A novel means to flexibly operate a hybrid concentrated solar power plant and improve operation during non-ideal direct normal irradiation conditions

Hybridization of concentrated solar power (CSP) with other energy sources can drastically increase how much solar energy is harnessed and potentially expand the current geographical deployment of CSP installlations. In this study, a novel operation strategy referred to as flexible heat integration (FHI), is proposed and applied to a hybrid CSP-natural gas power plant. The proposed plant, modeled in Simulink, employs a solar central receiver (SCR) and dual-source gas boiler to drive a steam Rankine power cycle. FHI involves collecting and dispatching solar energy at modified temperatures during off-design direct normal irradiance (DNI). During low-grade ( < 100 W/m(2)) and medium-grade (100-500 W/m(2)) levels of DNI, molten salt is used for steam boiling and feedwater preheating, respectively, rather than superheating usually seen in SCR steam plants. Hybrid gas-firing supplies energy to bypassed systems. FHI is applied to a hybrid plant over the course of a day from each season for a plant located in Salt Lake City, Utah, an unconventional location due to off-design DNI variability. A spring day exhibiting variable DNI is used as the main case study to demonstrate the dynamics and robust operation under the FHI framework. The operation of the plant over the winter day shows the largest improvement in solar-to-electric (STE) efficiency whereas the summer day exhibits the smallest improvement. Monthly results follow a similar trend with FHI improving STE from 15.3% and 16.3% to 17.0% and 16.7% in January and July, respectively. Yearly results show FHI improving STE efficiency from 16.1% to 17.1% relative to standard hybrid operation. Overall, the proposed concept expands the current understanding of energy management in hybrid SCR-natural power plants under non-ideal DNI conditions and locations that have lower DNI by applying FHI.