C. Bales1*, P. Gantenbein2, D. Jaehnig3, H. Kerskes4, M. van Essen5, R. Weber6, H. Zondag5

1Solar Energy Research Center SERC, Hogskolan Dalama, 78188 Borlange, Sweden
2SPF Hochschule fur Technik Rapperswil, Oberseestr. 10, CH-8640 Rapperswil, Switzerland
3AEE INTEC, Feldgasse 19, A-8200 Gleisdorf, Austria
4ITW, Pfaffenwaldring 6, D-70550 Stuttgart, Germany
5Energy research Centre of the Netherlands (ECN), P. O. box 1, NL — 1755 ZG Petten, The Netherlands

6EMPA Duebendorf, Abteilung Energiesysteme / Haustechnik, Ueberlandstrasse 129, CH-8600 Duebendorf,

Switzerland

* Corresponding Author, eba@du. se

Abstract

Six main groups have studied chemical and sorption storage within IEA-SHC Task 32 “advanced storage concepts for solar and low energy buildings”. Closed and open adsorption systems, two and three phase absorption as well as chemical storage have been studied. The main results of the work are: identification of potentially suitable materials for long term storage of solar heat and publication of material properties; development of new concepts of short and long term storage of solar heat to prototype stage with lab and field tests; development of models for simulation of chemical and sorption storage; simulation of three systems with long term chemical or sorption storage with the Task 32 boundary conditions; and support in the commercialisation of a chemical heat pump with short term thermal storage for solar heating and cooling applications. The main conclusion from the work is that there are a number of promising technologies and materials for seasonal storage of solar heat for single families but that a lot of research is required before it can be become practical and economical.

Keywords: Solar heating, thermal energy storage, sorption, chemical heat storage

1. Introduction

Task 32 of the International Energy Agency’s Solar Heating and Cooling Programme has studied advanced storage concepts for solar and low energy buildings over the period 2004-2007. The Task was split into four subtasks covering the following areas: evaluation and dissemination (A), chemical and sorption storage (B), Phase Change Materials (C) and advanced water storage (D). This paper describes the work performed in Subtask B on chemical and sorption storage, including results from basic research in terms of material and heat transfer characteristics, as well as store and system modelling.

Six groups have been active in this Subtask, as shown in Table 1 below, which also shows the type of technology that the groups have studied. EDF from France have also participated with work on chemical storage towards the end of the Task. The scope, in terms of general system aspects, for Subtask B was the same as that for the whole of Task 32, namely solar heating and cooling systems for residential buildings, principally detached houses for one up to a few families. Buildings with a larger specific heat load (>100 kWh/m2 for Zurich climate) were not considered. The main focus was to be storage solutions sized to achieve a significant solar fraction. In terms of temperature, the

storage solutions have been limited to temperatures < 250°C, with the emphasis on materials suitable up to around 150°C.

The scope in terms of storage concepts included chemical reactions and thermo-chemical storage, which was in practice restricted to sorption processes, both adsorption and absorption. Only one storage solution dealt with in Subtask B has become commercial within the time frame of Task 32, that developed by the Swedish company ClimateWell from Sweden, with over 35 stores/heat pumps having been sold, mostly for solar heating and cooling systems in Spain. A demonstration system of a closed adsorption store was made in the Modestore project, but the materials available for the field test were shown to be not suited for seasonal storage. Three other projects have got as far as design and testing of lab prototypes of sorption stores, and the sixth project was at the stage of material characterisation.

10 reports from the work on chemical and sorption storage are available from Task 32 website at www. iea-shc. org/task32, along with a number of reports on the work on phase change materials, advanced water stores and methods and intercomparisons.