Revisiting salt hydrate selection for domestic heat storage applications

In this work, we evaluate 454 salt hydrates and 1073 unique hydration reactions in search of suitable materials for domestic heat storage. The salts and reactions are evaluated based on their scarcity, toxicity, (chemical) stability and energy density (>1 GJ/m³) and alignment with 3 use case scenarios. These scenarios are based on space heating (T > 30 °C) and hot water (T > 55 °C) to be provided by discharge as well as on heat sources available in the built environment (T < 160 °C) for charging. From all evaluated materials, only 8 salts and 9 reactions (K₂CO₃ 0–1.5, LiCl 0–1, NaI 0–2, NaCH₃COO 0–3, (NH₄)₂Zn(SO₄)₂ 0–6, SrBr₂ 1–6, CaC₂O₄ 0–1, SrCl₂ 0–1 and 0–2) fulfil all of the criteria. Provided a suitable stabilisation method is found additional 4 salts and 13 reactions (CaBr₂ 6-0, CaCl₂ 6-0, 6-1, 6-2, 4-0, 4-1, 4-2, LiBr 2-0, 2-1, 2-0, LiCl 2-0, 2-1, ZnBr₂ 2-0) From this selection, only 2 salts/reactions (NaI and (NH₄)₂Zn(SO₄)₂) have not been extensively studied in the literature. Moreover, many well-investigated salt hydrates, such as MgSO₄ and LiOH, did not pass our screening. This work underlines the scarcity of materials suitable for domestic applications and the need to broaden the scope of future evaluations.