Design, commissioning and operation of a mini hybrid parabolic trough solar thermal power plant for direct steam generation

Abstract

Parabolic Trough Collectors (PTCs) are the most mature, reliable and widespread among Concentrated Solar Power (CSP) technologies for electricity generation. The conventional power plants relying on PTCs use synthetic oil as Heat Transfer Fluid (HTF) which has limited life span, has limited operation temperature, is expensive and harmful to the environment. In the present research work, a new perspective has been developed to directly generate steam in the collectors, eliminating the need for HTF in the solar field and avoiding auxiliary heat exchangers. A mini hybrid Direct Steam Generation PTC power plant having a boiler as a backup that can be operated with biogas or natural gas is installed at Ecole Nationale d'Ingénieurs de Tunis (ENIT) within the framework of REELCOOP project (Renewable ELectricity COOPeration). The description, commissioning and operation of the solar plant are presented in this paper. The plant is designed and tested under real-life operating conditions in the south Mediterranean region. The feasibility of the DSG process in horizontal parabolic trough collectors has been confirmed and an important know how has been acquired regarding the operation of DSG solar plant. The main instructions for the operation of the solar plant have been presented including start-up and shutdown procedures of the plant, as well as the safety measures to be considered.The development of this plant is aimed to address the challenge of coupling intermittent solar radiation and the presence of a two-phase fluid in the absorber tubes. An important know how has been acquired regarding the operation of DSG solar plants in solar only mode and in hybrid mode which allowed to balance strengths and weaknesses of solar and biogas/natural gas technologies. By combining both systems, we have tackled the problem of the controllability of the energy supply while exploiting as much as possible renewable sources.