New thermal storage systems are needed
An important contribution to the achievement of climate protection targets is an improved utilization ratio for both fossil and regenerative primary energy sources. This is done by secondary usage of energy which was not used during its first application. A case in point is the utilization of waste heat created by combustion engines during the generation of power from biogas. The waste heat produced typically makes up over 50 percent of the energy content of the biogas.This not only shows the great potential which lies in the increase of the degree of efficiency, but also the need for temporal and spatial decoupling of secondary energy utilization.In addition, there are many more processes in commerce, energy supply and manufacturing industry which generate large amounts of waste heat. Against the backdrop that 50-60 percent of the EU energy requirements are needed for heat [EUREC, European Renewable Energy Research Centres Agency, 2009] production it becomes apparent that there is great potential for optimizing energy use.
To optimize energy efficiency of processes, there is a need for compact and flexible storage systems to decouple or compensate the supply and demand for heat in terms of location through mobility and with regard to time through minimization of heat loss. Currently available industrially manufactured thermal storage systems regularly only store sensible heat. They usually use water as a storage medium thus restraining the storage density and limiting the storage temperature level to 100 °C at the most. Latent-heat storage units which may achieve slightly better storage density values regularly lack the required flexibility due to their defined operating temperature. The disadvantage of both systems is their permanent heat loss based on the fact that the driving gradient in both systems is the temperature difference between the medium and its environment. Insulation can reduce this effect, but only to a limited extent.