Long Term Storage of Solar Energy in Silicagel-Water Systems for Space Heating

Summary

The thermochemical reaction of silicagel-water is suitable for long term storage of solar energy. There is no thermal degradation and charging temperatures of 75 °C are sufficient. The useful heat from the storage depends strongly on some factors, like temperature and humidity of the inlet air, line temperature of the heating system at discharge. In a computer model we investigated the annual performance of a solar system with water and silicagel storage for autonomous solar space heating. 40 m² high performance collectors, two water tanks with 2 and 10 m³ and 26 t silicagel can match the annual demand of 10.3 MWh of a single-family house. The thermochemical storage supplies 4.6 MWh of the-total amount. The energy density is 175 kWh/ton silicagel or 50% of the heat input into the material. At the discharge process the water storage supplies 1.25 MWh at a temperature level of about 15 °C. Installation of a back-up system can provide heat if there is no additional energy from the water storage. This avoids unfavourable operating conditions and increases the energy density of silicagel. As an example 18 t silicagel supply 3.5 MWh heat energy combined with 1.1 MWh back-up energy.