Storing solar energy across seasons

This review presents the principal methods available for seasonal storage of solar thermal energy. It concentrates on residential scale systems, and particularly those currently used in practice which mostly store energy in the form of sensible heat.

For a high latitude country like Sweden, where seasonal variations result in small solar heat production during winter, the pertinence of seasonal storage is clear.

Finally, seasonal thermal energy storage (TES) can make the availability of heat match the demand. Seasonal storage systems are much larger than short-term ones. Braun evaluated that storage capacities per unit of collector area must be two to three orders of magnitude (100–1000 times) larger for seasonal storage than for overnight storage.

According to Braun et al., significant reductions in solar collector requirements for heating could be achieved by using seasonal storage at northern latitudes, where seasonal variations are large, and in cold climates, where DHW loads are much smaller than space heating loads.

The needed solar collector areas of the seasonal thermochemical energy storage system decrease by up to 2/3 compared with those of a water storage tank system in the condition of the similar storage system volume. The advantage of seasonal thermochemical energy storage is more obvious for the case of region with abundant solar energy supply.

The storage system consisted of a 68 m 3 (about 2 m 3 /m 2 of collector area) cylindrical steel tank, insulated and buried under the house. Storage temperatures reached 90 °C in August, making it impossible to store collected solar energy during the autumn and early winter since the collectors could not produce higher temperatures.