Even as researchers are working to turn skyscrapers into giant batteries, Polar Night Energy (PNE) in Finland has installed the first commercial sand battery, which can store energy for several months, to warm homes in winter when energy needs rise. “Production of renewable energy sources such as wind and solar power is highly volatile, and only partly overlapping with the consumption in time,” explains PNE on its website. “Our technology provides a way to refine cheap and clean surplus electricity to valuable heat in an affordable way to be used when most needed.”
Down to Earth
Put simply, a sand battery converts electricity to heat, which it then stores for later use. Sand is not only one of the cheapest mediums for storing heat, it’s also very efficient and loses little over time. Unlike a lithium-ion battery, a sand battery uses resistive heating to increase the ambient temperature, which is then transferred to sand with the help of a heat exchanger. Sand has a very high melting temperature that’s hundreds of degrees Fahrenheit. Importantly, sand can store heat energy for months on end, making sand batteries a viable long-term storage solution. PNE has erected the first commercial sand battery in a small energy utility in the town of Kankaanpää in western Finland. The battery takes the form of a silo that’s filled with about 100 tons of sand. Currently, the battery powers the central heating system for the district. According to PNE, when required, the hot air in the battery can be used to warm water, which is then pumped to offices and homes in the neighborhood. The Finnish sand battery has 100 kW heating power, and a total storage capacity of 8 MWh. According to the company, the battery costs less than $10 per kilowatt-hour, and once operational can last for “tens of years.” Besides this, PNE also has a smaller 3 MWh operational test pilot in Hiedanranta, Tampere, that’s connected to a local district heating grid, and provides heat for a couple of buildings. The company used this pilot to test, validate, and optimize the sand battery solution. The pilot project gets some of its energy from a 100-square meter solar panel array and the rest from the traditional electric grid.
Long Term Solution
The increased effort to maximize the generation of renewable green energy around the world has researchers scampering for innovative solutions to store this energy for later use. While traditional chemical batteries made with lithium and other minerals can be repurposed for this task, they aren’t sustainable nor cost-effective in the long run, when a large chunk of electricity will be generated from renewable sources, argues PNE. In addition to PNE, several other researchers are exploring the use of sand batteries as a means of energy storage. The US National Renewable Energy Laboratory’s (NREL) ENDURING project has successfully prototyped a thermal energy storage solution that uses sand as the storage medium. NREL researcher Patrick Davenport said the ENDURING project helped demonstrate a clear path to exceed 50% round-trip efficiency. Round-trip efficiency specifies the percentage of electricity put into storage and later retrieved. The higher the round-trip efficiency, the less energy is lost in the storage process. This is important since sand batteries are good for storing and releasing heat but aren’t very efficient when it comes to returning power to the electricity grid, observes the BBC reporting on the Finnish battery. In an email exchange with Lifewire, Davenport asserted that although the round-trip efficiency of sand batteries isn’t a match for modern chemical batteries, such as Lithium-Ion, they more than make up for the loss by being highly scalable, and for their exceedingly low capital costs. “With the prospect of regular low cost of electricity (free or even paid to use at times), the round-trip efficiency becomes less important,” asserted Davenport. “Instead, the economics hinge on system capital costs where thermal energy storage technologies show promise.”
