Decarbonising heating and hot water using solar thermal collectors coupled with thermal storage: The scale of the challenge

This paper explores the feasibility of using renewable solar thermal energy linked to a salt hydrate thermochemical store (reversible chemical reaction involving the addition / removal of water from a salt) to provide a zero-carbon heating and hot water option for an average UK home. Volumetric absorption based on diluted colloidal suspensions or nanofluids containing wavelength tuneable plasmonic silver nanoparticles are a possible means for enhancing solar thermal capture. To make full use of this captured energy, it requires inter-seasonal storage in a suitable energy dense, high efficiency thermal store. As such even the potentially highest energy density obtainable for a salt hydrate thermochemical store would still need a store of greater than 35 m3 (10 MWh) to nearly meet current winter heating and hot water demands (with 1 discharge cycle per annum). With a possible increase in collector efficiency to over 70% such a system would collect enough solar energy annually to become viable for homes with a greater than average (>15 m2) roof area, a lower than median consumption (<12,000 kWhyr−1) and enough space for a large thermochemical store (≤46 m3). This paper concludes by detailing the significant additional research efforts required to bring this possible decarbonising solution to a prototype level of maturity.