Electric Vehicles (EV’s), Solar power and their relationship on your property

With the recent uptick in interest in Electric Vehicles (EV’s), it’s a natural question to discuss how adding an EV to your home or work fleet will impact your electricity consumption.


All a person needs to consider is how adding ANY electrical appliance to your home/workspace will impact your bill from the power company. It’s pretty easy to conclude that adding something that uses electricity to your property will increase your electric bill.


But how much?


The answer to “how much” really boils down to the driver of the EV. Lots of miles per year equals more charging. More charging equals more electricity used. More electricity used means higher bills.


Pretty straight forward, right?


But…you ask…how MUCH higher will my bill be?


To answer this without “painting myself into a corner”, I’m going to use some “averages” that can be found among most electric vehicle blogs/tech specs/reviews/etc.

1) A typical driver will put approximately 10,000 miles (per year) on their vehicle

2) A typical EV will get approximately four (4) miles per kilowatt-hour of battery capacity


If we divide 10,000 miles by four (miles per kilowatt-hour), we get a total of 2,500 kilowatt-hours of energy used to drive 10,000 miles per year.


The total increased cost that you will see shown on your electric bill will depend on how much your local electric company is charging you for your power (per kilowatt-hour).


Portland General Electric represents their Residential (and small commercial) electricity rate at 13.5¢/kWh sold.


If we multiply the 2,500 kWh needed (to drive 10,000 miles per year) by our local utility rate, we come up with an added expense (per year) of $337.50


You read that right: it will cost you roughly $337.50 per year to drive 10,000 miles per year with an EV that is averaging 4 miles per kilowatt-hour of battery storage. That’s amazing! I know – I drive a Hyundai Kona EV with a 64kWh battery. These numbers (based on my experience) are conservative (which makes me a VERY happy owner!).


So…you’ve decided that an EV is in your future – and while you’re at it, why not stop paying your electric bill to the power company? So you decide that a solar array on your property is also in the cards. How (you ask) can the solar array charge your car so that you don’t pay for that power from the local electric company?


To understand this effectively, we must establish the basic functionality of grid-tied solar.


If you’ve come to this blog, my guess is that you’re familiar with solar, hence the reason your search found this blog post, so I’m going to assume a few basics:


1) You understand how solar power is generated (sunlight hits the panels, magic happens, electrons move, and DC power is generated)

2) You understand that DC power (like what we find in batteries) is not the same as AC power that we use to power our homes or commercial properties

3) You understand that we must convert the DC power from solar panels into AC power that can be used on the property (or sold back to the electric company for a credit – ie: net-metering).


If we establish these basics about solar power, then we can skip to the good stuff: how your power is “stored” (with a grid tied solar installation) and how your solar power is used (when the sun is shining).


So: How does solar power that you generate on your property get used? Well – it works like this: the power flows from your roof (or ground mounted solar array), through the necessary equipment to convert it to AC power (for your property) and it then is connected at your main electrical panel. From this connection, the power (when the sun is shining) will go to one of two places:

1) Into your property – as needed. If your solar panels are making power and your property is using power, then the solar panels will meet the needs of the property and stop the electric company from selling you THEIR power

2) If – on the other hand – the sun is shining and your solar panels are making power, but your property is not using any of it (think of an office space on Sunday – nobody’s there and yet the sun is shining and your solar panels are making power) – then the power will instead go BACKWARDS through the electric meter (turning it BACKWARDS and getting you credit) and onto the electric company’s power lines – flowing into your neighbors’ property instead.


Hopefully the above two options (for how the power flows into your property) will help you understand a very basic premise of how solar panels will “charge” your EV: they technically don’t, yet they DO.


Follow me here:


The solar panels are going to produce power (and turn your meter backwards) whether your car is plugged in (or not). When they turn the meter backwards, you’re getting credit from the electric company (in kWh’s).


Most of us drive our car to work, then come home at night and plug in the car (after the sun has already gone down). This means that the charge for the car is coming from the electric company, right?


