Mineral energy storage
Store excess renewable energy for later use with our hot mineral thermal storage systems.
Grensle technology
How it works
Seasonal usage
Grensle technology enables seasonal storage at a competetive cost level. The Grensle storage is the first of it´s kind that can be scalable big enough to make it profitable when used as a seasonal storage. The storage cost is just 1% compared to todays cheapest electric battery technology. It´s reliable with very low O&M cost, made for more than 50 years of operation.
When built large-scale, the heat is stored efficiently for long periods, with a minimum of energy loss. The storage owners charge storages at surplus occasions with cheap energy and discharge most of the energy during cold winter months when there is a big heating demand AND the energy price is high. Grensle technology can make owners of storages, district heating grids, wind- and solar plants earn money again.
Reduces emission
Grensle technology can store 100% of the annual energy used in European district heating grids, which is 550TWh, 4–5 times more than all Swedish electricity consumption.
The storages can abolish enormous carbon dioxide emissions from boiler combustion. There are 20,000 district heating grids in Europe. Most of them are heated by combustion of solid fuels.
Grensle’s technology make operators of heating stations in the district heating grids independent from imported solid fuels like coal, gas, waste or biomass. No more smoke and CO2 emissions from combustion in European district heating grids.
Stabilizing the grid
We saw the challenge: hydro, wind and solar produce more power than the grid can handle at certain times, but still not enough during peak demand.
Most wind plants have to shut down at perfect production conditions, wasting up to 20% of it’s annual production capacity. Similar situations also occur for solar plants, hydro, CHP and even nuclear power plants. Shut downs can be caused by national power grid limitations. And it is very common that the consumption pattern does not match current production.
When production capacity exceeds current consumption, the electricity price drops so low that it becomes negative. In parts of Sweden, there were over 500 hours with negative electricity prices in the first half of 2025. This means that 12% of the time there were negative electricity prices. It makes no sense running a power plant at those hours – unless you could charge a large-scale energy storage.
FAQ
How does hot rock thermal energy storage work?
Our system uses electricity from renewable sources to heat a large mass of rock. The heat is then stored within the rock and can be extracted later to generate electricity or provide heat. This is achieved using a heat exchanger system that circulates air through the hot rock, transferring the heat energy to where it is needed. This process allows us to store energy efficiently and release it when required, bridging the gap between renewable energy production and consumer demand.
What are the benefits of thermal energy storage?
Thermal energy storage offers several key benefits, including improved grid stability, increased utilisation of renewable energy sources, and reduced reliance on fossil fuels. By storing excess energy produced during peak renewable generation times, we can provide a consistent and reliable supply of clean energy even when the sun is not shining or the wind is not blowing. This makes renewable energy more dependable and cost effective.
What types of renewable energy can be stored?
Our hot rock thermal energy storage system is compatible with a wide range of renewable energy sources, including solar, wind, and hydroelectric power. Any excess electricity generated from these sources can be efficiently stored in our system, providing a versatile solution for integrating various renewable energy technologies into the grid. This flexibility makes our technology an ideal choice for diverse energy landscapes.
How long can energy be stored in the system?
Our hot rock thermal energy storage system is designed for long duration energy storage, capable of retaining heat for days, weeks or even months. This capability is essential for seasonal energy storage, such as saving solar energy from summer for use in winter. The longevity of energy storage depends on several factors, but our systems are optimised to minimise heat loss and ensure maximum energy retention over extended periods.