Comparison of Parabolic Trough and Linear Fresnel Collectors Based Concentrating Solar Power Plants Using Organic Rankine Cycle

Abstract

Concentrating solar power (CSP) plants with parabolic trough collector (PTC) using thermal oil as heat transfer fluid (HTF) and conventional steam Rankine cycle (SRC) as power generating cycle is the most commercially developed technology. Direct steam generating linear Fresnel reflector (LFR) systems are developed as a cheaper alternative to PTC systems. The major drawbacks of LFR systems are low optical efficiency and production of saturated steam. These result in higher solar field area requirement compared to PTC based plants of same capacity. Organic Rankine cycle (ORC) based power block, with dry working fluids, offers higher cycle efficiency as well as improved part-load turbine efficiency compared to SRC in modular scale plants with heat sources up to 400 °C. ORC is more suitable to LFR based CSP plants. In this paper, thermo-economic analysis of PTC and LFR based CSP plants with ORC has been presented. An approximate selection methodology, for LFR and PTC based CSP plants, is proposed and the selection diagram generated using the proposed methodology can be used for LFR and PTC based CSP plants with any working fluid of Rankine cycle. The applicability of the selection diagram is demonstrated using case studies of n-Pentane, Octamethyltrisiloxane (OMTS) and water working fluids based plants. Selection diagram captures the variations of power generating cycle efficiency, and costs of collector fields.