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Solar Airplane Brings Electrical Breakthrough Down to Earth
One of the most affordable and efficient solar arrays on Earth is being tested at NASA's Dryden Flight Research Center at Edwards, Calif.

This state-of-the-art array is an experiment designed to demonstrate that the new, high-efficiency solar cells being tested can power buildings better than standard solar cells, all while taking up less space.

Solar array demo site at NASA's Dryden
Solar array demonstration site at NASA's Dryden Flight Research Center, Edwards, Calif. (NASA photo by Tom Tschida)

The new solar array is a technology commercialization success for NASA. Dryden's Environmental Research Aircraft and Sensor Technology (ERAST) program developed the higher-output solar cell technology that has now been transferred to industry, allowing production of these cells for the commercial market.

The resulting A300 cells, the most advanced solar cells commercially available for use on Earth, are derived from NASA's Helios solar-powered aircraft project. The cells are built by the SunPower Corp. of Sunnyvale, Calif.

High efficiency distinguishes these advanced cells from commercially available solar cells. Typical cells are 12 to15 percent efficient at converting sunlight to electricity; the new cells are 20 percent efficient, a large leap in the world of silicon cells.

Improved efficiency is due largely to the routing of cell electrical connections behind the cells. This efficiency issue was originally driven by the Helios aircraft requirement to maximize the limited space available atop the aircraft's wing. The solar cells in use at Dryden could be used on Helios, but cells of traditional design cannot, due to their lower efficiency.

Dryden funded the five kilowatt demonstration array, which was built by Renewable Energy Concepts Inc. of Los Osos, Calif. Electricity from the array is supplementing power to Dryden's Public Affairs, Commercialization and External Outreach (PACE) building.

Helios Prototype solar-powered flying wing
Helios is shown near the Hawaiian islands of Niihau and Lehua during a test flight on solar power from the U.S. Navy's Pacific Missile Range Facility. (Photo by Nick Galante/PMRF)

"We are pleased that NASA was able to field the first commercial application of this exciting new solar electric power technology," said Jenny Baer-Riedhart, NASA Dryden's PACE chief. "Over the past seven years, we have worked with SunPower to develop high efficiency solar cells to energize our highly successful Pathfinder Plus and Helios solar-powered aircraft as part of the ERAST program. It's exciting to see this technology coming down to earth in this terrestrial product, " Baer-Riedhart said.

The experimental site consists of two fixed-angle solar arrays and one single-axis tracking array. One of the fixed arrays contains common less efficient cells, and is being used as a baseline comparison for the newer fixed-cell array. The sun-tracking array tilts to follow the sun using an advanced real-time tracking device that seeks the best sunlight angle throughout the day.

By design, the experimental site compares any potential advantage of the tracking array over the fixed array. The array is monitored remotely on a computer that displays pertinent information regarding the functioning of the arrays. The solar arrays are tough enough to last outdoors for 20 years.

This project represents a full-circle process of technology developed for NASA being transferred to industry, then returning back to NASA from industry as a technology spin-in to assist NASA programs. This cell technology development was part of the Innovative Technology Transfer Partnerships effort under NASA’s Aerospace Technology Enterprise.

Future plans include using a Web site currently under development for public outreach that will allow viewing real-time information on the functioning of the site.

In the future, a larger solar farm may be built at NASA Dryden to power up to one-third of the Center's electrical needs.

By Gray Creech
NASA Dryden Flight Research Center
Public Affairs