Integrating photovoltaic cells on vehicles is nothing new. In fact, solar-powered race cars have been around for more than 25 years, proving that the power of the sun can indeed provide enough energy to propel a car down the road.

Of course, these cars are ultra-lightweight and plastered with solar cells on every conceivable surface, tasked with carrying just a driver at a constant speed.

While not practical for driving as we know it, they are valuable engineering exercises that helped move the bar in developing electric vehicle efficiencies. Just one example is GM’s Sunraycer solar race car, built under the guidance of the renowned master of efficiencies, the late Paul MacCready of AeroVironment, which won the World Solar Challenge in Australia in 1987.

Lessons learned were applied to the GM Impact electric car prototype – precursor to the GM EV1 – that AeroVironment built under contract for GM and was unveiled by the automaker at the 1990 L.A. Auto Show.

Solar panels were notably integrated on the hood and rear deck of Solar Electric Engineering’s Destiny 2000, an electric car upfitted from a gasoline powered Pontiac Fiero we test drove back in 1994. Today, Audi uses a solar panel on its top-of-the-line A8. Toyota offers an optional Solar Roof package for the Prius.

While some might think these can help power an electric car, their relatively low energy output can realistically do little more than trickle-charge batteries or, more appropriately, power low-demand ventilation systems while an electric car is parked to help keep interior temperatures cooler on hot days without draining the battery.

Today there’s a new champion of solar ingenuity on the road. The Fisker Karma plug-in electric hybrid luxury sedan features probably the most sophisticated solar roof ever offered on a production model, using the world’s largest continuous-formed glass solar panel on an automobile. Not only does it keep the Karma’s interior cool on a hot day, but also supplies electricity to the car’s 12 volt system used for starting and accessories, relieving the high voltage lithium-ion battery system from tapping energy needed for driving. This can increase range, though admittedly a small amount.

To create the large solar panel, 80 small monocrystalline cells are individually hand-laid under automotive safety glass to follow the contours of the roof.  The solar panel has four electrically separate zones, each consisting of 20 cells in series. Each of the four zones incorporates MPP (maximum power point) tracking to optimize power output under various solar radiation angles and partial shading conditions. The splayed solar cell array design maximizes solar ray absorption under various lighting conditions, while the graphic accent running between the cells lends a unique and futuristic appearance.

A Karma driver can choose three solar power modes. In the Charging mode, as much solar energy as possible is stored in the battery. When Climate is chosen, solar power is used to ventilate the passenger compartment to reduce the effects of radiant heating. In the default Auto mode, the Karma will use solar power to maximize energy recovery and usage.

On a typical day, the solar panel supplies 0.5 kilowatt-hours of electricity. When used for battery charging, Fisker says over the course of a year that translates to maybe 200 emissions-free miles. That’s free energy, for sure. But how meaningful is that in the scheme of things? Like others before it, the Karma’s solar roof – with its imposing look and obvious green credentials – is a step in the right direction, showcasing innovation and yet another way to embrace renewable energy. It is an environmental friend, with benefits…but it’s hardly a statement that solar powered, highway capable cars are upon us. Still, free energy is, well…free energy…and we like it.

 

1 Comment

  • I am curious, by having a solar panel option on a Prius, how much more weight does it add.  And how does this added weight affect the overall efficiency?   It would seem that the only benefits are during hot sunny days and not during night, or rainy days.

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