Control systems for direct steam generation in linear concentrating solar power plants - A review

Concentrating Solar Power (CSP) plants generate renewable electricity using the conversion of solar direct normal irradiation into thermal energy, then into mechanical work and electricity through the use of a thermodynamic cycle. Among the several available technologies, Direct Steam Generation (DSG), in which steam is generated directly in the absorber tubes of the solar field, and then directly fed to the turbine or thermal storage, holds interesting advantages. However, the steam generation system shows a difficult dynamic behavior which constitutes a challenge for the control system design. It is mainly due to the conjunction of the natural transient condition of solar irradiation and the presence of two-phase flow in the absorber tubes. This paper reviews the control methods of the DSG systems used in linefocus CSP. The control systems are either proposed in literature, or actually applied in currently running plants or prototypes, although an extensive description is difficult to obtain in the case of the latter. The control systems are classified according to which DSG operation mode they refer to.