[ripegraph]

Hi all, first post. Hopefully my post is mostly following guidelines here.

I started leasing a 2017 Volt LT a month ago and am also in the process of going Solar (waiting for town's permit, haven't installed Solar panels yet).

The original design my Solar installer proposed (before this Volt) based on my $160 monthly bill was 23 panels of size 6.325kW covering an estimated usage of 7,959 kWh annually.

Driving my new 2017 Volt LT for a month, my new electric bill stayed around $160. That's probably because last month has been pleasant enough that we didn't use cooling or heating most of the time. I don't really know how much electricity my Volt have been using.

So I asked the Solar installer to increase the installation size of the solar panels so that they will be able to cover the extra usage of my Volt. I have a L2 charger (Clipper Creek HCS-40P), and my daily commute is about 25 miles, so at most 3 charges a week is sufficient. Assuming I go to work 48 weeks per year, with the 2017 Volt's battery capacity 18.4kWh, my estimated power usage would be 18.4 * 3 * 48 = 2649.6 kWh.

However, my solar installer has computed an estimated extra power usage to be 4480.4kWh. They explained that the EV battery is DC, and Solar power is AC. In order to provide ~2700kWh DC power for the EV, the estimated annual usage has to increase by that 4480.4 kWh (to cover for power loss converting AC to DC), thus I would need to increase my installation size from 23 panels to 36 panels.

That seems a big increase, because if 23 panels cover my current $160 monthly electric bill, 36 panels would be covering almost $250 monthly, meaning the new Volt is almost using $90 more per month. But researching this forum, people generally reported an increased $30~$50 electricity bill.

So my question is, whose calculation is right? Anybody updated their Solar installation after getting an EV?

Thank you in advance!

 

[PJL]

Your solar installer is trying to take you for a ride. I will do some analysis and post my experience as I got solar several months after I got the Volt and my commute scalable down to tours.

 

[Mcgsp]

Personally, i have had solar panels on my roof for the last 11 years and have not had to pay electricity for any of those 11 years. My house has 9.2kw system split between 6.4 for my use and 2.8 for the common areas of my brownstone. I charge my Volt and 1 electric dryer and of course all the other appliances, computers and peripherals and air conditioning in summer. I do take steps to minimize my energy use from using dishwashers and washing machines doing full loads of wash. I have energy efficient appliances and converted all lighting to LED. I try to be cognizant of phantom loads so I use smart plugs for all my electronics which are turned off whenever not in use. Bottom line I produce more electricity than I use, and being in net metering state, I end up not paying my gas bill for half of the year from what I sold back to the Utility.

That being said not knowing your lifestyle or energy use, it would behoove you to take stock on what your kWh usage is and not how much you spend per month which is what you mentioned. That should of been the first question asked by your solar installer even before they did a on sight visit. In fact they should of gone over a year use of electricity use before they walked onto your property.

The next step take, is an inventory of your energy usage and then see how you can conserve energy. Something owning a EV prepares you for in one's way thinking of how energy is used. So if you turn off computers, wifi routers and other device when not in use. You can purchase smart surge protectors, some now have built in timers. And of course replacing your lighting with more energy efficient bulbs and replacing appliances to more energy efficient units that are more appropriate to what your needs are and not what is the current appliance of favor. Its amazing how many kilowatts these simple procedures save a household and may alter your calculations on what you truly need on your roof. Try this for one month and see if this makes enough of a difference, before you add more panels to your for the installation. Good Luck.

Also keep in mind as well, unless your fulling discharging the Volt each day you are only doing a partial charge of the vehicle and thus maybe overstating the energy require to charge the Volt in real terms each day. Think of how often you went to gas station to fill up, and only added several gallons then filling it full from empty. Of course if your house is poorly insulated and during summer and blast the AC at 65ºand use an electric dryer and range then , with sub zero refrigerators(very inefficient units) 8 wifi routers going, heated sidewalk and such, then of course you maybe you need to have a larger system.

One other point to make, while a southern exposure gives you the best bang for the buck when it comes to net metering. A more south westerly orientation of the panels allows a longer day of the sun in which to power your house, though you wont be getting that super charge at high noon you will be utilizing more of the electricity you produce for a longer period throughout the day. In short a more efficient use of the sun for both feeding back the meter and powering your house.

 

[KenC]

Roughly, if you drive 12k a year, or 1k a month, about 700 miles would be EV. Adjust for your situation. Divide your monthly miles by 4miles/kWh, and you get 175kWh in a month. At the nat'l average cost of 12c/kWh, that's $21 a month. Adjust for Massachusetts utility rates. If your usage is 8000kWh/yr, then divide by 12 and your monthly is 667kWh/month. Add your 175kWh and you get 842kWh in your average month. Adjust for seasonality. Just extrapolating, it seems 29 panels should cover your average monthly use. Seasonality, if you want to adjust for your lowest month, would mean more panels.

