Harnessing the Power of the Sun
Environment and Resource
Management
Originating Technology/ NASA Contribution
The Environmental Research Aircraft and Sensor Technology
(ERAST) Alliance was created in 1994 and operated
for 9 years as a NASA-sponsored coalition of 28 members
from small companies, government, universities, and
nonprofit organizations. ERAST’s goal was to foster
development of remotely piloted aircraft technology
for scientific, humanitarian, and commercial purposes.
Some of the aircraft in the ERAST Alliance were intended
to fly unmanned at high altitudes for days at a time,
and flying for such durations required alternative
sources of power that did not add weight. The most
successful solution for this type of sustained flight
is the lightest—solar energy. Photovoltaic cells
convert sunlight directly into electricity. They
are made of semi-conducting materials similar to
those used in computer chips. When sunlight is absorbed,
electrons are knocked loose from their atoms, allowing
electricity to flow.
Under the ERAST Alliance, two solar-powered technology
demonstration aircraft, Pathfinder and Helios, were
developed.
Pathfinder is a lightweight, remotely piloted flying
wing aircraft that demonstrated the technology of
applying solar cells for long-duration, high-altitude
flight. Solar arrays covering most of the upper wing
surface provide power for the aircraft’s electric
motors, avionics, communications, and other electronic
systems. Pathfinder also has a backup battery system
that can provide power for between 2 and 5 hours
to allow limited-duration flight after dark. It was
designed, built, and operated by AeroVironment, Inc.,
of Monrovia, California.
On September 11, 1995, Pathfinder reached an altitude
of 50,500 feet, setting a new altitude record for
solar-powered aircraft. The National Aeronautic Association
presented the NASA-industry team with an award for
1 of the “10 Most Memorable Record Flights” of 1995.
Pathfinder was succeeded by Helios, a remotely piloted
flying wing aircraft also developed as part of ERAST.
It, too, was originally designed and manufactured
by AeroVironment with high-efficiency solar cell
arrays across the wing, as well as navigation and
emergency lights, improved avionics, and more efficient
propellers.
The two primary goals of the Helios prototype development
were to demonstrate sustained flight at an altitude
near 100,000 feet, and to fly nonstop for at least
24 hours, including at least 14 hours above 50,000
feet. In 2001, the Helios prototype achieved the
first of the two goals by sustaining flight above
96,000 feet for more than 40 minutes on a test flight
near Hawaii, during which it reached an unofficial
world-record altitude of 96,863 feet. On a later
flight in 2003, intended to evaluate a hydrogen fuel
cell system designed to provide power at night for
extended flight duration, Helios became
uncontrollable, broke up, and crashed into the Pacific
Ocean. The mishap resulted from the inability to
predict the aircraft’s increased
sensitivity to atmospheric disturbances, such as
turbulence, following all of the vehicle configuration
changes.
Partnership
SunPower
Corporation, of Sunnyvale, California, created
high-efficiency silicon cells for the NASA/AeroVironment
Helios and Pathfinder solar-powered aircraft under
the now-concluded ERAST Alliance. These photovoltaic
cells were the most advanced silicon-based cells
available for terrestrial or airborne applications
and, over time, evolved into the mass-produced A-300.
The A-300 is an efficient, high-performance, low-cost,
single crystal silicon solar cell, with a unique,
all back-contact design. It offers up to 50 percent
more power than conventional solar cells.
SunPower first became involved with NASA when the
Lawrence Livermore Laboratory, in California, transferred
a solar aircraft project under the Ballistic Missile
Defense Organization program to Dryden Flight Research
Center. SunPower had been making high-efficiency
solar concentrator cells for the laboratory. These
cells quickly became the solar cells of choice for
the prototype aircraft, now named Pathfinder and
Helios. SunPower’s cells
were selected for the program because of their high-efficiency
performance and lightweight design.
Out of these experiences, SunPower gained the confidence
to begin making cells on a much larger scale for
terrestrial applications. At the behest of NASA,
however, SunPower began to drive costs down, while
retaining the high-performance efficiency of its
products. Eventually, the company was able to bring
costs down to be competitive with conventional cells.
