The need to reduce gas consumption from homes has become increasingly urgent due to the conflict in Ukraine. A thermal household battery can represent an ecological and economical solution that can free millions of homes from the use of gas for winter heating.
The battery was developed by a consortium from Eindhoven University of Technology, TNO.
Thanks to the accumulation of heat in homes and the utilization of the large amounts of heat from industrial waste that would otherwise be wasted, the thermal battery represents a potential game-changer for the energy conversion.
A surprisingly simple technology
A simple experiment that can be performed in one’s own home reveals the essence of the thermal battery. Just fill a small bottle with coarse white salt and add a little water. The chemical process that is immediately generated is to hear a sigh inside the bottle that, as if by magic, becomes hot. The experiment has been demonstrated several times by TU / e professor and TNO researcher, Olaf Adan.
Operation of the thermal battery revolves around a relatively old thermochemical principle: the reaction of a salt hydrate with water vapor. The salt crystals absorb water, become larger and release heat during this process.
But the reverse process is also possible. By adding heat, the water evaporates and thus “dries the salt”, which reduces the size of the salt crystals. Until the water comes in contact with the dry salt powder, the heat remains stored inside and does not dissipate. Therefore, unlike other types of heat accumulators, there is no loss: on the same principle, the battery is also free of loss.
Qhis process can be repeated indefinitely, either in one direction or the other, which provides the basis for the construction of a thermal battery capable of storing heat and using it at a later time and place. The thermal battery can therefore be a solution for the supply of renewable energy. In fact, it would be charged with the “waste heat” coming from various places, such as from factories. Once the heat is stored, the battery can be transported and used to heat homes and office buildings.
Although the principle of thermal battery may seem simple, the application is not so simple. Yes, Adan has been working on this project for 12 years because there are several factors to consider. The first is the choice of the specific saline material. There are thousands of reactions of hydrates with water. These have all been studied by the TNO researcher and he found that only a very limited number have the right properties to be applied to the battery.
A salt crystal becomes smaller and smaller with continuous heat exchange. This causes the crystal to disintegrate rapidly or to aggregate with other particles. The TNO research team then identified potassium carbon as a base for the battery. This salt is readily available and is found in many products such as food, soap and glass.
After identifying the salt, the second problem was to identify a container that was able to take full advantage of the chemical process. Adan thus designed a closed loop system. This recirculation system is built with various components, including a heat exchanger, a fan, an evaporator / condenser and a boiler with salt particles.
From prototype to scale use
The prototype made by Adan is able to save 7 kWh, a fairly minimal capacity, but able to provide heat for two days to a family of four. It was therefore a larger system consisting of about thirty batteries identical to the basic prototype. This new system has a capacity of total storage of over 200 kWh.
The idea of using a modular system consisting of 30 small batteries allows you to combine them at will and use only the necessary ones.
heat transport and ecological conversion
Unlike other heat transport systems, such as ordinary metal pipes thermal battery is capable of storing heat without loss. As long as no water is added, no process in the dry salt is activated and the heat remains stored inside the battery.
The research team also focused on industrial residual heat as a heat source, a kind of “waste of heat”, such as that generated as a by-product in factories or heat produced by data centers.
The thermal battery would make it possible to store this heat that would be wasted and to transport it where it is needed, such as homes or offices. In this way, a double effect would be created, the homes can become independent of gas and lower CO2 emissions.
The main advantages of the thermal battery
According to Adan, the new thermal battery has three main advantages: It is one greener solution compared to other solutions it is much more economic (potassium carbon is readily available) and is easily feasible in the short term. In fact, there is no need to lay pipes, and the heat needed to charge the batteries is already available because the residual heat from the factories would be used.
The first practical tests will be launched at the end of the year and will be installed pilot batteries of about 70 kWh in two homes in Eindhoven, one in Poland and one in France. But the use of thermal batteries in offices, greenhouses, electric buses and luxury ships is also currently being considered.