The sand battery points the way towards carbon-neutral heat production

From now on, KPA Unicon will offer sand-based, renewable energy thermal storages in connection with its deliveries. The sand battery, an innovation by the Finnish company Polar Night Energy Oy, can be used to replace fossil energy sources in district heat production.

“We have a long history in heat production and heat networks, so we and Polar Night Energy have a lot of synergy benefits. In addition, we have a strong desire to support Finnish innovation and move it forward. This sand battery is a natural fit for our deliveries,” says Ilkka Linnas from KPA Unicon.

The cooperation is based on license manufacturing: KPA Unicon manufactures sand batteries under the license of Polar Night Energy and offers the batteries to its customers along with energy production plants. KPA Unicon is also responsible for any maintenance of the batteries for its customers.

“Fluid bed technology has the same idea: to store heat in the sand – so it’s something we’re familiar with,” says Linnas.

In a sand-based thermal storage, electrical energy is stored as heat in the sand when the conditions to produce renewable energy are favorable. Sand as heat storage is an old invention, but Polar Night Energy’s method of combining existing and new technology makes the energy storage economically profitable. The reasons include, among other things, a rise in the price of fossil fuels and a significant increase in renewable forms of energy.

“The ongoing energy crisis has emphasized the fact that the world needs heat production that is not dependent on fossil fuels – also for industrial needs in warm countries,” says Polar Night Energy’s lead scientist Ville Kivioja.

District heating without burning

The novelty value of the sand battery is based on its ability to store energy: heat up to 600–1000 degrees can be stored in a small space. According to Linnas, thermal batteries are very typical in larger district heating networks, but until now, the heat has been stored in water either at atmospheric pressure or overpressure.

“The temperature in the water tank can be no more than 100 degrees, or else the water will boil. In addition, the amount of water needed is huge. When pressurized, the water temperature can be raised to a maximum of 150 degrees. There are also steam batteries, but they have a small capacity compared with the size.”

With the sand battery, steam can be made directly when the temperature is raised to 650 degrees. In addition, the battery can be heated with electricity, in which case the battery works as a backup heat plant. It can be used as a backup plant, for example, when there are rapid changes in the energy production load, or when the backup plant is needed to produce the peak and minimum outputs of heat production.

“The peaks and minimums are usually made with fossil fuels. The battery can reduce not only burning, but also the use of nonrenewable fuels,” says Linnas.

Even in industry, where hot temperatures or steam is needed, the sand battery can reduce energy production based on fossil fuels.