PCM latent heat storage: development, testing and integration

Advantages of metallic PCMs – comparison with molten salt storage

High-temperature storage systems using metallic PCMs offer advantages over conventional sensible molten salt storage systems:

Power plant application: process steam backup for industrial parks

As the share of renewable energies increases, so does the number of start-up and shut-down cycles in power plants. Conventional power plants are often not designed for this type of flexible operation.

Through combined heat and power generation, industrial cogeneration plants supply not only electricity but also process steam to industrial and chemical parks. When a cogeneration plant is shut down – for example for maintenance inspections or during periods of low electricity market prices – steam generation is usually taken over by fossil-fired auxiliary boilers (backup boilers, reserve boilers). These have to be kept available in minimum-load operation, which entails high consumption of fuel oil or natural gas and correspondingly high costs.

A metallic high-temperature storage system can bridge the process steam supply during shut-down or part-load operation. The conventional auxiliary boilers can be switched to hot standby mode, thereby saving fuel costs. Initial economic feasibility calculations by Fraunhofer UMSICHT indicate short payback periods for this application.

Further user industries for metal PCM storage systems

Metal-based latent heat storage systems are also suitable for process heat applications with high, short-term steam or heat demand – for example in the food and beverage industry.

In breweries, for instance, the batch-based brewing process leads to irregular peak loads in steam consumption, which conventional storage systems can only partially buffer. In the ISSDEMO project, a pilot storage unit (temperature range 250 °C to 500 °C) is being tested for this application under real-world conditions at a partner from the brewing industry.

Pilot-scale facility in the TheMatIK project

In the TheMatIK project (funded by the BMBF, with the partners enolcon GmbH, Ostbayerische Technische Hochschule Amberg-Weiden and Uniper Technologies GmbH), metallic PCMs and metallic encapsulations were investigated for their suitability as high-temperature storage media – from the definition of requirement parameters through flow simulation and cycling stability tests at laboratory scale to process simulation of the storage system's integration into a real process steam network.

To replicate a realistic process steam supply, Fraunhofer UMSICHT operates a pilot-scale facility approximately 6 metres high.

Material selection: melting temperatures and enthalpies

Pure sugar alcohols and their mixtures exhibit different melting temperatures and enthalpies.

Through binary and ternary eutectic mixtures, the melting temperature can be specifically lowered compared to the pure materials and tailored to the application – while still maintaining a high storage density.

Melting temperatures and melting enthalpies of various sugar alcohols

Are you developing a thermal energy storage system or a phase change material and would like to verify its performance, efficiency or operational safety? Fraunhofer UMSICHT validates latent heat storage systems at both material and system level – under near-practice conditions and with scientific support.

At material level, we characterise phase change materials using methods including differential scanning calorimetry (DSC), thermogravimetry and optical analysis techniques. The focus is on melting temperature, melting enthalpy and cycling stability over repeated charging and discharging cycles. For supercoolable PCMs such as sugar alcohols, we additionally examine the long-term stability of the supercooled melt and its viscosity behaviour – both crucial for a controlled discharge that can be triggered on demand.

At system level, we can connect storage units to our test infrastructure and to our heating network. This allows charging and discharging processes to be replicated over defined load cycles and key parameters such as efficiency, storage capacity and power density to be determined under defined, near-practice boundary conditions. For metallic PCM storage systems, we additionally test the cycling stability of the encapsulation and the corrosion behaviour under operating conditions. Fraunhofer UMSICHT is continuously expanding its testing capacities for thermal energy storage, for example to precisely record charging and discharging processes with different media as well as standby losses over longer periods.

Services:

• Material characterisation of PCMs (melting behaviour, enthalpy, cycling stability, supercooling behaviour)
• Connection of the storage unit to our test infrastructure and heating network
• Charging and discharging over defined test and load cycles
• Determination of efficiency, storage capacity and further performance parameters
• Testing of encapsulation and corrosion behaviour (for metallic PCMs)
• Validation of simulation and design models
• Contribution to test methods and key performance indicator systems for comparable assessment of thermal energy storage systems
• Scientific support, data evaluation and customised test reports

Your added value:

• Objective, scientifically sound performance verification of your storage system or PCM
• Reliable key figures for development, approval and marketing
• Early identification of optimisation potential
• Reduced risk ahead of market launch or series production