At this stage, SunPower partnered with Cypress Semiconductor
Corporation, of San Jose, California, which brought
the capital resources and expertise in high-volume
manufacturing to the business picture. The first
ground installation that involved Cypress funding
was at Dryden, where SunPower was able to conduct
field tests and performance comparisons on its products
through a small solar power demonstration site that
provided power to one of Dryden’s buildings, and
several dimensions of insight came from the experience.
The first was the progressive evolution of cost reduction.
The installation also helped SunPower to identify
uses and performance advantages that would enable
the company to get more firmly rooted in large-scale
commercial applications.
The Dryden solar power demonstration installation
includes three systems: a traditional array and two
arrays with SunPower cells. One of the SunPower arrays
is mounted on a structure tilted to a fixed angle,
while another is installed in a “tracker” that follows
the courseof the Sun during the day. Staff can review
output data and dynamically compare the performance
of the side-by-side systems. Together, the systems
produce up to 5 kilowatts of direct current power
on a sunny day, which is equivalent to powering several
average California homes.
According to SunPower, typical commercial-grade solar
cells are in the range of 12- to 15-percent efficient
at converting sunlight to electricity, while its
A-300 cells are at least 20-percent efficient in
a ground application, or up to 50-percent better
than the older technology. The efficiency improvement
is largely due 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.
The demonstration system permits easy comparison
of the advantage of tracking over the fixed-tilt
array, verifying the effectiveness of models for
predicting array output, and the effect of dust on
the arrays. Array efficiency is monitored remotely
on a computer. Currently, it is providing supplemental
power to Dryden’s 7,870-square-foot Public Affairs
and Commercialization building.
Long-term plans for this project could include
construction of a solar “farm” at Dryden that would
power up to one-third of the Center’s electrical
power needs.
Product Outcome
Consumers can also purchase these same solar cells
from SunPower, as many people have elected to do.
Homes across the country are now being outfitted
with the modern, space-age solar power. The solar
panels were even featured on the ABC television show,
“Extreme Makeover: Home Edition,” which highlighted
a team of carpenters and designers who built a home
for a family in Flagstaff, Arizona. The donated SunPower
panels supply a significant portion of that home’s
electricity needs.
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The experimental site
at NASA’s Dryden Research Center consists of
two fixed-angle solar arrays and one single-axis
Sun-tracking array. Together they produce up
to 5 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. |
Solar panels appeal to consumers, because they preserve
the environment, save money on electricity bills,
and insulate them from escalating energy costs. Some
customers consider solar energy patriotic power:
a local power source that does not rely on imported
fuels.
SunPower’s solar panels have no moving parts, creating
pollution-free electricity with no noise and virtually
no maintenance. Furthermore, both SunPower’s all-back
contact solar cells and its high-tech, high-performance
solar panels perform better than most other solar
panels—even in overcast or very hot conditions.
In addition to the test facility at Dryden and home-consumer
uses, SunPower has recently partnered with SOLON
AG, Germany’s largest solar photovoltaic module manufacturer,
to open the first phase of the world’s largest solar
electric plant in Bavaria near Arnstein, Germany.
Solarpark Gut Erlasse is a 12-megawatt solar electric
plant located in a working agricultural field and
can serve the electricity needs of thousands of customers
each year. SunPower’s solar cells are used in SOLON’s
“Mover” electricity generation system, designed for
deployment in multi-megawatt solar power plants.
Movers automatically tilt and rotate during the day
to directly face the Sun at all times, similar to
the concept utilized at Dryden.
By combining SunPower’s industry-leading, high-performance
A-300 solar cells with the Mover’s ability to maximize
daily energy production, each square foot of solar
cells can generate up to double the annual energy
of a fixed solar array using conventional solar cells.
At Solarpark Gut Erlasse, SunPower’s cells are used
only in about one-third of the Movers, but generate
a higher proportion of the energy there, due to their
high performance.
Now that SunPower has achieved commercial success
with its mass-produced solar cells and modules, the
company is working with the U.S. Department of Energy’s
National Renewable Energy Laboratory on further improvements
in module design to reduce costs for solar power.
In addition, SunPower is working with several partner
companies on specialized, mass-produced, building-integrated
solar products that would leverage its A-300 cell’s
attractive all-black appearance. Roof tiles that
include solar cells and can be installed like regular
roofing are one example. SunPower is even looking
at other consumer products as a possible next step
to making solar energy successful in a variety of
markets.
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