Design of ORC Systems under Variable Input Parameters: a Multi-scenario Approach

orc2019 Tracking Number 173

Organic Rankine cycle (ORC) powered by solar energy is a viable and effective option for a high efficiency conversion of solar thermal energy into electricity at a distributed scale. However, the fluctuations of the thermal energy produced by the solar collectors often force solar-based ORC systems to operate at part-load conditions. Consequently, the intrinsic uncertainty of solar irradiation requires the development of novel approaches able to give robustness to the design phase of power generation systems fed by solar energy. A novel methodology for the preliminary design of solar ORC systems, based on the minimization of the expected Levelized Cost of Energy (LCOE) under variable input conditions is therefore proposed and analyzed in this paper. The expected variations of the solar irradiation together with the fluctuation in the ambient temperature that affects the condenser pressure, are considered during the design phase by adopting a multi-scenario approach. The proposed methodology has been tested by referring to a medium-scale ORC unit and by considering different working fluids. As case studies, the direct coupling of the ORC unit with a solar field and the integration of a Thermal Energy Storage (TES) system have been investigated. In all the cases, the results obtained by using a multi-scenario approach have been compared with those obtained by a single-scenario approach, achieving a lower value of the actual LCOE. In fact, the ORC configuration obtained by adopting a multi-scenario approach is characterized by lower performance under design conditions, but it is less sensitive to the variation of the main inputs. This fact is particularly evident for the case with the direct coupling of the solar field, where important fluctuations in the heat source mass flow rate are expected, while it becomes more and more marginal with the rise in the TES storage capacity.