Yup. That’s right – but…


…During the day (when you were at work), the solar panels turned your electric meter backwards all day (while you were gone) and ended up putting a lot of credits on your meter (for you to use at night when the sun doesn’t shine).


So even though you’re using the electric company’s power to charge your car back up, you’re ACTUALLY using up credits that your solar panels generated during the daytime.


So by the time you get your electric bill, odds are (if DPI Solar did their job), you’ve generated as much power as your property uses. And the electric vehicle’s power came right from the credits your system created during the day while you were at work.


So… what if you had DPI Solar design and install a solar array on your property BEFORE you purchase an EV?


Well, again, if we did our job properly, we designed a system that would use “net metering” to adequately cover your electric bill all year long (the excess credits generated during the summer will “roll over” into the winter months – when the solar panels generate far less power per month than they do in the summer).


So…if we designed your solar array to meet your needs BEFORE an EV purchase, then you could expect to start paying an electric bill again once you add the EV electricity consumption to the property (≈ $337.50 per year total).


Can you add more solar panels to offset this additional usage? You bet! ( I say this cautiously because some of our customers use every available inch of their roofs for solar, leaving them less room in the future to expand for new use like an EV).


Now let’s summarize:

1) Electric Vehicles plug into your home just like your other electric appliances do

2) Electric Vehicles will increase your electricity consumption, thereby also increasing your electric bill

3) Grid-tied solar panel installations generate power when the sun is shining and will turn your meter backwards if the property’s power consumption is less than the power production of the solar panels (minute-to-minute).

4) Turning your meter backwards (via Net Metering) will create a bill credit for you (in kilowatt- hours – kWh)

5) When you plug your car in at night, your kWh credits (created during the day by your solar panels) will offset the kWh’s used to charge the car back up

6) Folks who already have solar panels on their roof will likely need to add more panels to offset their new additional use if they add an EV to their property.



Finally – for those folks out there who are going to ask about charging up their cars with a battery-bank solar array: The answer is complex, but still YES – though you won’t be able to utilize your Level 2 (240v) charger to charge your car from the solar powered battery bank. You’ll need to use your Level 1 charger during these times as the majority of hybrid solar inverters (that will allow you to add a battery bank to your property) have a limited output (rated in watts) when they are in “off-grid” operating mode. A typical Level 2 Charger pulls no less than 6,000 watts (which is more power than the Tesla PowerWall can continuously output – at the time of this writing (9/2022). This means that in order for you to charge

your car and not over-load your off-grid hybrid inverter, you’ll need to do so SLOWLY with your Level 1 charger. Is this tedious and takes time? YUP. But… consider than anyone else who doesn’t have a hybrid inverter with battery backup won’t be able to charge their car at all!


Some of our hybrid inverters CAN handle a Level 2 EV charger (Q.Home ESS+ G1: output 7,500 watts, Outback Power Radian 8048A: output 8,000 watts). So…if you have one of our inverters, should you consider trying to charge your EV up with your Level 2 charger? In my opinion – no. The reason is, doing so will take up all of the available output power of these systems (in off-grid mode) and not leave you any power in reserve to run lights and plugs on your property. If you ended up deciding to do this, you’ll likely end up in an “over-load” situation on your hybrid inverter. It will shut down and wait for you to “shed” some of the loads that contributed to the over-load situation.


Also consider the size of the EV battery versus your battery backup you have on your property. In all likelihood, the EV battery is substantially larger than the battery you have backing up your property loads. This means that if you decided to try to charge up your EV at night from ONLY the battery bank, you WILL end up completely draining the battery bank and you’ll only partially re-charge your car. The lesson here (for our OFF-GRID charging folks) is to charge up your car when the sun is shining so that the power from solar panels (and not the battery bank) goes into your car’s battery. This will keep your backup battery charged and ready to handle the loads your property will throw at it during the day or night!


Well folks – this was a complex and challenging subject to address, but as we see more of our customers buying both of these products (three if you counting our battery backup options), it’s important that all involved understand how the power is generated, where it goes when you plug in your car, and if you should try to charge your car up from your backup battery when the electric grid is down.


Thanks for reading and feel free to contact us any time.


Josh, DPI Solar