Heat pumps that store heat like batteries

January 14, 2026

A joint research initiative between SINTEF and Swiss firm COWA Thermal Solutions has transformed conventional residential heat pumps into advanced thermal energy storage systems. By enabling heat pumps to function as thermal batteries, the innovation allows homeowners to store heat when electricity prices are low and release it during peak demand periods—reducing both energy costs and carbon emissions.

Heat pumps meet thermal energy storage

Heat pumps are already recognized as an energy-efficient solution for heating and cooling homes. By extracting heat from the surrounding environment, they provide warmth in winter and cooling in summer while using significantly less electricity than traditional systems. When powered by renewable energy sources such as solar or wind, heat pumps become an even more sustainable option.

However, household heating needs fluctuate depending on weather, occupancy, and time of day. Renewable energy generation does not always align with peak demand—especially in the evenings—forcing many heat pump users to rely on electricity generated from fossil fuels. The SINTEF–COWA collaboration addresses this challenge by integrating thermal storage directly into the heat pump system.

Thermal batteries powered by salt hydrates

While thermal energy storage technologies already exist, most are designed for industrial applications and are impractical for private homes. To overcome this limitation, researchers turned to salt hydrates—specialized phase change materials capable of storing and releasing large amounts of heat.

Unlike ordinary table salt, salt hydrates bind water molecules within their structure. When heated, they undergo a phase transition from solid to liquid, absorbing heat in the process. When cooling is initiated, they solidify again and release the stored thermal energy. This makes them highly effective for compact residential heat storage.

Salt hydrates offer several advantages over traditional water-based storage. They can store significantly more heat in a smaller volume and retain it for longer periods, improving both efficiency and space utilization.

According to senior research scientist Galina Simonsen, salt hydrates are non-toxic, non-flammable, and cost-effective—making them well suited for use in private homes. In addition, heat storage systems based on salt hydrates can require up to four times less space than standard hot water tanks.

Recycled aluminum improves efficiency and sustainability

SINTEF’s key contribution was the development of an efficient heat distribution system for the salt hydrate storage unit. Researchers designed specialized cooling fins made from recycled aluminum, a material chosen for its lightweight nature, excellent thermal conductivity, and ease of shaping. Using recycled aluminum also lowers production costs and reduces environmental impact, supporting circular economy principles.

One challenge with recycled aluminum is its susceptibility to corrosion, particularly when exposed to salt hydrates. To solve this, the research team applied plasma electrolytic oxidation (PEO)—a process that creates a durable ceramic coating on the aluminum surface. This protective layer significantly improves corrosion resistance while maintaining high thermal performance.

A smarter, greener future for home heating

By combining heat pumps, salt hydrate thermal storage, and recycled materials, this innovation paves the way for smarter residential energy systems. Homeowners can maximize renewable energy use, lower electricity bills, and reduce reliance on fossil fuels—all without sacrificing comfort or space.