Bronze Age firebricks may present an inexpensive solution to energy storage for modern industrial processes.

Scientists and early man have something in common when it comes to energy storage: the heat-absorbing bricks used to line primitive kilns and iron-making furnaces thousands of years ago may help store intermittent power from renewables to switch over to green energy sooner – and for a trillion dollars less – according to recent Stanford-led research published in PNAS Nexus.

"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 author Mark 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."

The modern version of this technology used by early man involves assembling heat-absorbing bricks in an insulated container, where they can store heat generated by solar or wind power at industrial process-equivalent temperatures in the modern day.

The heat can then be released when needed by passing air through channels in the stacks of firebricks, thus allowing energy-heavy factories for cement, glass, paper and steel to run steadily on renewable energy.

These systems, which several companies are already commercializing, are a form of thermal energy storage.

High heat storage

Many manufacturers use high-temperature heat in their industrial processes. Today, about 17% of all carbon dioxide emissions worldwide stem from burning fossil fuels to produce this heat, according to Jacobson and co-author Daniel Sambor's calculations.

Temperatures can reach at least 1,300 degrees Celsius (nearly 2,400 degrees Fahrenheit) to produce cement and 1,000 C (about 1,800 F) or hotter for glass, iron, and steelmaking. Generating industrial heat from renewable sources could all but eliminate these emissions.

"By storing energy in the form closest to its end use, you reduce inefficiencies in energy conversion," said 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.'"

Two scenarios

The researchers set out to examine the hypothetical impact of using firebricks to store most industrial process heat across the 149 countries responsible for 99.75% of global carbon dioxide emissions from fossil fuels. (In this hypothesis, each country has transitioned to renewables for all energy purposes.)

"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 team used computer models to compare various impacts, costs and emissions involved in two scenarios.

In the first scenario, the firebricks provide 90% of industrial process heat. In the other, there's zero adoption of firebricks or other forms of thermal energy storage for industrial processes.

In the no-firebrick scenario, the researchers assumed heat for industrial processes would come from electric furnaces, heaters, boilers, and heat pumps, with batteries used to store electricity for those technologies.

Their study found that firebricks could cut capital costs by $1.27 trillion across the hypothetical 149 countries while reducing the demand for energy from the grid and the need for energy storage capacity from batteries.

Jacobson's focus on firebricks is relatively new, in a career spent studying air pollution and climate problems and developing energy solutions for cities, states and countries. This line of exploration was inspired by a desire to identify fast, effective solutions to those problems.

"Imagine if we propose an expensive and difficult method of transitioning to renewable electricity – we'd have very few takers. But, if this will save money compared with a previous method, it will be implemented more rapidly," he said. "What excites me is that the impact is very large, whereas a lot of technologies that I've looked at, they have marginal impacts. Here I can see a substantial benefit at low cost from multiple angles, from helping to reduce air pollution mortality to making it easier to transition the world to clean renewables."