Turning captured carbon into natural gas could provide cost-competitive energy storage

Solar and wind energy are highly variable, dependent on the day, weather and location of the facilities. At times, they can generate more electricity than is needed, but they can also fall short when demand is at its peak. Unfortunately, any extra energy created by these sources is often wasted, as there are few methods that adequately store it long-term. To improve energy security in the United States, the nation requires both sources of energy and novel ways to store and distribute it.

In a new study, published in Cell Reports Sustainability, researchers from Lawrence Livermore National Laboratory (LLNL) have explored how a reactive carbon dioxide capture and conversion (RCC) process could be used to produce synthetic renewable natural gas—a chemical form of long-duration energy storage.

“Rather than sourcing carbon from below-ground, RCC enables the use of above-ground carbon as a resource,” said LLNL scientist and lead author Alvina Aui. “Synthetic renewable natural gas, when used as an energy-storage option, can reduce grid instability caused by the intermittency of energy sources like wind and solar.”

The proposed RCC process integrates carbon capture and conversion into one platform using a dual-function material. In doing so, it eliminates the need for energy-intensive carbon dioxide purification, a conventional intermediate step.

“The dual-function material is special in that it contains both the chemical components you need to perform carbon dioxide capture and conversion,” said LLNL scientist Simon Pang, corresponding author and principal investigator of the project. “The carbon dioxide is captured in the material and then converted before it can be released. This is distinct from a separated, conventional process, where you would employ two different materials with single functions.”

In the second conversion stage of that process, the excess solar and wind energy comes into play. Electricity from those sources can be used to split water into hydrogen and oxygen. The captured carbon dioxide is reacted with the hydrogen to produce methane, a main component of synthetic natural gas. That methane can be stored, distributed and used in the same way and with the same existing infrastructure as conventional natural gas.

This publication evaluates the economic feasibility of the RCC process and provides important performance targets that a dual-function material would need to meet to be competitive. It also suggests ways to reduce cost and improve the efficiency of the process.

“We collaborated closely with our experimental team to gain a detailed understanding of the underlying chemistry and material behavior to enable the modeling,” said Aui. “Our integrated approach allowed us to produce a realistic and unbiased assessment of RCC’s potential and limitations.”

In many cases, the team found that the RCC process is less expensive than other utility-scale long-term energy storage solutions, and it would be portable and dispatchable, since the natural gas product can easily be transported by existing pipelines.

In a parallel effort, experimental teams at LLNL are working to develop the dual-function material, perform the proposed RCC process in the lab, and partner with industry to scale up the technology.