Tina Casey - CleanTechnica
The climate news of the day is pretty clear on the fact that policymakers need to stop tiptoeing around the energy transition and spring into action. In past years, the technology tools were lacking, but that’s not an excuse anymore. Wind and solar power are widely available, and new long duration energy storage technology is emerging to help renewables replace fossil fuel power plants without a hitch.
The Long Duration Energy Storage Difference
Lithium-ion battery arrays are currently the energy storage medium of choice for wind and solar power. These systems can smooth out daily gaps in wind or solar generation, but only for a few hours at a time. Generally they run for about four hours.
The technology is improvement and running times of 6-8 hours are becoming more common. However, more wind and solar power plants are hooking up to the grid practically by the day. The US Department of Energy is looking ahead to longer-lasting alternatives that can handle grid services when the grid is saturated with wind and solar.
To motivate innovators in the long duration energy storage field, back in 2018 the US Department of Energy launched a program under the somewhat forced acronym DAYS, for Duration Addition to electricitY Storage.
The program is administered by ARPA-E, the Energy Department’s funding office for high risk, high reward projects, the reward being long duration energy storage systems that last for at least 10 hours, on up to 100 hours or more.
“Whereas most new energy storage systems today deliver power over limited durations, for example to alleviate transmission congestion, stabilize voltage and frequency levels, or provide intra-day shifts of energy, the extended discharge times of DAYS projects will enable a new set of applications including long-lasting backup power and even greater integration of domestic, renewable energy resources,” ARPA-E explains.
The US actually does have a substantial stock of long duration energy storage capacity, in the form of pumped hydropower systems. Pumped hydro technology has been around for 100 years or so and there is nothing wrong with it, except that can require some consequential geoengineering and water systems infrastructure. The DAYS program is looking for alternative storage systems with much wider applications.
Many Paths To The Long Duration Energy Storage Goal
Some of the alternative storage systems coming down the pike deploy a gravity-powered principle similar to that of pumped hydro, substituting various kinds of weights for water. Others hit the long duration mark with flow batteries, which produce electricity from a chemical reaction between two reusable fluids.
New long duration energy storage systems that deploy thermophotovoltaic (TPV) cells are also beginning to emerge. In these “heat batteries,” a storage material is heated up, and TPV technology converts the heat to electricity when needed.
TPVs are not engineered to convert visible light waves to electricity like an ordinary solar cell. Instead, they are designed to convert the very long, low-energy infrared radiation emitted by heat.
One thermophotovoltaic technology innovator to come across the CleanTechnica radar is the California startup Antora Energy. The company originated in research at MIT and it has the backing of private sector investors as well as ARPA-E and the California Energy Commission.
ARPA-E tapped Antora for funding under the DAYS program in 2019, tasking it to develop “a thermophotovoltaic heat engine capable of efficiently and durably converting high-temperature heat into electricity.”
“[The new battery] will seek to double panel efficiency through new materials and smart system design, potentially enabling a cost effective grid storage solution,” they added, referring to improvements in TPV technology.
In the latest news from Antora, earlier this week the company scored a total of more than $4 million in new grants from the ARPA-E and the California Energy Commission, aimed at scaling up its long duration energy storage technology.
“With TPV, Antora is capable of decarbonizing the entire energy demand of large industrial facilities — both heat and power — opening the fastest, least expensive path for the industrial sector to reach net zero,” said the company’s co-founder and CEO Andrew Ponec in a press statement.
How — And Why — Does It Work?
If you’re wondering what advantage TPV has over conventional steam-producing thermal energy systems, that’s a good question. Advocates for TPV technology underscore the potential to beat steam-driven turbines on cost, efficiency, complexity, and scalability.
That sounds simple enough, but the devil is in the details. Antora notes that improving the efficiency of TPV technology has been a decades-long process.
The company began collaborating on TPV development with the Energy Department’s National Renewable Energy Laboratory in 2018, when its long duration energy storage technology was selected for the first cohort of a new energy technology accelerator called the Shell GameChanger Accelerator Powered by NREL.
In a 2021 recap of its work with Antora, NREL traced early stage TPV research all the way back to a 1990s-era project funded by the US Navy. The idea appears to have been back-burnered in the early 2000s, but TPV continued to attract interest from the R&D community for its ability to deliver both heat and power without any moving parts.
The heart of Antora’s heat battery is an array of insulated solid carbon blocks as a heat storage medium. “While most chemical battery technologies only have mid-duration storage, Antora’s can provide power for days,” the GameChanger Accelerator has reported, adding that “Antora estimates that this project has resulted in energy storage that costs less than 1/20th of other conventional battery technologies.”
That remains to be seen, but the wheels are in motion. Antora’s initial work with NREL resulted in a system with 35% conversion efficiency. More recently, they bumped it up to the important threshold of 40%, considered a key milestone for commercial application. In September, the company also announced that it hit the 1,800°C-and-up heat mark for industrial applications.
Coming up with a manufacturing-friendly system is another part of the heat battery challenge. Antora has that in hand as well. Last January, the company began producing TPV cells at its Sunnyvale, California headquarters, and in October the company announced plans to build a commercial scale battery factory in San Jose, California, to crank out a modular, transportable, soup-to-nuts system.
“Antora’s factory-made thermal batteries consist of not only a storage medium — carbon blocks — but also insulation, enclosures, charging and discharging equipment, and other components that comprise an integrated module,” the company explains.
“These thermal batteries will leave the facility ready to be road-shipped and installed at industrial sites across the country, providing a drop-in decarbonization solution that directly displaces on-site fossil fuel use,” they add.
Antora has a system up and running at an industrial facility in Fresno on a trial basis. CleanTechnica is reaching out to the company for details, so stay tuned for more on that.
