Thermochemical Energy Storage for the Seasonal Balance of Surplus Electricity and Heat Demand in Domestic Buildings

Abstract

In Germany 65 % of the final energy demand in domestic buildings is required for space heating. Even though the electricity production from renewable sources increased considerably over the last decade, the heat energy in buildings is still mainly provided by the combustion of fossil fuels. Accordingly this sector accounts for 30 % of the overall yearly CO2 emissions in Germany. One reason for this is that the heat demand mainly occurs during the winter period whereas high shares of renewable energy production prevalently occur during the summer time. To overcome this seasonal discrepancy DLR is developing a long term storage technology based on the reversible chemical reaction of calcium hydroxide to calcium oxide and water vapour. Thermochemical systems are predestined for long term storage since the principal is free of losses and high energy densities can be reached. Beyond that, calcium hydroxide in particular is a very cheap, abundantly available and environmentally friendly material. Basic idea of this innovative concept is to use excess electricity in the summer, for example from private PV-panels, in order to drive the endothermic reaction to calcium oxide. The charged material can then be stored in inexpensive containers for an unlimited period of time. As soon as heat is required in the building parts of the material react with liquid water under exothermal heat release back to the starting substance. This presentation will introduce this novel power to heat storage concept and present the latest experimental results from our lab scale prototype of this technology.