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 performance preliminary assessed
through dynamic modelling tools. The main novelty is the integration in the plant’s 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. A practically feasible 100 kWEcase-study plant with 4 equivalent
hours of thermal storage is presented. The proposed system exceeds 25% cycle’s efficiency (air cooled with
◦
a condensing temperature of 80
18% global system 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.