Exergy and exergo-economic analyses of hybrid solar-biomass organic Rankine cycle cogeneration plant

This study is aimed at investigating optimization potentials in a conceptual hybrid solar-biomass organic Rankine cycle (ORC) cogeneration plant, through component-based exergy and exergo-economic analyses. The ORC is rated at 629 kWe, and it is related to a real existing ORC unit. Exergy balance of each system component is established, from where irreversibility rate in the respective components is obtained. Thus, exergy-based rational efficiency and efficiency defects are computed for each system component. Also, economic performance is assessed at component level, for the entire system, using specific exergy costing (SPECO) approach. Cost of destroyed exergy, exergoeconomic factor and relative cost difference are used as criteria for exergo-economic performance evaluation. Furthermore, the level of recoverability of exergy destruction in each of the system components is assessed, so as to determine the components with highest potentials for optimization. The judgement on optimization potentials considers intrinsic irreversibilities in the respective components, which are imposed by the assumptions of systemic and economic constraints, and thus cannot be eliminated. The analyses are carried out essentially at steady state, and system exergetic efficiency and exergoeconomic factor of 7.6% and 48.1% are obtained, respectively. Also, a cost of producing electricity of 9.92 c€/kWh was obtained. Moreover, parametric studies are introduced, to examine the effects of varying ambient conditions and part load ORC thermal demand on system performance.