Enter heat batteries. A growing number of companies are working to deploy systems that can capture heat generated by clean electricity and store it for later in stacks of bricks. Many of these systems use simple designs and commercially available materials, and they could be built quickly, anywhere they’re needed. One demonstration in California started up earlier this year, and other test systems are following close behind. They’re still in early stages, but heat storage systems have the potential to help wean industries off fossil fuels.
The toaster of the future
One key to heat batteries’ potential success is their simplicity. “If you want to make it to giant scale, everybody ought to agree that it’s boring and reliable,” says John O’Donnell, CEO of California-based heat storage startup Rondo Energy.
The startup deployed its first commercial pilot in March at an ethanol plant in California. It’s basically a carefully designed stack of bricks.
In Rondo’s system, electricity travels through a heating element, where it’s transformed into heat. It’s the same mechanism that a toaster uses, O’Donnell says—just a lot bigger and hotter. The heat then radiates through the stack of bricks, warming them up to temperatures that can reach over 1,500 °C (2,700 °F).
The insulated steel container housing the bricks can keep them hot for hours or even days. When it’s time to use the trapped heat, fans blow air through the bricks. The air can reach temperatures of up to 1,000 °C (1,800 °F) as it travels through the gaps.
How the final heat then is used will depend on the commercial process, O’Donnell says, though many facilities will probably use it to turn water into high-pressure steam.
At Rondo’s pilot project at a biofuel plant in California, steam is used during the fermentation process that produces ethanol. Many other industrial processes use steam for controlling temperature in reactors or in other steps, like purification.
Heat batteries could also be specially designed for higher-temperature processes that don’t use steam today, like cement and steel production, which require temperatures over 1,000 °C.
Many industrial processes run 24 hours a day, so they’ll need constant heating. By carefully controlling the heat transfer, Rondo’s system can charge quickly, taking advantage of short periods when electricity is cheap because renewable sources are available. The startup’s heat batteries will probably require about four hours of charging to be able to provide heat constantly, day and night.
A “monstrous” amount of heat
One of the major challenges for heat storage technologies will be building enough systems to meet heavy industry’s huge energy demand. The sector uses a “monstrous” amount of heat, says Rebecca Dell, senior director of industry at ClimateWorks. Of all the energy used each year in industry, about three-quarters is in the form of heat, while only one-quarter today is electricity. Industrial heat makes up about 20% of total global energy demand.
Fossil fuels have been the obvious, most economical way to power these massive industrial processes, but the prices of wind and solar power have fallen by over 90% over the past several decades. Dell says that’s opened the door for electricity to play a bigger role across industry.
“We’re at this magnificent moment where we can stop burning stuff for our heat and have it be cheaper,” O’Donnell says.
There are a few other potential options for using cheap renewable energy in industry. Some facilities could be adjusted to use electricity directly, instead of high heat. Companies are working on electrochemical processes to make cement and steel, for example, though replacing all the infrastructure in existing plants could take decades. Using electricity to generate hydrogen, which can later be burned for electricity, is another potential route, though in many cases it’s still cost-prohibitive and inefficient.
Any effort to fulfill industry’s massive heat demand will require dramatic expansions in electricity generation. A standard cement plant uses about 250 megawatts of energy, mostly in the form of heat, all the time, Dell says. That’s about 250,000 residents’ worth of power, so electrifying a large industrial facility will mean adding electricity demand equivalent to that of a small city.
One brick at a time
Rondo isn’t alone in its quest to deploy heat batteries in industry. Antora Energy, based in California, is also building heat storage systems, using carbon. “It’s super simple—it’s literally just solid blocks,” says cofounder and COO Justin Briggs.
Instead of using a separate heating element (like Rondo’s “toaster coil”) to turn electricity into heat, Antora’s system will use carbon blocks as a resistive heater, so they’ll both generate and store heat. This could cut down on costs and complexity, Briggs explains. But the choice will also mean the system needs to be carefully enclosed, since graphite and other forms of carbon can degrade at high temperatures in the air.
Instead of just supplying heat to industry, Antora plans to offer an option to provide electricity as well. The startup’s approach relies on thermophotovoltaics—devices similar to the solar panels that capture energy from the sun. Antora’s equipment instead captures heat energy radiating from the hot blocks, turning it into electricity.
While heat-to-heat storage systems can exceed 90% efficiency, turning heat to electricity is much harder. Antora’s devices will be less than 50% efficient when used for electricity, in the same ballpark as many conventional gas turbines in use today.
Antora is currently building its first pilot system in Fresno, California. The system will be about the size of a shipping container and should be operational later this year.
Even using commercially available materials, it’ll take a while for heat storage to prove its role to manufacturers and make a meaningful dent in industrial emissions. But the technology could be one building block of a new, climate-friendly industrial sector. “We have all the tools we need to transform to a zero-carbon economy,” O’Donnell says. Now it’s time to build them.
