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Finnish sand batteries store renewable energy as heat for district heating

Finnish sand batteries store renewable energy as heat for district heating

New Capabilities

Polar Night Energy's third commercial sand battery is under construction in Vääksy, targeting summer 2027

October 5th, 2026: Vääksy battery on track for spring 2027

Overview

Updated Oct 22

Polar Night Energy is building its third commercial sand battery in Vääksy, Finland: a 2-megawatt unit that will hold 250 megawatt-hours of heat. The company targets completion in summer 2027, when the plant will feed Lahti Energia's district heating network.

The battery heats about 2,400 tons of local sand above 500°C using cheap surplus electricity, then releases the heat to homes. Lahti Energia expects the plant to cut the network's fossil emissions by around 60% and to take part in Fingrid's reserve markets. The earlier Pornainen plant cut its network's emissions by 70% in its first year.

Why it matters

Sand batteries let district heating networks cut fossil fuel use by storing cheap renewable electricity as heat for days or weeks.

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Key Indicators

250 MWh
Vääksy storage capacity
Thermal storage capacity of the Vääksy sand battery, which Polar Night says will be the world's largest when complete.
2,400 tons
Sand in Vääksy battery
Polar Night says about 2,400 tons of local natural sand will be heated above 500°C to store energy.
70%
Emissions cut at Pornainen
Reported cut in climate emissions from the Pornainen heating network after the plant's first year of operation.
2 MW
Vääksy thermal power output
Heating power the Vääksy battery will deliver to the district heating network.

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People Involved

TE
Tommi Eronen
Co-founder and CEO, Polar Night Energy
Leading expansion into Baltic and northern European markets
 Annette Höglund-Dönnes
Annette Höglund-Dönnes
Chief Commercial Officer, Polar Night Energy
Overseeing commercial deployment of sand batteries
 Liisa Naskali
Liisa Naskali
Chief Operating Officer, Polar Night Energy
Overseeing Valkeakoski power-to-heat-to-power pilot
 Jouni Haikarainen
Jouni Haikarainen
CEO, Lahti Energia
Partnering with Polar Night Energy on Vääksy battery

Organizations Involved

Polar Night Energy
Polar Night Energy
Energy storage startup
Developing and deploying sand batteries in Finland and the Baltic states

Finnish startup developing sand-based thermal energy storage for district heating and industrial use.
Lahti Energia
Lahti Energia
Utility
Building Vääksy sand battery with Polar Night Energy

Finnish utility partnering with Polar Night Energy on the Vääksy sand battery.
Loviisan Lämpö
Loviisan Lämpö
Utility
Operates the Pornainen sand battery

Finnish utility that commissioned the world's largest sand battery in Pornainen.

Timeline

2022 October 2026

6 events Latest: October 5th, 2026 · 1 month ago
Tap a bar to jump to that date

  1. Vääksy battery on track for spring 2027

    Latest Report

    ENR reports the 2 MW / 250 MWh Vääksy sand battery on schedule; Baltic distribution deal signed.

  2. Vääksy foundation complete

    Construction

    Foundation work finishes at the Vääksy site; silo and technical building construction follow.

  3. Pornainen battery meets targets in first year

    Report

    After a year of operation, Polar Night reports the Pornainen plant cut local district heating emissions by 70% and charged at 70-80% below average spot prices.

  4. Valkeakoski pilot construction begins

    Construction

    Polar Night Energy starts building a pilot to test converting stored heat back into electricity.

  5. Pornainen sand battery begins operation

    Launch

    Loviisan Lämpö commissions the world's largest sand battery for Pornainen's district heating network.

  6. First commercial sand battery commissioned in Kankaanpää

    Launch

    Polar Night Energy's first commercial sand battery begins operating in the Finnish town of Kankaanpää.

Scenarios

1

Sand batteries expand across northern Europe

Likely Resolves by End of 2027

Discussed by: Corporate Knights, Engineering News-Record

Polar Night Energy's Baltic distribution deal with Solsiden Wangard Family Office and SIA Soldag opens the Latvian market. The company plans a 10 MW battery next and targets Germany and Switzerland. If utilities in these markets adopt the technology, sand batteries move from a Finnish niche to a broader European option.

2

Sand battery converts heat back to electricity

Possible Resolves by Q2 2028

Discussed by: Live Science, Polar Night Energy

The Valkeakoski pilot, running from late 2025 for about two and a half years, tests materials and designs for converting stored heat back into electricity. If it succeeds, sand batteries could output both heat and power at roughly 90% efficiency, opening industrial markets that need both.

3

High investment costs slow sand battery adoption

Possible Resolves by End of 2027

Discussed by: Liisa Naskali, Polar Night Energy COO

Naskali says the main barrier is cost: wood-chip boilers are cheap, and few utilities have invested. If the Vääksy and Baltic projects don't prove payback, adoption may stay limited to a handful of Finnish towns.

Historical Context

2 moments from history that rhyme with this story — and how they unfolded.

October 2013

Solana Generating Station (2013)

Arizona's Solana plant became one of the first large concentrated solar facilities with molten salt thermal storage, holding heat for up to 6 hours to generate electricity after sunset. The 280 MW plant stores enough heat to power about 70,000 homes.

Then

Solana proved thermal storage could extend solar generation beyond daylight hours.

Now

Molten salt storage became standard in new concentrated solar plants, though it remains costlier than batteries for short-duration storage.

Why this matters now

Like sand batteries, Solana stores heat rather than electricity, showing thermal storage can work at grid scale when the economics align.

December 2017

Hornsdale Power Reserve (2017)

Tesla built a 100 MW lithium-ion battery in South Australia in 100 days, paired with a wind farm. It was the largest grid battery at the time and quickly proved its value by responding to grid frequency events within milliseconds.

Then

The battery stabilized South Australia's grid and cut frequency control costs.

Now

Hornsdale helped drive down battery costs and sparked a global wave of grid-scale lithium-ion storage.

Why this matters now

Hornsdale showed how a single well-placed storage project can prove economics and trigger wider adoption, a path sand batteries are now trying to follow for heat.

Sources

(13)
+7
Engineering News-Record CNBC Polar Night Energy Corporate Knights Live Science via Yahoo Interesting Engineering Machinery Asia WattNeuf Polar Night Energy Polar Night Energy Polar Night Energy Polar Night Energy Polar Night Energy