Time-dependent behavior of a recompression cycle with direct CO2 heating through a parabolic collector array

The theoretical transient analysis of a recompression cycle is considered while directly heating the working fluid, CO2, in a solar trough field. The analysis explores the temporal behavior of the system's performance for three distinct, minute-based, solar irradiation profiles: (i) daylong perfectly clear skies, (ii) instantaneous on-off cloud shading and (iii) partially cloudy day. The key objective is to study the effect of the solar intermittency on the heat exchangers, solar collector and on the overall cycle's behavior - the thermal capacitance of the two first components is considered. The calculations reveal that, even though auxiliary heating systems was not considered, the heat capacitance of the working fluid and parabolic collector assembly is capable of instantaneously smoothing out the cycle's performance for on-off clouding conditions, such as the net power and thermodynamics efficiencies - note that the cycle's performance disregards the parabolic trough efficiency. Differently, the overall system's efficiency, which is regarded as the product of the efficiencies of the cycle and parabolic trough, is much more sensitive to irradiation changes. The study also specifically considers the effect of the clouding intensity and time, with the former being measured as fraction of clear sky irradiation on the system's performance. The analysis shows that it is possible to quantify the time scale available such that an auxiliary heating system delivers heat to the working fluid during a clouding scenario allowing the plant to work steadily.