Cars can’t run indefinitely on solar energy—at least not normal cars employing today’s solar energy technology. That’s because today’s best photovoltaic cells, even if they covered the entire exterior of a car, aren’t efficient enough to create the energy needed to run the car. So it got our attention when a team from the University of Newcastle announced plans to drive a Tesla Model 3 around the perimeter of Australia using only solar energy—from printed solar panels made from recycled water bottles and photovoltaic ink.
Offboard Printed Solar Panels
The first thing to know is that these solar panels are not part of the car. Rather, the solar array is 60 feet long, but it’s very light and it’s flexible enough to roll up and carry in the Model 3’s trunk. This array is said to be capable of recharging the Tesla after six hours baking in the Aussie sunshine, which is how the Model 3 expects to spend 84 days driving 9,400 miles around the continent, while stopping at some 70 schools to drum up interest in STEM subjects and spread the gospel of renewable energy.
Printing With Photovoltaic Ink
The concept of printing solar cells has actually been kicking around for more than a decade. Back in 2011 MIT proposed depositing photovoltaic cells on paper, textiles, even plastic food wrap, but that vapor printing process had to be done in a vacuum, and the power connections didn’t tolerate much bending. It’s sunnier in Australia than Boston, however, and the Victorian Organic Solar Cell Consortium there has been experimenting with semiconducting inks since 2007, applying them via spray coating, reverse gravure and slot-dye coating, as well as screen printing. And they’ve been printing on plastic, without a vacuum, in much the same way Australia pioneered printing its plastic currency in 1988.
Not Very Efficient
Today’s state-of-the-art silicon-based photovoltaic cells are roughly 25 percent efficient at turning the light energy in photons into electrons. These semiconducting ink-based solar collectors ones convert solar to electric energy at more like 2 percent efficiency, though the U of Newcastle folks reckon 4 percent efficiency is within reach.
Not Super Long-Lasting Either
Printing on polyethylene terephthalate (PET) plastic and covering the printed surface with another layer of PET means the printed solar panels are extremely flexible, but they don’t last terribly long. The Newcastle team says its panels have a useful lifetime of one to two years, though further development could improve longevity somewhat. And by utilizing organic electronics technology the panels should be fully renewable, hopefully reusable (if the PET layers can be separated), easily recyclable.
You pay for what you get. Most of the expense in today’s typical roof-top solar array is processing the silicon that holds the photovoltaic material. With no silicon wafers, the raw materials for printing solar cells are extremely cheap. There’s nothing exotic about the production process either—the cells can be printed at 33 feet per minute—so the University of Newcastle team reckons the printed solar panels can be produced for roughly $0.66/square foot. That means the energy they produce costs a similar $0.62 per kilowatt-hour.
Bright Future for Printed Solar Panels?
Scientists say it will eventually be feasible to print photovoltaic semiconducting ink on a huge range of surfaces and materials (even steel), making possible solar curtains, blinds, and possibly even windows using partially transparent photovoltaic ink. But it’s still way too early to expect a vehicle sized and shaped like today’s cars, powered by today’s motors, to drive all day without stopping to at least solar-charge for a bit.