A comprehensive comparative energy and exergy analysis in solar based hydrogen production systems

Abstract

In the presented paper, energy and exergy analysis is performed for thermochemical hydrogen (H 2 ) production facility based on solar power. Thermal power used in thermochemical cycles and electricity production is obtained from concentrated solar power systems. In order to investigate the effect of thermochemical cycles on hydrogen production, three different cycles which are low temperature Mg–Cl, H 2 SO 4 and UT-3 cycles are compared. Reheat-regenerative Rankine and recompression S–CO 2 Brayton power cycles are considered to supply electricity needed in the Mg–Cl and H 2 SO 4 thermochemical cycles. Furthermore, the effects of instant solar radiation and concentration ratio on the system performance are investigated. The integration of S–CO 2 Brayton power cycle instead of reheat-regenerative Rankine enhances the system performance. The maximum exergy efficiency which is obtained in the system with Mg–Cl thermochemical and recompression S–CO 2 Brayton power cycles is 27%. Although the energy and exergy efficiencies decrease with the increase of the solar radiation, they increase with the increase of the concentration ratio. The highest exergy destruction occurred in the solar energy unit. • Energy and exergy efficiencies of solar based hydrogen production system are investigated. • Low temperature Mg–Cl, H 2 SO 4 and UT-3 cycles are compared. • Reheat-regenerative Rankine or supercritical-CO 2 Brayton power cycle is integrated. • The system with Mg–Cl and s-CO 2 Brayton power cycles has maximum exergy efficiency. • The exergy efficiency increases with the increase of the concentration ratio.