Session: 06-03: Concentrated Solar Power II -- Power Block and Components

Paper Number: 142402

142402 - Performance and Technoeconomic Analysis of Supercritical Carbon Dioxide Power Cycles for Gen3 Particle Concentrating Solar Power Systems 

Abstract: 

Supercritical carbon dioxide (sCO₂) power cycles are being considered for future use in next generation (Gen3) CSP systems because they offer higher theoretical thermal efficiencies and potentially lower costs than steam Rankine cycles. Many cycle configurations have been analyzed for Gen2 systems that are constrained by relatively lower hot temperatures and the HTF freeze point temperature. Particle systems can reach both higher and lower temperatures, and a large temperature difference across the HTF may improve techno-economics, trading reduced cycle efficiency for reduced TES and lift particle costs and transport parasitics. Proposed waste heat recovery cycles could be ideal for systems with large temperature differences, because they prioritize extracting heat from the heat transfer fluid (HTF), rather than strictly focusing on thermal efficiency.

We evaluate six cycle configurations: simple (with optional recuperator bypass), recompression (with optional HTR bypass), partial cooling, and turbine split flow. The simple cycle contains a single recuperator to retain heat in the sCO₂, while the recompression cycle adds a recompressor to bypass the main compressor and low temperature recuperator, effectively avoiding pinch point issues in the recuperator. Each cycle can optionally have a bypass heat exchanger that directs a portion of flow to absorb heat from the HTF after the primary heat exchanger, decreasing the HTF outlet temperature further. The partial cooling cycle adds a precompression and cooling stage before the sCO₂ splits to the main compressor and recompressor. This cycle has shown promising results but increases cycle complexity and cost compared to the recompression cycle. The turbine split flow cycle prioritizes extracting heat from the HTF over thermal efficiency and has been studied for waste heat recovery cycles.

All six cycles are integrated into a design-point techno-economic model of the entire particle CSP system. We compare the system-level trade-offs between efficiency, temperature difference, cost, receiver efficiency, and LCOE for each configuration. The total recuperator conductance and HTF temperature difference are varied for each cycle configuration, producing the thermal efficiency and component cost of the power cycle. Internally, the power cycle optimizes the remaining free variables, including recompression fraction, bypass fraction, pressure ratio, and the ratio of total conductance that is assigned to the low temperature and high temperature recuperators. This performance is then integrated into the system level CSP model, which bases the TES sizing and receiver performance on the resulting HTF temperature difference. The system level model calculates total cost and LCOE, providing a metric to adequately compare the power cycle configurations. Finally, we present analysis of performance trends and identify optimal cycle configurations.

Presenting Author: Taylor Brown NREL

Presenting Author Biography: Taylor is a researcher in the Thermal Energy Systems group at NREL. His research focuses on modeling concentrating solar power systems and sCO2 power cycles. Taylor’s work includes modeling linear Fresnel and parabolic trough systems for NREL’s System Advisor Model.

Authors:

Taylor Brown NREL
Ty Neises NREL