The work of Subtask B has shown that there are promising chemical and sorption storage solutions that should be further developed and tested at least in field trials. One concept has gone from prototype to commercialisation in the time period of Task 32, where short term storage for both heat and cold is utilised. The work has also shown that current materials are a limitation for the processes that have been studied, both for short and long term storage. Simulation models have been developed and used for system simulations. These show that high fractional energy savings are possible using seasonal storage for single family houses. Economics have not been considered.

The following areas are suggested for future work in the field:

• Research in materials for seasonal storage. This is required for closed three-phase absorption, open and closed adsorption as well as chemical reactions. The current materials are either too expensive, do not have the correct properties, or have not yet been shown to work in prototypes with realistic boundary conditions. Fundamental materials research is needed to get a better understanding of the physicochemical mechanisms.

• The numerical modelling of the heat and mass transfer processes in thermochemical materials is still very basic. Model improvement will result in new tools to better understand the dynamic behaviour of the materials processes and assist the material development in this field.

• For short term storage, research is required to find suitable materials and operational conditions that give a suitable temperature lift for cooling and heating together with sufficiently high energy density for storage. The cost of the material is not as important as for seasonal storage, but it is still an important factor.

• Studies on sources of low grade heat for heat pumping using closed processes. The sorption (and chemical reaction) processes studied in this Subtask, all use water. This needs to be evaporated before it is recombined with the active substance. This energy has to be either extremely low cost or free, and additionally has come from a heat source of at least ~5°C.

• The Monosorp concept is very promising and is suited for a full scale field test. However, at present their is no commercial method for extruding the zeolite monoliths required in the store.

• Seasonal stores are not charged once and then discharged. During autumn and spring there are periods with both charging and discharging. The store operates at different temperatures for these two states. More study is required to understand how best to recover the sensible heat during these changes in store temperature and whether it is best to segment the store so that only smaller portions undergo these changes.

References

[1] Hadorn, J.-C., ed. Thermal Energy Storage for Solar and Low Energy Buildings.- State of the Art. 2005, Lleida University: Lleida, Spain. ISBN: 84-8409-877-X.

[2] Visscher, K., Veldhuis, J. B.J., Oonk, H. A.J., Van Ekeren, P. J. and Blok, J. G. Compacte chemische seizoensopslag van zonnewarmte, 2004, ECN report C04074.

[3] Bales, C., et al. IEA-SHC Task 32 report: Project Report B2 of Subtask B: Thermal Properties of Materials for Thermo-chemical Storage of Solar Heat, IEA-SHC, Paris, France.www. iea-shc. org. 2005.

[4] Bales, C., et al. IEA-SHC Task 32 report: Project Report B4 of Subtask B: Laboratory Tests of Chemical Reactions and Prototypes Sorption Storage Units, IEA-SHC, Paris, France.www. iea-shc. org. 2008

[5] Herbert Zondag, Martijn van Essen, Zeming He, Roelof Schuitema, Wim van Helden, Characterization of MgSO4 for thermochemical storage in Second International Renewable Energy Storage Conference (IRES II), 2007, Bonn, Germany.

[6] Zondag, H. IEA-SHC Task 32 report: Project Report B6.1 of Subtask B: Simulation report — System:

ECN TCM model, IEA-SHC, Paris, France.www. iea-shc. org. 2008

[7] Bales, C. and S. Nordlander, TCA EVALUATION — Lab Measurements, Modelling and System Simulations. 2005, SERC, Hogskolan Dalarna: Borlange, Sweden. ISRN DU-SERC—91—SE. www. serc. se.

[8] Bales, C. Solar Cooling and Storage with the Thermo-Chemical Accumulator. in Eurosun 2006. 2006. Glasgow, UK.

[9] Bales, C., et al. IEA-SHC Task 32 report: Project Report B5 of Subtask B: Store Models for Chemical and Sorption Storage Units, IEA-SHC, Paris, France.www. iea-shc. org. 2008

[10] Bales, C., et al. IEA-SHC Task 32 report: Project Report B7 of Subtask B: Final report of Subtask B “Chemical and Sorption Storage” — The overview, IEA-SHC, Paris, France.www. iea-shc. org. 2008

[11] Heimrath, R. and M. Haller IEA-SHC Task 32 report: Project Report A2 of Subtask A: The Reference Heating System, the Template Solar System of Task 32, IEA-SHC, Paris, France.www. iea-shc. org. 2007

[12] Letz, T., et al. IEA-SHC Task 32 report: Project Report A3 of Subtask A: Performances of solar combisystems with advanced storage concepts, IEA-SHC, Paris, France.www. iea-shc. org. 2007

[13] Letz, T., et al. IEA-SHC Task 32 report: Project Report A1 of Subtask A: The extended FSC procedure for large storage capacity, IEA-SHC, Paris, France.www. iea-shc. org. 2007.