Thermochemical Energy Storage Based On Hydrated/Quick Lime For Balancing Surplus Electricity And Heat Demand In Domestic Households

Abstract

Approximately 70% of the final energy demand of domestic households in Germany is used for space heating. To utilize the surplus electricity of private owned PV modules for heating, cost and energy efficient long term storage solutions are required to balance the supply peaks in summer and the demand in winter. Storing energy in chemical potential and separating the reactants allows for loss-free long term storage. Here, the reversible reaction of calcium hydroxide (Ca(OH)2) to calcium oxide (CaO) and water is analyzed, since lime is among the cheapest thermochemical storage materials, environmentally friendly and already available as an industrial mass product. The underlying principle is to charge Ca(OH)2 with surplus electricity when available and discharge CaO with liquid water if necessary. About 60% of the energy used during the charging process (see fig. 1) is stored in the chemical potential of CaO. The remaining 40% of the energy can be used directly for the daily hot water supply by condensation of the water vapor released during the dehydration reaction. A test infrastructure has been set into operation in order to experimentally demonstrate this concept in lab-scale (see fig. 2). The reactants are stored in two ordinary steel containers with a capacity for 100 kWhth (250 kg material). For the charging as well as the discharging process two reactors with a thermal power of 10 kW based on screw conveyers have been developed. To perform the charging reaction the screw is inductively heated and in the discharge reactor thermal oil flows through the screw to absorb the released reaction enthalpy. Due to unfavorable bulk properties, the movement of the material under reaction conditions as well as the heat and mass transport are challenging and currently investigated. In this contribution the concept of a seasonal power-to-heat storage and first experimental results will be presented.