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Solar Panels For EV

Posted: Tue May 01, 2012 12:19 pm
by gergg
I've read through these threads and still have a question.....Approx. how much would one have to spend to get enough solar panel power to fully charge a Leaf every day? And what would that equate to in solar panel lingo?

Re: Solar Panels For EV

Posted: Tue May 01, 2012 1:16 pm
by UkrainianKozak
Do you really mean every DAY or you want to charge at night?
For Daytime charging dedicated to leaf, you might need just small buffer battery, to charge after work in the evening/at night you'll have to have a battery of at least Leaf's capacity.

Another question is do you want to have L1 or L2 charging?
For L1 you'll have to maintain ~1.5KW output from solar panels, (I'll skip dependence on time of the year, weather and your location for simplicity) assuming 50% efficiency from rated output, you'll need 3KW of solar cells, so you'll need 10-11 of something like this: http://www.amazon.com/dp/B00635XSEG, that's $5000, plus buffer battery, you can go from small car-sized to avoid charge disruptions from stuff like clouds, to 20-25KWh battery, allowing night charging from the sun collected during the day, that would cost you from $100 to $10000
Plus inverter/controller, something like this: http://www.dhgate.com/3kw-inverter-sola ... d00c2.html, another $1200

So, you are looking at something in range 7-17 K$ for the materials

BUT if you want to just top off and you don't use full leaf "tank" every day, you can definitely some some $$ off solar panel and batteries in case of night charging.
gergg wrote:I've read through these threads and still have a question.....Approx. how much would one have to spend to get enough solar panel power to fully charge a Leaf every day? And what would that equate to in solar panel lingo?

Re: Solar Panels For EV

Posted: Tue May 01, 2012 1:27 pm
by gergg
Yes, I meant to charge at night.....thanks for the info.

Re: Solar Panels For EV

Posted: Tue May 01, 2012 2:53 pm
by Smidge204
I guess another way to look at it is to stay grid connected, and just generate enough power during the day to offset what you'd use at night. Also depends on where you live since the farther north you are the less you tend to get, and the more variable the output throughout the year.

I agree with UkrainianKozak's ~3kW system size, though for slightly different reasons. Where I'd live I'd oversize a bit to 5kW for better winter performance which would put the whole thing at like $11k, plus installation, minus rebates. Skip the battery unless you want to be off-grid for some reason.
=Smidge=

Re: Solar Panels For EV

Posted: Tue May 01, 2012 4:38 pm
by gergg
It sure seems to make sense to be on-grid, guess I am just trying to wrap my head around how much energy is needed to charge an EV, how many panels are needed, and the cost to make that happen.

Re: Solar Panels For EV

Posted: Tue May 01, 2012 5:13 pm
by Boomer23
My grid-tied 5.16 kW system in coastal Southern California (24 panels of 215 Watts each on a relatively unshaded 20 degree slope roof facing south with a single inverter) generated 8,556 kWh of power over the 12 months of 2011. I just finished driving my LEAF 11,249 miles in 12 months. That driving took 3,519 kWh of power to charge the car. Driving energy economy was 3.2 mi/kWh measured at the wall plug.

If you just want to offset the energy used to charge a LEAF to drive that many miles in a year, you'd need an array about 41% of the size of mine, or just 2.16 kW, equal to about 10 of the 215 Watt panels or 8 of the 280 Watt panels mentioned above. Make it 3 kW as others have suggested to account for years with fewer sunny days.

Note that with a solar array of that size, you would not be offsetting any of your household power use, just your EV charging.

With my system and a single meter Time of Use rate plan from my utility, and charging exclusively after midnight, I'm able to power my house and my LEAF for a utility bill of zero. I'd still be pulling about 1,400 kWh net from the grid for the year, though. The Time of Use rate plan gives enough credits for daytime power generation during Peak hours to offset that extra net power use and produce a power bill of zero.

Re: Solar Panels For EV

Posted: Tue May 01, 2012 6:28 pm
by gergg
Boomer23....that was excellent, and very helpful, thank you!

Re: Solar Panels For EV

Posted: Tue May 01, 2012 6:47 pm
by RegGuheert
gergg wrote:I've read through these threads and still have a question.....Approx. how much would one have to spend to get enough solar panel power to fully charge a Leaf every day? And what would that equate to in solar panel lingo?
Frankly, I don't think this question can be answered accurately without knowing your location (which city). This is because the amount of sunlight is drastically different at different locations. On top of that, if you plan to put the panels on your rooftop, the elevation and azimuth of your roof will also make a big difference. Finally, it would be good to know how far you plan to drive the LEAF each year. If you provide that information, we should be able to give a pretty accurate estimate. Better yet, perhaps someone near you can give you details on how their system performs.

Re: Solar Panels For EV

Posted: Tue May 01, 2012 7:09 pm
by gergg
Frankly, I don't think this question can be answered accurately without knowing your location (which city). This is because the amount of sunlight is drastically different at different locations. On top of that, if you plan to put the panels on your rooftop, the elevation and azimuth of your roof will also make a big difference. Finally, it would be good to know how far you plan to drive the LEAF each year. If you provide that information, we should be able to give a pretty accurate estimate. Better yet, perhaps someone near you can give you details on how their system performs.
True....I live near Atlanta, will drive the Leaf approx 15,000 miles/year, my house has great South facing area with little shading.

Re: Solar Panels For EV

Posted: Wed May 02, 2012 3:23 am
by RegGuheert
gergg wrote:True....I live near Atlanta, will drive the Leaf approx 15,000 miles/year, my house has great South facing area with little shading.
O.K. That's the main information we need. The U.S. Government has maintained a database of solar insolation for the past 40-odd years and they have nice resources to help you calculate the electricity production you might expect. The simplest calculator is PVWATTS. I put in the data I used for MY array into your location to see how your insolation compared with mine and it looks like your annual production predicted by PVWATTS is about 12% better than it predicts for us here in Virginia (assuming your roof points directly South and your roof pitch is 8:12 (33.69 degrees) elevation). My array is 9.87 kW and you can see the performance I have been getting by clicking on the link below in my signature. You can scale from my numbers by adding 12% and also adjusting for size to see what a similar system would do for you. (Note that your production only scales 12% on an ANNUAL basis, not month-to-month. For instance, in June, our systems are predicted to produce the same amount, since your temperatures are hotter. In the wintertime, your numbers are much better, however.) Note that if your roof pointing is within about 15 degrees of the boresight I used, then the annual production numbers are within about 1 percent or so of being accurate.

As far as cost of the array goes, I paid about $4/W installed, but I did the installation myself. If you pay someone to do it, you might expect to pay $6/W to $8/W installed.

As far as powering the LEAF, 15,000 miles at about 4 miles/kWh (wall) comes to 3750 kWh/year consumption to run the LEAF. Using PVWATTS for your location (again, assuming roof is directly South and 8:12 pitch) and using a DC to AC derate factor of 0.85 (open for some debate, it may be a little higher), I calculate that you will need an array size of 2.5 kW to produce the same amount of AC electricity that your LEAF would consume. At $6/W installed, that comes to about $15,000 before any tax credits and about $10,500 assuming you can still get a 30% Federal tax credit. Of course if you want to do more than just power your LEAF, you can go much larger.