Concentrating Solar Power (CSP) plants have the potential to provide dispatchable renewable power generation to support the baseload need currently supplied primarily by coal and nuclear plants and peaking power capability to reduce the use of natural gas for load following. However, these plants have had difficulty achieving widespread use due to the low cost of combined photovoltaic and battery systems capable of providing similar services to the electricity grid. A new generation of CSP technologies must be developed to reduce the levelized cost of electricity (LCOE) to 6 cents/kWh by leveraging heat transfer fluids (HTF) capable of operation at higher temperatures and coupling with higher efficiency power conversion cycles. Three promising pathways for Generation 3 CSP (Gen3CSP) technology development have been funded by the U.S. Department of Energy (DOE) leveraging solid, liquid, and gaseous HTFs to transfer heat to a supercritical carbon dioxide (sCO2) Brayton cycle.

The primary heat exchangers (PHX) necessary to couple these high-temperature HTFs to sCO2 are an essential new technology that must be demonstrated at a scale relevant to commercial CSP to validate design expectations for performance, lifetime, and operability. The demonstration of these PHXs need a reliable 1 MWth-scale sCO2 test system that can provide sCO2 coolant to the PHX in a compact package suitable for installation near any Gen3CSP thermal storage system. This paper outlines the final design of such a system including the expected operating range and off-design capabilities. The system uses a dense-phase high pressure canned motor pump as the sCO2 circulator and ambient air as the ultimate heat sink operating at pressures up to 250 bar and temperatures up to 715 °C with capability to supply up to 5.3 kg/s of sCO2 flow to the primary heat exchanger. Key component requirements for this system have been frozen and procurement is underway. The expected completion date for heated acceptance testing of this system is September of 2020.

This system is also capable of being upgraded through the addition of a turbo-compressor and turbo-generator to operate as a complete sCO2 Brayton cycle with power generation in order to demonstrate an integrated solar to sCO2 power pilot plant and understand transient interactions between the thermal storage system, sCO2 turbomachinery, and ambient air temperature. In addition, this upgrade would provide experience with plant operating considerations including balancing charging the thermal storage system with generating and dispatching power to the electrical grid. A roadmap for this upgrade will be discussed including limitations and requirements for the necessary turbomachinery.

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