How many solar panels do I need to charge a Tesla?
Own a Tesla or other electric vehicle? NICE. If you're interested in charging it with solar, here's how to calculate how many solar panels you need.
Many electric vehicle owners also happen to be interested in solar electricity. That makes sense, because if you’re an early adopter for either of these technologies, helping the environment was probably one of the factors in your buying decision.
If you have a Tesla now or you’re planning to get one, you might want to know how many solar panels will you need to install on your house to charge it. In this article, you’ll learn that it’s not a straightforward answer, but depends on a few key factors:
- Your local climate, which determines how much sunlight your city receives in an average year.
- Your rooftop, including the orientation and how much shading it gets. If your roof faces east-west, it will generate less electricity than a roof facing north-south, and shading is always bad for solar panels.
- How much you drive. The average American drives 13,476 miles per year. Driving more or less than that will change how much electricity your Tesla will need.
- How powerful the solar panels are. Residential solar panels are all approximately the same size, but have different efficiencies. A higher efficiency panel will have a higher wattage rating, meaning that it generates more electricity than a less efficient panel.
The quick answer is that, for the average American who drives 13,476 miles a year, you’ll need between 6 and 10 solar panels to generate enough electricity to keep your car charged. Keep in mind that this is a rough estimate, and how many solar panels you would need depends on the four factors listed above.
This article will go into the details of this so that you can you make your own personalized calculation for your Telsa (or other EV).
First off, let’s start off by discussing the energy efficiency of a Tesla.
What is the vehicle efficiency of a Tesla?
Electric vehicles don’t list their fuel economy as miles per gallon. Instead, they use units called miles per gallon equivalent, or MPGe. This is a measurement of how many miles a car can travel on the electrical energy that is equivalent to one gallon of gasoline.
One gallon of gasoline, if converted with 100% efficiency, is equal to 33.7 kilowatt-hours of electricity. This means that if your EV has a fuel efficiency rating of 100 MPGe, it can travel 100 miles on 33.7 kWh.
The other way that EV fuel economy is expressed is kWh per 100 miles, which tells you how many kWh of electricity is used to travel 100 miles.
For example, the Telsa Model 3 Standard range has an efficiency of 26 kWh/100 miles, while the Tesla Model X Standard Range has a rating of 33 kWh/100 miles. This tell us that the Model X uses more electricity to travel the same distance, which means that it’s less efficient than the smaller Model 3.
The table below lists the fuel efficiencies for a range of current Tesla vehicles, and how many kWh they would consume to drive an average number of miles each year. Note that these are EPA ratings for 2020 Tesla models. Earlier (and future) Tesla models will have different ratings.
| Vehicle | Fuel efficiency (kWh/100 mi) | annual kWh (to drive 13,476 miles) |
|---|---|---|
| Tesla Model 3 Standard Range Plus | 24 | 3,234 |
| Tesla Model 3 Standard Range | 26 | 3,504 |
| Tesla Model 3 Long Range AWD | 28 | 3,773 |
| Tesla Model 3 Long Range Performance AWD (20-in Wheels) | 30 | 4,042 |
| Tesla Model S Long Range Plus | 29 | 3,908 |
| Tesla Model S Long Range | 30 | 4,042 |
| Tesla Model S Standard Range | 31 | 4,177 |
| Tesla Model S Performance (21-in Wheels) | 35 | 4,716 |
| Tesla Model X Long Range Plus | 32 | 4,312 |
| Tesla Model X Standard Range | 33 | 4,447 |
| Tesla Model X Long Range | 35 | 4,716 |
| Tesla Model X Performance (22-in Wheels) | 43 | 5,794 |
| Tesla Model Y Performance AWD | 28 | 3,773 |
| Tesla Model Y Long Range AWD | 28 | 3,773 |
| Tesla Model Y Performance AWD (21-in Wheels) | 30 | 4,042 |
To find out the fuel economy of other EVs, go to fueleconomy.gov. You’ll be able to search the ratings of other popular EVs, such as the Nissan Leaf and Chevy Bolt.
How does the local climate affect how many solar panels I need to charge my car?
While solar may not always make financial sense (due to reasons such as cheap grid electricity), solar panels will function anywhere in the United States, including Alaska.
