Evaluation of tests of adsorption cycles showed an energy output of exactly 115 kWh/(m3 silica gel) in the adsorber 1 and 123 kWh/(m3 silica gel) in the adsorber 2 with a flow temperature out of the adsorber of 32°C minimum. The power values and energies during an adsorption cycle are presented as an example in figure 4. The high power peaks in the evaporator heat exchanger result from the high flow temperature in the collector loop. The average power of the adsorber heat exchanger during the test, which could be supplied to a load in a real application, equaled 2.87 kW with a maximum value of 3.9 kW. In this test, the energy input (evaporator) was

24.3 kWh and the energy output (adsorber 2) 27.4 kWh.

Simulations have shown that a storage tank density with a maximum of about 150 kWh/(m3 silica gel) can be expected with the type of silica gel used. With a density of 790 kg/m3 and a silica gel mass of 808 kg (dry substance) in adsorber 2, a storage tank density of 123 kWh/m3 was achieved experimentally. The theoretically calculated value of around 150 kWh/(m3 silica gel) could be reached with an optimized operating strategy.

Nevertheless, it must be realized that energy densities achieved with commercial silica gels under technical conditions are rather insufficient. The energy density that has been reached experimentally, is only in the range of latent heat storage with about 1.8 to 2.2 times the value of water. This means that the storage volume is cut

in half compared to a system with water. Modified sorption materials were tested by the Fraunhofer Institute for Solar Energy Systems, which achieve an energy density which is 5 times higher than water under technical conditions. But up to now, these materials showed insufficient stability under operating conditions. The development of stable modified sorption materials will be an important task and a great challenge.