How Thermal Batteries Store Renewable Power as Industrial Heat

A battery does not have to send electricity back to the grid to be useful. Rondo Energy’s heat battery stores electricity as heat in insulated bricks, then delivers that heat to industrial equipment, an approach aimed at factories that burn fuel to make steam.

The distinction matters as solar and wind expand: some facilities need heat more than they need another source of electricity. Thermal storage could connect surplus power to that demand, but it is not a universal replacement for lithium-ion batteries, gas boilers, or the grid.

What Rondo’s heat battery actually does

Rondo’s system uses electric heating elements to warm a stack of refractory bricks. The company says its Heat Battery can reach temperatures up to 1,500 degrees Celsius and retain heat inside an insulated enclosure. When the facility needs energy, the stored heat can be transferred to make steam or hot air for industrial processes.

Rondo and California ethanol producer Calgren have described a project at Calgren’s Pixley facility with 2 megawatts of charging power and 100 megawatt-hours of thermal storage. Those figures are from the companies, not an independent performance audit. They describe a heat-storage system, not a battery that can discharge 100 megawatt-hours of electricity.

That distinction is easy to lose in headlines. A thermal battery’s output is heat, and its usefulness depends on whether a nearby customer can use that heat at the right temperature and time. A grid-scale lithium-ion battery, by contrast, typically stores electricity and returns electricity to the grid.

Why factories are an interesting customer

Industrial heat is a large energy use that is difficult to electrify directly. The International Energy Agency has repeatedly identified industry as a major source of global energy demand and emissions. Boilers and furnaces supply heat for food processing, chemicals, refining, cement, and other operations, often by burning natural gas or other fuels.

A thermal battery offers a route to use electricity without requiring a factory to replace every heater with a new electric process. It can charge when electricity is available, store the energy as heat, and supply heat later. In principle, this lets a plant use renewable power when production schedules and weather do not line up neatly.

It also fits the physical shape of many industrial sites. A factory already has pipes, boilers, and steam users. If a heat battery can connect to that equipment at a useful temperature and pressure, the retrofit may be more practical than redesigning the entire production line. “May” is doing real work here: each site has different heat needs and operating constraints.

Fact: storing heat is not the same as storing electricity

The Department of Energy’s materials on next-generation batteries describe multiple storage technologies, with different materials, durations, and applications. Thermal storage belongs in that broader category, but its value should be measured against the job it performs. If a factory needs process heat, delivering heat directly can avoid converting stored energy back into electricity first.

That can make the system efficient for a heat customer, while still being a poor fit for a grid operator seeking electricity after sunset. Converting stored heat back into electricity is possible with some designs, but it adds equipment and conversion losses. Rondo’s industrial proposition is principally to deliver heat, not to act as a conventional power plant.

This is one reason comparisons with four-hour grid batteries can mislead. Those batteries are evaluated on electrical output, duration, and the services they provide to the grid. A heat battery competes with fuels and other heat sources at an industrial site. They may both charge from electricity, but they answer different questions.

Interpretation: the location matters as much as the storage medium

Thermal batteries make most sense where three things overlap: a dependable source of low-cost or low-carbon electricity, a customer with steady high-temperature heat demand, and enough space and grid capacity to install the equipment. Remove any one, and the economics can change sharply.

That makes the technology less like a standard appliance and more like a piece of industrial infrastructure. A project cannot simply be dropped anywhere electricity is cheap at noon. The grid connection must support charging, the heat system must match the factory’s processes, and the plant must be able to use the stored heat without disrupting production.

The storage duration is also not a free pass through a bad week. Rondo’s reported 100 megawatt-hours of thermal capacity, paired with 2 megawatts of charging power, implies a long charge window at full input. How that translates into useful hours depends on the facility’s heat draw and system design. Capacity alone does not tell a customer how much fuel it will displace annually.

This is a different bottleneck from the one facing solar projects that cannot connect or deliver power when needed. Our guide to energy storage and the grid explains why storage type, location, and duration have to match the grid problem. Here, the customer is a factory as much as the utility.

What has to be proven next

For a commercial buyer, the useful evidence is not simply that bricks can get hot. Operators need measured data on round-trip performance for heat delivery, uptime, maintenance, response to changing demand, and the amount of fuel displaced over a full operating year. They also need a clear installation cost and a realistic account of how the system interacts with existing boilers.

Project developers will have to show how heat batteries perform across different industrial processes, not just at one favorable site. Food production may need lower-temperature heat than cement or chemicals. A system that works well for steam at one plant may need a different configuration elsewhere.

Grid access remains part of the calculation. A heat battery can soak up power when it is abundant, but it still needs a connection capable of charging at the required rate. The broader challenge of getting new equipment onto constrained networks appears in projects discussed in our reporting on transformer bottlenecks.

Prediction: industrial heat is the stronger near-term case

The most plausible near-term growth for thermal batteries is at sites with large, predictable heat loads and access to electricity that is cheap or otherwise underused at some hours. In those cases, stored heat could reduce fuel use without asking the grid battery market to solve every industrial problem.

That is a narrower claim than saying heat batteries will transform the power system. Their prospects depend on project costs, operating records, local electricity prices, and whether factories can integrate them without risking production. The Calgren installation is a meaningful demonstration, but one project does not establish performance across industries.

Thermal batteries are best understood as a way to move renewable electricity across time and into a different form of energy. Their success will be measured less by how dramatic a storage headline sounds than by whether a factory can make the same product with less fuel, reliably, year after year.