Solar-charging FAQs

How big of a roof area will I need to solar-charge my EV/PHEV?
This depends on your total home electric use and how many Sun Miles™ — solar-powered miles driven by an electric vehicle (EV) or plug-in hybrid electric vehicle (PHEV) whose batteries have been charged using solar energy — you want to get from your EV/PHEV annually. Chances are good, though, you will need at least 400-square feet of sun-efficient roof space to power both your home electric use and a good portion of your EV/PHEV miles – and you might need considerably more than that.

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How powerful a solar system will I need to solar-charge my EV/PHEV?
This depends on a number of factors — with your home electric use being perhaps the most important one. If you are using 12,000 kWh per year to cover your household electric use, you will need a very large solar system – around 10 kW, or more — to add enough capacity to cover even part of the charging of your EV. However, if your yearly home electric use is in the 5,000 to 9,000 kWh range, you are potentially in good to excellent position to install a solar system that will partially, or fully, solar-power your EV/PHEV (or, really, its batteries). With an ideal south/south-west facing roof in a relatively sunny place, you will need somewhere between a 5 and 7 kW system – which will likely produce between 7,500 (5 kW system) and 10,000 kWh (7 kW system) — in order to cover your home electric use and power all, or most, of your annual EV/PHEV driving.

Though not everyone will be in position to do this, a good percentage of homeowners — especially those who live in a modest sized house, are energy conscious, and live in a sunny part of the U.S., or a sunny part of the world — should be able to cover at least part of their annual EV/PHEV charging via their home solar system.

I want to solar-charge my EV/PHEV. What should I tell a solar installer, what information will they need?
Make sure to tell your prospective solar installer you want to power an EV/PHEV off your home system. On your own, calculate the miles you will be driving annually, and add the annual kWh this will require — the average is 4 miles per kWh, meaning 12,000 yearly miles will require 3,000 kWh – to your total annual home electric use.

You should be clear about whether you want to be able to cover 100-percent of your annual EV/PHEV miles, 50-percent, etc.

It might turn out that for a variety of reasons – system cost being the most significant – you may not be able to fully charge your EV/PHEV off of your solar system. However, even if, annually, speaking, you are able to cover 50-percent, 25-percent, two-percent, or even not cover any EV/PHEV miles at all with your solar system, environmentally speaking, it still makes sense to go solar.

This is because, in going solar with, for example, a system that covers 50-percent of your home electric use but zero percent of your EV/PHEV charging, you will still be increasing the renewable energy mix of the entire electric grid! If enough people do this, then perhaps 50-percent, or even more of the electricity charging your EV off the collective power grid will be generated by solar.

What percentage of homeowners installing solar are looking to power a future EV/PHEV with sun power and asking to “oversize” their systems in order to support this possibility?
Very initial inquiry – basically, a question posed by the SCD.Com Editor to REC Solar and Real Goods Solar consultants about how many of their Colorado installations were customers looking to over-size their system so that they could partially or fully power their EV – found that, for now, a very small percentage of homeowners installing solar appear to be over-sizing to charge a future EV/PHEV. There’s a decent chance this number will grow, perhaps quite significantly, as EVs and PHEVs become widely available to consumers. In fact, SCD.Com plans to further investigate the question of numbers of solar-charged drivers, or how many people in the U.S. are partially, or fully, solar-charging their EV/PHEV as well as how many people are planning to do so in the next few years.

