Use Case 2: Key Results

Key conclusions from the implementation of RESTORE  Use-Case 2, Gmunden, Austria, are summarized and categorized as follows:

Specific conclusions about integration and feasibility

• Non-used thermal energy sources identification (waste heat). The Use Case has identified the possible storage of approximately 300 GWh/year that is currently not utilized by the facilities and dissipated into the ambient environment in the form of flue gas or cement mill.
• The high temperature of the waste heat gases (~400 °C) technological challenge. This issue has been successfully addressed through the implementation of an intermediate cycle, which significantly improves the overall utilization of waste heat by enabling the co-production of electricity and the supply of energy to the district heating network, even during the charging phase of the TCES.
• Favourable operating conditions for TCES in cement production. The cement industry, due to its stable and continuous production process, offers favourable conditions for the optimal sizing of the equipment required for TCES integration. Furthermore, this operational stability simplifies the charging process of the storage system, as it ideally receives a steady flow of heat throughout the charging phase.
• Full-year simulation demonstrates operational viability. The IPSE Go model successfully simulates 6326.3 hours of charging and 798 hours of discharging, confirming that the TCES system can be operated consistently within real plant conditions.
• ORC integration validated with detailed thermodynamic modeling. Simulated ORC performance shows net efficiency of 5.75%, turbine inlet/outlet flow consistency, and realistic pressure ratios - confirming proper coupling with the TCES discharge cycle. Although the electricity generation and efficiency of the ORC cycle installed at the discharge are limited, the cycle plays an important role by adapting the heat conditions coming from the TCES to the temperatures and requirements suitable for the district heating network.
• The presence of an existing connection to the district heating network. This further facilitates the integration of the RESTORE solution in this specific use case. This infrastructure significantly reduces the complexity and cost associated with establishing the necessary distribution system for thermal energy
• Storage capacity as the limiting factor in TCES waste heat utilization. The utilization of waste heat is primarily limited by the storage capacity of the thermochemical material (TCM), rather than by the availability of energy itself. This fact has a direct and positive impact on the viability of thermochemical storage (TCES) projects, particularly those involving shorter charge-discharge cycles. In such cases, a greater share of the available waste heat can be effectively harnessed.

  General conclusions

• Gmunden Cement Plant as a suitable site for RESTORE Implementation. The analysis conducted confirms the Gmunden Cement Plant as a highly suitable site for the implementation of waste heat recovery and TCES technologies. The combination of stable industrial processes, significant amounts of unused waste heat, and compatibility with district heating demands makes the plant an ideal candidate for the RESTORE use case. These findings validate its potential for supporting efficient, sustainable energy solutions through TCES integration.
• CuSO₄·5H₂O confirmed as a viable TCM for DH-scaled systems. The material shows high conversion efficiency in dehydration, stable cycling, and significant temperature lift (>60°C), making it suitable for seasonal storage applications.
• RESTORE Solution for waste heat recovery and district heating support. The solution proposed and adapted to the use case described, successfully takes advantage of an energetically intensive industry waste heat, storing it form of chemical energy, and releasing it when needed into a district heating. The solution fully satisfies the energetic necessities of the district heating during the cement plant-shutdown coinciding with the discharging period.