Seasonal Thermochemical Energy Storage with Affordable and High-Energy-Density Deep Eutectic Solvents

Abstract

Seasonal thermal energy storage technologies offer significant potential for addressing the temporal and intensity mismatch between energy demands and supplies across seasons. Absorption thermal energy storage, noted for its high energy storage density (ESD) and minimal energy loss, is well-suited for long-term energy storage but faces challenges including crystallization, high levelized cost, and declining discharging rates. To address these limitations, this study first proposes a multi-cell absorption thermal energy storage (MATES) using novel deep eutectic solvents (DESs) to achieve crystallization-free, cost-effective, and stable energy storage. For cross-seasonal scenarios, the device employs a multi-cell configuration with a once-through discharging strategy to ensure stable output; the proposed DES-based working fluids with low crystallization points and low costs further enhance the ESD and economic viability. A time-dependent mathematical model of the MATES has been developed and verified with high accuracies, by which the annual cooling performance is investigated considering real weather. The low ambient temperatures during winter allow the MATES to effectively harness low-grade solar energy below 50 °C. Among the identified DESs, Beta-EG demonstrates a substantial concentration glide and the highest ESD of 549.6 kJ/kg. As the solution charge rises or solar collector installation decreases, the ESD keeps decreasing while the unit cooling potential exhibits an opposite trend. A multi-objective optimization identifies the optimal design achieving a unit cooling potential of 1.71 kWh/m²/day and an ESD of 456.2 kJ/kg. In comparison to sensible and latent thermal energy storage, MATESs with DESs provide superior ESDs and competitive levelized cost of storage (0.032–0.040 USD/kWh), highlighting its potential for high-density and cost-effective seasonal energy storage.