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ECN publication
Development of a prototype system for seasonal solar heat storage using an open sorption process
Published by: Publication date:
ECN Biomass & Energy Efficiency 31-5-2014
ECN report number: Document type:
ECN-M--14-009 Conference Paper
Number of pages: Full text:
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The increasing share of renewable energy in the energy supply system requires a more balanced equilibrium between energy supply and demand. Research and development activities in the area of smart electricity grids is already a very visible result of that. The balancing of heat supply and demand is of equal importance when the use of solar heat needs to be increased. The Energy Hub (E-Hub) is a collaborative European project, funded by the EU under the 7th Framework Program. The project aims to demonstrate the full potential of renewable energy by providing 100% on-site renewable energy within an "Energy Hub District". The present work addresses the development of an innovative concept for thermal energy storage as a part of the E-hub system. Because thermal energy cannot be transported over long distances without significant losses, local storage of thermal energy must provide the required flexibility to match the heat demand and supply. Solar heat supply also fluctuates strongly between summer and winter, so to use this source of energy to its maximum, the storage should be capable of long term seasonal storage. Heat storage technology based on reversible sorption reactions offers the opportunity to store heat in a compact way and with limited heat losses over a long period. A laboratory prototype of a heat storage system is developed and its performance is tested. The concept of the heat storage system is based on an atmospheric open sorption system that contains 150 kg of zeolite sorbent, divided in two batches. Ambient air, containing a controlled amount of water vapour is blown through the bed of sorbent material. The air is used both as the heat transfer medium and to transport the water vapour to react with the solid sorbent. The test results show that this concept can provide a solution for long term thermal energy storage. It is capable of delivery of thermal energy at temperature levels useful for domestic applications. The aspects of this system concept that need further improvement in order to become a viable technology for seasonal heat storage are: the system thermal storage cycle efficiency, the air tightness of the open sorption concept, the stability of salt hydrates for increased energy storage density and the reduction of auxiliary electric consumption.

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