These giant sand batteries prevent renewable energy from going to waste.
By Tom Barton
Unfortunately, there’s a lot more to the energy transition than just building wind turbines and installing solar panels.
In most countries, energy grids were designed and built around fossil fuels. While coal, gas, and oil have serious downsides—most notably their contribution to climate change—they do have one big advantage: their output is easy to control. When electricity demand rises, power plants can simply burn more fuel to meet it.
Wind and solar energy don’t work that way. Sometimes, like at night or on calm days, they don’t produce enough electricity. At other times, on particularly windy or sunny days, they can produce too much.
Every grid has a maximum capacity—the most electricity it can safely carry at any given moment. If that limit is exceeded, the system can overload, damaging infrastructure and causing widespread outages. So, when supply exceeds demand, the energy is kept out of the system and instead just goes to waste.
This is not just a theoretical problem. In 2024, for the equivalent of more than 250 days, Scotland’s biggest offshore wind farm had to intentionally reduce its output. Not because the wind wasn’t blowing, or because the turbines weren’t working, but because the electricity grid couldn’t handle the power that it—and other Scottish wind farms—were producing.
The challenge is this: we need a way to capture and store energy when it’s abundant, so it can be put to good use instead of being wasted. A Finnish startup, Polar Night Energy, designs and builds giant sand batteries that do just that.
But before we get into what Polar Night Energy’s sand batteries do, we should first clarify what they don’t do. They don’t store energy and release it back to the grid as electricity… yet. That’s something that they plan to make possible further down the line!
For the time being, the batteries store excess renewable energy as heat, which can later be used for heating purposes in homes, businesses and factories. This is a lot more significant than it sounds. Heat is the main end-use for energy around the world, making it an important place to look when it comes to moving away from fossil fuels.
Polar Night Energy’s batteries essentially act as massive thermal reservoirs, capturing energy that would otherwise go to waste and putting it to good use. Here’s a basic step-by-step of how it works. Excess renewable energy is turned into hot air, which is pumped through pipes inside the sand. This process heats the sand to temperatures of up to 600°C. The sand retains this heat for weeks, even months. When the heat is needed again, the process happens in reverse. Cool air is pumped through, which is heated by the sand and then sent wherever it is needed for heating.
IMAGE CREDITS: Polar Night Energy
Of course, sand batteries aren’t a silver bullet. They can be used to heat homes, but only in places that have district heating systems. These centralised heating systems use one source to heat multiple buildings in an area. For now, they are uncommon outside of Scandinavian countries like Finland. Setting them up elsewhere will take time, investment and foresight.
Polar Night Energy’s sand batteries are surprisingly simple—and that’s what makes them brilliant! Sand is cheap, abundant, and a lot more environmentally friendly than other battery materials like lithium. They can be built relatively quickly as a result. Standing four meters wide and seven meters tall, their first battery in Kankaanpää was impressive. But their second one in Pornainen is even bigger – ten times bigger in fact. “Scalability” is an overused word, but if that’s not “scalability” then nothing is!
What the company is already doing is impressive. But what they could do further down the line could be game-changing. By 2026, they plan to develop a system that can convert the stored heat into electricity that can then be sent back to the grid when it is needed. Combine that with how cheap and easy they are to build and the energy storage problem seems a lot more solvable. Not bad for a big bucket of sand!