Use Case 4: Key Results

The RESTORE solution proposed and adapted to Use-Case IV has been thoroughly described in this document. This deliverable presents the design, simulation, and performance evaluation of the TCES (Thermo-Chemical Energy Storage) configuration developed by TURBODEN with support from SIMTECH.

The system demonstrates an annual energy storage capacity of approximately 28 GWh. One of the most critical challenges in scaling up to such large capacities is the quantity of thermochemical material required. Storing this level of energy demands a significant volume of active material capable of reversible reactions with high energy density and long-term stability. In this case, copper sulfate pentahydrate is used. Despite its favorable reaction enthalpies, the mass and volume needed to store tens of gigawatt-hours become substantial.

Therefore, while the thermodynamic performance is promising, the scalability of the storage medium remains a key area for further research and development—especially for industrial or grid-scale deployment.
It is important to note that the performance figures presented here assume an ideal scenario in which the reactor does not need to release any steam streams, as is currently required. Maintaining all stored heat becomes increasingly important at these large scales, and it is believed that future developments—driven by the experience gained through this project—will enable full heat retention.

As shown in the analysis of Figure 45, assuming this Scenario (A) the Carnot battery system achieves a round-trip electrical efficiency of approximately 20%, while its thermal round-trip efficiency exceeds 100%. Although direct comparison between thermal and electrical energy is not entirely appropriate due to their differing qualities and applications, it is worth emphasizing that if the electricity used to power the heat pump during charging comes from surplus renewable sources, its cost is effectively zero. In such cases, the low electrical round-trip efficiency becomes less relevant, as the system is primarily converting otherwise unused renewable energy into storable and dispatchable thermal and electrical outputs.

Scenario A: 2100 Hours of Discharging

Over the course of a year, with 2100 hours of operation in discharging, the system produces, assuming average load factor of 0.8:

• 1680 MWh of net electricity, generating €84,000 in revenue.
• 24,570 MWh of thermal energy, generating €1,228,500 in revenue.
• A total annual revenue of €1,312,500.

 In terms of environmental impact, the system avoids approximately 672 tonnes of CO₂ emissions annually, assuming an average grid emission factor of 0.4 kg CO₂ per kWh.

Scenario B: 357 Hours of Discharging

•  285.6 MWh of net electricity.
• 4,176.9 MWh of thermal energy.
• CO₂ emissions avoided: ~1.79 tonnes

In this alternative scenario, the TCES system is designed to directly utilize the steam stream produced during the discharge phase for district heating in the city of Brescia. This is particularly advantageous because the temperature of the steam—approximately 106°C—is perfectly aligned with the requirements of Brescia’s existing district heating infrastructure. This compatibility allows for seamless integration without the need for additional heat exchangers or temperature adjustments, maximizing system efficiency.

The steam generated from the thermochemical reaction is routed directly to the district heating network, where it is used to supply residential and commercial buildings with heating and domestic hot water. This approach not only enhances the overall energy utilization of the TCES system but also ensures that the stored thermal energy is delivered in a form that is immediately usable by the end consumers.

Importantly, this configuration remains effective even during the summer months. While space heating demand drops significantly in warmer seasons, the need for domestic hot water persists year-round. The system continues to operate by supplying hot water for sanitary use, maintaining its relevance and utility across all seasons. This year-round operation improves the economic viability of the system and contributes to a more stable and predictable revenue stream.

Moreover, this direct-use strategy supports the broader goals of decarbonization and energy efficiency in urban environments, as it leverages renewable energy stored in the TCES system to replace fossil-fuel-based heating sources.

The reduced discharge duration in this scenario—357 hours annually—reflects a more targeted operational strategy, focusing on periods of peak thermal demand or when renewable electricity is most abundant. Despite the shorter operating time, the system still delivers substantial thermal energy and contributes meaningfully to CO₂ emissions reduction.

In summary, the direct use of steam for district heating in Brescia represents a highly efficient and contextually optimized application of the TCES technology. It demonstrates how thermochemical storage can be tailored to local energy needs, offering both environmental and economic benefits, and paving the way for future large-scale deployments where full heat retention and utilization will be achievable.

Overall, the findings presented in this report reinforce the suitability of the integration of the RESTORE proposed solution to the as virtually demonstrated in Use-Case 4.