Adoption of CO2 mixtures as working fluid for CSP cycles with linear collectors and molten salts as HTF

This work deals with the adoption of CO2-based mixtures as working fluid in transcritical cycles for CSP applications. A direct comparison with the small-scale CSP plant based on a Rankine cycle operating in Partanna (Italy) is developed to verify the potential advantages of the proposed novel cycles both in design conditions and on yearly basis. The solar plant consists of linear Fresnel reflectors using solar salts as HTF and a large direct thermal energy storage. The solar to thermal performances of the power plant are evaluated with the software SAM, while the design of the cycle with the innovative working fluids (CO2+C6F6 and CO2+C6F12O) is developed in ASPEN Plus. An annual analysis based on hourly DNI data is then performed to assess the yearly electricity yield together with a preliminary economic analysis. The results of the most advanced cycle layout exploiting the innovative working fluid evidence a minor reduction of the computed LCOE when compared to the traditional technology (around 10%), a result highly sensitive to the power block costs, and a 2GWh increment in the yearly energy produced (13% of the Rankine production).