innovation

A heat battery for the home: compact, stable, and affordable

23 August 2019 • 3 min reading time

The supply of sustainable solar and wind energy is unreliable. Sometimes there is excess supply, and sometimes there is too little to meet demand – which is growing quickly. Storing energy when there is more than enough supply is a solution, but until recently the technology to do so was very inefficient. An innovative heat battery developed jointly by TNO and the TU/e is efficient, widely applicable, and ready for the market.

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If you wish to know more about what the heat battery can mean for you or your company, please contact Olaf Adan.

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Storing sustainable energy is not in itself a new idea, says Olaf Adan of TNO: “What is new is that TNO and the TU/e have developed a heat battery that is stable, has high levels of stored energy retention, and – used properly – could last at least twenty years. The battery is affordable, and it’s no bigger than a fridge. This is a breakthrough that makes energy storage a feasible application, right down to the level of residential blocks or even individual homes.”

The heat battery uses two components: water vapour and a salt hydrate. When the two are brought together the water binds to the salt, forming salt crystals. This process releases heat, which can then be transformed into electricity, for instance.

A reversible and stable process

The great advantage of this process is that it is reversible. When heat is put back into the system – using solar energy on a sunny day, for example, or from a wind turbine on a windy day – then the water and salt separate. In short: as long as the water and salt are separated, energy is stored. When the two are brought together, heat energy is released.

“We’re assuming a working lifetime of at least 20 years if the battery is fully charged and discharged once a month”

The TNO and TU/e heat battery can be charged and discharged without loss of energy, Adan says: “The trick was to prevent the salt granules from degrading during the conversion process, which would gradually stop them working. And we’ve succeeded in doing do. We’re assuming a working lifetime of at least 20 years if the battery is fully charged and discharged once a month.”

Far superior to existing systems


The heat battery has enough capacity to allow an average family to take showers for two weeks. This performance is ten times better than that of energy storage in water, and considerably superior to what the best domestic batteries can currently deliver.

“Heat batteries also help to absorb peaks in energy use on the grid”

The heat battery can be combined with a heat pump, which is expected to perform better at low-energy moments. The TNO and TU/e researchers also expect solar panels to perform better with this storage. Adan: “Another benefit that should not be underestimated is that these heat batteries could help to absorb peaks in energy demand on the grid.”

Wide applicability

All told, according to Adan it is an ingenious system whose operation is nevertheless very simple. That simplicity makes it possible to keep the heat battery affordable, for residential blocks and even for individual homes. The cost price is far below that of electrical storage systems, while its performance is considerably better.

“Market potential in the EU could be around 60 million homes”

This not only means that there is a market for the heat battery; it also means that the market potential could be very large indeed. In the Netherlands alone it could apply to about seven million homes, and market potential in the EU could be around 60 million homes. Naturally, other applications can also be envisioned.

Looking for partners

TNO and the TU/e are looking for partners to bring the heat battery to market. Adan: “We need to accelerate the development of this valuable innovation.” His first concern is to find investors and companies in the chemical and manufacturing industries: “The use of salt hydrates for compact heat storage is new, so for the producers of these materials this could mean new sales opportunities. The heat battery also offers opportunities to the Dutch installation sector, which already has a strong international position.”

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