Last month CSP Today covered SunShot’s award to NREL’s research into developing a s-CO2 power cycle, and spoke to NREL’s Craig Turchi about their $8 million award.
This month we speak to Tex Wilkins, past director of the CSP program at the DOE and with its current director, Dr. Ranga Pitchumani.
By Susan Kraemer
In a systematic funding approach, the U.S. Department of Energy (DOE) is backing the breadth and depth of research and development needed to drive the leveled cost of energy from CSP to 6 cents a kilowatt hour without subsidy by 2020.
This year, the SunShot Initiative announced funding of up to $56 million towards achieving that goal. The initiative will build upon previous research by the DOE, such as the ARPA-E awards of last year which investigated research and development into high temperature thermal energy storage.
SunShot’s three fold focus:
Pitchumani told CSP-Today, “We focused this funding on three areas in CSP that integrate together with storage to form the whole system.” The collectors which reflect the light, the receiver where the light is focused to concentrate the heat to generate the high temperatures, the HTFs and power cycle to convert that heat energy to electricity. We are investing in technologies to push the envelope of each of these.” While they are being developed independently for now, some of this year’s awards (including the $8 million award to NREL to demonstrate a multi-megawatt power cycle using s-CO2 as the working fluid) are focused on the promise of Supercritical CO2.
Heated and compressed CO2 (forming s-CO2) within a Brayton cycle loop in the power plant can increase the capacity factor of CSP to at least 75%. Mechanical systems adapted to the heat and pressure of the s-CO2 re-compression cycle represent a major advancement in CSP technology.
“Some of the grants among the 21 are looking at the hardware,” Tex Wilkins, who directed CSP funding until last year, told CSP Today. “Higher temperature containers are needed: first you need a material that can withstand the higher temperatures in the storage media, but then you need to contain that in a material that can deal with that for a longer period of time, so the DOE is looking at ways that the whole system can operate at these high temperatures."
Break down of Technology
Collectors: 3M will develop high-reflectivity films and high-rigidity structures to replace the current heavy glass mirror solar collectors ($4.9 million). BrightSource will help to automate the installation process by developing an efficient collector assembly platform ($4.9 million). JPL will improve components, to reduce weight, and optimize mass production ($2.3 million).
Receivers: Brayton Energy will demo a new solar receiver able to handle the high temperature and pressure of supercritical carbon dioxide ($1.6 million). Oregon State University will cut the size, weight and heat loss from high-temperature solar receivers with microchannel heat transfer technology ($800,000). San Diego State University will demonstrate a small particle heat exchange receiver with carbon particles ($3.8 million). NREL will develop a novel particle receiver with near-blackbody absorptive performance using falling particles ($3.8 million).
Power cycle and HTFs: Stanford will demo a high-temperature thermionic-based power cycle without moving parts that can integrate with conventional CSP cycles ($900,000). Southwest Research Institute/GE will develop a cheaper, high efficiency s-CO2 power cycle engine developer for modular CSP applications ($6.8 million) and develop a high temperature external combustor that can mix CSP-heated air with natural gas in hybrid plants ($3.1 million). MIT will develop a thermoelectric generator without moving parts that can be integrated with storage ($1 million). Argonne Labs will demonstrate the use of chemically reacting working fluids (CRWFs) for HTFs ($1 million).
One award, to Wilson Solarpower, from a previous funding opportunity in the SunShot Initiative's portfolio covers all three components. They will develop, build, test, and evaluate two prototype components—an unpressurized thermal storage system and an unpressurized solar receiver—and a full Brayton cycle system that includes them.
Future of Public-Private Collaboration in US CSP
Wilkins, whose tenure goes back to the Carter era, says this sort of collaboration between the national labs and the industry has been on-going. “A lot of work has gone into helping industry; sometimes directly, sometimes indirectly."
“Labs have not only done research on their own," he points out. For example, among this year’s awardees, 3M is the world leader in film technologies, while Brayton Energy is experienced in manufacturing compact s-CO2 heat exchangers and solar receivers. "A lot of research has been in conjunction with industry. However, of the work that’s being done on troughs and towers now; a significant proportion has come out of lab research and development. SolarReserve’s technology is a direct descendant from the solar I and II. NREL has been working on parabolic trough for 20 years.”
Dr. Pitchumani envisions taking the best of all of these concepts, and at some point in the future running another CSP funding opportunity to integrate all the subcomponent technologies, and further refining the best of the breakthroughs.
“These projects make significant advances in the way these technical targets are being aggressively pursued, and it's very refreshing to see that. It’s an exciting time. We had some great applications, that push the forefront of technologies significantly, not just incrementally,” he says, adding, “I think that CSP has been under-invested, compared to PV. But CSP is a beautiful technology; it’s a viable technology. The story of CSP with storage is a beautiful story.”
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