Europe’s rapid shift toward renewable energy has created an unexpected challenge: an oversupply of electricity that frequently drives market prices below zero. To address this, innovators are revisiting ancient thermal storage concepts using basic materials like sand and crushed bricks. These thermal batteries offer a cost-effective alternative to lithium-ion systems, providing long-duration storage that can heat homes and power industrial processes. By turning excess green energy into heat, these technologies aim to stabilize the grid and accelerate the continent’s energy transition while lowering costs for consumers and industry alike.
As Europe accelerates its transition away from fossil fuels, an old solution is making a high-tech comeback. Simple materials like sand, soapstone, and bricks are being reimagined as thermal batteries to solve the growing problem of renewable energy volatility. While the concept of storing heat in masonry dates back to the Roman Empire and traditional Turkish sand-brewed coffee, modern engineers are now applying these principles to manage the massive influx of wind and solar power currently flooding the European electrical grid.
The surge in renewable installations has led to a phenomenon where electricity production often exceeds demand. This surplus has caused the frequency of negative electricity prices to jump from 0.3% of all hours in 2022 to 3.6% in 2024. Without adequate storage, wind turbines and solar panels are frequently disconnected to prevent grid overloads. Thermal batteries offer a way to capture this excess energy by using electrical resistance to heat air, which is then pumped into insulated containers filled with sand or crushed stone, reaching temperatures as high as 600°C.
In Finland, the startup Polar Night Energy is leading the charge by utilizing soapstone debris to create large-scale sand batteries. Unlike lithium-ion batteries, which typically discharge their stored energy within a few hours, these thermal systems can retain heat for several days. This makes them ideal for district heating systems and industrial applications that require a constant supply of zero-emissions steam. While the efficiency of converting this heat back into electricity remains relatively low at around 30%—compared to 80% for lithium-ion—the primary value lies in its ability to provide cheap, long-duration thermal energy for heating.
Other projects are already demonstrating the commercial viability of this technology across the continent. In Portugal, a 100 MWh brick battery was recently installed at a Heineken brewery to provide round-the-clock steam for production. Meanwhile, Latvian firm Batsand is developing smaller sand-based systems for residential use. Industry experts, including representatives from the EU electricity lobby Eurelectric, suggest that these low-cost storage solutions will play a vital role in complementing the grid, offering the flexibility needed to handle the intermittent nature of green energy while reducing reliance on expensive and supply-constrained lithium resources.