Clean Energy 101: Thermal Batteries

The why, what, and how of this technology that's helping eliminate fossil fuel combustion in industrial heating.

Thermal batteries are hot. The technology, which promises to provide a cheaper, cleaner alternative for some of the roughly 20 percent of global energy consumption — usually derived from fossil fuels — that goes into industrial heating, is causing a lot of excitement, ranking as the reader’s choice for 2024 breakthrough technologies in MIT Technology Review.

Heat has long been a challenge in slashing carbon pollution from industrial processes. On-demand heat — including at temperatures of greater than 1,000°C, hot enough to melt glass — is necessary for a wide range of industrial applications, including food and beverage production, pulp and paper manufacturing, glassmaking, steelmaking, and most chemical manufacturing. By converting low-cost, low-value hours of electricity production into energy stored for long durations as high temperature heat, thermal batteries can deliver industrial heat and power cost-effectively and on demand, day or night, solving this crucial problem.

Thermal batteries aren’t just an industrial solution, they can also serve as backup energy for the grid, especially at times when other renewables production is low.

So how do they work? The steps below outline the process:

  1. Charging: Electricity, typically from renewable sources like wind or solar power when they are in oversupply and without impacting coincident peak loads, is drawn into the thermal battery system.
  2. Conversion: The electricity is converted into thermal energy, typically through resistive heating, where electricity is passed through a material with high electrical resistance, generating heat — just like a toaster.
  3. Storage: The heat is then stored in a high-heat capacity medium such as “hot rocks” like graphite, crushed rock, and bricks, or thermochemical media.
  4. Insulation: The heated material is held in an insulated environment to maintain temperature for very extended periods — from tens of hours to multiple days.
  5. Delivery: When needed, the stored heat is released, delivering on-demand energy to industrial processes or heating systems.

Thermal battery types
Thermal Technologies Sub-technology categories Most likely/current end use Example companies
Latent, phase change thermal battery Miscibility gap alloy technology Industrial heat MGA Thermal (Australia)
Latent, phase change thermal battery Ice-based technology Space cooling CALMAC, Baltimore Aircoil Company, EVAPCO
Latent, phase change thermal battery Cryogenic energy storage Power generation Highview Power
Sensible, non-phase change thermal battery Modular heat storage in hot rocks or concrete Industrial heat and power Rondo, Antora, Electrified Thermal Solutions, Kraftblock, Brenmiller, Storworks, EnergyNest
Sensible, non-phase change thermal battery Molten-salt technology Industrial heat and power Terrapower, Kyoto (Norway)
Sensible, non-phase change thermal battery Heat storage in tanks or rock caverns District heating, peak shaving Helen Oy (Finland)
Sensible, non-phase change thermal battery Hot silicon technology Industrial heat and power 1414 Degrees, Magaldi
Sensible, non-phase change thermal battery Graphite-based technology Industrial heat and power, district heating Kelvin
Sensible, non-phase change thermal battery Hot silicon technology Industrial heat and district heating Polar Night (Finland)
Sensible, non-phase change thermal battery Aluminum/rock composite, solid state technology Industrial heat Caldera (UK)
Thermo-chemical battery Adsorption (or Sorption) solar heating and storage Industrial heat, seasonal thermal energy storage ZeoTech, Bosch/ZAE Bayern (Germany)
Thermo-chemical battery Salt hydrate technology Seasonal thermal energy storage SaltX, TNO (Netherlands)
Thermo-chemical battery Molecular bonds Hydrogen production, long duration energy storage N/A (R&D phase)
Thermo-chemical battery Molecular solar thermal system (MOST) Combined heat and power N/A (R&D phase)
Holding heat and potential

Unlike the chemicals and raw materials needed to store electricity in more traditional batteries, such as lithium-ion batteries used in EVs, the materials needed to store heat are abundant and cheap. Some popular options, like salt, graphite, and clay bricks are in wide circulation and have mature supply chains, while others, like pure carbon, are byproducts of legacy industries like petcoke in need of use.

However, the system of pipes, insulation, and pumps that move the heat often add up to the majority of the costs of these systems. Although producing steam for lower heat industrial uses (<300°C) is relatively easy, moving heat at the highest temperatures required for some industries is more challenging. Companies are working on novel solutions to integrate these systems into industrial processes. Furthermore, replacing incumbent heating systems with electrified alternatives requires integrating thermal batteries into existing industrial processes, which can pose additional implementation challenges for some applications. Incorporating thermal batteries therefore requires consideration of both the thermal transfer infrastructure costs and careful integration planning to ensure compatibility with existing industrial processes and systems.

