Solar use cases

Electric car on solar panels – is it even possible?

Solar panels and an electric car seem like a nice pairing. PV modules generate electricity, which you can use to drive around. But are they indeed well-suited for each other? Or, in other words, can you run an electric vehicle (EV) on your residential solar panel system? If yes, how many panels do you need? Let's dig in.

Charging electric car at home is easy and cheap

The subject of this article is plug-in electric cars. Vehicles with solar panels on top or hybrid cars are not considered here.

Electric cars are easy to charge at home – in fact, 80% of EV owners prefer this option to charging stations. To do it you'll need to set up your own EV charging point where you park your car. Most electric vehicles you can plug into a regular socket, but it just takes too long to charge them this way.

The experts of the US Office of energy efficiency & renewable energy claim that charging an EV at home ends up being much cheaper than paying for gasoline. What is more, they say that an electric car can consume less electricity than an AC unit. That sounds optimistic – if running an air-con on solar panels is doable, charging a car battery can't be impossible, right?
80% of EV owners prefer charging their cars at home

Get to know your EV first

Calculating how much energy an EV needs might be challenging. First, all EVs are different. They spend different energy amounts per mile and their battery capacities vary.

At the moment Tesla cars are the most popular EVs in the USA with Model 3 leading the list of world best-selling electric vehicles of 2020. Therefore, we'll base our examples on the properties of this particular model.

Tesla Model 3 can be equipped with a battery of 54, or 62 or 75 kWh, depending on the exact model. Its electric range or distance which its battery can withstand without recharging varies from 220 to 350 miles. Charge time from 0 to 100% depends on the charger power rating. A 120kW supercharger can, in theory, refill the battery in 30 minutes. The car itself is sold with an 11kW on-board charger, which can charge your Tesla in 6-8 hours.

But not only the EVs are different, owners and their habits aren’t all the same either. Some use their car only for commuting to and from work, for example, others like to take long car-trips on a weekend. Let’s examine a couple of different scenarios.

Case study #1: going on battery-exhausting car trip

Let's set our example in Oklahoma, where EVs are most popular across the US due to low electricity rates. The owner of a Tesla Model 3 goes on a car trip on a Saturday afternoon, and returns home right as the electric car gets discharged. How many panels does it take to recharge the car on Sunday?

To charge a Tesla Model 3 in 30 minutes with a supercharger you'll need no less than a solar farm. Generating 11 kWh for a standard Tesla charger with a residential solar installation sounds more plausible. Let's say the battery capacity of the car is 62 kWh. The average number of peak sun hours during which solar panels generate the maximum amount of energy in Oklahoma is 5.6. Let's now figure out how much electricity solar panels need to generate per hour to fully charge the car on Sunday.

62 kWh ÷ 5.6 h = 11.07 kW

Very convenient, since the power rating of our charger is 11 kWh. Now we need to figure out the number of panels that all together would generate this amount of power. Let's say we have 440W panels, which are among the most powerful ones on the market. We'll need:

11000W ÷ 440W = 25 solar panels

Frankly, it's a lot. We don't even take into account all the other energy needs of a house here. If such all-out trips aren't frequent, you can leave your car recharging for several days. In this case, the number of panels you need will drop down respectively.

Case study #2: using EV for daily needs

Long knockout trips aren't a forte of electric cars. What they are best suited for are daily needs: get you to work or a supermarket and drive you back home. So how many solar panels do you need if you don't plan to drain your car battery every day?

An American citizen drives around 13,476 miles per year which translates to roughly 37 miles per day. It's unclear what the exact Tesla Model 3 energy consumption is: on paper it's around 4 miles per 1 kWh, but in reality it's closer to 2.6 miles. Let's go with the latter to have an energy backup just in case. The daily energy need for an EV approximately equals to:

37 mi ÷ 2.6 kWh/mi = 14 kWh

Now let's figure out how many panels we need to generate 14 kWh daily. Assuming we're still in Oklahoma,

14 kWh ÷ 5.6 h = 2.5 kW

Such a solar array can consist of, for example, eight 330W solar panels or nine 300W. This is a reasonable number and indeed somewhat comparable to running an AC unit.

To sum it up, solar panels can and should be used to power up EVs. However, charging a battery from zero takes too long and requires a lot of power. This is why the best strategy is to recharge the battery of an RV in small doses. Consequently, a conventional car is better for long trips, whereas an EV works better in short range. Keep in mind, that solar panels don't work at night. So, if you leave a car to charge overnight, it's going to get energy from your solar battery.

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Illustrations – Marina Fionova

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