Solar Panel Car Roofs: What Are They?

This is one of the more common questions we get asked here at Bluetti. Why do electric cars not just have solar panel roofs to charge their battery? 

At first, this seems like a grand idea, and in theory it actually is. The problem occurs when you try to put this theory into practise. Well, sort of. 

In this article, we go into detail about what solar panel car roofs are and if they are a viable solution to charging electric cars on the go. 

What are solar panel car roofs?

how much wattage our solar panel array would need to be to offset our ev's energy consumption

Solar panel car roofs are exactly that, an array of photovoltaic cells placed on a car roof to capture and transform the suns solar irradiation into useable electricity. 

Why space matters for solar arrays

First things first, you need to understand that it is unlikely solar panels will ever replace an EV battery. 

The reason for this is simple. There is just not enough space on a cars roof to host a big enough solar array to power the car solely on solar. 

To give you some perspective, an ordinary home in the U.S. generally requires a solar array that covers between 300 - 500 square feet to offset its energy consumption. 

In comparison, the average sized car roof has approximately 16 square feet of space. But you may be thinking, yes sure, but what about the hood, trunk and doors of the car, this is also useable space. 

Well, assuming you have a 4-door sedan, and taking into consideration the roof, trunk, doors and hood of your car, you will be left with approximately 70 square feet of space for solar panels. 

As you can see, this is still much less space available when compared to the roof of a home. 

They're not as efficient as rooftop solar panels

Now, it is not all doom and gloom, just because we have limited space does not mean it is impossible to put solar panels on your car. 

Yes, fitting your EV with solar panels will be possible, and they will generate electricity. However, it is important to note they will be less efficient than a roof top solar array. And not because of the technology itself. 

Rooftop solar arrays have the added benefit of the following features: 

  • Tilt angle
  • Azimuth angle
  • No shade (in most cases)

Car roofs on the other hand need to be streamlined, this takes tilt angle possibilities out of the equation (at least while you are driving).

Secondly, your car is a constant moving object, so positioning it in accordance with the suns azimuth trajectory is not always possible. 

Lastly, the same goes for shade, finding areas with no shading in a car is not alway easy. Especially if you happen to live in a big city with lots of skylines. 

But what do all these points mean? 

Less efficiency, thats what. 

In order for solar panels to convert solar irradiation into electricity they need to have the above points checked off, if they don't, they will produce much less electricity than desired. 

Wattage is important when considering the size of the solar panel

Space available and the wattage of a solar panel go hand in hand. That is, the larger the solar panel (generally) the higher the wattage. 

The higher your solar panel arrays wattage, the more potential sunlight will be converted into useable electricity to charge your car. 

We can use a very simple formula to determine how much wattage our solar panel array would need to be to offset our EV's energy consumption. 

It looks like this: 

how much wattage our solar panel array would need to be to offset our ev's energy consumption

The durability of a car's solar panel is important.

Let's not forget something, a car travels at high speeds, generally between 60 - 80 mph. Right off the bat, that is much faster than any residential solar panel array will travel, probably ever (not taking into consideration logistics when it is being transported to your home in the back of a truck).

Because of this, solar panel car roofs will need to be built to last, and by last, we mean take an impact from a coin sized pebble travelling at 60+ mph. 

Additionally, you will need to take environmental factors into consideration, such as dust, mud, bird poop, bug splatters etc. All these factors can either damage or reduce your solar panel car roofs efficiency. 

Will solar panel car roofs work where I live?

This is a difficult question to answer and really depends on where you live. First and foremost, remember that the more sun your area receives, the better equipped you are at transforming that sunlight into electricity through the photovoltaic effect. 

For this example we will assume you live in Los Angeles, California. 

The average EV will use 30 kWh to travel 100 miles. Let's say for work you travel 50 miles in total, 25 miles to work, and 25 miles back home. 

This means your EV will consume on average 15 kWh a day. 

We already know that you have about 70 square feet of space available for a solar panel array, assuming you where to install solar cells on every part of your vehicle, like the doors, trunk, hood and roof of your car. 

This means you could actually fit around 1500 watts of solar on your vehicle. For arguments sake let's say that every single cell was working optimally in accordance with tilt angle, azimuth, and no shading. 

This is how much energy your solar powered cars array would generate per month: 

Month Solar Radiation
( kWh / m2 / day )
AC Energy
( kWh )
January 4.47 164
February 5.04 165
March 6.25 223
April 6.89 237
May 7.15 253
June 6.99 236
July 7.51 262
August 7.55 262
September 6.81 229
October 5.77 202
November 5.03 174
December 4.07 150
Annual 6.13 2,557

 

So in the peak of summer you'd be looking at around 8.7 kWh of solar production per day. More or less half your needs assuming your drive 50 miles per day.

Final Thoughts

Remember, our above example assumes your solar panel car is sitting at optimal angles all round. In reality, you would actually want to drive the thing, moving in and out of shady areas, and out of line of the suns axis. 

This means your solar production would be significantly less than mentioned above. 

On the hand, if you are driving an 18 wheeler truck, things become a bit more interesting ;) 

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