Orbiting space satellites need high-capability, reliable power sources that can fit in compact spaces. For long-term missions like scientific Earth observation or satellite communications devices, solar power is perfect. Especially with the recent announcement by Sharp that they have created the world’s most efficient compound solar cell.

Sharp has been a leader in space-based solar power for more than 40 years, from early science satellites in the 1960s to the rapid development of orbiting communications satellites in the 1990s -- and beyond. That technological leadership was evident once again with the announcement in October 2009 that Sharp had developed an innovative “triple junction” cell with 35.8 percent efficiency that eclipsed the old 31.5 percent standard. With the new release, Sharp raised the technological bar substantially. “It was a very important advance,” says Tatsuya Takamoto, a senior Sharp engineer who led the compound solar cell development.

Sharp’s pioneering solar spirit continues to propel innovation – sometimes well ahead of any mass-market applications. When Sharp began mass producing solar cells in 1963, it would have been hard to predict that in 30 years, solar-powered satellites would supply essential voice, data and video communications links to much of the planet. Their lengthy track record of innovation and reliability has made Sharp the main supplier of solar cells to the Japanese Aerospace Exploration Agency (JAXA).

For solar use in space, says Takamoto, the imperative has always been to raise efficiency, lower weight, increase longevity, and reduce costs of solar cells. So in 2000, Sharp began researching new ways to build more efficient solar cells by designing one that didn’t use silicon. Instead, they combined different elements into three absorption layers, which increases the amount of solar energy each cell captures.

Today, Sharp’s compound solar cells can withstand temperature extremes from 150 degrees Celsius down to minus 150 degrees Celsius, and function for many years amid the intense radiation that satellites must face in orbit. They can supply up to 25 kilowatts of orbiting power, and new solar cells in development are expected to be lighter, reducing launch costs.

Looking ahead, compound solar cells have more promising uses – both in space and on Earth. Researchers are investigating ways to design a space-based solar power generating station, which will collect the sun’s rays in space, then send them via microwave down to earth to power electrical grids. Compound solar cells may provide an opportunity for engineers to supply electrical power to aircraft and ships, saving on jet fuel and diesel. Already, compound solar cells are being developed for concentrated solar collectors on Earth, which may provide utility-scale power production in parts of the world. And with a Sharp-powered car win in the Global Green Challenge solar car race, compound solar cells are fueling the imagination of engineers who dream of solar car fleets. “We can increase production capacity and reduce costs,” says Takamoto. “This is a continuous effort.”