1966 Volkswagen Bus Runs Entirely on Sunshine

December 29, 2014

<http://www.xconomy.com/> –*

[image: VW bus]

Trying to run an electric car from solar cells on the car’s roof makes no
sense—or so I thought. Earlier this week, I met with Daniel Theobald, the
CTO of healthcare company Vecna, who has been driving a solar-powered
Volkswagen bus for a year.

His project won’t transform the auto industry overnight. But by taking on
what most engineers would consider foolishly ambitious—a solar-powered
car—he’s created a proof of concept that could lead to commercial solar
vehicles, at least for some uses. In the process, he and his colleagues
have created power electronics technology that could be applied to other
products for Cambridge, MA-based Vecna, including its delivery robots for

Certainly, combining solar power and electric vehicles isn’t new. Many EV
owners have rooftop panels on the homes. And some Toyota Prius models are
equipped with solar cells embedded into the roof, which power a fan to cool
the car. But making car-attached panels serve as the primary energy source
is very hard. The big challenge is that on-board panels put out a tiny
amount of juice compared to the power a car needs to run.

[image: Daniel Theobald]Theobald was also under the impression that a
solar-powered car was essentially impossible. But he wanted an electric or
hybrid car that could transport his large family, so he decided to
challenge his assumptions and see where it would lead. He bought a 1966
Volkswagen minibus off Craigslist, converted it to electric power (in an
afternoon), and started reengineering the vehicle for solar.

His conclusion: “You can have a practical vehicle that runs completely on

To be sure, the VW bus looks funny—there are 10 solar panels affixed to its
roof, some of which hang over the front and back. The cost of the vehicle
and equipment, including very efficient, but pricey, solar panels is about
$30,000. Driving on solar also restricts his range to about 20 miles if
there’s no sun.

But in taking on the challenge, Theobald and other Vecna engineers working
on the project have created technology they’re seeking to patent, which
could lead to new business opportunities. For example, airport service
vehicles are outside for long periods of time and don’t need to go long
distances. This is a situation in which having a solar-powered vehicle—one
that wouldn’t necessarily need to be charged by plugging in—could make
sense, Theobold says.

“Making practical solar vehicles is something most people wrote off so in
many ways, it’s a fairly unexplored problem,” he says. “But there are a lot
of applications where solar-powered vehicles make a ton of sense.”

There’s some crossover with Vecna’s current business, too. Engineers are
now working to outfit the bus with a lithium-ion battery, which will be
used in Vecna’s healthcare robots

*Optimizing for the Solar+Mobility*

Engineering-wise, Theobald’s project uncovered some conventions that make
solar-powered passenger cars such a tough challenge. For example, the
electronic components normally used in electric cars, such as the battery
packs, are not optimized for the voltage that solar panels put out. Also, a
significant portion of energy is lost in charging and discharging a
battery, but that can be minimized.

In early tests, Vecna engineers tried to have the bus run directly off the
solar panels, rather than charge the battery and run off the stored energy.
Powering a car largely from solar panels limits the acceleration
significantly, but it can be done in city driving, they found. Driving the
car at highway speeds (it can go 80 miles per hour) requires much more
power than what the panels can generate in full sun.

[image: Solar panel hookup]Theobald also found that the topography of a
given route makes a huge difference. Driving up a big hill to bring his
kids to school would kill his battery, but taking a slightly longer yet
flatter route used about one-quarter of the energy. “This idea of being
aware of the energy as we travel is going to become much more relevant as
we start using electric vehicles,” he says.

The solar-powered bus also uses a number of tricks to lighten the weight
and reduce aerodynamic drag, such as using thin tires and lightweight
wheels and bumpers.

With more tinkering, the energy use and efficiency can be optimized
further, Theobald says. For example, the lithium-ion batteries are lighter
and last longer than their lead-acid cousins now installed.

Another possibility is to use batteries in conjunction with ultracapacitors
a type of storage device that can very quickly discharge power to
accelerate a car, for example. Engineers are also trying to find
lighter-weight versions of some of the electrical components, such as the
motor and battery charger, by converting products used in other industries.

Theobald’s ride certainly won’t work for everyone—even with solar charging,
the car has a range of about 30 miles. But he’s made something that
electric car enthusiasts could only dream about: an electric car that
rarely needs to be plugged in.

“Given my normal driving, I don’t need to charge it all—the sun gives me
all the energy. It’s incredibly convenient. As long as I’m not parking
under a tree, I’m covered,” he says.

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