Solar Panels on an Electric Vehicle

I’ve seen this question asked a ton of times;

Would it be worthwhile to put solar panels on an EV?

It’s a great sentiment, as the two seem to go together quite well. In short, however, the answer is no.

Now, I’m talking specifically about outfitting an Electric Vehicle with photovoltaics. Installing them on your home or business makes a ton of sense, with or without owning an Electric Vehicle. It’s just not sensible to do so on the car itself.

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The above photo is of a Fisker, and is basically what a car lined with photovoltaics would look like.

Disclaimer; when you talk about solar energy, the devil is in the details. What’s the rating of the panel? What’s the inverter and wiring efficiency? What’s the distance between the panel, inverter, and meter? What’s the geographical location and time of year? What’s the local weather patterns like? In short, there is no one-size-fits-all answer to questions about solar energy.

With that in mind, I’ll be using data from my own home solar system, so the data matters to me and maybe not so much to someone else. I’m selfish like that. Also, I’m not an electrical engineer so I might be missing certain details. Bah humbug.

With that said, let’s dive right in.

I drive a Tesla Model S. The specs don’t give details of the specific area of the car’s surface that I can find, so I had to grab a tape measure and do it myself. Assuming you’re replacing the sunroof with the panels, and putting them on every inch of the body of the car that isn’t a window,  windshield, or light, here’s the breakdown of my rough measurements (in inches) of various areas of the car:

Hood – 48 x 60
Roof – 46 x 60
Trunk – 10 x 54
Rear – 70 x 28
Back corner – 36 x 30 (twice)
Side – 90 x 32 (twice)

Put it all together and you’ve got about 111 square feet of surface. Any inaccuracies here can be blamed on the fact that I was taking these measurements with my 7 year old son holding the end of the tape measure and I was more concerned about making it fun for him than being precise.

On my home I have SolarWorld 280 panels, which give 280 watts at peak, and 18 square feet each. So, the car has enough area for 6 of these, once they are properly chopped up to fit on the various surfaces. All in all, you’re going to get 15 watts per square foot of panel at peak output with this system.

That’s a 1,680 watt system. I paid about $3.60 per installed watt on my home solar system before government incentives, so this hypothetical Tesla Solar system would run just over $6,000. Being built into the car, it would probably cost a lot more.

However, at any given point, you’re going to have, at most, about 66% of the surface of the car in the path of sunlight. Also, most of it won’t be optimally facing the sun, so you won’t get the peak output. Therefore you have a massive drop in capacity.

So, let’s call it 75 square feet at 10 watts per square foot, or an average output of 750 watts. That’s being incredibly optimistic, and not taking cloudy days into account.

A really good week with lots of sun looks like this:

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A bad week with cloudy days and lots of rain looks like this:

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A loss of 20% overall production due to weather seems like an accurate estimate.

Additionally, you have added weight and aerodynamic concerns. For arguments sake, let’s say the car’s shell was made of the panels, that they fed directly into the battery (no inverter needed), and there are no changes in weight or aerodynamics to the car, which toes the line of being unrealistic.

On a nice and sunny day during spring or fall, when there is the year’s average amount of daylight, Salt Lake City gets 5.25 hours average of solar radiation. 750 watts x 5.25 hours x 80% weather = 3150 watt hours, or 3.15 kWh in a single day, give or take. That’s an oversimplification of the equation, but is close enough.

What would that power?

Tesla Model S has a range EPA of 300 watt-hour per mile, so 3.15 kWh of energy would give you roughly 10 miles of range. However, if we’re talking about the car just sitting there all day, the topic of vampire drain applies. This is the amount of power the car draws to power its systems even when the car isn’t in use.

I want to say I lose about 10 miles in a 24 hour period while not plugged in. That number varies from day to day depending on a lot of factors, but 10 is an easy to remember number. You’ll lose maybe half that in energy saving mode, which the car automatically after it hasn’t been driven in a while.

In short, my car covered in a magical photovoltaic shell would cover the vampire drain, and maybe add a few miles to the meter during the summertime. And that’s best case scenario. Then again, my car is in covered parking at work all day, getting no sunlight, so really it wouldn’t do me any good.

Now, you can argue that the system I’m analyzing is a far cry from the latest and most efficient, that you may not drive very much on a daily basis, etc etc. The real question ought to be; do you want to spend thousands of dollars to never have to plugin your car for your short daily commute? If you have more dollars than sense, then go for it. Otherwise, you’re better off spending that money properly installing the panels on a roof that will optimally capture that sunlight, and taking the 10 seconds a day it takes to plug and unplug the car.

For comparison, that same $6,000 system when optimally installed on a south facing roof would produce a year-average of at least 6 kWh per day, with the above weather taken into account. That’s twice the energy, and it’s without the cost and headache of figuring out how to line an entire car with photovolatics. Not to mention how ugly it would look. Just pay someone to bolt the panels onto your roof, and you’re done.

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