Thermo-economic analysis of a novel cascade integrated solar combined cycle system

Integrated solar combined cycle (ISCC) systems have been demonstrated to be more promising than solar-only power generation systems in terms of higher solar heat conversion efficiency and lower cost. In most ISCC projects, concentrating solar fields (e.g., parabolic trough solar fields with heat transfer (HTF) technology or direct steam generation (DSG) technology) are integrated for solar heat production with a temperature up to 400 °C to substitute for water preheating, evaporation or steam superheating in heat recovery steam generator (HRSG) for conventional combined cycle (CC) power systems. Although the ISCC scheme is effective for solar thermal energy utilization, the intermittent nature of solar energy usually causes this kind of systems to run inefficiently at part-load conditions when no or low solar radiation is available because most of the state-of-art ISCC systems are not equipped with costly thermal storage. To improve ISCC system performance, a new solution is proposed and investigated. This paper presents a novel cascade integrated solar combined cycle system, in which parabolic troughs solar collectors with DSG technology and non-concentrating solar collectors (e.g. evacuated tubes) are simultaneously integrated into the combined cycle power system. Thermodynamic and preliminary economic analysis for the new system are conducted to look into its feasibility and advantages. The results show that higher solar-to-electricity conversion efficiency and lower levelized electricity cost for the proposed system are achieved than for a reference ISCC system coupled with only DSG technology. Integration of both concentrating and non-concentrating solar collectors into an ISCC system in a temperature cascade way is viable and more efficient than the use of parabolic trough solar collectors alone.