Life cycle assessment of innovative materials for thermal energy storage in buildings

The politically endorsed reduction of greenhouse gas emissions entails the transformation of thermal energy systems towards renewable energies, especially in the building sector. This comes along with a demand in energy storage, as there is a time offset between energy availability and demand. As sensible heat storages induce major losses and have limited energy density, current water-based solutions are only partially sufficient to meet these demands. Within the project ""Speicher-LCA"" the environmental performance of a variety of innovative materials available for energy storage in buildings is assessed. The project provides the first extensive comparison of environmental profiles of various thermal energy storage materials, including phase change, thermochemical and sorption materials. The specific performances in the storage cycle are taken into account. All results will be publically accessible through a spreadsheet tool including a comprehensive set of materials, components as well as their integration into different building types. This paper discusses the methodological framework of the study and presents the environmental assessment results for selected materials. It highlights the main challenges in the assessment of innovative storage materials on different system levels which require specific definition of functional units accordingly. The first assessment results on material level for selected phase change (PCM) and thermo-chemical materials (TCM) allow an environmental characterization regarding their potential application in thermal storages. In addition, ranges of required numbers of storage cycles for amortization have been calculated for the non-renewable primary energy demand. For PCMs amortization cycles range between ∼20 to 150 cycles for salt hydrates and up to ∼280 cycles for paraffins. Regarding TCM, energetic amortization of silica gel and zeolite 13x is reached after ∼60 and ∼260 cycles respectively. Since the realization of storage components and systems which can actually be used in real applications will further increase the cycle number required for amortization, these storage materials may thus not be suitable for applications with a low number of cycles over lifetime, such as seasonal storage.