A multi-criteria decision analysis for recovery, storage and transport of ultra-low-grade heat with liquid desiccant solutions in the United Kingdom

• Assessment of ultra-low-grade heat recovery at 25–40 °C with liquid desiccants. • Evaluation of 466,560 designs integrating performance and economics. • Calcium chloride could store up to 994 MWh of energy per year cost-effectively. • Transported desiccant enables humidity control at distance. • Energy cost, transport distance, characteristics and frequency dominate economics. Ultra-low-grade heat from industrial processes remains a largely available but underutilised energy resource. If harnessed with suitable recovery and storage technologies, this otherwise wasted heat could make a significant contribution to decarbonisation. This study aims to assess whether using liquid desiccant solutions to recover heat between 25 °C and 40 °C from a manufacturing plant producing radiation detectors, store it in an absorption-based form and deliver it to an end user by truck is techno-economically viable. To test this, a comprehensive modelling framework simulating the performance of aqueous solutions of lithium chloride, calcium chloride and potassium formate under varying operating conditions and system configurations, including systems with one and two regenerators, different flow rates, storage tanks and frequencies of the transport cycles, was developed. The analysis covers 466,560 design scenarios and investigates energy storage capacity, dehumidification potential and cost-effectiveness. Results indicate that 25 % wt. aqueous calcium chloride regenerated in a system with two regenerators using a hot-solution approach offers the best overall trade-off, delivering up to 994 MWh of energy per year when heat is available at 40 °C. Multi-criteria decision analysis confirms that this configuration performs optimally for several end users, including archives and indoor swimming pools. Sensitivity analysis identifies transport cost, energy prices and cycling frequency as key economic drivers, with payback periods being highly dependent on these factors. The results demonstrate the potential of liquid desiccant-based storage for utilising ultra-low-grade thermal energy in decentralised energy networks, especially in applications where temperature and humidity control are critical.