Using Home Solar to Charge your Bolt for Free

[oilerlord]

This comes up every so often, and I figured it deserves it's own thread.

Can you really charge your EV for free? The answer is a theoretical yes. It depends on how many miles you put on your car, and how much you paid for your home solar system, and where you live. All-in, I'm into my project for CDN $19,000 / $2.06 per watt - and that's without rebates since there are none available in Alberta. At some point in the future I will recover that investment in lower electricity bills and by putting some of that energy into my EV. With that said, people need to know that doing solar "right" isn't cheap, and if your only motivation for doing it is to save money on gas - that money can buy a lot of gasoline.

The most important point I can make, and can't stress enough is - an improperly installed home solar system can kill you. If it isn't done right, you run the risk of getting electrocuted or burning your house down. For that reason, and unless you're a qualified electrician and have experience with installing home solar - please hire a reputable solar installer. With that said, I was involved in the design, and permitting, and sourced all of the equipment on my own but during the installation I was just a third set of hands involved in grunt work. I didn't come anywhere near high voltage danger areas.

I'll start off with some background about my solar project. It began with humble beginnings, more of a science project than anything else. I figured I'd start with 4 panels, but it eventually morphed into this (photo taken during install):

41 SunPower 225 watt panels. 9.2kW of clean DC power. You can access it's production in real-time here:

https://easyview.auroravision.net/easyview/index.html?entityId=7466210

Here is a photo of my 2014 Mercedes B250e:

My car's battery has a usable capacity of 28kWh. I expect I'll put about 10,000 miles on it per year. During the summer, it was easy to get about 100 miles on a charge, but in the extreme cold of the last few days, I'm only managing around 50 miles. I suspect that If I had a Bolt, it's 238 EPA mile rating would be cut in half too, but that's another discussion.

For the sake of figuring out how many kWh's I need for those 10,000 miles, let's assume a year average of 80 miles per charge. That amounts to 125 full charges per year. 125 charges x 28kWh = 3,500 kWh's. Of course, YMMV based on your car's efficiency and how you drive. Where I live, my system that's rated at 9.2 kW generated 9100 kWh last year. If you live in California, there's no doubt that you will generate more than my system will, so your payback will likely happen sooner depending on your cost per watt, and what you pay per kWh from your power utility.

So to figure out the ROI, let's assume I need to generate 3,500 kWh's per year to drive my EV for "free". My installation cost is $2.06 per watt, and I need 3.5kW of solar to fuel the car for a year. That equals $7,210.

First off, my apologies to another member for doubting his calculations on a 2-3 year ROI. In my case, he was right, and in SoCal with a system on a budget, he'll easily accomplish that too. Theoretically, the math does suggest that I'll be charging my car for free in a little over 2-years. With that said, my $2.06 per watt all-in cost definitely is low, mostly because the panels I bought were 5-years old. Solar installation companies in my area were quoting $4.50 per watt, so I'd be closer to 5-years had I opted for a turnkey solution.

There are mitigating factors too that puts the "charge for free" argument into question. This is one of them:

This month, I'm only going to generate about 200kWh from my system. The good news is that in July, I'll generate 1200kWh.

A few things to keep in mind is that your car isn't always plugged in when the sun is shining (and if the sun is shining). Also, your home's power consumption may be soaking up much more than your solar system produces not leaving anything left for your EV. Also, my EVSE supplies 7.3 kW to the car - my system peaks at around 7 kW from May thru August so most of the time, I'm buying power from my poco to charge my EV. Many jurisdictions allow you to "bank" your the excess power you generate but mine isn't one of them. When the sun goes down, and regardless of how much excess kWh's I export to the grid, I'm buying electricity from my poco.

All in all, I'm glad I installed the system, and have no regrets. I still think that claims that you can charge your car for free from home solar are somewhat dubious but as we all know there's more to installing solar than saving money. Feel free to ask questions or comment. I'm interested in hearing your point of view.

 

[leodoggie]

What a great title for a thread, I wish I had thought of that, just friendly banter.
On a more serious note I would echo your your words on making sure you have professional help if you don't have the expertise your self.
Although I did all the work on my system myself, the solar array is fully permitted by my city and was inspected twice my the city inspector and our city Fire Marshal.
The reason for this is that if anything goes wrong like a fire you are risking your families life, also your insurance company will not cover you if have a non permitted system.
In the bay area we don't have to look far to see this in action, as this happened in a devastating fire in Oakland recently.

 

[summit]

For the time being with the ability to use the grid as a "battery", to save excess kwh during the summer and to draw on the saving in the winter, it is the annual total kwh one needs to look at. The solar PV + EV makes a lot of sense when considering well-to-wheel benefit (climate, politics, clean air ....) plus ancillary benefits such as not having to stop to re-fuel typically.

