Are Solar Vehicles Becoming Viable?

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Recently, Toyota announced a special research and development project. With Sharp and the New Energy and Industrial Technology Development Organization (NEDO), it has put a special test vehicle together that uses solar panels to generate almost 1 kW of energy during daylight hours, whether the vehicle is driving or sitting.

Rather than doing a quick regurgitation of Toyota’s press release, I wanted to provide some more context to explain why this is important, what the limitations are (for now), and where direct-mount solar EVs are headed.

The Challenge

People are rightly skeptical of solar-electric vehicles. Getting electricity from the sun is a great thing for both the environment and the wallet, but it’s not known for being light and compact enough to be worth putting on vehicles. That appears to be changing, though.

Conventional wisdom tells us that solar is something that lives on your roof, or out in a big field. Solar panels on cars have been little more than an expensive gimmick in the past, powering cooling fans in some hybrids. Other CleanTechnica authors who owned a Prius with the solar roof option said it wasn’t terribly effective or helpful. Even the first-generation Nissan LEAF’s optional solar panel in the spoiler makes just enough power to help maintain the car’s 12V battery when sitting. There just wasn’t enough room to get much power, and a bigger system would involve raising the price of the car anyway, which would have taken the LEAF in the wrong direction at that stage of the market.

For these reasons, the only onboard solar vehicles we hear of now are university projects, racing experiments, and concepts from niche startups. People have driven across great distances in solar cars, and even race them, but they’re often designed to carry just one person and little or no cargo.

Electric vehicles were once in the same spot. Only a decade or two ago, you’d have to choose between having short range or paying big bucks for batteries. A few experimenters would build EVs to go short distances, and manufacturers weren’t that far ahead of the home tinkerers. The technology just wasn’t as mature as it is now. 

As it improved and prices fell, EVs became more affordable and more capable, and are now poised to start outperforming combustion vehicles in almost every way. Just like battery technology, solar cells have continued to improve, and we are starting to see practical solar vehicles emerge.

Toyota’s Test Vehicle

There doesn’t appear to be anything special about Toyota’s test car itself. It’s a plug-in hybrid, and looks to be nearly identical to the Prius Prime. It has a hybrid drivetrain and a large enough battery pack to power the car for a number of miles on electricity alone, but has a gas engine that can power the car once the battery is depleted. There’s nothing new about any of that.

Even the idea of adding solar cells is nothing special. Toyota has been doing that for over a decade. The first factory hybrids with a solar roof generated just enough power to run a cabin cooling fan. Later, they added larger panels to the roof of the Prius Prime, and they charged the car’s drive battery, but in a whole day, you could count the number of miles added on one hand.

The only thing that makes this car special is the cells used. Toyota partnered with NEDO and Sharp to come up with solar cells that are 10% more efficient than the best cells currently on the market, and almost double the efficiency of typical cells put on houses today. Additionally, they installed these 34% efficient cells on the hood, over the back window area, and on the trunk/spoiler area. 

Between the increased efficiency and the increased area covered by cells, they estimate the car will be able to add around 27 miles of range per day, assuming good conditions. Under bad conditions, the car can still plug in and charge. If all else fails (or you’re driving long distance), it can still fire up its Atkinson-cycle 4 pot like any Prius. If something like this went to production, there are a lot of options for powering one’s trips.

Why This is a Big Deal

27 miles of range might not seem like a big deal, but when you consider that the average American’s daily driving is 29.2 miles, it could clearly have a big impact. For many people, they would be able to drive to work, charge in the sun while they’re at work, and then drive home. For people with longer drives, many will be able to charge at home, drive to work, and leave for home with 100% battery. Unexpected trips, cloudy days, and anything else in the way would be covered by gas.

Perhaps more importantly, people without home charging wouldn’t be left out of the EV revolution. People in apartments, people in HOAs that won’t allow charging installations, students, and many other people would be able to do most or all of their normal driving on the power of the sun. When you consider that apartment dwellers and renters are often also not able to install solar where they live, it’s a double benefit.

Environmentally, it’s another big plus. I’ll give the most extreme example: people living in apartments. Today, their only option for electrification is probably a hybrid or charging up something like a Tesla once or twice a week. Given the lack of convenience compared to home charging, many apartment dwellers will continue avoiding battery EVs for the time being. With solar charging, many apartment dwellers will cover a big portion of their daily driving on solar, and use that much less gas. That reduces their vehicle pollution by anywhere from 50–100%. (Editor’s note: While I do agree with this assessment, it’s worth noting that many people in apartments without home charging can do fine with an EV if there are adequate charging stations where to work, shop, or chill out. We have a 71-mile BMW i3 without home charging and have no problem with that because there are charging stations almost everywhere we go. That said, many apartment dwellers are not so lucky.)

Another big social benefit is resilience. By charging batteries directly, this negates the need for power plants, transmission lines, and charging infrastructure, all of which are vulnerable to failure. We’d avoid transmission losses, and in the worst case, wildfires caused by increasingly strained power lines that droop. Even in large-scale disasters that cripple infrastructure, decentralized charging of transportation could keep the world moving that much better.

Where Solar EVs are Headed

Toyota is not the only automaker looking at solar-powered charging for EVs or plug-in hybrids. I previously covered Sono Motors’ Sion solar vehicle. Unlike the Toyota test car, Sono plans to build a battery EV with 150 miles of range and no gasoline backup. With DC fast charging and a larger battery, this could prove even more useful for many drivers. 

In the ideal case, an apartment dweller with such a car who typically drives less than the solar range added to the battery each day would have “rollover miles” that would accumulate in the pack, and hopefully cover some of the off days without having to plug in.

Other automakers, like Tesla, have not yet publicly expressed interest in solar charging, but with Toyota and Sono looking to do this, that might change. Under market pressure, it would be cool to see something like an optional solar roof for a Model 3, LEAF, or Bolt. This could prove to be a viable option for nearly any full-size vehicle.

It’s important to keep in mind that solar technology continues to improve. There are already 43% efficient solar cells in development that are almost ready for production. In the pipeline, more advanced designs offering up to 90% efficiency are looking more and more feasible. For the Toyota test car, just switching to these future 90% cells would increase the daily charge range to around 81 miles. For a BEV like the Sion, such cells would add around 70 miles daily.

Predicting when we will see these advances isn’t as easy, but it’s clear that we are going to start seeing more and more solar cars in the next few years. They will still need some level 2 and level 3 charging, or possibly range extenders, but they will provide the flexibility and ease needed to help EVs achieve greater and greater market penetration.