Two blankets of solar cells make up a solar array wing, or SAW. Each wing is 115 feet long by 38 feet wide. Each SAW weighs more than 2,400 pounds and uses 32,800 solar array cells. Image Credit: NASA
How do you get electricity 220 miles above Earth? No extension cord or power cable is available for that job, so the best source of energy for spacecraft is sunlight. Engineers have developed technologies to convert solar energy to electrical power efficiently.
Solar arrays that convert energy to electricity on the space station are made of thousands of solar cells. The solar cells are made from purified chunks of the element silicon. These cells directly convert light to electricity using a process called photovoltaics.
NASA and its partners developed a method of mounting solar arrays on a "blanket." The blanket can be folded like an accordion for delivery to space and then deployed, or spread out, to its full size once in orbit. Once in orbit, ground controllers sent commands to deploy the blankets to their full size. Gimbals are used to rotate the arrays so that they face the sun to provide maximum power to the space station. Each of the eight solar arrays is 112 feet long by 39 feet wide.
Two solar array wings make up a set of solar arrays. The two wings are deployed in opposite directions. The total wingspan is more than 240 feet, including equipment that connects the two halves and allows the SAW to turn toward the sun. Image Credit: NASA
The space station's solar arrays were installed over several space shuttle missions. When astronaut Bill McArthur was on the station, it had one set of solar array wings. McArthur was the commander of Expedition 12 from October 2005 through April 2006. In March 2009, the STS-119 space shuttle crew installed and deployed the fourth and final set of solar arrays.
Altogether, the four sets of arrays can generate 84 to 120 kilowatts of electricity -- enough to provide power to more than 40 homes. Electricity is measured in units of power called watts. A kilowatt equals 1,000 watts. An active computer and monitor may use up to 270 watts. A small refrigerator uses about 725 watts.
The solar arrays produce more power than the station needs at one time for station systems and experiments. When the station is in sunlight, about 60 percent of the electricity that the solar arrays generate is used to charge the station's batteries. At times, some or all of the solar arrays are in the shadow of Earth or the shadow of part of the station. This means that those arrays are not collecting sunlight. The batteries power the station when it is not in the sun.
The International Space Station has four sets of solar arrays. Image Credit: NASA
On Earth, the electricity that comes from power plants is called alternating current, or AC. In the United States, this means that the direction of the current, or flow, of electricity changes about 60 times per second. The alternating current is the best way for electricity to travel over long distances. On the station, the electricity does not have to travel as far. The solar arrays convert sunlight to direct current, or DC, power. DC flows in the same direction at all times.
There is also enough electricity to run experiments and equipment in the U.S., Russian, Japanese and European laboratories.
Solar Array Facts
Together the arrays contain a total of 262,400 solar cells and cover an area of about 27,000 square feet (2,500 square meters) -- more than half the area of a football field.
A solar array's wingspan of 240 feet (73 meters) is longer than a Boeing 777's wingspan, which is 212 feet (65 meters).
The space station's electrical power system is connected by eight miles (12.9 kilometers) of wire.