balloon, but if a roof larger than ours (the Fisker Karma) with a very high tech solar system can only manage 1/2 Kwh per day, then I really doubt there's much hope for bolting a few panels on the tiny roof of our car and getting any meaningful range extension. If you could match their 1/2 Kwh, that would only get you 2 or 3 extra miles at best and less than that if you were driving down tree-lined streets, or if it was cloudy or raining. I could well imagine that the 'harm' done to the aerodynamics could easily cost you what little you gained

True, you could carry around more batteries - In effect, the Leaf does this and the extra weight costs them a good bit of the range gained by having more Kwh's aboard . . . . their MPGe is lower than ours

If someone donates the parts you need for your experiment, I hope you go ahead with it and see what you can do, but if you have to spend several hundred dollars trying this, I suspect you'll eventually wind up feeling like you could have made better use of your money

If I needed extra range because my work was a bit farther away than the iMiEV's practical range, I would make some sort of arrangement whereby I could charge it somewhere while I was at work - Maybe make a deal with someone who lived nearby so I could park and charge at their place and walk the last block or two to work . . . . I can imagine all sorts of more practical scenarios than trying to add solar panels to the roof of my car. I have plenty of experience with them - I had two 120 watt 12 volt panels on my sailboat for 6 or 8 years which nearly kept up with my DC refrigeration system, so I'm well aware of what they can do . . . . and I'm also pretty familiar with how much 'real world' energy you can expect to gain. If you actually get 60% of the theoretical maximum from panels mounted on a movable vehicle which are not correctly aimed at the sun, you're doing very, very well and panels fixed to the roof of your car will seldom be positioned for maximum gain. I know it sounds like a good idea, but . . . . .

Don
2012 iMiEV SE Premium, White
2012 iMiEV SE, White
2014 Ford Transit Connect XLT SWB wagon, 14,000 miles
1994 Miata 60K miles - Soon to be sold
1979 Honda CBX six into six

JoeS
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Re: solar on the car roof

Mon Jul 23, 2012 2:05 am

moneythat, leec, and PV1 - :geek: just for fun, a few years ago for an Earth Day demonstration I did something akin to what you're suggesting as I had four 130W solar panels lying around and I used six small battery chargers instead of the large onboard one. I've dug up a photo and old crude block diagram of the setup (the cardboard was covering the inverter and battery bank as it was a very hot day). I was only running a 72V system in the Sparrow at the time, and this setup actually topped-up that Sparrow's 4kWh battery pack that afternoon (wife hauled up the panels, batteries, etc. in her station wagon).
Hint: "do the math first" :cry: (and, while you're at it, a cost analysis) :roll:
Image
Image
EVs: 2 Wht/Blu SE Prem., '13 Tesla MS85, 3 156v CorbinSparrows (2 Li-ion), 24v EcoScoot(LiFePO4)
EV Conv: 156v '86 Ram PU, 144v '65 Saab 96
Hybrids: 48v1kW bike
ICE: '88 Isuzu Trooper. Mothballed: '67 Saab (orig.owner), '76 MBZ L206D RHD RV

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