SunShot_Logo_coiorWith recently awarded funding from the US Department of Energy SunShot Initiative’s CSP: APOLLO Program (Concentrating Solar Power: Advanced Projects Offering Low LCOE Opportunities), Sandia is working with a team led by the University of Wisconsin–Madison to evaluate the potential for significant improvements in the commercial viability of supercritical carbon dioxide (sCO2)/Brayton-cycle power conversion as an option for concentrating solar power (CSP) plants. The team brings together the expertise of two universities, two national laboratories, and two private companies.

A schematic of the team’s proposed switched-bed regenerator—to replace conventional recuperators. The planned device will have six regenerator beds; four multi-port ball valves, to reduce development costs and increase reliability; two large rotary actuators, which reduces system cost; and common inlets/outlets, to facilitate interface compatibility with the rest of the sCO2/Bratyon-cyle power-conversion system under development.

A schematic of the team’s proposed switched-bed regenerator—to replace conventional recuperators. The planned device will have six regenerator beds (blue/red); four multi-port ball valves (green), to reduce development costs and increase reliability; two large rotary actuators (grey), which reduces system cost; and common inlets/outlets, to facilitate interface compatibility with the rest of the sCO2/Bratyon-cyle power-conversion system under development.

CSP: APOLLO projects address challenges in CSP plant technical systems, including solar collectors, receivers and heat-transfer fluids, thermal energy storage, power cycles, as well as operations and maintenance. These R&D projects will improve the performance and increase the efficiency of every component within a CSP plant, ultimately lowering CSP electricity costs. The projects awarded under CSP: APOLLO each address challenges in CSP plant subcomponents, which will eventually be integrated into next-generation plants to deliver electricity at low-cost, whenever required by the electric grid.

Our focus is on the use of switched-bed regenerators for recuperative heat transfer within the cycle, which from initial design estimates could be less than half the cost of the currently used printed-circuit heat exchangers (PCHEs). This recuperative heat transfer can be several times the duty of the primary heat exchanger, accounting for roughly 25% of the overall cycle’s cost.

Our team, including representatives from UW-Madison, Sandia, the National Renewable Energy Laboratory, FlowServe, Colorado School of Mines, and Comprex, will design, fabricate, and experimentally evaluate a 25 kWth switched-bed regenerator system representative of that needed for a 10 MWe power cycle to assess suitability with the high static pressures, differential pressures, and thermal performance required by the sCO2 cycle.

Sandia will consult on the design and fabrication of a subscale unit and the 25 kWth unit, and will carry out experiments with the 25 kWth unit in Albuquerque, NM. The device will be installed in the test loop located at Sandia’s Nuclear Energy Systems Lab (NESL) in order to demonstrate the operation of the regenerator at prototypical conditions.

About the SunShot Initiative

The US Department of Energy SunShot Initiative is a collaborative national effort that aggressively drives innovation to make solar energy fully cost-competitive with traditional energy sources before the end of the decade. Through SunShot, the Energy Department supports efforts by private companies, universities, and national laboratories to drive down the cost of solar electricity to $0.06 per kilowatt-hour.