In order to be able to use the surplus of solar energy during the summer and to deal with periods with low solar irradiation, thermal energy has to be stored. Depending on the length of the time period the energy is stored, a distinction is drawn between short-term, long-term, and seasonal storage. The store has to meet additional conditions to guarantee an optimal operation of the solar system, e.g. the formation of thermal stratification during charge while sustaining the same during discharge in case of a water tank.
In an effort to increase the share that solar thermal systems can contribute to domestic hot water production and space heating, arsenal research concentrates on improving existing systems and development of new storage technologies.
The initial test of novel storage concepts is done via computer simulations. A suitable numerical model is developed and connected with existing models to form a complete solar system. The annual performance of this system is simulated for various climatic conditions. The results obtained in this way are used to evaluate the new concept.
The application of materials that undergo a phase transition in an appropriate temperature interval (PCMs – phase change materials) is a promising approach to improve solar storage tanks. The latent heat that is consumed or released during the phase change can be used to store energy. However, when dealing with PCMs, long-term stability, subcooling, and superheating effects remain challenging problems. In addition, the optimal integration of PCMs in a solar storage tank is an unsolved issue that is being addressed at the AIT Energy Department
michael.monsberger@ait.ac.at