Brick Thermal Batteries vs. Sand Batteries: How They Differ
Brick thermal batteries vs. sand batteries: both store energy mainly as heat in a solid material, rather than as chemical energy in a lithium-ion cell. But they differ in the storage material, engineering and typical customer. Refractory-brick systems are often designed for high-temperature industrial process heat; Finnish “sand batteries” have prominent examples providing district heating.
This is a practical comparison, not a claim that one material is universally superior. For a different approach—phase-change materials built into walls—see our thermal battery bricks explainer. This comparison instead focuses on industrial refractory-brick storage and granular-solid sand batteries.
How Both Systems Store Energy
When electricity is available at a favourable price or from renewable generation, electric heaters convert it into heat. That heat raises the temperature of a large insulated mass of solid material. Later, flowing air or another heat-transfer medium picks up the stored heat and carries it to a district network or factory.
Because the stored output is heat, these technologies suit customers that need hot water, hot air or steam. Turning the stored heat back into electricity is possible in principle, but adds equipment and energy-conversion losses. Do not treat a megawatt-hour of thermal capacity as identical to a megawatt-hour of electricity delivered to a socket.
Comparison Table: Brick vs. Sand Storage
| Question | Refractory-brick battery | Sand or granular-solid battery |
|---|---|---|
| Typical medium | Specially selected high-temperature ceramic bricks | Sand, crushed stone or other granular solids |
| Common purpose | Industrial steam and process heat | District heating, hot-water and industrial heat projects |
| Materials engineering | Brick arrangement and high-temperature heat transfer | Granular bed geometry and air/heat movement |
| Output | Often superheated air or process steam | Often district-heating water; also other heat outputs |
| Commercial examples | Rondo Energy installations | Polar Night Energy installations in Finland |
The materials do not dictate a single universal temperature or efficiency. These are properties of specific designs, insulation, charging equipment and end-use conditions.
A Real Brick Battery: Rondo’s Industrial Heat
Rondo Energy uses refractory bricks and electric heating elements for energy storage. Its October 2025 announcement described a 100 MWh heat battery supplying industrial steam in California. In an October 21, 2026 announcement, Rondo and Rio Tinto reported front-end engineering work for a proposed 360 MWh / 30 MW thermal-storage project at an alumina refinery in Australia.
The Australian proposal is not the same as a commissioned facility. Project stages matter when comparing maturity and scale. Rondo says its batteries can feed existing steam networks, allowing factories to use lower-cost electricity at certain hours and receive process heat when needed.
A Real Sand Battery: Polar Night Energy’s District Heating
Polar Night Energy commissioned a 100 MWh thermal battery in Pornainen, Finland, in June 2025. The operator describes 1 MW of thermal output for a district heating network, with energy stored in crushed soapstone—even though the technology family is popularly called a “sand battery.” This detail illustrates why the label refers to a granular-solid storage approach rather than sand alone.
In June 2026, Polar Night Energy reported a 70% reduction in network emissions after a year of operation. That is a site-specific company-reported outcome, not proof that every sand battery will deliver the same carbon savings.
Which Type Is Better?
The deciding factors are less glamorous than the name of the storage medium:
- Required temperature: a refinery’s steam requirements differ from a town’s heating network.
- Daily load shape: the storage must bridge the specific hours when useful electricity is scarce or expensive.
- Space and infrastructure: tanks, insulation, piping, pumps and controls impose constraints.
- Local electricity and heat prices: financial outcomes depend on both the charging tariff and the displaced fuel.
- Verified performance: examine actual delivered heat, losses, availability and maintenance, not just advertised storage capacity.
Capacity vs. Power: The Most Common Confusion
A system rated 100 MWh thermal / 1 MW thermal could, in a simplified idealized calculation, supply its rated heat output for 100 hours. In practice, heat-transfer constraints, reserve margins, changing load and losses affect the usable duration. A larger MWh number means more stored heat, while a larger MW number indicates faster potential output.
FAQ
Are brick and sand batteries replacements for lithium batteries?
Not necessarily. Thermal storage is well suited to heat demand; lithium-ion batteries deliver electricity. Some applications could use either as part of a larger energy system, but the useful outputs differ.
Is a sand battery literally filled with beach sand?
Some systems use sand or crushed rock; the Pornainen installation uses crushed soapstone. Check the actual project rather than the category name.
Can these systems power houses overnight?
They can supply heat to district networks or local systems. Producing household electricity is a separate engineering question, and heat-to-power conversion introduces losses.
Sources: Rondo/Rio Tinto announcement, October 21, 2026; Polar Night Energy’s Pornainen project; thisisFINLAND’s technology overview. Related: thermal battery bricks explained.
