Solid-to-solid phase change transitions to enhance solar heat storage of bitumen used in domestic hot water collectors

The reduction of energy consumption in buildings requires the development of advanced thermal energy storage (TES) materials. In this work, the feasibility of TES materials to be applied in solar domestic hot water (DHW) collectors was evaluated. These TES materials are composed of bitumen (B) and different concentrations of pentaglycerine (PG), which act as supporting engineering material with high solar radiation absorptivity and solid-to-solid phase change material, respectively. Results indicate that these TES materials show good thermal stability, whereas their consistency improves as PG content increases over the whole temperature range at which a solar DHW collector operates. Interestingly, blend containing 30 wt% PG shows a high heat storage capacity (ca. 50 J/g), suitable thermal cycling reliability and excellent relative enthalpy efficiency (ca. 90 %). In addition, this binder also presents improved thermal properties (thermal conductivity and specific heat capacity). As a result, the heat charge/discharge performance evaluated by indoor thermoregulation tests leads to a Latent Heat Thermoregulation Index (LHTI) higher than those reported for other TES building materials. Therefore, B/PG blends may be considered a promising TES material for improving energy efficiency in solar DHW production. • Thermal energy storage materials composed of bitumen and pentaglycerine. • The energy efficiency for the production of solar domestic hot water is improved. • Materials exhibit enhanced consistency in a wide in-service temperature range. • Temperature profiles for the discharge stage reveal a great thermoregulation effect.