The switch to green energy would necessitate enormous amounts of energy storage since wind and solar power are unpredictable, producing energy when it is available rather than when it is needed.

There are several possible configurations for this, including:

Each has its advantages and disadvantages regarding size, location, installation and operating costs, efficiency, how long it can store the energy, input and output power ratings, and longevity. Therefore, different solutions will meet different needs – some will support the power grid during sudden spikes in demand, others will even out the daily demand and renewable supply curves, and others will help with seasonal supply drops, like when solar production declines in the winter.

Here is another from Finland to add to the collection. A few hours outside of Helsinki, Polar Night Energy claims to have just inaugurated its first commercial sand battery at the headquarters of “new energy” firm Vatajankoski.

This thermal energy storage system is essentially a large, insulated steel tank filled with plain sand and measures around 13.1 feet (4 meters) wide by 23 feet (7 meters) high. This system can store an astonishing eight megawatt-hours of energy at a 100 kW nominal power rating, with the sand heated to somewhere between 932 to 1112°F (500 to 600°C), using a heat exchanger buried in the midst of it.

The energy is similarly extracted as heat when it is required. For example, to fuel the neighborhood’s district heating system, which distributes heat using piped water, Vatajankowski uses this stored heat and extra heat from its data servers. Then, it can be applied to heating structures, swimming pools, industrial processes, or any other situation requiring heat.

In a video interview with Disruptive Investing, the company explains how this contributes to its incredibly efficient nature. “It’s really easy to convert electricity into heat. But going back from heat to electricity, that’s where you need turbines and more complex things. So as long as we’re just using the heat as heat, it stays really simple,” explained Polar Night CTO Markku Ylönen. The firm claims a lifespan of decades, an efficiency factor of up to 99%, and the ability to retain heat for extended periods with minimal energy loss.

The manufacturer claims that the sand must only be dry and clear of flammable material; it has no unique properties. The firm views it as a very inexpensive or even free storage medium. Polar Night Energy says that the setup expenses are less than US$10.27 (€10) per kilowatt-hour and that it operates entirely automatic and inexpensively without using consumables.

The company also plans to scale up, with installations of 20 gigawatt-hours of energy storage producing hundreds of megawatts of nominal energy and the sand heated up to 1,832°F (1,000°C) in some configurations. Unused mining shafts can be converted into extensive underground storage facilities if they are in the proper shape. No high-pressure vessels are required, and the piping is usually the most expensive component.

The name Polar Night refers to the fact that sections of Northern Finland get no sun during the winter since they are above the latitude (68 degrees north), where there is no direct sunlight for weeks on end during the dead of winter. The business points out that times like these—when its long-duration storage will keep buildings warm affordably and sustainably through the brutal Finnish winter—are when its sand battery will have its most significant impact.

The design allows for many energy storage “zones” within the sand, where the solid sand storage medium truly shines. For example, a system intended for longer-term heat storage can be constructed closer to the center of the sand cylinder and closer to the top surface or the exterior for repeated short-term use cycles. However, since the liquids are constantly mixing and flowing, this would not be possible in a liquid medium like molten salt or water.

It’s safe to say that only locations with district-level heating will use this method extensively. However, there is a surprisingly large quantity of district heating in use. It can be found in several other places, such as Northern China and the USA, and it is used in over half of all Scandinavian homes.

Therefore, the deployment of Polar Night’s energy storage system to its full potential could replace many carbon-burning heat sources. Indeed, according to estimates made by Mission Innovation’s climate solutions framework, it could replace enough sources to cut annual greenhouse emissions by between 57 to 283 megatons of CO2 equivalent each year by 2030. That would be quite a substantial contribution.