Influence of thermal energy losses on the yearly performance of medium size CSP plants

This work focuses on a detailed performance analysis of a medium size Concentrating Solar Power (CSP) plant based on linear Fresnel collectors, an Organic Rankine Cycle (ORC) power generation unit, thermal oil as heat transfer fluid and a two-tank direct Thermal Energy Storage (TES) system. In particular, the study aims to carefully evaluate the main plant sections thermal losses (solar field, ORC unit and TES section) during daylight and night periods, as well as during its different operating phases (start-up, continuous operation and shut-down). The analysis was carried out on hourly basis for a typical meteorological year by using a detailed simulation model that evaluates both performance and thermal losses of the CSP plant as a function of solar radiation, solar position, ambient temperature and wind speed for given values of the main geometrical and technical characteristics of solar receivers, piping and storage tanks. In addition, the simulation model evaluates the heat losses related to the warm-up phase of the solar field and to the start-up (both warm and cold start-ups) of the ORC unit. The performance assessment demonstrates that thermal energy losses determine a reduction in the net energy production of the CSP plant by about 9% on yearly basis. Almost 61% of the thermal losses are located in the solar field (receiver tubes and hot and cold oil pipes), 22.3% in the hot and cold oil tanks and the remaining 16.6% is represented by the thermal energy required by ORC start-up phases