Thermal batteries also offer another significant advantage: they can reduce reliance on more complex, expensive, and higher-risk industrial decarbonization solutions. This is particularly relevant when compared with hydrogen, which presents major challenges in both storage and transport due to its small molecular size. Hydrogen may also not ensure actual emissions reductions given the prevalence of “grey” hydrogen and its own greenhouse gas properties, and the significant nitrogen oxide emissions from hydrogen combustion.

Thermal batteries as grid assets

Thermal batteries can also deliver significant benefits to the electricity grid. Thermal batteries can store excess electricity generated during periods of high renewable output, reducing curtailment and providing on-demand energy when renewables are not available. This stored heat can then be used to power industrial processes and heating systems, or can even be converted back into electricity using steam turbines or other thermal-to-electric conversion methods.

Because of their flexibility and long duration energy storage capabilities, thermal batteries can charge when electricity is cheapest (typically during windy or sunny times when wind and solar generation exceeds demand), soaking up energy that would otherwise be wasted and storing it for later use. This not only helps to reduce grid congestion and improve grid reliability, but it can also reduce the cost of deploying more low-cost renewable generation for all grid-connected consumers. Thermal batteries can also operate independently of the grid system and charge with renewable energy, which improves overall system resilience and may be attractive to those in markets with unreliable infrastructure.

What comes next?

With solid science, proven technology, and promising economics, it’s now time for thermal batteries to prove themselves in the real world.

The most effective proof of concept is in the industrial setting, and this is where work is already underway to pilot this technology. For example, Since 2023, the fuels company Calgren has used a thermal battery from Rondo Energy at its production plant in California.

These applications come as the startup world is racing to mature this technology. A host of companies are competing in the space (some of which are being supported by RMI’s Third Derivative startup accelerator program) and the investor money is flowing.

There are many other innovative companies developing thermal battery solutions including Antora Energy, which has already demonstrated its technology through a successful implementation in Fresno and has scaled up its commercial manufacturing in the United States. Earlier this year, five US thermal battery companies — Antora, Electrified Thermal Solutions, Fourth Power, RedoxBlox, and Rondo — launched the Thermal Battery Alliance, a first-of-its-kind industry association.

Though climate technologies overall have seen a decrease in investment year over year from highs in 2021–2022, investment in industrial decarbonization has increased over that time, peaking in 2023 at $5 billion across the sector and remaining consistent in 2024. Thermal batteries have been a key recipient of this increased interest, seeing new investment spike to over $350 million in 2024.

Challenges and opportunites

Right now, the highest hurdle for widespread adoption is more practical than theoretical: access to low-cost electricity. Under current market regulations, thermal batteries cannot always access location- and time-specific electricity pricing already available to electric batteries in wholesale electricity markets, which would allow them to compete against gas-fired heating in many regions.

But this gap is set to narrow significantly. Renewable electricity prices continue to fall on a predictable downward trajectory, while natural gas remains subject to volatile price swings due to fuel costs and market dynamics. Setting a more level playing field and giving thermal batteries access to wholesale electricity rates would accelerate this convergence.

The technology itself offers inherent advantages for rapid cost reduction. Thermal batteries are modular systems that can be manufactured on assembly lines rather than being fully constructed on site. This industrialized production approach typically leads to steep learning curves and accelerated cost declines — similar to what we’ve seen with solar panels and batteries. By deploying on-site low-cost renewables and/or soaking up excess production on the grid, thermal batteries can operate as swing producers, driving down electricity costs and improving the efficiency of the overall grid.

The second major challenge involves integrating new sources of heat production into complex high-temperature heat industrial facilities. This integration presents two distinct opportunities: retrofitting existing facilities as older heating systems reach end-of-life, and incorporating clean heating solutions into new industrial facilities, particularly in rapidly industrializing regions like China, India, and the Global South. When retrofitting or building new facilities, significant up-front investments with long-term payouts are required. Drawing in a day’s worth of power for heating loads over the course of a couple of hours requires major power infrastructure connecting these industrial facilities to local or regional clean power facilities.

Industrial heat has long been a major source of harmful emissions. But, like their rare mineral-based cousins, the potential for thermal batteries to create a reliable, less polluting alternative to the status quo is real and could lead to cascading effects as other industries benefit from their advantages. This new technology holds promise to continue manufacturing the food, materials and chemicals we rely on, with a fraction of the climate impact — now is the time to implement it.