#insights

Decarbonising high-temperature industrial processes is crucial to achieving carbon neutrality targets. Thermal Energy Storage(TES) technologies make it possible to electrify these industrial processes by integrating renewable energy sources and recovering waste heat. They are available as modular commercial solutions that are increasingly competitive compared with other developing or higher-cost alternatives.

The industrial sector is responsible for between a quarter and a third of global CO₂ emissions. Some sectors — including steel and metallurgy, refining, chemical and petrochemical, cement and lime, among others — havehard-to-abate emissions, either due to the high-temperature requirements of their processes or the intrinsic CO₂ emissions of the processes themselves.

CO₂ emissions by sector

TES systems withpower-to-heat schemes make it possible to electrify thermal industrial processes, replacing natural gas or fuel oil boilers. These systems are charged using electricity — preferably renewable — and supply high-temperature heat when needed.

Specifically, sensible heat-based TES stores thermal energy by raising the temperature of a material without a phase change, making them operationally simple and technologically robust. The materials used include crushed rock, concrete, steel, and molten salts, each with specific thermal and mechanical properties that define their optimal application range.

Unlike other thermal storage technologies — such as latent heat or thermochemical reaction-based systems — or emerging energy carriers like hydrogen, sensible heat TES is already commercially available in increasingly competitive modular solutions. Moreover, some manufacturers offer these systems underHeat-as-a-Service (HaaS) models, removing the client’s upfront investment (CAPEX) and reducing financial exposure, thereby accelerating the adoption of thermal electrification solutions in industry.

Although electric boilers have a lower CAPEX, they do not, on their own, allow for the use of renewable surpluses or the decoupling of generation and demand. In contrast, TES systems are particularly useful for maximising the use of renewables and enablingenergy-shifting strategies, taking advantage of hourly price variability in the electricity market.

However, for large-scale applications, bespoke solutions may be more appropriate than modular systems.

When adopting this type of system, the role of an integrator engineering firm with experience in large-scale thermal energy storage can be especially valuable for industrial clients, helping to identify the most suitable technology, define system sizing, and integrate it into production environments that are typically already in operation.

Modular TES Systems

Below are five types of modular power-to-heatTES systems currently being deployed, capable of supplying high-temperature industrial heat in the form of saturated or superheated steam for integration into production processes.

Modular TES systems

• Solid Rock Bed TES: A compact bed of crushed rock stores heat up to 650 ºC. Charging is done via electric resistances, and discharging occurs through water circulating in a central pipe, producing superheated steam at the outlet. An external tank adjusts the steam flow and temperature to process conditions. The technical and economic viability of this system has been demonstrated in various industrial applications, particularly as a replacement for fossil fuel boilers, significantly reducing emissions and operating costs.
• Solid Concrete TES: Uses high-thermal-conductivity concrete blocks as the storage medium, penetrated by metal pipes carrying a heat transfer fluid (synthetic oil). The storage temperature is limited to 400 ºC by the thermal stability of the oil. During charging, externally heated oil transfers heat to the concrete. During discharging, the flow is reversed and the oil transfers heat to a steam generator. This solution has been used to decarbonise industrial processes by leveraging renewable electricity surpluses.
• Solid Steel TES: Heat is stored in structural steel blocks, which provide high energy density and good thermal conductivity, reaching over 600 ºC to supply high-quality process heat. Charging and discharging are performed using a closed-circuit air system, heated with electric resistances and then transferring heat to water in a fire-tube boiler. This technology is particularly suited to industries with highly variable thermal demand and availability of renewable electricity surpluses.
• Molten Salt TES: Molten salts act as both the storage medium and the heat transfer fluid. Charging is done via electric resistances, and discharging occurs in a shell-and-tube heat exchanger to generate steam. Typically, ternary salt mixtures are used, with a stable operating range between 180 ºC and 400 ºC, with no crystallisation or chemical degradation. Systems can also be designed to operate up to 565 ºC using binary solar salts. Although this is a mature and widely tested technology, it still poses challenges involving continuous thermal maintenance and operational cycling control.
• Fluidised Sand Bed TES: This system lies between solid and liquid thermal storage, using sand particles as the storage medium, which are mobilised and heated via closed-circuit air. This approach allows temperatures close to 1,000 ºC due to the high thermal stability of the material and efficient heat transfer under fluidised conditions. Discharging is performed via submerged heat exchangers and external tempering units, which allow the temperature of the resulting steam to be adjusted. This technology is especially suitable for very high-temperature industrial applications.

Technical Analysis

The differences in the materials and design of the thermal energy storage (TES) systems analysed determine their operating temperatures, energy density, efficiency, and overall cost.

Systems using solids or fluids with a high thermal conductivity offer higher energy density compared with other materials, but are often penalised by higher installation or operational costs: steel is expensive on the market, molten salts require continuous energy input to prevent crystallisation, and fluidised sand beds entail greater technical complexity and the need for intensive thermal insulation to minimise losses.

As for the operating temperatures, systems based on molten salts or thermal oils are limited by the chemical degradation of these fluids. Their degradation due to thermal cycling must also be considered, although it is generally negligible for solid materials. In the case of solids, the maximum temperature is constrained by the effectiveness of heat transfer, which improves significantly by reducing the size of the solid and increasing the exchange surface, as occurs in fluidised sand bed systems.

All the systems analysed achieve efficiencies — the ratio of useful thermal energy delivered to the electrical or thermal energy used to charge the system — above 90%, although fluidised sand bed systems have higher losses due to fluidisation.

Finally, while the modular nature of these systems allows the thermal capacity to be adjusted to each process, manufacturers typically define optimal ranges for economic competitiveness, depending on size, scale, and operating regime.

Conclusion

Sensible heat-based thermal energy storage represents a mature and technologically proven solution for decarbonising industrial processes that require high-temperature heat, particularly in sectors where direct electrification is not viable. Its ability to integrate renewable energy, utilise waste heat, and provide operational flexibility positions it as a competitive alternative to electric boilers and other emerging technologies.

The choice of the optimal solution should be based on a rigorous technical/financial analysis, taking into account the characteristics of the process and the boundary conditions of the facility where it is to be implemented, the associated energy demand and renewable generation profiles, available space, energy prices, and CO₂-related costs under different future projection scenarios, as well as the system’s CAPEX and OPEX.

As new projects are developed and operational experience accumulates, a progressive reduction in costs and continuous improvement in TES system efficiency are expected. Large-scale deployment will depend on institutional support, developments in the energy market, and the industrial sector’s ability to adapt to innovative solutions.