FEB 14

1989 Record for Solar-to-Grid Efficiency Finally Broken

Written by on February 14, 2008

This January, on an exceptionally clear and cold day, scientists for the Sandia National Laboratory and Sterling Energy Systems recorded a 31.25% solar-to-grid efficiency, nearly 2% better than the 1989 record.

The efficiency record, according to the scientists working on the project, brings us another step closer to getting solar to compete with coal power prices.

Solar-to-grid efficiency is very different than solar panel efficiency, which already has exceeded 40%. Unfortunately, getting the power from a solar panel (which is direct current) onto the grid (which is alternating current) requires several steps, each of which eats away at efficiency.

These solar collectors, which use concentrators to heat a Sterling engine, produce alternating current, so less energy is lost getting the power onto the grid.

The scientists contribute their success to 1. The increased reflectivity of the mirrors, which now approaches 95%, and 2. A rather ironic "Perfect Storm." This perfect storm consisted of a perfectly clear day, with 0% moisture and no particulates, the day was 10% brighter than average.

Additionally, the cold weather helped as well. Sterling engines operate by exploiting the difference in temperature between a hot end and a cold end. Solar energy heats up the hot end, but the only thing to cool the cold end is the ambient temperature.

Now we just have to hope that these solar concentrators can be scaled up, or made cheap enough to start, at least on cold days in New Mexico, to compete with coal.

Read the full press release after the jump.

Via Metaefficient

Sandia, Stirling Energy Systems set new world record for solar-to-grid conversion efficiency

31.25 percent efficiency rate topples 1984 record

Sandia and Stirling Energy Systems set new world record for solar-to-grid conversion efficiency. The record establishes a new solar-to-grid conversion efficiency of 31.25 percent. The old record, which has stood since 1984, was 29.4 percent.
Sandia and Stirling Energy Systems set new world record for solar-to-grid conversion efficiency. The record establishes a new solar-to-grid conversion efficiency of 31.25 percent. The old record, which has stood since 1984, was 29.4 percent. (Photo by Randy Montoya)

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ALBUQUERQUE, N.M. —On a perfect New Mexico winter day — with the sky almost 10 percent brighter than usual — Sandia National Laboratories and Stirling Energy Systems (SES) set a new solar-to-grid system conversion efficiency 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.

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, SES 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 intense beam.

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.

Sandia 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.

Sandia 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.

Sandia news media contact: Chris Burroughs, [email protected], (505) 844-0948
SES media relations contact: Lori Hecker, [email protected], (602) 957-1818


7 Responses to “1989 Record for Solar-to-Grid Efficiency Finally Broken”

  1. pl says:

    I despair that the public will ever have a clue about these kinds of things. There is no coal power plant that achieves an efficiency anywhere close to 70% (unless one redefines efficiency); I can’t say with wind power, though in that case efficiency is perhaps less an issue.

    Bob Musselman did do a nice job of examining some of the confusion in the article, especially that between photovoltaic and thermodynamic power generation.

  2. o2xlc says:

    I don’t understand why are you so angry. Efficency increase of 2% in 20 years means that it is very difficult process.

    You should be thankful that someone “waste his time” to achive this…

    An efficiency of average coal power plant is approximately 70% and wind power plant has maximum efficency about 59%.

  3. VP
    This is an interesting article, but they do mix up comparisons of photovoltaics (direct conversion of photons to electricity) with solar-thermal (using photon energy converted to heat then converted to mechanical energy—the Sterling—engine, then driving a generator to generate electricity).

    Photovoltaics (PV) have a max conversion of 40% in the laboratory but more typically 14% to 18% in practical modules. There is some energy lost then in converting DC to AC.

    Solar-thermal can generate higher practical efficiencies, between 20% and 38%, as in this perfect experiment.

    However you can see from my description above, the PV model is less complicated and requires less maintenance:

    1. Solar module made up of many PV cells, generating direct current.
    2. A solid state (no moving parts) inverter to convert DC to AC.

    The solar-thermal model requires more and complicated components:

    1. Perfectly shaped and clean mirrors.
    2. A solar collector which receives the light from the mirrors, focuses the light and generates heat.
    3. A thermal converter which heats some kind of liquid (water, glycol, etc.) and boils it (converts from liquid to high pressure gas).
    4. A thermodynamic engine (like a steam engine) using a turbine or some kind of sterling cycle to generate rotary mechanical motion.
    5. A generator which converts the rotary mechanical motion to AC electricity.
    6. Recycling and condensing systems which condense the now low-pressure gas to liquid and return it to the sterling engine.

    The efficiency record they broke was for the solar-thermal cycle, which has lasted for many years. Their achievement had as much to do with perfect conditions (no moisture, no smog, no clouds) as technology improvement.

    The efficiencies of PVs have improved about 100% in the past 10 years based purely on new technology of solar cells themselves, and meanwhile PVs have become more reliable and inverters have become more maintenance free.

    There are situations where either type of system is optimum.

  4. pete says:

    a couple thoughts
    Wow I can’t believe I wasted time reading this and typing a comment! I’m with Alan: 20 yrs. for 2%, “perfect storm” conditions, and how much money spent? Talk about failed science.

  5. Josh says:

    I recently read that these power stations are producing electricity for about $16c/KWH, which is about 4x the cost of coal, 2x wind, and about 33% more than natural gas power. They have quite a ways to go to compete with coal, though natural gas peak power stations are within striking range.

  6. alan parolini says:

    after approx. 20 years, some of our best scientists have increased efficiency 2%


  7. Michael says:

    Have ecogeek readers checked out http://www.openeco.org yet? I’m new to the site but they have a lot of metrics and tips to reduce carbon footprints in industry… just thought I’d pass it along.