One of the more noteworthy cars to debut at the recent Consumer Electronics Show in Las Vegas was Ford’s C-MAX Solar Energi Concept, a version of its compact plug-in hybrid vehicle that can draw power from the sun’s rays.
The combination of a special concentrator-lens parking canopy, a solar cell array on the hybrid's roof, and the vehicle’s ability to autonomously reposition itself to follow the focal area of the lens as the sun moves across the sky enables the system to fully recharge the little MPV’s 8-kW·h battery in about 8 h, providing electric-only range of about 21 mi (34 km) without the need to plug into the utility grid, according to Dave McCreadie, Manager of Electrical Vehicle Infrastructure and Smart Grid Technology at Ford. Using the car’s electric cord and plug port, such a recharge would typically take about 4 h.
The novel, patent-pending concept is the result of a collaborative effort by the carmaker, San Jose-based SunPower Corp., and the Georgia Institute of Technology. “We pursued this recharging concept because of the confluence of several nearly practical technologies that made it potentially feasible,” McCreadie said. “If it works as we hope, it’ll be a convenient and inexpensive way to power up.”
SunPower, which has partnered with Ford on solar technology since 2011, is supplying its high-efficiency crystalline-silicon photovoltaic cells for the car’s 1.5-m² (16-ft²) roof panel. Georgia Tech researchers designed the lens canopy to amplify solar exposure.
The special solar concentrator—a static canopy that incorporates flat Fresnel lenses that are made of low-cost acrylic—operates like a giant magnifying glass to boost the amount of sunlight that strikes the panel by as much as a factor of eight, McCreadie explained. Fresnel lenses, which were originally developed to reduce the mass of the huge, conventional lenses that were once used in lighthouses, work by dividing the standard bulging lens body into a compact set of concentric, confocal annular lens sections.
The team charted different locations in the nation and the different seasons to determine what it would take to keep the car under the static concentrator canopy. “We sized the lens array so that someone living in an are of the U.S. with an average amount of solar exposure such as Raleigh, N.C., would be able to recharge the battery during the course of a day,” he said. The Ford supervisor added that a parking canopy with a lens area from 12 to 20 m² (129 to 215 ft²) would be used in Phoenix, whereas “it would need a larger footprint where there’s less sun.”
The system is designed to keep the car aligned with the sun by continuously repositioning the vehicle under the canopy throughout the day. To accommodate the daily traverse, the space below the canopy would be somewhat larger than a typical parking spot.
Ford data indicate that the sun could power as many as three out of four trips made by an average driver in a solar hybrid vehicle. This capability could be important in places where the electric grid is underdeveloped, unreliable, or costly to use. By using renewable power, C-MAX Solar Energi could cut the annual greenhouse gas emissions that a typical owner would produce by an estimated 4 t (4.4 ton)—the equivalent of the amount that an American house creates in four months.
The Ford C-MAX Energi hybrid has a maximum range of 620 mi (998 km) and has a U.S. EPA-estimated mileage of 108 MPGe city and 92 MPGe highway for a combined 100 MPGe.
McCreadie emphasized that the system is still in the early stages of development: “We have not yet physically tested the concept.”
Ford and Georgia Tech engineers are now just starting to test the off-the-grid vehicle in various real-world scenarios. The outcome of those evaluations will help to determine if the concept could be feasible as a production car.