Fueled by solar

Solar car: Tesla’s hidden history revealed

The developer of a solar car explains why the future is looking bright for electric vehicles.

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Could solar panels solve the electric car’s most significant pain points? After all, who needs to worry about the next charging point when your energy source is beaming down on you?

  • Sono Motors’ €25,000 ($29,332) Sion electric car, due for production 2023, offers 189 miles of range. Its solar panels can add up to 152 miles of charge per week. Read our Inverse interview here.
  • The €150,000 ($175,994) Lightyear One, set to start deliveries mid-2022, offers 450 miles of range and adds 7.5 miles of charge per hour from solar.
  • Even Musk, who said in 2017 that solar on a car is “not that helpful,” announced two years later that the Cybertruck would offer optional solar wings to generate 30 to 40 miles per day.

The solar car has a surprisingly deep history, with strong interest from big-name automakers.

The Bridgestone World Solar Challenge, founded in 1987, invites teams every two years to build a solar-powered vehicle and travel the approximately 2,000 miles between the Australian cities of Darwin and Adelaide. Participants can’t use more than six square meters (64.6 square feet) of solar panels.

The winner of the inaugural competition back in 1987? None other than General Motors.

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Key quote

“That’s probably the untold story to solar car development … very flashy headlines in terms of solar panels, but the really interesting work … if anywhere, it’s with people behind the scenes.”

What you need to know:

  • Zhang led Cambridge University Eco Racing to develop the Helia solar car. The car could hypothetically drive forever at 20 mph, powered only by solar cells.
  • The team took part in the Bridgestone World Solar Challenge. It counted automakers like General Motors and Honda among its participants, highlighting how the industry shifted.
  • The solar car indirectly led to the founding of Tesla. General Motors won the first Bridgestone challenge in 1987, built an EV off of its success, and suddenly halted its EV efforts in 2003. Musk has described this as the catalyst for Tesla.
  • J.B. Straubel, the company’s co-founder and chief technology officer until 2019, also participated in Stanford University’s Solar Car Project
  • Zhang described the event as “the most stressful thing I have ever done in my life.” Helia didn’t make it past the first stage, but won third place in practicality.
  • But Zhang cites three big issues that electric cars need to tackle: cost, range, and infrastructure
  • Solar panels are cool, but they add cost. They also might not add much range, and they constrain vehicle design.
  • The real benefits will come from efficiency improvements, Zhang says. “If you can eke out a few percent here and there...suddenly it all adds up to an extra 10, 20, 30, 40 percent range for the same cost.”

The deep dive:

Xiaofan Zhang made headlines in November 2019 when he unveiled the Helia, an energy-sipping solar car. The four-seater used just 50 watt-hours per mile, around five times less than the Tesla Model 3 of the time.

It could also reach a staggering 560 miles per charge — without even using the solar cells. It has a top speed of over 60 mph. The car could hypothetically drive forever at 20 mph, counted powered on solar cells alone.

“Pretty much across the vehicle, you could kind of look at every single part and it had some influence from industry in terms of either an exciting concept or technology that they were using,” Zhang tells Inverse. “We were able to put it all together and do the integration to make a vehicle that did something quite exciting.”

Zhang was the program director for Cambridge University Eco Racing, a student-run team that started over a decade ago. The team builds cars for the Bridgestone World Solar Challenge.

He graduated from the university in 2020. Inverse interviewed Zhang in July 2021, at which point he was working on a series of freelance projects. His comments reflect his broad, personal view of the industry. Today, he’s a member of Rivian’s strategy team.

Solar car: how it led to Tesla

The competition used to count automakers like General Motors and Honda among its participants, but today student-led teams dominate the accolades.

It’s one of the underreported stories behind the electric car. The 2006 documentary Who Killed the Electric Car explains how AeroVironment and General Motors developed the Sunraycer for the 1987 competition.

After winning the event, with an average speed of 42 mph, General Motors CEO Roger Smith asked the design team to move ahead with a prototype consumer EV. That led to the Impact, a concept car demonstrated at the 1990 Los Angeles Auto Show.

The Impact goes to YouTube.

That led to the introduction of the EV1 in 1996, the first mass-produced electric car. It could have sparked a new era of clean transportation — but General Motors recalled and crushed the EV1s in 2003.

Musk, who recommended fans watch the documentary, described the incident in 2017 as the catalyst for starting Tesla.

