While alternative fuel transportation advocates have rallied around renewable natural gas (RNG) and near-zero emission natural gas vehicles (NGV) in the heavy-duty fleet sector, “cleaner” versions of diesel, propane and hydrogen are bidding to compete in the sector.
The Advanced Clean Transportation (ACT) Expo hosted a renewable transportation fuels webinar on Wednesday, outlining comparisons between RNG, renewable diesel (RD), renewable propane (RP) and a hydrogen-natural gas storage alternative.
Significant growth for RNG began in 2011, but it was first developed for commercial use in New York City in 1982. More than half (31) of the 57 national production locations have been developed only in the past seven years, according to RNG Coalition CEO Johannes Escudero.
Produced as biomethane from food waste, wastewater treatment plants, dairies and landfills, U.S. RNG facilities are undergoing a major build-out, with 20 at landfills and 10 at dairies among the 30 new production sites in various stages of development.
At least 37 states have at least one RNG facility, with a total of 57 nationwide.
"In 2011, nearly all of the U.S. RNG production was dedicated to onsite electric generation, but with the founding of the RNG Coalition, we're seeing a shift in the public policy driving RNG, and it's influencing its transportation applications today," Escudero said. "Increasingly, federal and state programs are driving production of RNG in recognition of its role as an ultra-low carbon fuel."
Escudero said that since 2014, the use of RNG as a transportation fuel has increased tenfold. Of the 57 production plants in operation, 46 are supplying the transportation market while 11 serve as onsite generation fuel sources. Sixteen existing production facilities also are being expanded.
Nationally, there are thousands of potential production sites, including 8,000 dairies from which 265 have been identified longer term for development, Escudero said.
In California, which has three RNG production facilities, there are 200 dairies, 100 wastewater treatment plants and 50 landfills that collectively have the potential to produce between 1-2 billion diesel gallon equivalents of RNG.
Senior Vice President Jon Leonard of the energy consultancy, Gladstein, Neandross & Associates, updated the audience about renewable versions of diesel and propane, which he called "emerging clean transportation fuels." The emphasis is on RD, which is considerably more advanced than RP.
RD is a "drop-in" renewable fuel, and is comparable to ultra-low-sulfur diesel (ULSD) fuel, he said.
"RD is widely accepted by diesel engine makers as a substitute for ULSDs," Leonard said. While RD enjoys technical and combustion advantages, it is awaiting a breakthrough in engine advancement to compare with RNG and low-nitrogen oxide NGV engines, said Leonard. While RD demand is picking up, supplies remain constrained.
Jack Brouwer, who directs the National Fuel Cell Research Center at the University of California (UC), Irvine, described research into mixing hydrogen with natural gas to form a stored energy resource that could be used to smooth out the grid as renewable resources gain market share, including wind and solar.
Longer term, Brouwer said California’s current natural gas storage system could be used for the mixture in the existing underground storage and transmission pipeline system.
Storing hydrogen in this manner in California would be the equivalent of a $2.6 trillion battery, based on U.S. Department of Energy costs, Brouwer said.
By mixing up to 5% hydrogen with gas, "this would be a $130 billion battery," he said. "Hydrogen in its end use offers some interesting features for end-uses in transportation that are difficult to electrify, such as quick fueling, long driving ranges and you can accommodate large payloads."
In a pilot project, the UC Irvine campus in Southern California is for the first time in the nation producing and injecting renewable hydrogen into the campus natural gas system.
The renewable hydrogen is fed in doses of up to 7.8% into a combined-cycle gas-fired generation unit. The emissions are monitored and researchers check the performance characteristics during ongoing operations.
"So far, we have produced and injected more than 2,400 kilograms of renewable hydrogen into our system," Brouwer said.