Highest efficient solar-to-grid convertor-world record set
National Laboratories and Stirling Energy Systems
(SES) set a new solar-to-grid system conversion efficiency
world record by achieving a 31.25 percent net efficiency rate.
The old 1984 record of 29.4 percent was toppled
Jan. 31 on SES’s “Serial #3” solar dish Stirling system at
Sandia’s National Solar Thermal Test Facility.
(Photo by Randy Montoya)
The conversion efficiency is calculated by measuring
the net energy delivered to the grid and dividing it by the
solar energy hitting the dish mirrors. Auxiliary loads, such
as water pumps, computers and tracking motors, are accounted
for in the net power measurement.
“Gaining two whole points of conversion efficiency
in this type of system is phenomenal,” says Bruce Osborn,
president and CEO. “This is a significant advancement that
takes our dish engine systems well beyond the capacities of
any other solar dish collectors and one step closer to commercializing
an affordable system.”
Serial #3 was erected in May 2005 as part of a
prototype six-dish model power plant at the Solar Thermal
Test Facility that produces up to 150 kilowatts (kW) of grid-ready
electrical power during the day. Each dish unit consists of
82 mirrors formed in a dish shape to focus the light to an
The solar dish generates electricity by focusing
the sun’s rays onto a receiver, which transmits the heat energy
to a Stirling engine. The engine is a sealed system filled
with hydrogen. As the gas heats and cools, its pressure rises
and falls. The change in pressure drives the pistons inside
the engine, producing mechanical power, which in turn drives
a generator and makes electricity.
Lead Sandia project engineer Chuck Andraka
says that several technical advancements to the systems made
jointly by SES and Sandia led to the record-breaking solar-to-grid
conversion efficiency. SES owns the dishes and all the hardware.
Sandia provides technical and analytical support to SES in
a relationship that dates back more than 10 years.
is a National Nuclear Security Administration laboratory.
Andraka says the first and probably most
important advancement was improved optics. The Stirling dishes
are made with a low iron glass with a silver backing that
make them highly reflective —focusing as much as 94 percent
of the incident sunlight to the engine package, where prior
efforts reflected about 91 percent. The mirror facets, patented
by Sandia and Paneltec Corp. of Lafayette, Colo., are highly
accurate and have minimal imperfections in shape.
Both improvements allow for the loss-control
aperture to be reduced to seven inches in diameter — meaning
light is highly concentrated as it enters the receiver.
Other advancements to the solar dish-engine system
that helped Sandia and SES beat the energy conversion record
were a new, more effective radiator that also costs less to
build and a new high-efficiency generator.
While all the enhancements led to a better system,
one aspect made it happen on a beautiful New Mexico winter
day — the weather.
“It was a ‘perfect storm’ of sorts,” Andraka
says. “We set the record on Jan. 31, a very cold and extremely
bright day, a day eight percent brighter than normal.”
The temperature, which hovered around freezing,
allowed the cold portion of the engine to operate at about
23 degrees C, and the brightness means more energy was produced
while most parasitic loads and losses are constant. The test
ran for two and a half hours, and a 60-minute running average
was used to evaluate the power and efficiency data, in order
to eliminate transient effects. During the testing phase,
the system produced 26.75 kW net electrical power.
Osborn says that SES is working to commercialize
the record-performing system and has signed power purchase
agreements with two major Southern California utilities (Southern
California Edison and San Diego Gas & Electric) for up to
1,750 megawatts (MW) of power, representing the world’s two
largest solar power contracts. Collectively, these contracts
require up to 70,000 solar dish engine units.
“This exciting record shows that using these
dishes will be a cost-effective and environmentally friendly
way of producing power,” Osborn says. “SES is actively engaged
in the commercialization of the system, called the ‘SunCatcher,’
including continuing to prepare it for mass production, completing
project site development and preconstruction activities, and
establishing partnerships with substantial manufacturing and
industrial organizations to develop a cost-effective manufacturing
process and supply chain. The demonstrated high efficiency
means more energy is generated for the given investment, lowering
the cost of the energy delivered.”
SES was formed in 1996 to develop and commercialize
advanced solar technology. The company maintains its corporate
headquarters in Phoenix, Ariz, project and technical development
offices in Tustin, Calif, and engineering and test site operations
at Sandia National Laboratories in Albuquerque.
is a multiprogram laboratory operated by Sandia Corporation,
a Lockheed Martin company, for the U.S. Department of Energy’s
National Nuclear Security Administration. With main facilities
in Albuquerque, N.M., and Livermore, Calif., Sandia has major
R&D responsibilities in national security, energy and environmental
technologies, and economic competitiveness.