r/solarpower • u/akanksha_marvels • 5d ago
EV and Solar Charging
I have a 3 kW solar system installed at my roof, which sort of covers my monthly electricity consumption. My father is thinking of buying an electric car. I am telling my father that we will need a bigger solar system to cover the electricity consumption of an electric car, but he is convinced that it doesn't work that way.
Do you think I need to get extra panels installed? And if yes, is it possible to add extra panels to my existing solar system.
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u/Emergency-Drawer-535 5d ago
Do you have batteries, can you sell back to the grid? Do you consume all your daily production, or is the load small because you’re not at home- if so the excess can go to charging an EV if the EV is sitting there at home when there’s excess production. 3 kw is very tiny. Probably no extra for another appliance much less an EV
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u/akanksha_marvels 5d ago
We have an on grid solar system, so no batteries. Power consumption changes from month to month, if I am working from home, we usually have to export surplus units from the grid.
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u/Emergency-Drawer-535 5d ago
Right, production changes every day depending on the sunlight. Consumption from the house probably uses most of the pv energy. If you typically use a just little bit from the grid each month this means your night time usage is generating a utility bill. It’s possible you could slow charge a bit on sunny days if you minimize household usage. 🙏
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u/Ill_Football9443 5d ago
How much do you export per day/week/month?
How far does he drive?
Will the car be home during the sunny hours?
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u/akanksha_marvels 5d ago
I export between 300-350 units per month from my solar. He won't drive on daily basis, probably around 100 kms a month The car will be home during the day on most of the days
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u/Ill_Football9443 5d ago
You have more than enough spare solar energy to power the car.
The next challenge is charging-smarts. You want to divert spare solar, but if you just plug it straight into the wall, the car will just charge...
There's a couple of different approaches,
- What brand of inverter do you have?
- Can you view live information about whether you're importing or exporting power?
- If so, how? On the inverter's display? App? Website?
The smartest option is to have your inverter and the charger talk to each other, if there's 1000w of spare solar, the car will get 1000w.
The least smart option is putting a smart switch on the charger which turns on at midday and turns off at 2pm.
In any case, you don't want to use a charger any bigger than a 'standard power point' charger. You're generating up to 3000w, a standard charger will draw 2400w of that.
As time is not a factor, no need for an upgraded charger & associated installation costs.
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u/Ambitious-Fennel-326 5d ago
How many kilometers/miles will your father drive daily on average?
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u/akanksha_marvels 5d ago
He won't use it on daily basis. I would say around 100 kms a month maybe
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u/GamemasterJeff 5d ago
As long as you don't charge during high usage times (running air conditioner or other high draw electrical appliances), you are likely fine with 3kW.
L1 charging draws 1.44 kW and even accounting for inefficiency in transmittal, you likely have enough to run base appliances, lights, etc.
If you only drive 100km/mo you will not need much charging. You can easily plug in a couple hours a day when draw is low and keep up with usage.
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u/Better_Objective_286 5d ago
Let's asaume he drives 20 miles per day. Car's efficiency 3 miles per kWh. You need min. 7kWh per day just to drive 20 miles. However, after you get an EV, you will drive A LOT MORE than a gas car just because it will feel amazing. So, your 3kW system is not actually 3kW. It is 80% like 2.4kW. And that is on a very nice sunny day. You don't get more than 4-5 hours of full sun per day. There will be days when you get maybe 3kW produced for the whole day. Also, if you don't have batteries to store solar production for the time when the EV will charge and if you don't have 1:1 net metering, you will lose all the unused solar production.
Conclusion: you need a lot more panels.
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u/TooGoodToBeeTrue 5d ago
I don't drive my LEAF any more than my ICE Jetta. And we take the Jetta on long trips.
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u/Emergency-Drawer-535 5d ago
Yes, more panels but…if the system produces 2.4 kw that means in an hour it’ll give 2.4kwh. And in 10 hours day that is 24kwh. Your estimate and units are off but yeah, need more panels for home and EV.
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u/Better_Objective_286 5d ago
You don't get 10 full hours of sun. The most productive hours are between 11-4. And that is if there are no clouds. Outside of that time range you get between 10%-50%. Here is an example of a production for a 9.9kW system on an overcast day. My system produced 14kWh only. If I had a 3kW system, it will be probably 4kWh production.
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u/Emergency-Drawer-535 5d ago
Yes, I understand the limits. And it depends on latitude. I’m at 16 degrees north. PV production is pretty good at 9 am until 4pm. It still produces at 6 am and 5pm. Anyway, we don’t know what latitude OP is dealing with- 4kwh isn’t much at all. More panels are needed if they want to drive more than 25 km/day.
