Impacts of solar multiples on the performance of integrated solar combined cycle systems with two direct steam generation fields

Abstract

Integrated solar combined cycle (ISCC) systems coupled with direct steam generation (DSG) are more promising in terms of system efficiency and electricity cost than current solar-only power generation systems, as ISCC–DSG offers the advantages of higher net thermal efficiency and lower cost. However, the ISCC systems usually have to be operated at part-load conditions with low system efficiency when no or lower insolation than that at design point is available as most of state-of-the-art such systems have no thermal storage equipped. In order to improve system performance and prolong the system full-load operation hours, a proper solar field size represented as the solar multiple is a prime parameter to be determined during the design stage of the ISCC system. A too large solar multiple might cause the collected solar thermal energy to become partially useless without thermal storage and high investment cost, while a smaller one might worsen the part-load performance of the system.This paper presents the thermodynamic and economic analysis for an ISCC system with two pressure level DSG solar fields (ISCC–2DSG), aiming to study the impacts of solar multiples on system performance with or without consideration of thermal storage. In the ISCC–2DSG system, the solar thermal energy produced from two solar fields is only used to supply latent heat for low- and high-pressure water vaporization, respectively. Feedwater preheating and steam superheating are achieved in a HRSG. The annual thermodynamic performance of several such ISCC–2DSG systems, with different solar multiple values but with identical design parameters in the power subsystem, is characterized. Based on these features, the LEC for each system is calculated and compared. An optimum solar field size (solar multiple), which gives the minimum LEC, for the ISCC–2DSG system can be finally obtained.