You can always start small, then add more panels later. Solar pricing is getting better all the time, though I feel a nudge given the incoming administration, which may nix the current 30% rebate.

 

[oilerlord]

What a great title for a thread, I wish I had thought of that, just friendly banter.
On a more serious note I would echo your your words on making sure you have professional help if you don't have the expertise your self.
Although I did all the work on my system myself, the solar array is fully permitted by my city and was inspected twice my the city inspector and our city Fire Marshal.
The reason for this is that if anything goes wrong like a fire you are risking your families life, also your insurance company will not cover you if have a non permitted system.
In the bay area we don't have to look far to see this in action, as this happened in a devastating fire in Oakland recently.

You did think of the title

I visit a solar forum and there are a lot of posts / claims along the lines of charging an EV for free. It's a concept that captures the imagination, and from experience, I find myself waiting to plug in during full sun when those opportunities present themselves. It's a great feeling that those electrons going into the battery are 100% home grown.

I searched threads on this board and didn't find anything on the subject. A lot of people are interested in solar, and not only to charge their cars. I hope this thread spurs discussion, and provides answers that readers may have. One of the questions I would like to explore is if using solar really does charge your car "for free".

Technically, you can generate enough electricity with an array to charge your car but like the sun being followed by your tracking array, I think that goal is somewhat of a moving target.

 

[leodoggie]

Your moving target analogy is a good one in the sense of it depends on your environment and circumstances.

My location in California is ideal for solar. My utility has net metering, which allows me to use them as a large battery. I have the expertise to design, build and install the entire system myself, so I can keep costs to an absolute minimum. I have had a system running for four years, so I have a pretty good idea how solar works in my environment.

Therefore putting all those elements into my calculations, I can say with absolute confidence that when I get my Bolt in 2-3 years ( ROI for my system ) I will be able to charge if for free.

Hopefully this clarifies the issue somewhat.

 

[oilerlord]

My location in California is ideal for solar. My utility has net metering, which allows me to use them as a large battery.

I can say with absolute confidence that when I get my Bolt in 2-3 years ( ROI for my system ) I will be able to charge if for free.

I'm grid tied, and have net metering too however I'm not able to use the grid as a large battery. I do get paid for the power I export, but as soon as my solar stops generating enough for our needs, I'm buying power from the grid regardless of how much I exported throughout the day. On paper, that's sounds fine, but though I'm getting paid $0.04 per kWh, I'm buying back power at $0.04 + fees which works out to more like $0.06. Still cheap I know, but for that reason it isn't in my best interest to export to the grid - I'm better off using that electricity...hence the EV.

I'm assuming that your existing arrays fulfill all of your existing power requirements, and the tracking array is being designed to generate the extra kW needed to charge your car. I've thought about that too however I don't have a spot to install a ground-mounted tracker without it sticking out like a sore thumb. It took a lot of effort to get my wife to sign off on the project as it is. There may be roof-mounted tracking systems available, and the only possible place I could see installing it would be behind my 7-panel south facing array. Not sure that's advisable however since it would act like a sail in high winds.

Please describe the tracker that you're building.

 

[leodoggie]

When you produce more power than you use does your meter go backwards?

 

[wwhitney]

I think photovoltaics and EVs are a great combination, for the obvious reasons.

But it is hyperbole to say that PV lets you charge your EV for free. The average cost of a solar kWh put into the EV won't be zero--it will be at least the cost of the solar PV system divided by the lifetime kWhs it creates. That can be a little hard to determine up front, but even if you assume a 20 year or 30 year life span of the PV system, the cost will be non-zero.

Now because of net metering, you can get into a situation where the marginal cost of charging your EV is zero. For example, with California's PG&E if you have a net dollar credit at the end of a 12 month billing cycle, but because of TOU rates you were still a net energy consumer, you lose that dollar credit (to my knowledge). So in that situation, if you drive an extra 3-4 miles and therefore charge your EV an extra kWh, it costs you nothing extra.

However, that situation arose only because you oversized your PV system, economics wise. In other words, your energy costs (including PV installation costs) over the lifetime of the PV system would have been less by installing a smaller PV system. So that extra kWh wasn't really free.

Cheers, Wayne

 

[oilerlord]

But it is hyperbole to say that PV lets you charge your EV for free. The average cost of a solar kWh put into the EV won't be zero--it will be at least the cost of the solar PV system divided by the lifetime kWhs it creates. That can be a little hard to determine up front, but even if you assume a 20 year or 30 year life span of the PV system, the cost will be non-zero.

Now because of net metering, you can get into a situation where the marginal cost of charging your EV is zero. For example, with California's PG&E if you have a net dollar credit at the end of a 12 month billing cycle, but because of TOU rates you were still a net energy consumer, you lose that dollar credit (to my knowledge). So in that situation, if you drive an extra 3-4 miles and therefore charge your EV an extra kWh, it costs you nothing extra.

