Editor’s Note: This article is partially reprinted from 1BOG’s blog (see the original here: Charging an Electric Car at Home: How many more Solar Panels do I need? by Clayton Cornell)
For many, buying an electric car isn’t simply a means to an end, it is a whole statement on their lifestyle; it stems from a desire to simultaneously help the environment and increase energy security. But, one of the biggest worries I hear is that EVs only switch pollution from one source to another, given that 52% of our electricity in the U.S. comes from coal power.
Although there are plenty of studies that now show EVs are much cleaner than combustion cars even when ‘fueled’ from our current energy grid and there are plenty of other reasons to switch to EVs, wouldn’t it still be nice to provide all the power for that car from solar panels on your roof?
So, if you’re planning on putting solar panels on your house, and you imagine an electric car is in your future, how much bigger does your solar array need to be provide enough electricity for your spanking new EV to get from A to B every day?
Clayton over at One Block Off the Grid thought it would be helpful to put together an analysis of building home solar systems with electric cars in mind. Here are the numbers and some important points to keep in mind (Reprinted courtesy 1BOG.org):
1. It’s hard to add solar panels later – make sure you buy the right number up front.
Seems like it should be easy to tack on another solar panel or two to accommodate an electric vehicle, but solar arrays aren’t easy to upgrade. The inverter (which takes DC electricity from the panels and converts it to AC electricity that can be used by your home) is sized for a specific number of panels, so you may have to replace it in the event of an upgrade. It’s much cheaper to get it right the first time. 1BOG can help you figure out how much additional capacity you might need for an EV.
2. Most of the new electric vehicles (e.g. Chevy Volt, Nissan LEAF, Mitsubishi i-MiEV) require about the same additional electrical usage – about 200-250 kWh / month.
1BOG has based this number on the average efficiency for the Chevy Volt, Nissan LEAF, and Mitsubishi iMiEV — around 4-5 miles / kWh, and for an average driver in the US (12,000 miles per year). It also assumes you use the vehicle for all of your driving and you charge it exclusively at home. How much would an extra 200-250 kWh cost per month? Just multiply 200-250 by your local utility rate — US average is $0.11 / kWh, so at this average the additional usage would cost you about $22-$27.5 / month. If you have no idea what your utility rate is, just check your bill, or you can see averages for every state on the U.S. Energy Information Administrations’s website.
And now, the details on home electric vehicle charging….
Last week, 1BOG was featured in the LA times article Driving in savings-neutral territory so far, written by 1BOG customer and early electric vehicle adopter Susan Carpenter. She went solar through 1BOG and wanted to understand how much additional capacity she would need to charge her leased BMW Mini-E or a future Nissan LEAF.
1BOG did some calculations for the article, which assumed a 20-mile per day commute in a Nissan LEAF, with all charging done at home. Keep in mind that a lot of variables will affect cost and payback time calculations, including:
- Assumptions about electricity rates (this example assumes charging is always done at the baseline rate in a tiered rate structure).
- Assumptions about charging locations (this example assumes that all charging is done at home).
- Extra stuff that might offset costs, like feed-in-tariffs (payback time calculation here assumes that you don’t get paid for extra electricity generation).
Here are the calculations 1BOG did for the article :
1. Electrical cost for 20-mile daily (weekday) commute in the Nissan LEAF:
- Weekday mileage: 20 miles per day x 5 days per week x 52 weeks = 5200 miles per year
- Additional Usage: At 4.5 miles / kWh that’s about 1156 kWh per year or 96.3 kWh per month additional usage if charging exclusively at home. 96.3 kWh per month / 30 days per month = 3.21 kWh per day. Assuming 5 hours per day of good sunlight, 3.21 kWh / 5 hours = 0.64 kW.
- Additional capacity: this means it would require a 0.64 kW addition to the solar array to accommodate your electric vehicle commute. With 200W solar panels, this is approximately 3 additional panels (0.64 kW = 640 W / 200 W = 3.2 panels).
- Additional cost: 1BOG ran these numbers for Los Angeles – the last 1BOG price in the Los Angeles solar campaign was $5.56 / DC watt, so you’d be looking to spend an additional $1,808 after rebates and tax credits (note: we used some fancy spreadsheets to factor in all rebates and tax credits. 1BOG’s solar estimate tool will do this for you as well, and 1BOG can walk you through it on the phone).
2. Payback period for additional solar panel cost.
- Driving the Nissan LEAF 5,200 miles a year will save 216 gallons of gasoline per year (assuming typical midsize car 24mpg).
- If gas is $3.00 / gallon that’s $650 per year spent on gasoline.
- Going back to the above calculations, the Nissan Leaf example adds 96.3 kWh usage per month to the electricity bill, or 1156 kWh per year.
