Solar Cogeneration Utilizing Solar Tower Integrated with sCO2 Brayton Cycle and MEE-TVC Desalination

Abstract

Renewable energy sources have become nowadays an efficient alternative to fossil fuels. Solar energy is one of the widely used renewable energy technologies. Recent advancement in the solar tower technology has made it an attractive choice of energy harvesting. In this study performance analysis is conducted for a solar driven supercritical CO2 (sCO2) Brayton cycles combined with multiple effect evaporation with thermal vapor compression (MEE-TVC) for power and desalinated water production. The study includes finding two configurations based on two different supercritical cycles, namely, the regeneration and recompression sCO2 cycles and performing parametric studies for each. Monthly averaged study for each of the months of the year and the average for the whole year are present as well. The entropy generation evaluation for the system is also studied as well as the capital and operating cost estimation. In this study, a new efficiency equation for the combined power and water production is developed. The study is performed over different regions of Saudi Arabia. From the energy analysis, it is found that the highest productivity is that of the region of Yanbu, followed by Khabt Al-Ghusn in the second place, and the rest are as follows, Jabal Al-Rughamah, Jizan, Al-Khafji, and Dhahran in descending order. The number of heliostats utilized is 2646. It is also deduced that the effective efficiency is the highest at the minimum fraction possible of heat entering the sCO2 cycle. For the area of Dhahran, this value is 0.32 for the regeneration cogeneration cycle and 0.34 for the recompression cycle at a fraction of 0.19 and 0.21, respectively. From the entropy analysis, it can be deduced that the highest contributing component in the MEE-TVC subsystem is the steam jet ejector, which is varying between 50 % and 60 % for different number of effects. The specific entropy generation in the MEE-TVC decreases as the fraction of the input heat to the desalination system decreases; and the specific entropy generation of the sCO2 cycle remains constant entropy generation. The solar tower is the largest contributor to entropy generation in both configurations, reaching almost 80 % from total entropy generation, followed by the MEE-TVC desalination system, and the sCO2 power cycle. The entropy generation in the two tank thermal storage is almost negligible varying around 0.3 % from total generation. The cost results reveal that the regions characterized by the highest average solar irradiation throughout the year have the lowest LCOE and LCOW values. The region achieving the lowest cost is Yanbu, followed by Khabt AlGhusn in the second place, and the rest are as follows, Jabal Al-Rughamah, Jizan, AlKhafji, and Dhahran. The LCOE of Yanbu at a fraction of 0.5 for regeneration and recompression solar cogeneration cycles are 0.0915 $/kWh and 0.0826 $/kWh, respectively.