How far are we from a self-charging solar car?

A few years ago I wrote about the Catecar dragonfly, a lightweight electric car that could be charged entirely through its integrated solar panels. It was due to be trialed at airports and on corporate campuses, but the website hasn’t been updated for years and it doesn’t seem to have got out of beta.

That’s a shame, as there are a bunch of reasons why a self-charging solar car would be helpful. Lack of charging infrastructure is holding back wider adoption of electric vehicles. If your car could charge from the sun while parked, even it was just recovering a portion of its overall battery power, that may be enough for many more people’s commute or daily car use. On a sunny day your car would be trickle charging as you drive, and extending the car’s range. And you’d know it was charging on renewable energy, eliminating the main environmental loophole on EVs – if it’s charged on coal power, there’s little point. So with the Catecar apparently gone, is anyone else working on it?

Last year there was a bit of a buzz around the Fisker Karma. An earlier version of this sports car had a solar roof that ran the air conditioning and accessories, a feature that you can get on the Toyota Prius. The roof on the latest version of the Fisker Karma charges the battery too, but this is a high performance car, and it’s a small roof. It’s only going to contribute a tiny fraction of the energy needed. Looks like a token effort to me.

stella-luxThat’s not an accusation you could level at the Stella Lux, the world’s first energy positive family car. Lightweight and clad generously in solar panels, under normal usage it should create more energy than it uses over the course of the year. You can plug it in at home and use it as a domestic battery. Should you wish to take it long distance, at a full charge it will go 1,000 km. The downsides are that it makes no concessions to style, and looks like someone put wheels under a rooftop solar installation. So I’m not sure we can count this just yet.

The rooftop installation is what you get from SolarDrive too. They offer a solar retrofit to electric golf buggies, which is a great idea and there’s no reason why every golf buggy in the world shouldn’t have one. But it’s not a car.

To make any impact in the real world, I’d want to see a big car company looking into this, and the only example I’ve found so far is Ford. They have experimented with a solar roof on the hybrid version of their C-Max hatchback. It’s not a large amount of solar capacity, and not enough to keep the battery charged. Their solution is to pair the car with a special charging canopy that uses Fresnel lenses to direct more sunlight onto the panels. (Those are the same lenses that lighthouses use to amplify their light) Ingeniously, the car can optimise the sunlight it receives by autonomously scooting itself backwards or forwards as the sun moves in the sky.

That’s a clever solution, but not a practical one. Nobody wants to build a new garage that’s tailored to one specific model of car, and I’m not surprised to see that Ford didn’t pursue the idea much further. Ultimately the Fresnel lens canopy is solving the wrong problem. The question to be asking isn’t how to get more light to fall on the panels, but why have you only got 1.5 metres of panel on there in the first place? And the reason is that the solar roof is an afterthought. To do this properly, you’d have to design the car to be solar powered from the start.

hanergy-solar-aThat’s what Chinese firm Hanergy are doing. Last year they demonstrated four prototype vehicles that are clad in their own thin-film flexible solar panels. The most practical looking of the four is the Hanergy Solar A. Taking the roof and side panels into account, it has 7.5 square meters of solar panels. The company claims that five to six hours of sunlight would generate sufficient power to drive around 80km – plenty for most people. On a cloudy day or if you need to go further, you can plug it in and a full battery will take the car 350km.

As a global leader in thin-film solar panels, Hanergy have done what no-one else has so far managed to do, and covered the whole car in solar panels rather than just the roof. And it still looks like a car. Unfortunately Hanergy is a solar company, not a car company. Building a new car company is difficult and expensive at the best of times, and Hanergy’s reputation has suffered a fairly catastrophic hit in the last couple of years. Can they finance a project like this? If they can, they’d like to have their solar cars available commercially by 2019. The main reason for the delay is that Hanergy want to wait for the price of batteries to fall a bit further, and then they can price the cars for the mass market.

So we’re a couple of years off the self-charging electric car just yet as a mainstream option. But it does look possible, at least for smaller city cars. I suspect that larger car firms are working on it, and that we’ll have more announcements in 2017. If you hear of any, let me know.


