A proposed utility program in Minnesota that would let customers choose to pay a premium for renewable natural gas (RNG) has stirred up debate among renewable energy and climate change advocates seeking to phase out all fossil fuels.

Since CenterPoint Energy's Minnesota utility proposed a voluntary RNG offering on a "green tariff" pilot program to test consumer and small business interest, state officials and clean energy advocates have pushed back, arguing there are better ways to cut carbon emissions.

CenterPoint's gas utility contends it is one of the first natural gas providers to propose offering RNG to customers. If the program is approved by the Minnesota Public Utilities Commission (PUC), the utility plans to begin offering it this spring.

However, the state Department of Commerce has raised a lot of questions about the proposal, and the Attorney General's Office is recommending that the PUC reject the idea. Clean energy groups, such as the Minnesota Center for Environmental Advocacy, and the Sierra Club are opposing the proposal, while the city of Minneapolis has endorsed the idea without committing to buy any RNG.

Under the pilot program, up to 8,000 residential and small business customers would be eligible to  voluntarily agree to pay a fixed monthly premium for the RNG, which could come from landfill supplies, farm/dairy manure-to-digester operations, and wastewater treatment plants. Suppliers would capture methane that otherwise would be vented into the atmosphere.

"The proposed pilot is designed to operate similarly to electric green tariffs, through which customers may choose to spend more to buy renewable energy," said CenterPoint spokesperson Alejandra Diaz. "Residential and commercial customers will be able to voluntarily enroll in the RNG program, and those who do will pay only the amount they individually designate."

In August, the utility petitioned the PUC for permission to provide the RNG program, and the public comment process on the petition is still ongoing. The regulatory commission will consider the petition at a public hearing later this year, Diaz said.

"If the program is approved, CenterPoint will file annual status reports with the PUC describing program operations," she said. "In the last year of the pilot, [we] plan to file a program evaluation report with the commission. At that time, CenterPoint may request to continue the program, terminate it, or make changes to the program."

A sign of the growing sentiment against fossil fuels in the state emerged last year when a gas-fired generation plant was turned down by state officials. It is still in the regulatory process at the PUC and would not be built until 2021.

A PUC administrative law judge has already concluded that Minnesota Power Co. failed to demonstrate a need for the 525-625 MW, $700 million plant in Superior, MN, which it is pursuing in partnership with the Dairyland Power Cooperative.

Meanwhile, Sempra Energy's Southern California Gas Co. (SoCalGas) has increased supplies of RNG by connecting its system to a group of biogas producing dairies in central California. Biogas producer Calgren Dairy Fuels LLC sent supplies from its digester in Pixley, marking the second interconnection with a major RNG source by the utility and the first interconnection with manure-based dairy-produced supplies.

"It's a smart and cost-effective solution to reducing greenhouse gas [GHG] emissions," said SoCalGas Vice President Sharon Tomkins, who handles customer solutions and strategy.

Calgren collects biogas from anaerobic digesters at 12 dairies in Tulare County to produce the RNG at the largest cluster system in the state. California has 24 dairy methane capture projects operating or in development, and SoCalGas estimates there could be up to 120 projects in the next five years.

SoCalGas has said it would be capable of adding up to 2.26 Bcf a year of RNG from the Calgren facility. The company plans to file a request with the California Public Utilities Commission to offer customers the choice of using RNG.

Last year Navigant Consulting Inc. completed a study that recommended California policymakers consider RNG to reduce GHG emissions. Studies last year and in 2017 also concluded California was a prime target for more RNG use.

According to SoCalGas, RNG's use can help meet a mandate in state Senate Bill 1383, to reduce so-called "short-lived" climate pollutants, 80% of which are from waste streams, dairies and agriculture. Last year, SoCalGas committed to providing RNG at all 25 of its natural gas vehicle fueling stations.