By Cliò E. Agrapidis, PhD
Data from the International Energy Agency shows that, in 2022, the industrial sector was responsible for emitting 9 Gt (gigatons) of carbon dioxide (CO2). This is roughly equivalent to the annual emissions of 1.9 billion gasoline-powered passenger vehicles—more than the current number of vehicles operating globally. A significant portion of these emissions comes from industrial heating processes, which still rely heavily on fossil fuels. Finding more efficient ways to store and use thermal energy is crucial for reducing this footprint while maintaining productivity. A circular approach, which reuses heat that would otherwise be wasted, can support the decarbonization process and help meet the EU’s goal of becoming the first zero-net-emission continent by 2050.
A Smarter Way to Store and Reuse Heat
The SUSHEAT project is working on a novel Thermal Energy Storage (TES) tank. This type of technology is already in use, with studies showing a reduction of up to 30% in energy cost for industrial applications (along with a related decrease in emissions). The SUSHEAT project aims to improve the thermal conductivity of TES and extend the temperature ranges for operation.
To achieve this, they are developing a new bio-inspired TES tank, with a design inspired by branching veins found in plants and animals. This design will incorporate a phase change material (PCM). Since PCMs are central to this design, the SUSHEAT team analyzed different candidates to identify the best options for industrial applications. The results of this analysis are presented in a recent publication. The team focused on identifying the best candidates for industrial applications within two predefined temperature ranges: a mid-temperature range of 60°C to 80°C, and a high-temperature range from 150°C to 250°C.
The Power of Phase Change Materials
PCMs are ideal candidates for thermal storage applications due to their unique properties. They can absorb and release large amounts of heat (or energy) during a phase transition. Thanks to their high latent heat capacity, they can store more energy in a smaller volume compared to traditional materials. Additionally, they maintain a nearly constant temperature during the phase change process. The ability of PCMs to absorb and release significant amounts of energy at a consistent temperature makes them valuable for improving energy efficiency and managing heat in diverse systems.
Why Material Properties Matter
The group of analysed materials included seven chemicals from different suppliers and four commercial PCMs. While the suppliers provide the physical properties of the materials, this data is not always reliable or representative of the actual samples. Therefore, researchers performed measurements on all the materials, focusing on the melting temperature (the temperature at which the material transitions from solid to liquid), melting enthalpy (a measure of the energy stored during the phase change, which is fundamental for TES applications), specific heat for both the solid and liquid phases (which affects the heat energy absorbed by the PCM), density (how much material is present within a specific volume), thermal conductivity (a measure of the power for charging and discharging the TES), degradation temperature (the temperature at which the material degrades without possibility of recovery, which is fundamental in defining the temperature range for material application), and the category for hazardous materials.
The analysis revealed that the values provided by the suppliers were not always consistent with the actual properties of the materials. This discrepancy was observed across multiple properties, including melting temperature and melting enthalpy—both of which are crucial for TES performance. Most notably, degradation temperature data—a key safety factor—was missing in the literature. Determining values for this property was essential, as it defines both safety and operational boundaries. This highlights the critical role such characterization studies play in technology development.
From Lab to Industry: What’s Next?
Next, it is important to determine the temperature range at which the TES will be operating, to determine which PCMs are the most suitable. Another refinement in the selection comes from the melting enthalpy and the thermal conductivity, both affecting the actual energy and power available in the TES during the charging and discharging processes.
This characterization lays the foundation for selecting the most effective PCMs for industrial TES systems. The next step is to integrate the best candidates into a functional prototype, bringing us closer to scalable, cost-effective energy storage solutions for industry