It should also be noted that there is an intrinsic value to a kWh regardless if you buy or sell it to your poco. For that reason, if a solar-generated kWh went into your car's battery at 6PM, it still has a TOU peak value of $0.39. So in essence, you collected and spent that $0.39 to put 1 kWh into your battery instead of getting paid for it by selling it to the poco. "Free" implies zero cost but every kWh generated on a net metered system has value.

Leo, yes, I'm net metered. My meter's LCD arrow points backwards when I'm exporting to the grid.

 

[leodoggie]

If your meter can go backwards, then you have the ability to use your utility as a large battery.

When I sized my fist solar system it gave me the ability to pretty much mirror my yearly electricity useage averaged over a whole year. The savings in electricity cost paid off my system in three years ( ROI 3 years ).

I have sized my new system to be able to fully charge the Bolt four times a month equating to roughly 850 miles a month 10,000 miles a year ( average 250 Kw a month ). I will not be buying any gas because my new PV will be my new energy delivery system for my new EV. The savings in not buying gas will pay for my new system in 2-3 years ( ROI 2-3 years ).

This is as simplistic as I can make it.

 

[wwhitney]

If your meter can go backwards, then you have the ability to use your utility as a large battery.

Whether that use as a battery is free depends still depends on the utility's rate schedule. For example, oilerlord indicated that when he's a net producer, he gets a credit totaling $0.04/kWh, but when he's a net consumer, he's charged a total of $0.06/KWh. So the utility makes $0.02/kWh on the round trip based on those numbers.

I have sized my new system to be able to fully charge the Bolt four times a month equating to roughly 850 miles a month 10,000 miles a year ( average 250 Kw a month ). I will not be buying any gas because my new PV will be my new energy delivery system for my new EV. The savings in not buying gas will pay for my new system in 2-3 years ( ROI 2-3 years ).

The savings in not buying gas may pay for the new system in 2-3 years, but that's not the breakeven period on the PV system. Because some of those savings would have been realized even without a PV system. [Assuming as is usually the case that electricity from the grid for an EV is cheaper per mile than gas for a car] Those savings go to reducing the Total Cost of Ownership of the EV and have nothing to do with the PV system. The breakeven period on the PV system would be determined using only the savings on electricity cost that a PV system provides.

Cheers, Wayne

 

[leodoggie]

If you wish to make a simple issue convoluted and complicated be my guest. I will stick with my basic principles of engineering , science and math that have served me well for forty years. I wish you luck.

 

[wwhitney]

I'm all for appropriate simplicity. But when you want to calculate ROI or breakeven period, you need to do the accounting properly.

Cheers, Wayne

 

[oilerlord]

Leo,

Read what he wrote again:

"The savings in not buying gas may pay for the new system in 2-3 years, but that's not the breakeven period on the PV system. Because some of those savings would have been realized even without a PV system. [Assuming as is usually the case that electricity from the grid for an EV is cheaper per mile than gas for a car] Those savings go to reducing the Total Cost of Ownership of the EV and have nothing to do with the PV system"

Wayne makes a good point.

He's basically saying that the the cost of operating an EV (vs ICE) is cheaper because electricity is usually costs less than gasoline - regardless if you generate it with home solar or you don't. Using my car as an example, it's offered in Canada as a 4-cylinder gasoline model (the electric version is only sold in the US). The gas model has an EPA combined rating of 24 mpg. For nice round numbers, let's assume that premium gasoline costs $2.50 per gallon, and I'd need 400 gallons per year to drive 10,000 annual miles. That's about $1,000 per year. If I didn't have solar, and given my calculation of 3,500 kWh to drive the same distance with the electric version, I'd be paying only $210 because my cost per kWh is $0.06. Based only on the cost of different fuels, I'm already saving about $800 per year with the EV version vs the gasoline version of the same car. I didn't need solar to realize those savings.

So really, you need to look at how many kWh you need given the miles per year you intend to drive your EV and your poco's cost per kWh. As it costs me only $210, to drive 10,000 annual miles with my EV, that's really the starting number that determines years of ROI. My start value is $210 but in SoCal 3500 kWh at $0.20 per kWh from PG&E would cost you $700. You mentioned that your tracking array would cost $2800. That's a 4-year ROI. Engineering and science have nothing to do with it.

 

[GetOffYourGas]

The savings in not buying gas may pay for the new system in 2-3 years, but that's not the breakeven period on the PV system. Because some of those savings would have been realized even without a PV system. [Assuming as is usually the case that electricity from the grid for an EV is cheaper per mile than gas for a car] Those savings go to reducing the Total Cost of Ownership of the EV and have nothing to do with the PV system. The breakeven period on the PV system would be determined using only the savings on electricity cost that a PV system provides.

