Two Diesel Generators

A pair of 2.25-MW diesel generators. The CEC this week postponed an exemption review for 54 similar generators at a data center in Silicon Valley.

The California Energy Commission on Sept. 9 postponed its decision to provide a small-power-plant exemption for 54 large diesel generators near an elementary school in Santa Clara, because of "recent energy emergencies" in the state, Commissioner Karen Douglas said at the CEC's board meeting.

Last month, the CEC granted exemptions for two similar fleets of diesel generators at nearby locations in Santa Clara: one for about 30 3-MW generators at the Walsh Data Center and another for 43 2.5-MW generators at the Mission College Data Center (see CEM No. 1603). But at this month's board meeting, the commission paused its exemption decision for the new generators, saying commissioners needed additional air-quality and greenhouse gas emissions studies before making a decision.

The 54 2.25-MW diesel generators would be installed at the Sequoia Data Center about 1.5 miles from Scott Lane Elementary School, which has a student body population that is about 75-percent Hispanic, 15-percent Asian and 5-percent white. The area already has high levels of toxic air contaminants, according to the Bay Area Air Quality Management District's Community Air Risk Evaluation Program. The generators would provide backup power to the data center; however, at least one unit could fire up most days of the year, while the whole fleet—96 MW in total—would be used during grid power outages, such as California's recent rolling blackouts and ongoing public-safety power shutoffs.

In its proposed committee decision, the CEC chose not to calculate the Sequoia Data Center diesel generators' criteria pollutant emissions during emergency operations because such a calculation would require too many assumptions, the decision says. There is no known predictor of actual use of the backup generators; however, the generators will emit criteria air pollutants, according to the decision.

Robert Sarvey, a shoe-shop owner in Tracy who has participated in similar proceedings at the CEC, argued that the generator project is not consistent with "Diesel Free by '33," an initiative sponsored by BAAQMD. Sarvey said the initiative would require the project developer to consider using other sources of backup power, such as battery energy storage or fuel cells, according to the decision.

Diesel exhaust causes significant public health effects and accelerates climate change, BAAQMD says on the initiative's website. The impacts of diesel emissions will fall most heavily on communities and populations already significantly impacted by air pollution, environmental hazards and economic inequality, the district says.

Santa Clara Mayor Lisa Gillmor signed the Diesel Free by '33 initiative's statement of purpose in August 2018. The first goal named in the signed letter states that signatories will "[c]ollaborate and coordinate on ordinances, policies, and procurement practices that will reduce diesel emissions to zero within their jurisdictions, communities or companies."

Neither Gillmor nor the Santa Clara City Council has considered the diesel generator project at the Sequoia Data Center, Gillmor said in an email response to California Energy Markets.

The CEC has exclusive jurisdiction to approve or deny applications for the construction and operation of thermal power plants that will generate 50 MW or more of electricity. In cases such as the diesel generator fleet at the Sequoia Data Center, the commission may provide a small-power-plant exemption if the following criteria are met: the plant's generating capacity is less than 100 MW; the plant does not create a substantial adverse impact on the environment; and the plant does not create a substantial adverse impact on energy resources. The CEC in 2019 appointed a committee consisting of Douglas and commission member Patty Monahan to lead the Sequoia Data Center's exemption review process. The commission did not provide a date by which it will decide on the proposed exemption.

At the board meeting, the commission also approved a grant of about $8.4 million for the installation of a solar-photovoltaic and battery storage system at a hospital in Ontario, California.

Charge Bliss, a company in Lake Forest that develops and designs renewable-energy projects, will use the grant money to install a 2.2-MW solar PV system and an 8-MWh flow redox battery at Kaiser Permanente's medical center in Ontario. The solar and battery storage systems will supply 90 percent of the medical center's essential power needs for more than 10 hours, and could do so during a PSPS or rolling blackout, both of which have been implemented in California this summer.

The project will provide the CEC and other industry experts with battery performance data that will help them better understand the benefits and pitfalls of using flow redox batteries instead of lithium-ion batteries. Technical performance of the solar and battery system will be measured by its energy production, round-trip efficiency, capacity decay over time, demand reduction, islanding event number and duration, and ancillary services, the award says.

The commission also approved the following items:

  • A new ordinance in San Anselmo that requires newly constructed buildings to be all-electric or, if the building is mixed-fuel, to meet higher efficiency standards than current building codes.  
  • A new San Mateo County ordinance that requires some newly constructed buildings to use all-electric equipment. Buildings could be exempted if they house laboratories or commercial kitchens, or if a building is a publicly owned emergency shelter or does not have an all-electric compliance pathway.

Staff Writer

David Krause is an energy reporter covering the California Energy Commission and Air Resources Board. He writes about transportation, climate change, utilities, and wildfires. He has an MFA in Writing, an MA in English, and a BS in Civil Engineering.