 

[freshcut]

Since you've had your Volt for about a month, if what you've driven has been about your expected average you can get a pretty good idea what it will require in kW on the myvolt page in the charging as well as the efficiency section. You can see how much energy used. For example mine used 274kW in the past 30 days with 927 electric miles. I tend to drive a lot (20 miles RT work 6x's/wk) both work as well as semi-regular trips out of town. All of my in town driving however is electric. So perhaps using my figure you can get an idea how much additional output your system needs to compensate for the additional load of daily charging.

 

[firehawk72]

You are both right, but your solar installer is wrong for the wrong reasons. The AC to DC line is simple bull.

What I believe you are stating is correct.

What I believe your solar installer is also correct.

I simply believe you are arriving at your assumptions based on different criteria.

You are only wanting to cover your limited drive.

Your solar installer doesn't want you disappointed and is covering your limited drive, plus some.

13 extra panels for your Volt is not out of reason as that puts you at roughly an extra 13 kWh per day. That is almost fully depleting your Volt every day, not quite, but close.

Do the math and see what you actually want.

Also, if this is a SolarEdge design, or not an Enphase design, your installer might be dealing with having to deal with an additional string in the calculations to wake up the inverter(s).

 

[alfon]

I understand that some new solar panels are very efficient and produce over 300 Watts of electricity per panel. It seems like a 10 -12 KW system should cover most larger households. In sunny areas perhaps you may receive a check from the electric company from buying your surplus of electricity. Our electricity cost from Pacific Power, even with our Volt charging every day, has not seem to increase very much at all. Are electric rate with all cost etc. total bill divided by KWH used, is .112 - .117 per KWH.

 

[ripegraph]

Wow, that's a lot of information and very helpful replies, thanks all!

@PJL and @firehawk72, it does strike me when the installer brought up the AC to DC reasoning. They have otherwise been very good to deal with. And by the way, it's a SolarEdge design with the inverter.

@KenC Thanks for the careful calculus

@freshcut which myvolt page were your referring to? I could only find the "Efficiency" section in "myChevrolet" app, and there's only a lifetime mileage (electric vs. total).

The ideas @PJL mentioned are all very helpful! The installer also said that they can add more panels later with the current design and my roof layout. So I think I'll stay with the current design and see from there.

 

[snic]

@PJL and @firehawk72, it does strike me when the installer brought up the AC to DC reasoning. They have otherwise been very good to deal with. And by the way, it's a SolarEdge design with the inverter.

There is some loss when you convert from AC to DC, but it's not as large as your installer claims. There is also loss from storing and then using the energy in the battery - e.g., it takes more than 1 kWh DC to charge the battery so that it contains 1 kWh of usable energy. I'm not sure exactly what the combined loss is, but I don't think it's more than about 10 or 15%. People have discussed this a lot in this forum, using data from devices that measure energy use from an a/c outlet, allowing them to determine how much energy was used to fully charge the Volt battery. I suggest doing a search and drawing your own conclusions, rather than relying on your installer.

The installer also said that they can add more panels later with the current design and my roof layout. So I think I'll stay with the current design and see from there.

One thing to keep in mind is exactly how the incentives from Massachusetts are structured. In NY, for instance, you get a credit towards the cost of the system that is based on the system's size, but you do not get a credit for adding panels at a later date. It therefore makes the most sense to size the system correctly from the outset. MA might have a simpler system, but make sure you understand it. The installer might tell you that you can easily add panels later, but he might NOT be telling you that the cost per panel for the later addiitions will be much higher due to the incentive structure.

Also, as I understand it, SolarEdge systems have a single large inverter which is designed for a certain number of panels. So that might limit the number of panels you can easily add later. (A bigger constraint for many people is roof space, but it seems you don't have that problem.) Enphase systems, on the other hand, use microinverters so they are more easily scalable. Supposedly the microinverters last longer, too.

 

[Splitting Atoms]

I am guessing he was trying to get at the fact that the solar panels are DC, which is then converted to AC, which then converts back to DC once more when charging. So if that round trip efficiency is factored in at something like 75-80%, it will increase the number of panels compared to what would be otherwise apparent.

 

[firehawk72]

Also, as I understand it, SolarEdge systems have a single large inverter which is designed for a certain number of panels. So that might limit the number of panels you can easily add later. (A bigger constraint for many people is roof space, but it seems you don't have that problem.) Enphase systems, on the other hand, use microinverters so they are more easily scalable. Supposedly the microinverters last longer, too.