Approximately how many American homeowners could build a large enough solar system on their home, or elsewhere on their property, in order to partially, or fully, power an EV or PHEV off the sun?
This is a fascinating – and difficult to answer – question. It’s also one SCD.Com will definitely pursue further in another place. What makes it so difficult to answer? First, as far as we know, few people are even thinking about solar-charging their cars – in fact, many people probably don’t even know it’s about to become a widespread possibility. Second, as far as we know, no one is keeping tabs on who might be able to squeeze enough sun power off of their roof to power their home electric use and partially or fully charge one, or more, EVs/PHEVs. Third, there are many factors to consider. These include geographic/sun factors, roof size, pitch, and shading issues, and, most importantly, perhaps, individual electric use. All of these have to align favorably in order for a homeowner to be able to put up a solar system which powers both home electric use and covers EV/PHEV charging. Of course, many Americans use far more electricity than they need – average annual household use falls somewhere between 8,000 and 12,000 kWh per year. This means there are a significant number of Americans who could cut back enough on their electric use so that they might be able to partially or fully charge an EV/PHEV off of their roof.

How much money will I save by solar-charging an EV or a PHEV?
Honestly, we’re not sure yet, as this is new territory for us – and for the masses. There are any number of factors to take into consideration. These include, but are not limited to: the cost of installing a solar system, the cost of buying an EV/PHEV, the mileage of that EV/PHEV, the cost of buying a gas-powered car, the mileage it gets, the cost of gasoline, maintenance costs for the EV/PHEV vs. a gas-powered car, etc.

One web page, created and posted to “Associated Content” online by IT programmer and solar-charged driver Doug Korthof in March 2007 (yes, that’s awhile ago), makes the following claims:

“Our modest solar system cost us $19,000. We’ve driven, so far, 160,000 miles on our two Nickel Metal Hydride (“NiMH”) battery-powered Toyota RAV4-EVs, avoiding purchase of 8,000 gallons of gasoline. At even $2 gas it’s $16,000 after-tax dollars that we didn’t have to spend supporting oil wars. Then, we get the satisfaction of sailing right by gas stations, don’t need ’em, and of donating excess electricity to the grid at the time it needs it most (over $200 this year so far!). And all of our domestic electric power for no additional cost. This will last as long as the PV system, at least 25 years, and as long as we can get plug-in cars (the difficult part).”

And, of course, Korthof is saving on his home utility bill as well. He claims that solar-charged drivers who cover 100-percent of their home electric use and 100-percent of their driving will realize the break-even point on their solar system in three years, which is a lot less than the seven to 10 year average for a system that covering all, or part, of a given household’s electricity use.

In the end, some things are certain:

1. Once you get reach payback time on your solar system (usually 7 to 10 years), the sun is free, and will continue to be free!
2. As the years and decades pass, gasoline costs will go up, and up, and up!
3. The world’s oil supply will run dry, almost certainly within the next 100 years!
4. Sun energy will be around for another four billion!

What if I can’t solar-charge one-hundred percent of the miles I drive?
Every little bit matters. Even if only five percent of the miles you drive qualify as genuine Sun Miles™ — solar-powered miles driven by an electric vehicle (EV) or plug-in hybrid electric vehicle (PHEV) whose batteries have been charged using solar energy, you’ll be making an important contribution toward green driving and a greener world.

Just as important, if you’re using solar to cover one-hundred, or 50, or even 25 percent of your home’s electricity needs, you’ll be reducing your carbon footprint, and reducing other forms of pollution associated with fossil-fuel burning, including sulfur dioxide emissions, particulate emissions, and the release of mercury into the environment.

By going solar, you’ll be driving solar and clean, renewable energy forward. You’ll also get the satisfaction of spinning your home electric meter backwards at least some of the time. Additionally, you’ll get the satisfaction of displaying your commitment to a cleaner, greener world to your neighbors by way of the solar system on your rooftop. Finally, you could be motivated to reduce your home energy electric use so that you can put some of the energy generated by your home solar system for the drive.

Another option is to power only your EV or PHEV by way of solar panels installed on your garage roof, or on a Solar Carport. This might be a good option for people who don’t have the rooftop and/or yard space to power both their home electricity and an EV off of solar panels. Some companies, among them, Envison Solar in California, have recently begun building and selling solar systems designed specifically for a garage roof or as a stand-alone, metal Solar Carport. It’s called the LifePort. It doesn’t necessarily have to be tied into the power grid, though it does need to be on the grid in order for buyers to eligible for the power company and federal tax credits Envision trumpets on its web site.

