By Maurice Smith
Southern California Gas Co. (SoCalGas) has installed a novel bioreactor system that will be used to test power-to-gas technology at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) in Golden, Colorado. The project is the first of its kind in the United States converting hydrogen generated from excess renewable power into pipeline quality methane.
Power-to-gas technology is a cutting-edge method of storing excess renewable energy, according to Los Angeles-based SoCalGas, the largest natural gas distribution utility in the United States.
Last month, researchers at NREL’s Energy Systems Integration Facility (ESIF) in Golden, Colorado, installed a 25-foot tall bioreactor system, which will be used to produce renewable natural gas from excess renewable electricity using archaea microorganisms that consume hydrogen and carbon dioxide and emit methane.
“Power-to-gas technology can significantly increase the overall amount of renewable energy we use, by providing an economical method of storing excess solar-and wind-generated electricity,” Jeff Reed, director of business strategy and advanced technology at SoCalGas, said in a statement. “And this technology takes advantage of existing infrastructure, and can hold excess renewables for days, weeks or months to shift solar from day to night, address weather patterns and even seasonal patterns.”
“Archaea are uniquely capable of handling fluctuating levels of hydrogen produced by electrolyzers as wind and solar generation systems cycle up and down,” added Kevin Harrison, senior engineer for NREL. “That’s in part why we believe this technology could provide a superior large-scale, cost-effective solution for storing excess renewable energy using our nation’s natural gas distribution system.”
According to a 2017 Lawrence Berkley National Lab study, by 2025, between 3,300 and 7,800 gigawatt-hours of excess solar and wind energy will be curtailed in California. If all that excess solar and wind energy were converted to methane through the biomethanation process and stored as renewable natural gas, it would provide enough renewable energy to heat 158,000 to 370,000 homes or provide renewable electricity to 80,000 to 187,000 homes.
The pilot project will be used to help assess the commercial viability of this power-to-gas approach to energy storage and provide insights into potential megawatt-scale system designs. The team will combine these insights with renewable energy resource data to identify optimal locations in California and the western half of the U.S. where this grid-scale energy storage would be the most beneficial and cost-effective, said SoCalGas.
Power-to-gas technology uses renewable electricity when prices are low—including times when renewable supply exceeds demand and would otherwise be wasted—to power an electrolyzer, which splits water to produce hydrogen. The hydrogen is then combined with carbon dioxide and fed to a biomethanation reactor where it is converted into renewable natural gas, or RNG, by special micro-organisms.
RNG can be used in any application currently served by natural gas, from home appliances to industrial processes, heavy duty vehicle engines and power plants.
The research will also test how effectively the microbes convert hydrogen to methane and how efficiently the storable methane can be converted back to electricity. Tests will examine the potential of power-to-gas technology to store large quantities of renewable energy for up to an entire year and how it compares in performance and cost to battery storage. Initial reports are expected beginning in 2018. The study will continue for several years.