A power purchase agreement lets a California agency benefit from a fuel-cell-based generation system without investing up-front capital.
A California clean-water plant has moved closer to a vision of being off the grid by 2020 through a partnership that now fulfills about 50 percent of its power needs.
Regional Water Recycling Plant No. 1 (RP-1), located in the City of Ontario and operated by Inland Empire Utilities Agency (IEUA), delivers biogas to run a privately owned fuel cell installation, then buys the power at rates below utility grid prices.
The 44 mgd (design) tertiary plant treats an average of 28 mgd. Its effluent, along with that of IEUA’s other three wastewater treatment plants, goes into the utility’s reclaimed water system, where it is used for in-house processes; for irrigation of parks, golf courses and farms; for industrial purposes; and for groundwater recharge.
Its biosolids system uses three-phase digestion, which provides some 700,000 cubic feet of biogas every day for the fuel cells. The biosolids are trucked to an IEUA composting facility in Rancho Cucamonga that produces more than 230,000 cubic yards of SoilPro Premium Compost per year.
IEUA needed a new plan when air-quality regulations required a reduction in output of RP-1’s two 1.4 MW cogeneration engines. While their total output capacity was the same as the new 2.8 MW fuel cell installation, the agency was limited by emissions standards to operating just one of engines.
The agency decided on a partnership with a private firm, which owns and operates the fuel cell plant and handled its design, financing and construction. The system uses a DFC3000 Direct FuelCell power plant from FuelCell Energy, which calls the project the largest digester gas fuel cell installation operating in the United States. It went online in January 2013.
In exchange, IEUA signed a 20-year power purchase agreement (PPA) to buy all the electricity the fuel cells generate. “Most of the biogas is used by the fuel cells,” says Pietro Cambiaso, IEUA senior engineer for environmental compliance. “Excess gas is used in boilers to heat the digesters.” Heat from the fuel cells is also recovered.
Switching to fuel cells, which don’t require combustion, greatly reduced emissions:
Carbon monoxide (CO) by 92 percent
Nitrogen oxides (NOx) by 6 percent
Volatile organic compounds (VOCs) by 91 percent
Sulfur oxides (SOx) by 72 percent
Particulate matter by 86 percent
A small amount of gas from the acid phase of digestion is flared because it is low in heating value and would require substantially more cleanup of hydrogen sulfide and siloxanes than the rest of the digester gas.
No capital investment
The PPA gives IEUA a set cost for electricity into the future without having to fund the project from its capital budget. “There was no capital outlay,” says Cambiaso. “We’re only purchasing the power at an established rate. We didn’t want to assume the risk, so the PPA was a good solution.”
Jesse Pompa, senior associate engineer in environmental compliance, adds that the PPA addresses some issues the agency had heard of with other projects. “With other agencies, we had seen that the gas conditioning skid and the fuel cells would be from separate manufacturers, and there would be a lot of finger-pointing if there was any downtime.
The fuel cells can also be powered with natural gas, in which case RP-1 still pays the guaranteed starting rate for the power: 12.6 cents per kWh with a 2.5 percent annual escalation. That is comparable to the price now paid to Southern California Edison. “The assumption is that Edison’s rates will increase between 4 and 6 percent based on historical data,” says Cambiaso. “Over time, we’re going to see the savings.”
Supply and demand
RP-1’s electrical demand ranges from 3.5 MW in winter to just above 4 MW in summer. “There is some parasitic load for the 2.8 MW fuel cell plant, so we see a maximum of around 2.4 MW,” says Pompa.
The fuel cells are supplemented by a 4-acre, 800 kW solar array, installed in 2008, that uses both fixed and tracking solar panels. IEUA installed similar systems at all its locations through a PPA with SunPower, for a total of 3.5 MW solar generating capacity. The solar installations provide 8 percent of the utility’s electrical needs, replacing power previously purchased off the grid.
“We’re still working on implementing some efficiency projects at RP-1 to conserve energy,” says Cambiaso. “Ultimately, the goal is to be self-sufficient. We have higher demand in summer, so we need to work on that. In winter, we make some excess power and are working with the local utility to export that power back to the grid.”
At present, biogas generation matches up well with the need for gas on site, but the agency is considering adding gas storage. “The demand may change or the production may change,” says Cambiaso. “So we’re looking to see if it would be cost-effective to add gas storage.”