Preliminary Assessment of a Novel Small CSP Plant Based on Linear Collectors, ORC and Direct Thermal Storage

A novel power block for medium temperature concentrated solar power (CSP) applications based on the organic Rankine cycle (ORC) technology is presented in this paper, and its dynamic performances preliminary assessed by means of simulations. The main novelty is the integration in the plant layout of a direct thermal energy storage (TES) system, which stores the same working fluid used in the power cycle. This allows for an unmatched simplification with respect to current state-of-the-art solutions, eliminating any intermediate heat transfer fluid (HTF) loop and its related components; however, in its simplest form, this concept yields to comparatively low storage densities. An exemplary advanced 100 kWE power plant is simulated as a test case. The plant features 4 equivalent hours of thermal storage. The proposed system exceeds 25% net conversion efficiency (air cooled with a condensing temperature of 80 ◦C) which, considering the coupling with parabolic trough collectors, yields 18% solar-to-electric efficiency in design conditions. In order to investigate the control issues related to the proposed configuration, dynamic models have been developed for both the linear collectors and the TES system. These tools have been validated against literature data, and coupled to the recently developed model of a complete ORC unit, validated against proprietary experimental information. The possibility of ensuring safe automatic (and potentially unmanned) operations, while maintaining high conversion efficiency, is firstly assessed considering extreme conditions: the aspect of controllability is in fact considered of the utmost importance for the envisaged distributed applications.