  1. Jeremy I love the way you delve into these topics. I am in the process of committing to a solar grid for my home in the mountains of Virginia. Unfortunately my electric provider limits the kW hours I can generate, so I cannot 100% swap out the exchange of cash. I have hesitated however, due to advice from my financial advisor that new regulations may be on the way with the new American president to alter the way solar is regarded. I also got some information from the provider I was considering that just sounded a bit shady, making me wonder how accurate it was. Do you have an solar knowledgeable friend sin the United States I might talk to?

    1. Hi Joe, I’m afraid I don’t have any contacts that might be useful on that front – I gather that regulations are different in every state. As you say, there’s a lot of uncertainty on the solar front at the moment too.

      Sorry I can’t be more helpful, but I hope it works out.

  2. Hi Jeremy, the sums below should help explain why we are not quite there yet with self charging cars (particularly in the UK).

    If you take flexible thin film CiGS panels like those mentioned in your article then the maximum panel efficiency is somewhere in the region of 13% which gives you roughly 130w per square meter. Using the car above that gives us just under a kilowatt maximum power, but as there are panels on both sides of the car and you wont normally be able to park it facing due south every time we can assume roughly 1/3 of the panels will be in shade give in us 660w of usable panels. Put very simplistically on a very very sunny summers day we might expect 8 hours of usable sunshine which would be equate to 5.28kWh of energy.

    One of lightest and smallest electric cars the Peugeot ION has a 16kWh battery and a real world range of 60 miles so our solar panels would give us roughly 20 miles of travel in a best case scenario. On a sunny day in autumn or spring we might see that drop to 5 or 6 miles and in mid winter it would be unusual to achieve more than 1 or 2 miles of charge on any given day.

    On the positive side the technology is moving forward, crystalline silicon panels (albeit rigid ones) are now achieving efficiencies of 25% with lab tests indicating that 35% may be feasible. Alongside this we would also need cars to become increasingly lighter and aerodynamic. Also, in the UK at least, we would have to be able to supplement the charge from the grid in winter. Luckily or us this is when our wind farms are most productive! The other side of the coin is to think smaller and look at urban mobility type vehicles rather than traditional cars – this is one of my favourites: but the wife is yet to be convinced.

    1. A great summary of the challenge. I didn’t want to outline the technical side of it myself, as maths is not my strong point, so I’ll glad someone else did – thanks!

      I have also been sceptical about this, but the choice of panel on Hanergy’s prototypes is more convincing than you might think – they’re gallium arsenide panels from Alta Devices. At 31.6% they’re the most efficient in the world.

  3. “The downsides are that it makes no concessions to style”

    I guess this is the crux of the matter. Citizen of the developed world have been spoilt with lugging more than a ton of metal with them for personal transport. It’s really hard to be realistic from now on for personal transport.

    I guess I’m lucky being live in place where cycling is easy. Electric Bicycle charged with solar panel is the most sustainable AND cheapest solution:

    1. Yes, we’ve become accustomed to a certain definition of a car and we’re stuck with it. Much of that is down to the combustion engine though. Because they’re heavy, cars need a steel chassis and the whole thing is going to be heavy if it’s not going to be dangerous. Modern electric cars also have to be steel in case they get hit by another heavy car.

      Fast forward twenty years and things might look different. Though it does seem like a long time to wait…

      I will write about electric bicycles at some point, as you’re right about them being a promising solution.

  4. Hello. Next year Sono Motors plans to produce the Sion, which corresponds your wish (and the limitations calculated above). Pure self-charging ist not (yet?) possible, but 30 km free on a sunny day would already be nice 🙂

  5. As the world grows, more and more cars are a major cause of our environmental pollution. And it seems that most people do not pay much attention to this issue. Perhaps most of them have been caught up in the work, following the development of the world, and forgot that the habitat was becoming increasingly stifling and that it was getting worse. Perhaps it is time for people to wake up, use more solar energy to replace gas engines, which will be good for everyone.
    Your article is great, thanks for sharing it.

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