​Storing energy in sugar sounds a little unconventional. But it could help urban heating networks get the thermal storage they need to do two things: manage supply and demand and integrate more intermittent renewable energy. Several phase change materials have garnered interest for their capacity to store heat, and sugar alcohols are near the top of the list. Sugar alcohol xylitol was used in a demonstrator developed as part of PhD dissertation research done at CEA-Liten.

This inexpensive, non-toxic, and readily available sugar alcohol is processed from birch trees. It is among the densest materials in the temperature range of interest (below 100 °C). It does have the major drawback of supercooling, which means that it remains liquid even below its theoretical freezing or crystallization temperature. This makes it impossible to recover the energy stored inside the material during crystallization. One way around this is to add seed crystals to initiate crystallization, and then produce bubbles to speed up the phenomenon by a factor of ten.

In the demonstrator developed here, a needle was used to inject sugar crystals and air into the bottom of the tank, solving the supercooling problem completely. The demonstrator also released all the energy stored in the sugar very rapidly. The next steps will be to automate the sugar supply, scale the demonstrator up, and test it with other kinds of sugars.