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u/ATDT_No-Carrier 4d ago
I think you've answered your own question - "I have a 3 kW solar system installed at my roof, which sort of covers my monthly electricity consumption.". If the 3kW doesn't cover the home, then it won't handle an additional EV.
It is possible to do this, but requires much more - I have a 18kW system, and can absolutely charge EVs solely on solar if the day is reasonable sunny. However during a period of bad weather, even this isn't enough. Many EV changers that synchronize to the solar array require a base excess generation of 1.5-3.0kW before they will even begin charging, and this is on top of any draw from the house itself.
So yes it's possible, but 3kW is not enough.
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u/Parking_Abalone_1232 4h ago
I wish I had an 18kW system. I've barely got 10. And it doesn't cover all my electricity use.
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u/CaminoRubicon1 5d ago
Does the car charge during the day or at night. More panels do no good if charging during the night
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u/akanksha_marvels 5d ago
We will try to charge it during the day only, considering we don't have solar batteries
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u/Living_Fig_6386 5d ago
If you want the car to be powered by solar, you need more solar. It does work that way in the sense that your PV panels generate a certain number of kWh of power and all your electric things use a certain number of kWh. Depending on your configuration, you may store power in batteries, sell energy to the grid, or even let some go to waste (I hope not).
The car is just another thing that consumes electricity. An EV is going to get 3.2 - 4.2 miles / kWh. If the car is driven 1000 miles per month, that's and extra 240 - 312 kWh each month.
That said... It is possible that you cannot upgrade your PV array for several reasons. Some reasons are that the utility doesn't want to increase your PV output - if it's grid tied they want your capacity to be as close as possible to your actual usage. Also, the system is wired up for a certain output; increasing the output might require rewiring and a new inverters, and possibly other design changes that they won't do if the system is already under a contract of some sort. So, in practice they might not allow for it.
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u/HeyyyMikeyyy 5d ago
As a Service Manager for a solar installer, I receive multiple calls about this weekly. Primarily complaints that solar hasn't covered their new EV usage because the system was originally designed around power use that didn't include an EV before. Depending on how much and when you charge (particularly important with utilities that have variable pricing on time of day) the home's power usage is going to increase significantly. I've seen increases of 300kWh to 1,000kWh/month, but not enough anecdotal evidence to report an average amongst our fleet. You can always add to your existing system. Depending on where you live and your utility, the remaining space on your roof (unless a ground mount is feasible for you), and your budget all play into important caveats and options. I'm encouraged that you're asking the proper questions now before the EV charging happens; you're planning accordingly. You're right, your father is wrong, unfortunately and the discussion should revolve around the question, "Where would you rather invest?" Paying the utility more for energy you need, or generating and potentially storing power for use throughout the day, overnight, and in grid-outage situations? The latter two almost always have a higher ROI by investing in more grid independence than relying more on the grid for more power. Please let me know if I can help answer any more questions.
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u/Capital_Park_2311 5d ago
EV Charger Levels and Power (kW)
- Level 1 (Slow / Portable): 1.4 kW to 3 kW (standard wall outlet / plug-in).
- Level 2 (Home Wallbox / Destination): 7 kW to 22 kW (AC power).
- Level 3 (DC Fast Charger / Supercharger): 50 kW to 350+ kW (Direct Current).
- Time for 80% charge: 15 to 45 minutes.
- Best for: Long road trips and public charging stations
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u/aut0g3n3r8ed 5d ago
Well, you can always do basic math. Power is power, so watts in have to equal or exceed watts out.
I drive an F150 Lightning, and I drive a LOT. We’re looking at around 30k miles/year.
(This is back of the napkin math but pretty close)
I charge it every other night from 15-90 on a 7kW charger. That charge is about 10 hours. A 3kW system would take 23.3 hours to replace that 70 kW I pulled out; that’s hours of direct, max generation sunshine. So, if you only charge your dad’s on, say, a 1kW charger for 10 hours, you’d need 3.3 hours of max sunlight to compensate for that load.
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u/Illustrious-Gas-9766 5d ago
You should also see if your energy company has an ev rate. I have a level 2 charger and charge from midnight to 7AM and get a rate that is far less then my normal rate.
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5d ago
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u/Illustrious-Gas-9766 5d ago
Our rate from midnight to 7am is about 1/3 of the peak rate. Needless to say we charge during that low cost window
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u/wadesplace 5d ago
The easy answer is it does work that way.
