Researchers at Norway-based research institute SINTEF and the Swiss heat storage solutions company COWA Thermal Solutions have developed a new battery system for storing heat from heat pumps.

Heat pumps extract energy from their surroundings and transport the heat into buildings. However, heat demand varies in households and other buildings, depending on usage patterns, time of day, outdoor temperature, and weather conditions. A constantly running heat pump is expensive and energy-intensive, and it can overload the power grid.

The new battery system aims to address these issues.

Explaining the battery system. Galina Simonsen, a senior research scientist at SINTEF, said, “Think of it as a thermal battery, which stores the heat from the heat pump and can be used later. In practice, this means people get more energy from the stored heat. It becomes easier and more comfortable to use, and the energy is also used in a smarter way.”

Batteries will be highly efficient, charging and delivering heat quickly. “With the new batteries, heat pumps combine storage and smart distribution of heat,” said Simonsen.

Basic Design

The heat storage system utilizes salt hydrates, which lock water into their structure and have unique reactions to heat exposure.

“Salt hydrates aren’t toxic, they’re not flammable, and they are also relatively inexpensive. This makes them a safe and good choice for use in private homes. Heat storage with salt hydrates also takes up less space than a traditional hot water tank, often up to four times less,” said Simonsen.

These battery systems utilize this technology to act like sponges. The material changes from solid to liquid at a certain temperature, storing heat. They return to the solid state when cooled and release the stored heat.

The batteries can store considerably more thermal energy than substances like water. They also retain heat longer, even if temperatures do not change significantly.

Improved Efficiency

To improve the efficiency with which heat is stored and released in batteries, researchers designed and tested a heat sink that enhances heat transfer in thermal batteries.

The heat storage system incorporates cooling fins made from recycled aluminum, which are effective heat conductors. The fins will help distribute the heat quickly and evenly through the salt hydrate.

Recycled aluminium reduces the system’s environmental footprint and costs, promoting circular use of materials.

Corrosion Challenges and Solutions

Recycled aluminum can contain impurities that can increase vulnerability to corrosion.

Salt hydrates affect aluminum considerably in the presence of impurities. The cooling fins can degrade over time. This can reduce their performance and shorten the lifespan of the entire system.

Researchers coated the fins with plasma electrolytic oxidation (PEO), forming a thin, ceramic layer on the aluminum’s surface.

Researchers said the PEO coating is similar to that used on non-stick pans, providing a durable and corrosion-resistant barrier.

Other Advantages

According to SINTEF, the new battery system will offer financial benefits as it can store excess heat when electricity is affordable or produced using environmentally friendly methods.

Storage systems incorporating salt hydrates can have broader applications, as heating can be shifted to periods of low energy demand.

An International Energy Agency report said that heat pump sales worldwide increased by 11% in 2022, spurred by the global shift towards reliable, environmentally friendly heating. This was the second consecutive year with a double-digit growth rate.

Rising energy demand from energy-intensive systems, including heat pumps, is forecasted to help strengthen the EU’s solar market starting in 2028, according to the EU Solar Market Outlook 2025-2030 report by SolarPower Europe.