If the (fill in the baseline electricity rate for your utility in Los Angeles here) average electricity rate in the US is $0.11 / kWh, then we’re looking at an additional cost of $127.16 / year.
So, $650 in annual savings – $127.16 in additional costs = $522.84 savings (cost difference per year between gas and fully electric).
You’d save $522.84 per year by commuting in the Nissan LEAF and juicing it up with your own solar panels.
Payback time for additional solar panels: ~14.2 years
While 14.2 years might seem like a long time, keep in mind that solar panels are warrantied for 25 years of clean energy production for your home (for comparison, on strictly economic terms the Nissan Leaf will take 50 years to to pay itself off).
This example also inaccurately assumes that electricity prices won’t go up. Solar panels are a long term investment that save you money and cut out the biggest sources of CO2 emissions and pollution for most of us: home electricity and, in this case, driving.
A lot of calculations were completed here, so if we’ve made an error or you need additional information, please let us know! Special thanks to solar advisors Brad and Jonathan for assisting with these calculations!
If you’re considering solar for your home, then sign up for 1BOG’s group discounts and They’ll help you figure out the details.
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Nick,
As your article underscores, there are a lot of variables in the solar-charged driving equation. But for many people, it will end up saving money, quite a lot of money.
For instance, we’ll be solar-charging an EV soon in Colorado. I’ve crunched our numbers here — http://tinyurl.com/28qc45n
They show that in our case, we will save money — a lot of money, while also cleaning up the air we breathe.
However, our savings are heavily dependent on:
1. Utility rebates for solar (which are all over the map in the U.S.)
2. State tax incentives for EVs (comparatively few states have these)
3. Roof orientation, shading other solar system issues.
Just to name a few factors.
A final bit of advice to those thinking about adding extra panels to solar-charge an EV (which is a great idea!):
1. Most (perhaps all) utility rebates in the U.S. for solar systems are tied to total household electric use. This means that in many cases, you will forgo the ENTIRE utility rebate if you propose to build a solar system that produces more than 100-percent of your current household use. In our case, in Colorado, it’s 120-percent of household use, meaning we can get the utility rebate for a solar system that produces up to 120-percent of our annual household electric use, but no more.
2. Given the reality of No. 1, if you’re hoping to cover 100-percent of your household electric use + 100 percent of your annual miles in an EV with your home solar system (again, a great thing to aim for), I would strongly suggest considering getting the EV first and upping your electric usage for a year before going solar. That way, you ensure your usage is high enough to get a full rebate from your utility for the size solar system you would need to 100-percent power your home electric + your EV.
However, there is a potential downside to getting an EV first and waiting a year to put the solar system up on your home: utility rebates are falling nationally.
Nick,
As your article underscores, there are a lot of variables in the solar-charged driving equation. But for many people, it will end up saving money, quite a lot of money.
For instance, we’ll be solar-charging an EV soon in Colorado. I’ve crunched our numbers here — http://tinyurl.com/28qc45n
They show that in our case, we will save money — a lot of money, while also cleaning up the air we breathe.
However, our savings are heavily dependent on:
1. Utility rebates for solar (which are all over the map in the U.S.)
2. State tax incentives for EVs (comparatively few states have these)
3. Roof orientation, shading other solar system issues.
Just to name a few factors.
A final bit of advice to those thinking about adding extra panels to solar-charge an EV (which is a great idea!):
1. Most (perhaps all) utility rebates in the U.S. for solar systems are tied to total household electric use. This means that in many cases, you will forgo the ENTIRE utility rebate if you propose to build a solar system that produces more than 100-percent of your current household use. In our case, in Colorado, it’s 120-percent of household use, meaning we can get the utility rebate for a solar system that produces up to 120-percent of our annual household electric use, but no more.
2. Given the reality of No. 1, if you’re hoping to cover 100-percent of your household electric use + 100 percent of your annual miles in an EV with your home solar system (again, a great thing to aim for), I would strongly suggest considering getting the EV first and upping your electric usage for a year before going solar. That way, you ensure your usage is high enough to get a full rebate from your utility for the size solar system you would need to 100-percent power your home electric + your EV.
However, there is a potential downside to getting an EV first and waiting a year to put the solar system up on your home: utility rebates are falling nationally.
Interesting and promising article, only one thing that I think should be considered: The e- car will usually be charged at home at night time – so would you need to charge additional batteries during the day and then plug the car to the batteries at night? Please comment.
Interesting and promising article, only one thing that I think should be considered: The e- car will usually be charged at home at night time – so would you need to charge additional batteries during the day and then plug the car to the batteries at night? Please comment.
I inquired about solar panels, and you folks connected me with your contractor in the area, but when I checked with BBB, he did not have a good reputation. I’m still interested, but stymied as to which way to turn.