But Tesla’s roots in solar don’t stop there. J.B. Straubel, the company’s co-founder and chief technology officer until 2019, participated in Stanford University’s Solar Car Project. The project, founded in 1989, builds and races a solar car every two years, including in the Bridgestone World Solar Challenge.

In 2016, InsideEVs reported on Straubel’s speech at the Ontario Centres of Excellence Discovery 16 Conference, where he explained how the solar car factored into his future experience:

“[It] got me thinking about how we could make a much better all-electric car: they didn’t need to have solar on the roof, but could take advantage of battery improvements, could offer [the] same efficiency and benefits that solar cars have."

Solar car: A new era dawns

Zhang knew about the project before arriving at the University of Cambridge. While there, he took a year-long sabbatical to run the project full time. The team decided to build a vehicle for the Cruiser class, a category introduced in 2013 judged on practicality.

Helia packed:

  • High energy efficiency, using 2.5 kilowatts of power at 50 mph — the equivalent of powering a kettle
  • A 28-kilowatt-hour many lithium-ion battery pack
  • A battery range of 560 miles with no solar input
  • The ability to drive permanently at 20 mph using just solar panels

The team received support from companies like Formaplex, which produces a lot of composites for Formula 1 racing, and Bridgestone, which supplied low rolling resistance tires.

Helia takes part in the 2019 Bridgestone World Solar Challenge in Coober Pedy, Australia.

Mark Evans/Getty Images Sport/Getty Images

The car was pretty barebones. It had a carbon fiber chassis and a steel roll cage to meet crash safety regulations but would likely need tweaking for mass production.

The competition’s specs were released in June 2018, around a year and a half before the competition. Time was of the essence — while other teams had several full-time members, Zhang was the only full-time member of the Cambridge team.

The team had to overcome numerous hurdles, including remanufacturing a battery pack in around five weeks before leaving for Australia. Zhang estimates that, in total, the project took approximately 35,000 person-hours to build.

“It is the most stressful thing I have ever done in my life,” Zhang says.

The final event saw 13 teams competing in the Australian sun. Unfortunately, Helia didn’t make it past the first stage. It did, however, come third in terms of practicality in its class.

Stanford, Straubel’s old team, also struggled — the car’s battery caught fire around 30 minutes outside the starting city.

Solar car: the dark side

The Helia boasts impressive specs, but because of the competition’s stringent solar panel requirements, most of those boosts came from non-solar improvements.

“All the incredible, interesting stuff that's happening is designing a vehicle and integrating all the parts in such a way that you can maximize the energy use from that fairly limited source of solar power,” Zhang says.

He explains that around “90 percent” of the team’s efforts went into making the car as lightweight and aerodynamic as possible.

That means most of these improvements could apply to a non-solar car.

Zhang cites three major problems hampering electric car adoption:

  1. Cost — EV prices are high, primarily due to expensive batteries
  2. Range anxiety — people don’t want to run out of charge
  3. Infrastructure — people need places to charge

So would solar fix these? Not necessarily, Zhang argues.

“Chasing the solar is not necessarily where you want to be focusing a lot of efforts,” he says. “There are a few downsides to having solar panels on vehicles.”

These include:

  • They add extra cost to the car. That’s not ideal if you’re trying to reduce costs.
  • They work when they’re all pointed the same way on a sunny day, which isn’t very practical with a car
  • Solar panels constrain vehicle design. The team had to design a relatively flat roof with a minimal curve for aerodynamics.

What about the benefits? Mathieu Baudrit, head of research and development for solar integration at Sono Motors, told Inverse in October 2019 that solar cars could work well for Europe, where fewer people have a garage to park a charging car than in the United States.

Zhang highlights chargers as just one of the many areas where manufacturers are making efficiency improvements. If owners without a garage can charge at a public space in just a few minutes, it could solve several issues.

“I don't want to be too much of a downer on solar panels, specifically on cars,” he says. “But I think the focus should be on efficiency gains.”

“That’s probably the untold story to solar car development,” he says. “Very flashy headlines in terms of solar panels, but the really interesting work … if anywhere, it’s with people behind the scenes.”

Zhang instead cites technologies that “we’re about to potentially see coming into the mainstream,” like high-efficiency silicon carbide, motor controllers, and chargers.

“If you can eke out a few percent here and there...suddenly it all adds up to an extra 10, 20, 30, 40 percent range for the same cost and the same battery size,” he says.

It’s a story that repeats itself throughout the decades: solar cars are cool, but the real story is in the efficiency gains they encourage.


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