A few years ago, Donald Müller-Judex was driving around the villages of Bavaria, where he lives, when an idea struck him. Why are all the solar cells on the roofs and not in other surfaces like roads or bike paths?
Three years later, in 2012, Müller-Judex started Solmove, which is developing a flexible glass carpet filled with solar cells. It's meant for footpaths, cycle lanes and flat roofs, and will see its first full incarnation next month. Müller-Judex is setting up a showcase in Berlin, near the Haus der Zukunft (a museum of the future).
Solmove is one of several solar road projects. With $2.2 million in crowdfunding money, Scott and Julie Brusaw have installed a prototype solar parking lot near their home in Idaho. There's the SolaRoad bath path in Amsterdam. And a company in France plans to put down 620 miles of "energy-generating pavement."
At a time of rapidly falling solar costs and increased efficiency, some have questioned whether we need solar roads. Why not just blanket every rooftop with a technology that we know works? The U.S. could meet 39% of its electricity needs just by exploiting existing roof space, a recent National Renewable Energy Laboratory report found.
But Müller-Judex says road-solar has advantages over rooftop solar, and Germany's situation is not America's. "Everything is small in Germany compared to the U.S. There are a lot of people. Maybe we can use the landscape. But this is a smart way to use places we use already," he says.
Besides, if Germany moves to electrified transport and it closes its nuclear power stations as planned, it's likely to need much more renewable electricity than now. Some estimates show advanced countries needing double the electricity by the middle of the century. And Germany, as Müller-Judex says, has less space. One study showed it getting about 10% of its energy from about two-thirds of its rooftops. (The NREL estimate is based on 2013 demand, not possible future demand.)
Solmove's product has a ruggedized glass surface which deflects light coming in at different angles, so it can be captured in the cells underneath. Müller-Judex claims they have an efficiency of 10%-15%, which isn't as good as modern rooftop solar, but not far away either.
"You will not see it really, though you might feel it if you drive over it," Müller-Judex says. "And we can use the energy for lighting the street and traffic management."
Bavaria is already a world leader in solar. With abundant sunshine, it generates almost a third of Germany's solar power already. Maybe one day it will be covering not just its rooftops but its other hard surfaces as well.