Session: 08-02: Technoeconomic Analysis of CSP and Thermal Energy Storage Systems

Paper Number: 169645

169645 - Technoeconomic Analysis of Supercritical Carbon Dioxide Power Cycle Designs for Particle-Based Csp Systems 

Abstract: 

Supercritical carbon dioxide (sCO2) power cycles are being researched for concentrating solar power (CSP) systems because they are capable of high thermal efficiencies with compact turbomachinery, making them competitive with traditional steam power cycles. The next generation of CSP systems, Gen3, can operate at higher temperatures than the current Gen2 systems that are limited by the temperature constraints of molten salts. To increase temperature flexibility, particles are being considered for the heat transfer fluid (HTF) and storage material. The large potential operating temperature range of particles requires researchers to consider a wide range of sCO2 power cycles designs. Various sCO2 cycle configurations exist, offering different benefits, from high thermal efficiency, to large HTF temperature difference, to low cycle cost. For CSP systems, cycles with higher efficiencies require less heat from the solar field, saving significant installation costs; however, cycle efficiency is often inversely related to HTF temperature difference, which negatively impacts thermal energy storage (TES) costs and conveyance parasitic losses.
 
We model six sCO2 cycle configurations: simple recuperated (with optional recuperator bypass), recompression (with optional high temperature recuperator bypass), partial cooling, and turbine split flow. The optional bypasses in the simple and recompression cycles are designed to increase the HTF temperature drop by adding a second HTF heat exchanger after the primary heat exchanger (PHX). A portion of sCO2 flow bypasses the respective recuperator and absorbs additional heat from the HTF. Similar in purpose, the turbine split flow cycle is designed to maximize heat extraction from the HTF and was originally developed for waste heat applications. We perform a parametric sweep of each configuration’s design variables, including pressure ratio, split flow fractions, and recuperator conductances, to encapsulate the full design space.

Each case from the parametric sweep is integrated into a system level CSP design point model, which uses the cycle efficiency, cost, and HTF temperatures to design the CSP system, calculate installation cost, and simulate design point performance. The performance of each case is compared by calculating the cost per net power produced. The cost is the total system installed cost, including heliostat field, tower, receiver and storage. The net system power  subtracts particle conveyance parasitics, which vary depending on thermal power and HTF temperature difference. In addition to presenting results for a ‘baseline’ case with common assumptions, we also perform a sensitivity study that varies cycle and system characteristics, including cycle turbomachinery efficiencies and PHX approach temperatures. We also vary the cost of the PHX, recuperators, heliostats and TES due to the cost uncertainty of cycle and system components. 

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.