In fact, there is a decent sized solar industry in Alaska. In a state where many communities run on microgrids powered by expensive oil-fired generators, solar electricity can be a smart supplemental source of electricity during the very long sunny days of the Alaskan summer.
If you live in the continental US, there is quite a wide range in the amount of sunlight that hits the ground. This is known as solar irradiance, and it’s not just affected by how far south you are, but by the local climate, especially the average cloud cover and precipitation.
The difference between a sunny, cloudy, and average city will have a big effect on the number of solar panels you would need to charge your car. To illustrate this, I’ve chosen three representative cities:
- Yuma, Arizona (very sunny)
- Marquette, MI (average)
- Quillayute, WA (very cloudy)
For example, in Quillayute, only 33% of the sunlight makes it to the ground because it’s so cloudy. Meanwhile, in Yuma where the skies are clear, 90% of the sunlight reaches the ground. In Marquette, it’s 50%.
That’s a big range. To illustrate what this translates to, the table below shows how many 340 watt solar panels you would need to power a Standard Range Tesla Model 3 in each of the cities. (A 340 watt solar panel, by the way, would be an average premium solar panel, but not the most powerful or expensive.)
And remember that the Standard Range Model 3 uses 26 kWh to drive 100 miles, and we’re assuming an average annual drive of 13,476 miles.
| City | Number of panels needed |
|---|---|
| Yuma, AZ | 6 |
| Marquette, MI | 8 |
| Quillayute, WA | 10 |
As you can see, you would need a lot more solar panels for your electric car if you live in a cloudy region.
How does my roof orientation affect how many solar panels I need to charge my car?
In the northern hemisphere, your solar panels will generate the most electricity if they’re facing south. However, your roof might not be pointed that way, or you might have a roof with a southern exposure that’s shaded by trees.
If that’s the case, your panels might need to face a different direction. That’s often okay, but your solar production will be reduced. To see how this affects our estimate of the solar panel count to charge our standard model Tesla, here’s a table below that compares the number of solar panels we would need for our hypotheical home in Marquette, MI with different roof orientations:
| Direction solar panels face | Number of panels needed |
|---|---|
| South | 8 |
| East or West | 10 |
| North | 14 |
As you can see, an east or west facing array is still viable, but one that faces directly north generates much less electricity. Most solar installers won’t recommend a north-facing solar array.
Other factors that affect how big a solar array you need to charge an electric car
If you live in a perfectly average place and drive a perfectly average number of miles in a year, you would need 8 solar panels to generate enough electricity to power your Standard Range Model 3 each year.
But as you can see, there are many variables involved in this: panel efficiency (budget vs premium), the amount of miles you drive, the efficiency of your particular vehicle, where you live, and how suitable your roof is.
One thing I haven’t mentioned so far is shading, which can absolutely kill your solar electricity production, even if you live in a very sunny city like Yuma. If a big building or tree blocks the sunlight from reaching your solar panels, it doesn’t matter if you live in the sunniest place on earth. Solar isn’t going to work for you.
How much shade is too much shade is a question for a professional solar installer, so if you’re not sure, reach out to one to get a technical estimate.
How to calculate how many solar panels you need to power your electric vehicle
So far I’ve given some general examples, but it’s easy to calculate a custom estimate for yourself. Here are the steps:
- Go to fueleconomy.gov and find out the efficiency of your vehicle, expressed as kWh per 100 miles.
- Estimate how many miles you drive in a year.
- Calculate how many kWh you will use per year. To do this, take the number of miles you drive annually, divide by 100, then multiple by the efficiency in kWh/100 miles. For example, if you drive 15,000 miles a year, divide that by 100 to get 150. If your car uses 30 kWh/100 miles, multiply 150 by 30 to calculate that you will use 4,500 kWh per year.
- Take that annual usage and plug it into the Solar Nerd Calculator. (Keep in mind that the calculator asks for monthly kWh, so divide your annual usage by 12.)
The calculator will give you a range of estimates for the number of solar panels you need, depending on whether you choose budget or premium panels, and also a range of cost estimates. It’s meant to be a quick tool you can use in a minute, but for an accurate estimate, you will need to reach out to a professional solar installer who will generate a customized proposal based on a proper technical assessment of your property.
