Polar Night Energy has recently powered up the world’s largest Sand Battery in Pornainen, Finland. Standing 13 metres tall and 15 metres wide, this modern marvel is packed with 2,000 tonnes of crushed soapstone sand, a by-product of the local fireplace manufacturing industry.
The Sand Battery is a thermal energy storage (TES) system. Excess energy from renewable sources heat up the sand through resistive heating, with hot air circulated in the container through a heat exchanger.
The unit stores heat at temperatures of around 450°C for weeks, and provides affordable heating for the Loviisan Lämpö district. It delivers 1MW of thermal power, and has a storage capacity of 100 MWh. Round trip efficiency is stated to be around 85-90%.
The battery replaces the existing woodchip power plant, and reduces CO₂ emissions by around 70%. The design can output hot water, hot air, or steam, all valuable for industrial processes and power generation.
🍃 Intermittent renewable sources, such as wind or solar create a mismatch between energy production and consumption. In a repowering context, coal-fired power plants (CFPPs) struggle to operate where power prices are very volatile.
Adding TES to a CFPP prepares the plant for a repowered life beyond coal. It’s an intermediary coupling between a low-carbon heat source which replaces the coal boiler, (e.g., nuclear or geothermal), and the existing steam cycle and condenser cooling system of a coal plant. These are technically difficult to match without such a system.
For example, nuclear technologies should ideally not be ramped up and down continually. With a TES, surplus energy could be captured continually, and stored for reliable baseload when the grid demands it: at night, in winter or when the wind dips.
The real advantage of TES such as this Sand Battery is the modularity; they can be scaled up for longer durations. The TES medium is side-stream from manufacturing or mining industries, so these units are economically viable, and reduce waste too.
This autumn, Polar Night Energy start construction on a pilot project in Valkeakoski, which will store heat in a 1.1 million cubic meters cavern underground. The full capacity of 90GWh could heat a medium-sized Finnish city or town for as long as a year. The pilot will explore the conversion of stored thermal energy back into electricity in a process called power-to-heat-to-power (P2H2P). We look forward to hearing their progress!
💡 Learn more: Repowering with Thermal Energy for Germany
Our recent study showed an increase in VRE integration, and reductions in:
↘️ Emissions
↘️ Electricity prices
↘️ Price volatility
↘️ Import dependence
Interested in repowering coal with the TES pathway?
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