A new concept of solar thermal power plants with large-aperture parabolic-trough collectors and sCO2 as working fluid

Abstract

The use of pressurized gases as working fluid in parabolic troughs has been proposed in recent works to avoid environmental issues and reduce electricity costs in solar thermal power plants. However, such technology still poses great uncertainties regarding its efficiency and feasibility. To overcome the limitations of pressurized gases, this study proposes a new concept of solar thermal power plant with large-aperture parabolic-trough collectors using CO2 in supercritical state (sCO2) as working fluid and molten nitrate salts as thermal storage medium. A modular design for the solar field, reducing the number of blowers and heat exchangers and minimizing the molten salts hydraulic circuit, is also described. To assess the performance of the new concept, its expected annual efficiency is compared to the efficiency of a reference solar thermal power plant using thermal oil as heat carrier in the solar field. To that purpose, two simulation models are developed in the TRNSYS software environment to reproduce the behaviour of both the new solar power plant with sCO2 and the reference plant. In addition, a parametric study is carried out by means of the simulation model to optimize net annual production as function of outlet temperature and collection area of the solar field. Besides, a preliminary economic assessment is performed to predict expected costs of electricity generated with the new concept of plant. The results of this work suggest that the new concept of solar plants proposed can achieve higher annual efficiencies (about 0.5% increase) and lower electricity costs (around 6% savings) than conventional solar thermal power plants with thermal oil.