Willdan Wins $31 Million Contract to Take a Carlsbad Wastewater Plant to 100 Percent On-Site Power
- Contract Value: $31 million
- New Generation: 0.99 MW linear generator
- Battery Storage: 2 MWh
- Existing Cogeneration: 750 kW
- Residents Served: 379,000
Encina Wastewater Authority awarded Willdan Group a $31 million design-build contract on July 15, 2026 to convert the Encina Water Pollution Control Facility in Carlsbad, California into a biogas-fired microgrid that covers all of the plant’s electricity. The package adds a 0.99 MW linear generator, a 2 MWh battery paired with a microgrid controller, and a digester biogas conditioning facility. The plant already runs four Caterpillar engine-generator sets rated at 750 kW that supply more than 80 percent of its load and cut about $2 million a year from its energy bill. Encina treats sewage for more than 379,000 residents across six member agencies in northwestern San Diego County.
What the Contract Buys
The work is filed with California as the EWPCF Cogeneration Low Emissions Augmentation and Retrofit project, or CLEAR, at 6200 Avenida Encinas. Beyond the new linear generator and the 2 MWh battery, the scope covers oxidation catalyst emissions controls retrofitted onto the existing cogeneration engines and new biotowers built inside the plant’s blower room. The authority filed a Notice of Exemption for the project on April 13, 2026, stating the work adds no biogas production and produces no net increase in air emissions.
Anaerobic digestion of wastewater solids yields a gas that is 60 to 65 percent methane. Encina’s Alternative Fuel Receiving Facility takes restaurant grease and other outside feedstock, which lifted biogas output 29 percent in its first two years. The conditioning step scrubs that gas so the new generator burns it cleanly, and the linear generator itself is chosen for tolerance of variable fuel quality, which is the practical constraint on any digester-fed plant.
“This project allows us to provide continuous service to North San Diego County communities, ensuring uninterrupted operations even during periods of constrained utility power or grid disruptions,” said Scott McClelland, general manager of Encina Wastewater Authority. The six owners are the cities of Carlsbad, Vista and Encinitas, plus Vallecitos Water District, Buena Sanitation District and Leucadia Wastewater District.
Why It Matters
A wastewater plant is the rare industrial load that owns its own fuel supply, and Encina shows what that is worth once a battery and a controller sit on top of it. The jump from 750 kW of engine capacity at 80 percent self-supply to full coverage is not a generation problem so much as a dispatch problem: digester gas arrives at a steady rate while plant load swings with influent flow and blower duty, and the 2 MWh battery is what absorbs that mismatch and holds the site through a utility outage. Public agencies weighing the same move should note the shape of this deal, which pairs the emissions retrofit with the resilience build rather than treating them as separate capital cycles, because the air-permit driver is what carried the business case. For San Diego County, where wildfire-season public safety power shutoffs put treatment plants at risk of spilling, a facility serving 379,000 residents that rides through a grid outage on its own sludge is a resilience asset for the region, not just a utility-bill line item.
Critical Perspective
Encina is paying $31 million to move from more than 80 percent self-supply on four 750 kW Caterpillar sets to full coverage, which prices the last stretch of self-supply well above the roughly $2 million a year the existing cogeneration already saves. The new generator is sized at 0.99 MW, just under one megawatt, and the fuel case rests on the Alternative Fuel Receiving Facility, where imported restaurant grease lifted biogas output 29 percent in its first two years, so full coverage depends on a feedstock stream the plant does not itself produce. The East Bay Municipal Utility District ran its Oakland plant into the first net energy positive wastewater operation in North America by importing food waste and grease, and its energy position has tracked the tipping-fee volumes it can attract ever since. What happens to 100 percent coverage in a year when regional organics diversion rules send that grease to a competing digester?
Sources
- Willdan Group: Willdan Selected by Encina Wastewater Authority for $31 Million Cogeneration Project (July 15, 2026)
- Microgrid Knowledge: Designing a $31M biogas microgrid to power Encina wastewater plant (July 15, 2026)
- CEQAnet, California Office of Land Use and Climate Innovation: EWPCF Cogeneration Low Emissions Augmentation and Retrofit (CLEAR) Project, Notice of Exemption
- Encina Wastewater Authority: Energy Recovery program
- StockTitan: Willdan Selected for $31M Cogeneration Contract (July 15, 2026)
