This is an excerpt from EERE Network News, a weekly electronic newsletter.
NASA Delivers Solar-Powered Vehicles to Mars
Thanks to the National Aeronautics and Space Administration (NASA), Mars is now the planet in our solar system with the highest percentage of solar-powered electric vehicles. In fact, 100 percent of the Mars fleet is now solar-powered, a feat not expected to be repeated here on Earth anytime soon! NASA even managed to double the size of the Mars fleet in a single day, when it landed a second vehicle on Mars on January 24th. With the two vehicles on the opposite sides of the planet, NASA has also dramatically extended the geographic coverage of its solar-powered fleet.
Of course, we're referring to the two Mars Exploration Rovers, Spirit and Opportunity, each of which is powered by 140 watts of solar power. Each craft carries two rechargeable batteries that are energized by the solar cells. See the Mars Exploration Rover Mission Web site, provided by the Jet Propulsion Laboratory.
In defense of the fleet of vehicles here on Earth, the Mars fleet falls short on a couple items, including its top speed of two inches per second, an average speed of less than half an inch per second, and a price somewhat higher than the average Earth vehicle (the pair cost roughly $800 million). The rovers do, however, feature six-wheel drive. See the "Wheels" section of the Rover Mission Web site.
Spectrolab, Inc. is the proud manufacturer of the high-efficiency solar cells used on the Mars rovers. The "triple junction" cells use three layers of photovoltaic material to capture a high percentage of the solar energy striking the cell and convert that energy into electricity. Each rover carries 1.3 square meters (about 14 square feet) of solar cells. See the Spectrolab press release.