Exergetic analysis of hybrid power plants with biomass and photovoltaics coupled with a solid-oxide electrolysis system

• Hybrid power plants with biomass, photovoltaic panels and electrolysis systems.
• Examination of different structures of the electrolysis unit.
• Maximum efficiency when a recycling sweep gas stream is used in the biomass plant.
• Variation of irradiation levels to test their influence on the efficiency of the plants.
• Better hybrid performance than the reference when the irradiation drops to 36–46%.

This paper studies four hybrid systems that couple a reference –biomass and photovoltaic– power plant with four different structures of a steam electrolysis system for hydrogen production. The four hybrid plants are initially examined incorporating the same capacity components as the reference plant. The integration of different structures of the electrolysis process results in operational penalties when compared to the reference plant, due to added irreversibilities intrinsic to the electrolysis process and the reduction of the biomass plant efficiency from the extraction of low-pressure steam used to evaporate the electrolyzer feed water. The magnitude of these penalties depends on the power consumption of the electrolysis system, thermal demand and/or pressure losses within incorporated plant components. Among the alternative scenarios, the maximum efficiency is achieved when the electrolysis system works with a recycling sweep gas stream further used in the boiler of the biomass power plant. Furthermore, the efficiencies of the electrolysis hybrid plants only surpass that of the reference power plant when the solar irradiation drops to 36–46%. This is a direct result of the lower operational efficiency of the solar panels versus the biomass plant.