Development Line A – Solid Sorption
In the case of solid sorption heat storage, solar heat is used to drive the moist out of the active storage material, a zeolite for instance. Solid sorptive materials have the ability to store thermal energy in a nearly loss free way over longer periods of time. When heat is needed, water vapour is led through the material. The water vapour is adsorbed and the released heat of adsorption can be gained for space heating purpose or domestic hot water preparation.
For the generation of water vapour, low temperature heat sources can be used. The theoretical potential of solid sorption storage in terms of energy density is over 170 kWh/m3, but this strongly depends on the type of material used.
The regeneration process of the storage material, called desorption, works the other way around: Heat is supplied at high temperature levels in order to desorb water vapour from the sorption material, i.e. the material is dried. This can be realized with heat coming from solar thermal collectors during the summer period. If the dried material is hermetically sealed from any moisture, charged status can be maintained indefinitely
The starting point of this development line is the experience of the consortium partners in investigation, design and evaluation of solid sorption storage concepts in past projects.
Development Line B – Liquid Sorption
In the charging phase of the second development line, liquid sorption storage, a diluted mixture of sodium hydroxide (or sodium lye) and water is concentrated by evaporating the water. The concentrated lye is stored without heat losses until heat is needed. To produce heat, water vapour is led over a series of two reactors, diluting the concentration and generating heat. The first reactor gives
low temperature heat for space heating, the second high temperature heat for hot tap water. The storage potential of the material is between 170 and 400 kWh/m3, depending on the charging and discharging parameters. The starting point of the development is the experience of design, monitoring and optimisation of a one-stage reactor in consecutive Swiss national R&D projects.
Development Line C – Supercooling Phase Change Material
With the third development line, supercooling phase change material (PCM), solar heat is used to melt the phase change material completely. As phase change material sodium acetate trihydrate is used. During storage, gradual heat loss will cool down the material to temperatures below its melting temperature, but the material will not solidify, due to the super cooling effect. To deliver the heat in cold season, the heat of solidification becomes available
by triggering the solidification process. The heat becomes available at 58 °C and is used for hot tap water or space heating. The potential of the material is over 100 kWh/m3.
In an earlier project, the feasibility of the concept was studied and proven and a prototype heat storage module was built to study the control of the solidification, and the heat exchange to and from the PCM.