A state-of-the-art solar array is providing a unique opportunity to
demonstrate the latest in high-efficiency solar cells available for
terrestrial use at a demonstration site at NASA’s Dryden Flight
Research Center at Edwards Air Force Base, Calif.

Manufactured by SunPower Corporation of Sunnyvale, Calif., the A-300
silicon cells were derived from those developed for the NASA /
AeroVironment Helios and Pathfinder-Plus solar-powered aircraft under
the now-concluded Environmental Research Aircraft and Sensor
Technology (ERAST) program. They are considered to be the most
advanced photo-voltaic cells available for terrestrial applications.

The experimental site consists of two fixed-angle solar arrays and one
single-axis sun-tracking array. Together they produce up to five
kilowatts of direct current power on a sunny day, which is equivalent
to powering two or three average California homes. The sun-tracking
array tilts to follow the sun using an advanced “real-time” tracking
device rather than normal pre-programmed mechanisms. One of the fixed
arrays contains standard less-efficient cells, and is being used as a
baseline comparison for the newer fixed-cell array. According to
SunPower, typical commercial-grade solar cells are in the range of 12
to15 percent efficient at converting sunlight to electricity, while
the new cells are 20 percent efficient, or up to 50 percent better
than the older technology.

The efficiency improvement is due largely to the routing of cell
electrical connections behind the cells, which was required in the
original design for the solar-powered aircraft to maximize the
limited space available atop the wings.

“It is a grid-connected system, so it is putting power back into the
electrical grid,” stated Jon Ferrall, NASA Dryden electrical
engineer, who managed the installation of the solar array
demonstration site. “The system is providing significant power to the
7,870 square foot Public Affairs and Commercialization building here
at Dryden.”

The demonstration is comparing the potential advantage of the tracking
array over the fixed array, verifying the effectiveness of the
dirt-repellant coating over the protective glass housing the solar
cells, and the effect, if any, of dust and dirt on the arrays. Array
efficiency is monitored remotely on a computer.

Should the demonstration be successful, it would be a major step
toward transferring the technology to the commercial market, allowing
for mass production of these high-efficiency solar cells for a
variety of residential, business and governmental applications.

Charlie Gay, chief array installer of SunPower, said they have been
able to actively predict the output of the system.

“SunPower’s ability to predict energy delivery over the span of the
past year is attributed to the modules and system working well,” Gay

Jennifer Baer-Riedhart, NASA Dryden’s project manager for the solar
demonstration site, estimated that the life expectancy is at least 25

A second phase of the demonstration will consist of establishing an
Internet web site that will allow the public to view “real-time”
information on the Dryden solar demonstration site, as well as other
solar array sites that are planned for construction in Hawaii and

Long-term plans include construction of a solar “farm” at NASA Dryden
that would power up to one-third of the center’s electrical power

The solar power demonstration site was funded through a technology
commercialization allocation from NASA’s ERAST program at a cost of
around $130,000. It was constructed by Renewable Energy Concepts Inc.
of Los Osos, Calif.

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