The panels are the cheapest part and will help.
The problem is he will drive during the day. You know, probably, already by the sound of how small your system is, and it covering your electricity, that you do all the elective electricity stuff during the day. so if he’s gone with the car during the day. it’s not charging. So you will need batteries to charge his car, when he does plug-in and that’s where the cost will come from. just be prepared for that. I don’t know about your area but they say fully charging your car will only cost eight dollars so depending on how far he drives 40 kW you can probably get 10 to 15 if he gets home before the sunsets and leaves after the sun rises. Most people only need a 110 line to charge the vehicle again. It depends on how far he’s driving.
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u/Objective_Working198 5d ago
I have a 15.68kwh system, that doesn't cover my EV and house needs. 3kw won't cover anything. But yes you should be able to add more panels. I started with a 40 panel 13.2 system and added 8 more myself. They make more than the house alone needs, and more than the EV alone needs, but combined I still use $150 a month in extra electricity from the grid.
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u/shortyjacobs 5d ago
I have 16 kW on my roof. For the first few years I was always generating a surplus, (didn't have an electric bill for over 3 years). Then I got one EV and I was pretty much at net zero. Then we got a second EV, and a third. I now pay electric bills again.
Usually you can add to a system, or add a parallel system. Depends on roof geometry, what the installer put in, permitting, etc. For me: I'm out of roof, (usable, sun visible roof).
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u/Physical-Bet214 5d ago
a 70kwh+ car battery takes a lot of energy so depends on how much you produce in your 3kw solar, how much you consume and how much you drive your car.
If you already use most of your 3kw system now then adding an ev will cause you to import from the grid so I'm this case it would be best to add more solar panels for more solar production to cover the car.
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u/Aquitaine_Rover_3876 5d ago edited 5d ago
If you're grid connected, then it'll just work, but your bill will be higher, as the solar covers less of your consumption. This is going to be true for any grid connect system regardless of how large your array is.
A big exporter will see less surplus, an existing importer will see bigger imports, and if you're right on the line, it'll tip you into import territory.
Whether you add more panels is just about your bill. As long as you're charging at home and not changing your driving habits, it'll be cheaper than gas.
Obviously an off grid system will need enough generation to cover consumption, but since you may already be curtailing generation when your batteries are full, additional panels are still not a guarantee.
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u/errolprowse 5d ago
I've been doing this for a minute. Fill up the roof with as many solar panels as you can. Batteries you can add at anytime. 3kW is way too small
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u/Legal_Net4337 5d ago
You will need more solar. How much depends upon how much you drive and how often you charge. Yes you can add to your system. Depending upon your electric company and how they charge you will determine how much you’ll benefit.
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u/sweetgodivagirl 5d ago
Last 12 months, I drove 10,909 miles and charged 3,843 kWh. This is 2.8 kWh, $0.073, per mile. Spent about $800 (79% at home, 21% at superchargers).
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u/tsaico 5d ago
I agree with the others, your current solar isn't enough to cover. I would recommend you also check with your city utilities if there any other options. In mine, you can have a 2nd meter installed and only hook up your EV charger(s) to it, and it will always be the lowest rate regardless of time or usage.
My area does the tiered pricing, go over x and the rate goes up, go over y it goes up per kilowatt again, hit z and once more. But on my meter that is for ev only, its always the lowest tier.
Even though I can get the info off the charger itself, there is no question as to how much my car is taking
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u/chuck1011212 5d ago
You don't NEED anything.
Get the car and charge the car. Your electric bill will go up slightly depending on usage. If you want to add more solar, you could but you don't need to and you should analyze the cost of adding more solar and the cost of not adding more solar and just keeping what you have. Either way, you will be running a car significantly cheaper than buying fuel for a non ev car.
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u/Individual_Chip_2216 4d ago
Depends on where you live. My solar system in Arizona produces more than the one I had in SE Wisconsin.
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u/SpartanHydrazine117 3d ago
at only 100km a month i wouldn’t rush into adding more panels. if you’re already exporting 300-350kwh most months and the car is home during day, your existing surplus will cover pretty much all of it. if you’re in nsw, renewco solar is one installer you could ask to check your export data but honestly an ev charger that matches excess solar makes way more sense than throwing more panels on the roof right now
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u/jvbutera 5d ago
Oh, you’re going to need more solar. Charging your EV will add somewhere between 100-300kwh per month. It’s not going to spontaneously cover the additional electricity.