What if my annual home electric use, my roof size, the direction my roof faces, and/or where I live prevent me from building a system that can also solar-charge an EV and/or PHEV?
If you can afford a solar system, please install it anyway – and buy an EV/PHEV anyway! Every little bit of solar power helps. To put it more concretely, if 100-percent of Americans, including corporate and other large users, could only cover 40-percent of their electric use through solar panels on their property, and 100-percent of these people chose to put up systems that covered 40-percent of their home use, 40-percent of the total electric grid would be powered by solar, and your EV/PHEV would therefore be 40-percent solar charged. And, if utilities build large solar farms and concentrated solar plants, along with wind farms, biomass plants, etc., your EV/PHEV could be powered even more by renewables.

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What are the most important things I can do to help make solar-charging my EV/PHEV a possibility for me?
1. Reduce your home electric usage.

What counts as a solar-charged car? What if I charge my EV/PHEV at night and drive my EV/PHEV the next day? Does this count as solar-charged driving?
Ultimately, it depends on one’s definition of solar-charged driving. We at SCD.Com define a “truly” solar-charged car, or one that is putting on “true” Sun Miles™, in the following way:

If the yearly output from your solar system equals, or exceeds, the total amount of electricity you use for your home and which you need to charge your EV to drive it the number of miles you have driven it, this is, indeed, “true” solar-charged driving. Purists might say 100-percent of the juice that flows into your EV’s battery during the year must come directly from the sun, or it’s not “true” solar-charged driving. Of course, unless you live in the desert, few people would be able to achieve this, though it is certainly an enviable ideal.

In terms of a PHEV and solar-charging, the same things discussed above apply — with a caveat: Sun Miles™ for a PHEV are, of course, only those miles powered solely by the PHEV battery. Plus, only the annual battery-powered miles you accrue on your PHEV which allow you to keep your home electric usage and your PHEV battery miles within the total yearly output of your home solar system qualify, according to the SCD.Com schemata, as “true” Sun Miles™.

What are some of the positive environmental benefits of solar-charging an EV or PHEV?

• No emissions. Zero. None whatsoever.
• No need to drill for oil, natural gas, or mine for coal.
• No need for any refining process whatsoever.
• No need to transport the fuel – by cargo tanker, rail, truck, or by all of these methods – none whatsoever.
• Because there’s no need to explore, drill, refine, or transport, sun-running your EV and/or PHEV is much more efficient than any other form of fueling. In fact, it’s about as direct a form of auto-fueling as you can achieve!

I want to let the world know that I’m driving on the sun – and encourage others to do the same. What are some different ways I can do this?
The most obvious way to advertise the fact that you’re running your EV/PHEV partially, or fully, on sun, is to plaster this fact on your car! We highly encourage this! Doing so: a) raises consciousness about the fact that it is even possible to run your car on sun (not many people know about this); b) promotes solar power in general; c) shows the world that driving can be much more environmentally friendly than it is right now.

What are some things I can do to help promote and grow solar-charged and solar-powered driving?

1. If you have the economic means and are a homeowner, put a solar system on your house and buy an EV/PHEV!
2. Talk to your friends, coworkers, family, neighbors about solar-charged driving and encourage them to look into it, or better yet, do it themselves!
3. Blog about your experiences. Here is somone who is doing just this
   1. “Life with a solar-charged Mini-E”: http://www.genesisenergycorp.com/mini/
4. Generally promote solar and EVs/PHEVs generally — by voting for politicians who are pro-solar and pro-EV/PHEVs, lobbying your current lawmakers to support solar and EV/PHEVs, etc.
5. If you decide to solar-charge an EV/PHEV, advertise the fact that you are doing this on the car itself, the more eye-catching your advertising, the better!