Yes, I am not a fan of SolarEdge for many reasons. I am a fan of Enphase and I have really tried to be as fair and as balanced as possible coming to that conclusion. Having said that, they both do work and will serve their customers well. The main problem with SolarEdge is what you stated and what I stated earlier. With Enphase, if you want to add 1 panel or 25 panels, it makes zero difference as the microinverter is right there with the panel. With SolarEdge, you simply can't do this as it generally takes about 8 panels (minimum,) to wake up an inverter. Solar installers would never mention this if they wanted you to install a SolarEdge system. Also, they love to point out that Enphase has more points of failure over SolarEdge. I actually find that hilarious as I can count; and when that big central inverter(s) does fail, you are without your whole system.

 

[firehawk72]

I am guessing he was trying to get at the fact that the solar panels are DC, which is then converted to AC, which then converts back to DC once more when charging. So if that round trip efficiency is factored in at something like 75-80%, it will increase the number of panels compared to what would be otherwise apparent.

Total hogwash, you calculate what the panels will produce. It is dirt simple. It is no different than getting electricity from the grid.

 

[ripegraph]

Yes, I am not a fan of SolarEdge for many reasons. I am a fan of Enphase and I have really tried to be as fair and as balanced as possible coming to that conclusion. Having said that, they both do work and will serve their customers well. The main problem with SolarEdge is what you stated and what I stated earlier. With Enphase, if you want to add 1 panel or 25 panels, it makes zero difference as the microinverter is right there with the panel. With SolarEdge, you simply can't do this as it generally takes about 8 panels (minimum,) to wake up an inverter. Solar installers would never mention this if they wanted you to install a SolarEdge system. Also, they love to point out that Enphase has more points of failure over SolarEdge. I actually find that hilarious as I can count; and when that big central inverter(s) does fail, you are without your whole system.

Very educational! I think my agent did provide options about the inverter (but I don't remember Enphase in the list), but at that time they also mentioned that there were not much differences, going with either will serve you well, so I just went with the defaults they gave.

 

[freshcut]

@freshcut which myvolt page were your referring to? I could only find the "Efficiency" section in "myChevrolet" app, and there's only a lifetime mileage (electric vs. total).

myvolt.com. It uses your onstar data and gives you quite a bit of detail on efficiency, charging and mileage for either the last 7 days, 30 days or 12 months.

 

[solar_dave]

We make a 25 mile round trip run everyday.
So our pair of Gen1 Volts uses this much electric every month according to the TED:

 

[ripegraph]

myvolt.com. It uses your onstar data and gives you quite a bit of detail on efficiency, charging and mileage for either the last 7 days, 30 days or 12 months.

Thanks! I was able to find it:

"View Charging Details" button on home screen after login,
then there's a pop-up window, in its "Charing" tab, I could view charging history for last 7 days / 30 days / 12 months.
The total kWh is displayed in the bottom of the table.

 

[freshcut]

no prob. That should give you a little more idea what real world usage should be rather than trying to calculate based on battery size and charging cycles.

 

[Random]

Read the post more carefully, I see you are looking for the correct number of panels to cover the energy usage of the Volt ... you already have a solar panel system designed for installation and are looking to expand it for the increased energy use.

+1 for enphase, the analysis software is very comprehensive, and fun to watch if you are so inclined. I run 28 panels of LG315 mono panels (19% efficient) on enphase S280s over here in upstate, NY. My panels are East facing at about 20 deg, not optimum, but the system makes plenty of power for my needs, and looks like it will store enough energy credit kwHs (NY - net metering) to get me through the winter. I do not have a daily commute.

Something to consider is that if you go with too many panels, with Net Metering, the extra credits are lost at your anniversary date (probably March or April) with no annual carry over of credits (at least over here in NY). An oversized system (credits lost annually without annual rollover) is just wasted money. There is no return (system pay back time) over the years for annual over-production.

 

[RonfromNJ]

Just had to move from MI - was in facilities in building maintenance. Fell broke lower spine. Daughter going to take my wifes volt. I need a larger GM now... uggg... need room while i have to rehab for next year or two. can not get into the volt. When i had it at home and solar charged, made me smile coming home every day. Been out of GM now since accident 14-1/2 months does anyone have a GMS they can share. Buying now is not great news but any discount will help. thanks PS drove past a HUGE windmill farm the other day, i am so happy to see more and more going up.

 

[Random]

This calculator might be helpful: http://pvwatts.nrel.gov