Finland: Sand Batteries For Energy Transition

Finland has created an application that can make a significant contribution to the transition to green technology – it’s the sand battery. We know that the biggest problem with renewable energy, especially photovoltaics and wind, is instability. Hence the need to create particularly powerful batteries that can store the excessively produced energy and then feed it into the system at night, in the case of solar, or during calm weather, in the case of wind power.

Finnish startup Polar Night Energy has taken a major step in this direction with a sand battery that can “hold” energy in the form of heat for months. The first installation is located in the town of Kankaanpää in western Finland, where a sand battery is connected to the district thermal power plant. The sand, enclosed inside a steel casing, is heated to 600° and, when the network requires, the battery is able to heat the water supplied to the network. The system simply consists of an insulated silo with a capacity of 100 tons of sand and a heat exchanger.

“Sand is a cheap and abundant material that can be heated to 1000°C or even higher,” explains Polar Night Energy. “Inside the sand, we build our heat transfer system, which allows us to efficiently transport energy to the storage and back. Adequate insulation between the storage and the environment guarantees a long storage period, from hours to months, with minimal heat loss.” Sand deposits are virtually unlimited and can also be buried, minimizing visual impact.

A similar system has also been developed in Italy, and the first installation will take place in 2024 in the province of Salerno. The battery will be built by the Magaldi Group and operated by Enelx. The MGTES (Magaldi Green Thermal Energy Storage) system is designed for the production of green thermal energy (steam or hot air) for easy implementation in industrial facilities. In this case, the energy is stored “for up to days and weeks.” The system consists of insulated modules containing quartz sand heated to temperatures above 600°C.

Excess energy obtained from renewable sources is used to charge the system, and electrical resistors (in the case of electrical energy) or an integrated heat exchanger (in the case of thermal energy) are immersed in a fluidized sand layer (a process that increases the heat transfer coefficient). The sand then accumulates heat and, due to the insulation of the storage tank and the absence of convection, energy losses are kept to a minimum. A heat exchanger built into the sand will allow the system to “unload.”