Assessment of the Supercritical Carbon Dioxide Cycle for Use in a Solar Parabolic Trough Power Plant

by Daniel J. Chapman & Diego A. Arias
Abengoa Solar Inc.

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Advances in materials and solar concentrator design allow parabolic trough power systems to output higher temperatures than currently operating plants, which historically use a steam Rankine power cycle. The supercritical carbon dioxide (S-CO2) Brayton cycle is assessed as a power conversion system for future solar parabolic trough solar plants incorporating higher output temperature and a thermal storage system. S-CO2 is modeled as a heat transfer fluid in the solar field, and in a thermocline storage system, with hopes that heat exchangers at the power block can be abandoned. It is found that the S-CO2 Brayton cycle can reach higher efficiencies than the steam Rankine cycle at temperatures of 500ºC and above under solar power plant conditions, but more information on S-CO2 cycle technology, such as effect of daily startups and accurate cost estimates, are necessary before a full financial analysis can be completed. Several modifications to the solar field are required to accommodate the high-pressure CO2, including using thicker pipes and redesigning welds and ball joints. A preliminary analysis shows that a S-CO2 thermocline storage system is not practical due to the high cost of pressure vessels.