Power-to-gas, a technology that converts excess renewable energy to gases that can be stored, is cost-competitive with lithium-ion batteries in microgrids, according to Matt Gregori, technology development manager, Southern California Gas.

Gregori spoke at a solar conference last week at the University of California, Riverside.

Southern California Gas recently conducted a computer simulation of using power-to-gas in an existing microgrid at University of California Irvine (UCI), and concluded that the amount of renewable energy used could jump from 3.5 percent to 35 percent, Gregori said.

In addition, researchers at University of California in Irvine created a sophisticated financial model comparing power-to-gas to lithium-ion batteries.

“They found that power-to-gas, using a natural gas pipeline, is cost effective with lithium-ion batteries,” he said. It’s especially cost-competitive for longer charging durations, he noted.

The UCI microgrid has a central plant with combined-cycle turbines, chillers, thermal energy storage and some solar. “It’s an interesting test bed for new technology to support microgrid applications,” he said at the conference, “Solar Power: Past, Present and its Future in Inland Southern California.” He was one of three speakers on a panel about microgrids.

The UCI demonstration included a 60-kW proton on-site electrolyzer, and on-campus pipeline blending, he noted.

“Batteries are good at shifting from day to night, but if you store energy for a week or month, the round trip efficiency falls apart,” he said. “We think power-to-gas can be cost competitive, particularly for long-term storage,” he said. Gases created from power-to-gas can be stored in pipelines, he said.

“Power to gas is the opposite of gas-to-power. This is taking power and using it to create renewable natural gas,” he explained during a panel about microgrids.

Solar paves the way for power-to-gas

Power-to-gas makes sense especially in California, where 99 percent of planned renewable projects are solar.

“There’s all this solar power coming on the grid during the day; I’m sure you’ve seen the duck curve. We have a tremendous amount of excess renewable electricity. The concept is to take excess and convert it to gaseous fuel, hydrogen or methane. You can store it in above-ground tanks or in a pipeline system and use it later at a higher value,” Gregori said.

The seasonal nature of solar production, especially in California, creates an opportunity for power-to-gas, he noted. While there is lots of solar produced in the spring, when it’s sunny and cool, it isn’t always used because consumers and businesses haven’t turned on their air conditioners. In summer, however, the demand jumps with the hot temperatures and increased use of air conditioning.

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“Power to gas allows for long-term seasonal energy storage; instead of shifting from day to night, it can shift from March to August,” he said.

Southern California Gas’s pipeline system has about 13 tWh of equivalent electricity storage, he noted. Building battery storage facilities with the same amount of storage capacity would cost about $2.6 trillion.

‘That’s the cost of replacing a natural gas pipeline already available,” Gregori said.

Power-to-gas is currently not considered an eligible storage technology under the CPUC’s energy storage procurement mandate which requires state investor-owned utilities to procure 1.3 GW of storage by 2020, he noted.

How battery prices affect microgrids

Also at the conference, the microgrid panel participants identified the major challenges to moving the microgrid industry forward.

Chris Linn, project manager, Smarter Grid Solutions, said that the cost of batteries is a major challenge. “With decreasing battery costs, there will be more opportunities to create microgrids because there’s enough on a line segment or circuit to be self-sustaining.”

Eric Bakke, project development executive, EnSync Energy Systems, agreed that prices are the biggest challenge. “Once the price of energy storage gets down to $200/kWh, and energy generated by solar decreases to 8 cents/kWh at the residential level, pretty much everyone will have production, storage and resilience,” he said.

The complexity of the grid system is the biggest challenge, said Gregori. “As we see more distributed energy deployed, there are complicated energy markets. Looking at power-to-gas, we’re overwhelmed by who will buy grid services. I’d like to meet the people who are building algorithms and software to manage it; that will be critical,” he said.

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