MODESTORE - Modular High Energy Density Sorption Heat Storage
For an efficient use of solar heat for domestic hot water and space heating, it is necessary to store the solar energy available in summer for the winter months. An energy store that can store heat for several months, has a high energy density and small thermal losses would be a big step towards solar thermal systems without the need for an auxiliary heat source such as natural gas or wood pellets. Such a store would improve the contribution of solar thermal systems to the overall energy supply significantly.
One option for such an energy store is a store based on sorption technology where water that is adsorbed on a highly porous material (in this case silica gel), is desorbed using solar energy. The two components can then be stored separately and the energy is stored without thermal losses. To discharge the store, water is evaporated at a low temperature level and adsorbs on the silica gel. During the adsorption process, heat is released. In a narrower sense, this kind of system is not a store but a thermally-driven heat pump.
Based on previous projects where a sorption heat store with the material pair silica gel and water was developed, the system was scaled up for use in a single-family house and a first pilot plant was built.
In this project, it could be shown for the first time that sorption technology for heat storage is technically feasible in a live test. The system concept as well as the control strategy have been proven to be functional under real operating conditions.
The operation of the system was satisfactory and the system concept could be implemented in further systems. It has been shown that sorption storage with the used material combination is technically feasible. However, the temperature lift that can be achieved is only technically useful in a relatively small range of water contents. As long as the silica gel is very dry, the temperature lift is sufficient. But starting at a water content of approximately 13%, the temperature lift is not large enough to compensate for higher losses in heat exchangers, pipes and tanks. That means that the energy density of the material that can be used in a real application is much smaller than both the theoretical one and what has been measured under laboratory conditions. Therefore, a large quantity of materials would be necessary which makes sense neither technically nor economically.
The used material has been chosen because it is manufactured in mass production and therefore inexpensive. Up to now, there are very few research institutes that develop sorption material specifically for heat storage. In most cases, the focus is on heat pumps, cooling machines or gas separation and drying processes. Singular projects have shown that the development of sorption materials for heat storage is technically feasible. So far, these materials have been expensive or for example corrosive.
The next step towards monosolar (100% solar) heat supply for space heating would be an intensified research program on sorption materials for this purpose. Existing zeolites that are used on a grand scale for example in the cleaning agent industry, have the disadvantage that high temperatures are necessary for desorption. One possible development topic could be to modify these zeolites in such a way that the desorption temperatures decrease but the temperature lift still stays at a higher level than it is the case with simple silica gels.
Ing. Waldemar Wagner, AEE INTEC Arbeitsgemeinschaft Erneuerbare Energie
Solution Solartechnik GmbH
Ing. Gerald Jungreithmayr
Hauptstraße 27, A-4642 Sattledt
Behältertechnik PINK Ges.m.b.H.
Ing. Werner Pink
Bahnhofstasse 22, A-8665 Langenwang
AEE - Institut für Nachhaltige Technologien
Ing. Waldemar Wagner
A-8200 Gleisdorf, Feldgasse 19
Tel. + 43 (3112) 5886-28
Fax: +43 (3112) 5886-18