Mercedes says this new innovation could let an SUV-sized electric vehicle travel as much as 20,000 kilometres a year without plugging in
Mercedes-Benz really upset the automotive apple cart last week when it announced it was developing a “solar coating” which when applied to, say, a mid-sized sport-ute-sized electric vehicle, could generate enough electric energy for 20,000 kilometres of driving per year. Considering that Natural Resources Canada’s annual estimations of the cost of running an automobile here in the Great White Frozen North are based on a yearly average of 25,000 kilometres, and that energy created from the sun’s rays is the ultimate in renewability, that would seem make Mercedes’ proposed solar-coated car as close to the mythical perpetual-motion machine as ever imagined.
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The big question, then, is once we’re past all the hyperbolic headlines, has Mercedes-Benz indeed invented the perfect automobile, not only free of harmful tailpipe emissions, but virtually free to fuel as well?
By the numbers
Mercedes’ calculation
In Mercedes-Benz’s estimation, this giant expanse of solar-irradiated surface could produce enough energy to let said SUV travel up to 12,000 km (7,456 miles) a year in Stuttgart, Germany. That’s “under ideal conditions,” which, in Germany, probably includes a lot of cloud and snow. In sunnier Los Angeles, California, however, that number, says Mercedes, would be closer to 20,000 klicks; and in Beijing, some 14,000 km per year.
By the company’s reckoning — based on an average daily commute of 52 kilometres — a typical Stuttgart commuter would power 62% of their daily drive using solar power; in Beijing about 72%; and, in L.A., virtually all of the daily drive would be covered by solar, with enough left over that it “could be fed directly into the home network via bidirectional charging.”
That Mercedes also claims this new solar paint is “considerably cheaper to produce than conventional solar panels” would seem miraculous enough that it solves all the issues surrounding EV adoption — namely range anxiety and the need for infrastructure, both on a macro- and micro-scale — with a simple coat of paint.
The real numbers
Also optimistic is Mercedes’ claims of photovoltaic efficiency, which the company trumpets as around 20%. That’s about equal to solar panels, which while, again, optimistic, may not be unrealistic.
What might be a hopefulness too far, however, is applying that same exemplary efficiency to all the solar paint on an SUV. While the roof, hood, and trunk are certainly optimally angled to collect the sun’s rays, the doors and fenders are not, and are more equivalent to mounting solar panels on the walls of your house. Even with optimally angled panels on roofs, many solar roofing experts recommend using a real-world efficiency of 15% in calculations.
By the company’s reckoning, a typical Stuttgart commuter would power 62% of their daily drive using solar power; in Beijing about 72%; and, in L.A., virtually all of the daily drive would be covered by solar
Tally it all up and, in a more real-world scenario, our Stuttgart-ian EV owner might manage but 15 klicks a day — 5,500 km per year — via solar energy. That’s a still substantial efficiency, but not the home-charging-never-needed some headlines have trumpeted.
And I think it goes without saying that all these efficiency gains only matter in urban driving. Whether we’re working with Mercedes’ optimistic 32 kilometres of extended range or my hopefully more realistic 15- or 20-kilometre freebie, neither is of consequence on any kind of extra-urban road trip. Indeed, coating your car with solar cells would seem most beneficial to those whose daily drive is short, frequent, and predictable.
The bottom line
Perhaps the biggest knock against solar paint, at least in energy-abundant Canada, is how little it will save you over the long run. For instance, in my hometown of Toronto, the current off-peak price (when most home charging is done) of electricity is 7.6 cents a kilowatt-hour. If my estimation of 5.5-kWh bears any resemblance to reality, that would represent a savings of 40 cents a day, or a maximum of $145 a year. I think it’s fair to say no one’s buying a specific car of any kind — let alone a Mercedes — just to save 145 bucks a year.
On the other hand, in Germany, home of the most expensive electricity in Europe, you might save as much as CDN$1,000 (out of a total energy cost of CDN$9,000 annually). I’m still not sure whether that justifies buying a Merc, but if the technology ever gets cheap enough to be applied to economy cars, the option would surely be attractive, especially, again, for those whose usage is mostly confined to short, daily commutes.
In the end, the worth of Mercedes’ proposed solar coating will be, as the savings estimates above illustrate, very much dependent on the cost. As I said, the company claims the paste used to coast the body panels costs less than an actual solar panel. That’s significant from a technology point of view, but it still doesn’t tell us what the final value proposition might be, and whether it will be affordable for mainstream cars.
As well, the solar coating requires a special “nano-particle” paint to let the sun shine through to the photovoltaic cells (Mercedes claims a 94% transmission ratio). Exactly how much the company charges for this ground-breaking technology will be the final determinant of how successful it is in reducing the total cost of ownership of an electric car. In other words, contrary to hyperbolic headlines, solar paint, at least as we know it now, is not going to render home charging obsolete any time soon.
Author’s note: As much as today’s column is festooned with facts, figures, and calculations, I actually did try to resist the desire to completely geek out. For those who don’t mind an extended trip down Nerdery Lane, the following is how Mercedes’ solar paint might work (the emphasis here is on the might, since the company is most definitely not specifying what technology it’s using).
It’s also thin enough, the quantum dots barely a few nanometres in size, more than able to meet Mercedes’ claim that its solar coating is but five micrometres (0.0002 inches) thick.
Whichever solution wins out, Mercedes did disclose that the energy produced by the paint gets back to the battery the good old-fashioned way. First, a wiring harness takes it from the body to a power converter, which then converts the low voltage from the solar cells to the much higher voltage (400 or 800 volts) required by the main battery. Mercedes also says the system is protected against corrosion and scratches in the coating, but doesn’t say exactly how.
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