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Development and Validation of an Innovative Solar Compact Selective-Water-Sorbent-Based Heating System

Periodic Reporting for period 1 - SWS-HEATING (Development and Validation of an Innovative Solar Compact Selective-Water-Sorbent-Based Heating System)

Reporting period: 2018-06-01 to 2019-11-30

Project Overview

the SWS project aims at further developing a novel storage technology of thermal energy in order to utilize solar energy in buildings in the most efficient way throughout the year maximising the fraction of thermal energy demand of a building that is covered by solar energy (i.e. the solar fraction).

The project concept is to develop an innovative Seasonal Thermal Energy Storage (STES) unit with a novel sorbent storage material embedded in a compact multimodular sorption STES unit. This will allow to store and shift the harvested solar energy available abundantly during the summer to the less sunny and colder winter period thus covering a large fraction of heating and domestic hot water demand in buildings.
The solar compact Selective-Water-Sorbent (SWS) Seasonal Thermal Energy Storage (STES) concept relies on applying an innovative class of water sorbing material embedded in an intelligent configuration with an advanced control system.

Solar heat will be used to provide domestic hot water (DHW) up to 60 °C, while the remainder will be used mainly to charge the seasonal storage unit during summer, allowing to store the heat for several months, bridging the summer-winter period. During winter, the stored heat will preferentially be used for space heating, and a backup heater will operate only when all stored heat has been fully discharged to cover the heat demand.
Including also heat storage for DHW, recovering heat produced during the charging cycle and making use of even the lowest grade heat amounts (within 5 – 30 °C), the system will allow to reach solar fraction currently not achievable at reasonable price and small space demands (e.g. with solar collectors and water-based Thermal Energy Storage). The detailed concept is presented in Figure 1, based on its two main operating modes (summer/winter).


The core objective of the SWS-HEATING project is to develop a new sorbent material of the SWS family with optimised sorption properties, matching the working conditions of a heat storage cycle with low temperature solar heat charging (70 – 95 oC) to allow efficient application also in northern European countries.
"During the first 18 months of the project various Tasks have been running in parallel. The different building typologies for theclimatic zones considered (i.e. Stockholm, Regensburg and Madrid) have been studied while an analysis of the generic solar assisted heating system boundary conditions and requirements for each climatic zone has been conducted. According to this analysis, a seasonal thermal energy storage system (STES) is not required in Madrid to reach a SF of 60% and therefore this climatic zone is not further considered in this project. Two optimised configurations for central and northern Europe systems have been concluded (confidential). As for the building typologies, a single typology of an nZEB family house has been selected and the respective Key Performance Indicators (Milestone #1) for the SWS-HEATING system have been selected and defined.

As regards the SWS material which is the heart of the adsorption STES system, an initial analysis on the definition of the working boundary conditions was conducted and accordingly some first candidate host porous matrixes were selected, combined with different candidate active salts at various concentrations (confidential). The most promising combinations where synthesized in the lab and after their characterization the most suitablu SWS-material composition was identified (Milestone #2) . Further tests will be performed to identify the final expected TES density under the identified operating conditions.

Another core task of the project is the development of new and optimised components for the SWS system. To this aim, a multi-modular SWS-STES configuration has been first developed. High performing heat exchangers (HEXs) acting as adsorber/desorber and evaporator/condenser are key-components. Thorough experimental and numerical investigations have been carried out onvarious typed of heat exchangers leading to the final design of the SWS-HEATING’s HEXs, which shall be testedvwithin the demo prototype. Furthermore, advanced components like an innovative vacuum tube for the advanced solar collector, a vacuum insulated combi-storage tank, a PCM buffer tank has been designed and fabricated. A setup for experimental investigation of the advanced components together with the peak load boiler within the hydraulics developed for the generic heating system is being constructed at NTUA.

A key aspect of the SWS system is the development of a smart control environment for its optimal its operation and the maximisation of its energetic benefits. A development of a simulation platform of the system is first required to this aim. First a an NZEB family house building model has been developed, integrating the dedicated occupant-building interaction models developed, in order to fully define the demand profiles in the considered climatic zones. The various components have been modelled at least at a basic level. Different basic strategy scenarios have been defined and will be numerically assessed based on the system simulation models and weather forecast in order to conclude the optimal control strategy."
The SWS HEATING ambitions at different levels are summarised next while the envisage progrees from the conception of the idea to the commercialisation of technology is schematically presented in Figure 2.

• Reach compact solutions that can be integrated in new or existing buildings.
• Potential to reduce system cost by up to 20-30% compared to other solar seasonal storage units.
• Optimised system design and sizing for achieving very high solar fraction - i.e. the amount of energy provided by the solar technology divided by the total energy required for domestic heating and hot water throughout the year - of over 60% in south, central and north Europe.
• Validation of SWS-heating system in an intended environment (TRL5) and preparation of its further development stages.

At material level
• Develop a family of advanced SWS-materials with tailored sorption capacity adapted to typical working conditions of the sorption module.
• Achieve very high heat storage density, in the range of 1.1-1.3 GJ/m3 (over 30% higher than the best SWS sorbent material and 40-60% than state of the art for the same temperature range) that would allow reaching compact seasonal storage solutions.
• Validate the stability of the new sorbent material against hydrothermal cycling under severe working conditions, up to 1,000 cycles that correspond to more than 50 years of operation, with at least 10 charging/discharging cycles per year.
• Evaluate enhanced STES capacity of the developed SWS, and prove the low production cost potential to less than 5 €/kg at commercial level, according to estimated cost of raw materials (currently it is about 10 €/kg for the delivery of few quantities).


The targeted benefit of this next generation solar heating technology is to reach and overcome a seasonal solar fraction of domestic energy systems of 60% in central/north Europe, reaching 80% in the sunnier south of Europe, with a compact and high-performing STES system at low cost. The overall aim is to validate this new technology in an intended environment (TRL5) and to proof all challenging objectives.
SWS-heating concept and main operating modes (summer winter)
SWS HEATING: From idea conception to commercialisation