The Department of Energy’s National Renewable Energy Laboratory (NREL) is working on a “Power to Gas” (P2G) experiment to make a renewable form of natural gas, using solar/wind energy, water, carbon dioxide (CO2), and tiny microbes called archaea.
In the 1970s, Swiss engineers isolated this microorganism living in the 150°F hot springs in Iceland. Laurens Mets, a molecular biologist at the University of Chicago, began studying archaea and its ability to produce heat and methane. Mets had been researching storing renewable energy as hydrogen, but had doubts whether this flammable atom could be stored safely and cost-effectively. His testing led to finding one strain of archaea as being extremely efficient in producing methane. Mets patented the selected strain and started a company called Electrochaea in 2010. Because of the boom in natural gas production due to hydraulic fracturing, U.S. gas prices dropped, so there was little interest in this new method of producing methane at the time.
However, European countries were interested in this form of biotechnology. Energinet, the Danish state-owned operator of electricity and natural gas systems, had excess wind power, and financed an experiment with Electrochaea at a Danish university. It was successful, and led to the construction of a 10-megawatt pilot plant in Hungary, the first commercial-sized utility plant to produce renewable natural gas in this manner.
Europe’s consideration of carbon taxes to help reduce greenhouse gas emission led the German carmaker Audi AG to invest in Electrochaea. The tax break for lowering carbon emissions helped sell the Audi A3 Sportback, a car that can run on gasoline or natural gas with minor adjustments.
As one of the largest natural gas distributors in the US with over 21 million customers in a state that encourages low-carbon fuels and where there is more available solar and wind power than can be sold, Southern California Gas Co. (SoCalGas) heard of Electrochaea’s work and was intrigued. They reached out to the Department of Energy’s NREL to work on a pilot project here in the U.S.
For the project, NREL designed, built and operate a 250-kilowatt electrolyzer system that uses solar and wind power to split water into hydrogen and oxygen. The hydrogen and carbon dioxide are move into NREL’s 25-foot tall pilot bioreactor under pressure, where it is fed to the archaea to produce methane. Methane, the primary ingredient of natural gas, can be stored in the already existing natural gas pipeline systems for later conversion into electricity as needed.
"This is a viable, albeit two-step, approach for energy storage for renewables," said Kevin Harrison, NREL's principal investigator on the project. He and Nancy Dowe, a fermentation microbiologist at NREL, spent time with Electrochaea researchers in Copgenhagen and Munich prior to the project.
"It's a really interesting project for me," Dowe said. "I really like the biology element because the biocatalysts are completely renewable. You can keep these cultures going as long as you're supplying them CO2, hydrogen, and whatever nutrients they need. It's a self-replicating catalyst, and it's exciting to use biology as an energy storage solution."