Heat-retaining bricks could hold the key to bringing renewable energy to heavy industries that require a lot of heat to produce everything from steel to baby food. So far, these industries have largely obtained heat by burning fossil fuels such as natural gas, which accounts for about a quarter of global emissions. While alternative energy sources such as wind and solar energy produce fewer greenhouse gases, they have so far not been able to consistently generate the required amounts of heat.
A growing number of companies are working to develop systems that can capture the heat generated by clean electricity and store it in brick stacks for later use. The heat batteries, based on simple structures and commercially available materials, could be erected quickly anywhere. Though most systems are still in the early stages, thermal storage systems have the potential to free industry from fossil fuels.
A key to the potential success of thermal batteries is their simplicity. They need to be boring and reliable on a large scale. For example, the pilot project at the California-based thermal storage start-up Rondo Energy is essentially a carefully designed stack of bricks. In the Rondo system, the current flows through a heating element and is converted into heat to radiate through the stack of bricks, heating them to temperatures in excess of 1,500 degrees. The insulated steel container that houses the bricks can keep them hot for hours or even days.
Many industrial processes run 24 hours a day and require constant heating. Careful control of heat transfer allows Rondo’s system to be rapidly charged to take advantage of short periods when electricity is cheap due to the availability of renewable energy sources. The start-up’s heat batteries will likely need to be charged for around four hours to provide constant heat day and night.
One of the biggest challenges for thermal storage technologies is building enough systems to meet the enormous energy demands of heavy industry. The sector consumes a monstrous amount of heat. Of the total energy consumed annually in industry, about three quarters is consumed as heat, while electricity accounts for only one quarter.
Fossil fuels have been the most obvious and economical way to power these massive industrial processes, but wind and solar energy prices have fallen by over 90 percent in the last few decades. This has allowed electricity to play a bigger role in the industry. Using cheap renewable energy in industry is possible in a few ways. Some plants could be switched to use electricity directly instead of high heat. Companies are working on electrochemical processes to make cement and steel. Using electricity to produce hydrogen, which can later be burned to produce electricity, is another possible route, but in many cases, it is still too expensive and inefficient.
Brick by brick, Rondo is not alone in its quest to bring thermal batteries to industry. The Californian company Antora Energy also builds heat storage systems based on carbon. “It’s super simple – it’s literally just solid blocks,” says co-founder and COO Justin Briggs. Rather than using a separate heating element like Rondo’s “toaster coil” to convert electricity into heat, Antora’s system uses carbon blocks as resistance heaters that can both generate and store heat. This could reduce costs and complexity, though the system must be carefully contained as carbon can decompose at high temperatures in air.
In addition, Antora plans to offer an option to generate electricity. The start-up’s approach relies on thermophotovoltaics, devices that resemble solar panels and capture the sun’s energy. Instead, Antora’s devices capture the thermal energy radiated by the hot blocks and convert it into electricity.
