Firebricks — heat-resistant bricks designed to withstand and store high temperatures without getting damaged — were developed during the early Bronze Age. They were used to line primitive kilns dug into the ground. Now, researchers believe they could play a role in our energy transition.

Heat batteries

These bricks are composed of specific materials such as alumina, silica, and magnesia, which give them high densities, and melting points. This makes them ideal for storing heat generated from excess renewable electricity.

The cost advantage of firebricks is significant, though it’s not obvious at first glance. They’re really expensive compared to regular bricks. However, these bricks really are excellent at storing heat — and they are certainly cheaper than batteries.

“The difference between firebrick storage and battery storage is that the firebricks store heat rather than electricity and are one-tenth the cost of batteries,” said lead study author Mark Z. Jacobson, a professor of civil and environmental engineering in the Stanford Doerr School of Sustainability and School of Engineering. “The materials are much simpler too. They are basically just the components of dirt.”

Many industrial processes use high heat. Jacobson and colleagues calculated what would happen if this type of brick were used for heat storage in industrial processes, in a scenario where there is 100% renewable energy usage.

The cost per kilowatt-hour-thermal (kWh-th) for a firebrick storage system is less than one-tenth the cost of a battery storage system per kilowatt-hour-electricity (kWh-e). This cost efficiency makes firebricks a promising tool in the effort to transition to 100% renewable energy.

Industrial fire bricks

Industrial processes that require high-temperature heat are responsible for approximately 17% of global carbon dioxide emissions. These processes include the production of cement, steel, glass, and chemicals.

Traditional methods of providing process heat involve burning fossil fuels, which are both carbon-intensive and costly. By contrast, using renewable electricity to generate heat and storing it in firebricks presents a sustainable and economical alternative, the researchers calculated.

Essentially, firebricks could serve as “batteries” for this heat. This stored heat can then be used on demand for various industrial processes. The firebricks are arranged in patterns that allow air to flow through them, either emitting infrared radiation directly or heating air that is then used in industrial applications.

“By storing energy in the form closest to its end use, you reduce inefficiencies in energy conversion,” said co-author Daniel Sambor, a postdoctoral scholar in civil and environmental engineering. “It’s often said in our field that ‘if you want hot showers, store hot water, and if you want cold drinks, store ice’; so this study can be summarized as ‘if you need heat for industry, store it in firebricks.’”

Why this is such a good idea

The primary advantage of firebricks over traditional battery storage is cost. While batteries are effective for short-term energy storage, they are significantly more expensive per unit of energy stored compared to firebricks. Additionally, batteries have lower capacity factors, meaning they are not utilized as efficiently as firebricks for long-term storage.

Firebricks also offer greater flexibility. They can store heat for extended periods, making them ideal for industries that require a continuous heat supply. This flexibility helps to smooth out the variability of renewable energy sources like wind and solar, which may fluctuate based on weather conditions.

However, there are several caveats. Firstly, there’s the uncertainty in the daily heat loss rate of firebricks. Current estimates suggest a loss rate of about 1% per day, but further research is needed to optimize insulation and minimize losses. Then, the study assumed that virtually all the energy in the world is renewable — which is not the case yet.

“Ours is the first study to examine a large-scale transition of renewable energy with firebricks as part of the solution,” Jacobson said. “We found that firebricks enable a faster and lower-cost transition to renewables, and that helps everyone in terms of health, climate, jobs, and energy security.”

The study was published in PNAS Nexus.