Cheers, Wayne

This is exactly my issue with many of these analyses. Thank you, Wayne, for stating it so clearly. You can't run a Bolt on gas at all, so it's really not worth comparing.

My system cost me about $0.80/watt (DC), thanks to VERY generous subsidies by the federal government (30%), New York State (25%), and New York State Energy Research and Development Authority ("NYSERDA" @ $1.75/watt). My average exposure for a year is only about 800 hours. So for each kW of rated power, I only produce 800 kWh in a year. (It can be cloudy here, and we get lots of snow in the winter.) My electricity cost hovers around $0.10/kWh. So each kW saves me $80/year, but cost me $800 to buy upfront. The break-even is therefore right around 10 years. (These are obviously all very round numbers, so the result is close enough). The beauty is that the system is warrantied for 25 years

Since my panels produce less than my house + BEV + PHEV consume, it really doesn't matter who uses the electricity. The payback is still 10 years. It has been 5 years so far, and I'm right on track. After 10 years, I will happily tell people that I charge my cars "for free", because the panels have paid for themselves. Right now I think of it as if I have pre-paid for 10 years worth of electricity.

 

[oilerlord]

This is exactly my issue with many of these analyses. You can't run a Bolt on gas at all, so it's really not worth comparing.

My system cost me about $0.80/watt (DC), thanks to VERY generous subsidies by the federal government (30%), New York State (25%), and New York State Energy Research and Development Authority ("NYSERDA" @ $1.75/watt).

That was the point of this thread...qualifying "free". ROI's can be all over the map depending on electricity rates and your annual power generation. Even when you plug in your car matters in the calculation when TOU rates are factored into the mix.

That's some inexpensive solar you have there. Was that installed at $0.80/watt or was it DIY?

 

[GetOffYourGas]

That was the point of this thread...qualifying "free". ROI's can be all over the map depending on electricity rates and your annual power generation. Even when you plug in your car matters in the calculation when TOU rates are factored into the mix.

Yes, I know. That's why I chimed in with my opinion. I thought that kind of discussion was invited, and not frowned upon here.

For me, the calculations are easier. I don't have TOU, and do have net metering. Moreover, I consume more than I produce in a year, especially with two plug-in cars. So time of use/generation of power makes no difference in my numbers. I recognize that isn't the same for everyone.

My point was still that solar should be compared to charging an EV from the grid, and not against filling a tank with gas.

That's some inexpensive solar you have there. Was that installed at $0.80/watt or was it DIY?

Believe it or not, that was a professionally installed system, complete with a supply panel upgrade (from 100A to 200A). The system is rated at 3,680 Watts, DC. It cost just a hair over $20k. Then you take off 30% from the feds ($6k) and 25% from NYS ($5k) and $1.75/Watt from NYSERDA ($6440), and you get an out-of-pocket price of under $3k. For a 3.68kW system. NYSERDA lowered their rebate program every year since 2011. I caught them at a sweet spot of still-high incentives and quickly dropping retail prices. If I expanded the array today, I'd certainly pay more than $0.80/watt.

 

[oilerlord]

Yes, I know. That's why I chimed in with my opinion. I thought that kind of discussion was invited, and not frowned upon here.

For me, the calculations are easier. I don't have TOU, and do have net metering. Moreover, I consume more than I produce in a year, especially with two plug-in cars. So time of use/generation of power makes no difference in my numbers. I recognize that isn't the same for everyone.

My point was still that solar should be compared to charging an EV from the grid, and not against filling a tank with gas.

Believe it or not, that was a professionally installed system, complete with a supply panel upgrade (from 100A to 200A). The system is rated at 3,680 Watts, DC. It cost just a hair over $20k. Then you take off 30% from the feds ($6k) and 25% from NYS ($5k) and $1.75/Watt from NYSERDA ($6440), and you get an out-of-pocket price of under $3k. For a 3.68kW system. NYSERDA lowered their rebate program every year since 2011. I caught them at a sweet spot of still-high incentives and quickly dropping retail prices. If I expanded the array today, I'd certainly pay more than $0.80/watt.

I welcome yours and everyone's opinions - none are "frowned upon". All are invited.

3.68kW DC at under $3,000. That is crazy cheap, especially for a turnkey installation. That doesn't even cover the labor from my solar guys and electrician. With falling electricity prices where I live, my ROI is being pushed further out. The last two weeks were bitterly cold here but our 30-day average pool (wholesale) price is still only 2.3 cents per kWh. I'm on a spot plan that bills out at pool price + 1 cent. We should be seeing more EV's here based on that alone however we have no incentives for electric cars in Alberta (yet).

 

[sam]

Love the idea

 

[jimmyjon]

I would never attempt this installation on my own. Professionals all the way for me