I would love to get out from under the power company and I would REALLY to get out from under ABDUL.
Amazing that a 20 mile commute in an EV uses about the same amount of electricity as drying 1 load of laundry in an electric clothes dryer.
Amazing that a 20 mile commute in an EV uses about the same amount of electricity as drying 1 load of laundry in an electric clothes dryer.
In a single hour, solar energy can supply all the energy consumed worldwide in one year.
http://www.sharp-solar.com/vision/index.html
In a single hour, solar energy can supply all the energy consumed worldwide in one year.
http://www.sharp-solar.com/vision/index.html
@Premo – Better to go with a Time of Use smart meter and connect your solar panels to the grid. Not only do you avoid buying batteries to store your energy, you also get credited 30 cents or more per KWh from the electric company during the peak daytime hours. Then at night you charge the EV for 8 cents per KWh or even less (which is the off-peak rate).
@Premo – Better to go with a Time of Use smart meter and connect your solar panels to the grid. Not only do you avoid buying batteries to store your energy, you also get credited 30 cents or more per KWh from the electric company during the peak daytime hours. Then at night you charge the EV for 8 cents per KWh or even less (which is the off-peak rate).
Verde, thanks for your comment! I live in NZ, as far as I know we are not that far down the track yet in terms of feeding the grid with ‘home grown’ solar energy. But hopefully at some stage….. Cheers
Verde, thanks for your comment! I live in NZ, as far as I know we are not that far down the track yet in terms of feeding the grid with ‘home grown’ solar energy. But hopefully at some stage….. Cheers
Premo, check into this further because it appears that there are grid-tied options in New Zealand (although perhaps not in you area). I found information about grid-tied PV Solar at the following web site http://www.energywise.govt.nz/how-to-be-energy-efficient/generating-renewable-energy-at-home/grid-connected-systems
Premo, check into this further because it appears that there are grid-tied options in New Zealand (although perhaps not in you area). I found information about grid-tied PV Solar at the following web site http://www.energywise.govt.nz/how-to-be-energy-efficient/generating-renewable-energy-at-home/grid-connected-systems
Verde – Be careful with the dollar comparisons. As you know, each state is different. Here, in Nevada, we don’t even have feed-in tariffs yet.
Premo – If a person wants to go totally off-grid, yes, you will need batteries for back-up storage. I would recommend checking out the residential versions offered by Rolls, Trojan, or International.
Verde – Be careful with the dollar comparisons. As you know, each state is different. Here, in Nevada, we don’t even have feed-in tariffs yet.
Premo – If a person wants to go totally off-grid, yes, you will need batteries for back-up storage. I would recommend checking out the residential versions offered by Rolls, Trojan, or International.
Very good article, Nick. This is what we need more of – simple, hard-core numbers the general public can understand.
Very good article, Nick. This is what we need more of – simple, hard-core numbers the general public can understand.
Oh, by the way, the micro-inverters which are coming out can/will help alleviate any upgrade worries. Each micro-inverter attaches to a separate panel, and sends the juice straight to the electrical system. Since no central inverter is involved, it makes upgrades or switch-outs all the easier.
Oh, by the way, the micro-inverters which are coming out can/will help alleviate any upgrade worries. Each micro-inverter attaches to a separate panel, and sends the juice straight to the electrical system. Since no central inverter is involved, it makes upgrades or switch-outs all the easier.
check your math on the payback $1808/522.84= 3.5 yr payback
check your math on the payback $1808/522.84= 3.5 yr payback
200+ KWh.
I only use 50 in a month. By getting an electric car, my bill goes from $180 to $720 per month.
I’m going to need a bigger roof.
200+ KWh.
I only use 50 in a month. By getting an electric car, my bill goes from $180 to $720 per month.
I’m going to need a bigger roof.
Thanks for this article – I’ve been trying to figure this out for a couple of weeks!
I live in the Caribbean, and all our utility power is generated by diesel generators or bunker C fuelled steam turbines. My daily commute is about 10 miles total (out AND back). A Leaf is my ideal car, and since we get more solar than most places, PV is the way to charge it!
IF the electrons for EVs come from solar panels that’s wonderful. My guess is that most of those electrons will still come from burning coal. If my calculations are correct each EV will require at least a ton of coal per year to keep running. If we all switch to EVs (not including the trucking and transportation industry) that is about 200 million tons of coal. In Appalachia In 2004, 389.3 million short tons of coal were extracted from Appalachia: 65% via underground mining & 35% via surface mining. (that’s 136 million tons from MTR) That’s roughtly half what would be needed to power the Evs. That’s a hell of a bunch of mountains blown up and left as flat waste land and thousands of miles of streams ruined forever and a lot of cancer and birth defects.
Until we have the solar capacity to run all these EVs then I want to keep them in the design stage.