Conceptualization and analysis of a novel combined sorption and phase-change material thermal storage system

•A new sorption-based, long-term thermal storage cycle proposed.•Enthalpy of dilution, instead of enthalpy of absorption, used to deliver heat.•Evaporator and absorber replaced with a sensible heat exchanger and a liquid-liquid mixer.•Second law criterion established to evaluate working fluids.•Cycle integrated with PCM to achieve higher efficiencies for seasonal storage. A new sorption-based thermal storage cycle is proposed. Energy is stored chemically by separating the constituents of highly non-ideal solutions, yielding much lower stand-by losses than in conventional approaches. The cycle avoids limitations of previously proposed sorption-based storage cycles by using a liquid-liquid mixer, and does not require a thermal source during discharge. A criterion based on a second law analysis is developed to evaluate potential working fluids for the cycle. Different cycle configurations are analyzed. An enhanced combined sorption and phase-change material (PCM) cycle is also investigated and compared with conventional thermal storage systems. For delivering 100 GJ of energy after 8 months, the combined cycle has an efficiency of 11% and lower storage volumes (down to 0.1 ×) than conventional thermal storage technologies. The energy density of the combined sorption-PCM system is 30 kWh m − 3.