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October/November 2015

Backup Power for Backup Data: Computing Yields More BUGs

An inspector with the Bay Area Air Quality Management District checks a backup diesel generator. Photo by Sharon Beals.

By Leslie Stewart

The Bay Area is known worldwide for its technological accomplishments. One side effect of Silicon Valley’s success has been a proliferation of data centers, massive buildings containing computer servers that store, process, and distribute dizzying amounts of data. “Green computing” advocates have raised awareness about the significant energy requirements of these centers, which have been popping up all over the world, including within this region. Along with their daily energy usage comes an additional environmental concern — the huge diesel backup generators needed in case of a power outage.

While the surge in data centers has drawn fresh attention to these generators, they’ve already been relied upon for a long time to deliver substitute electricity in many other capacities. For health and safety, hospitals and critical care facilities are required to have backup power systems that start automatically and can operate at full capacity within 10 seconds after a power failure. Water and wastewater facilities also need uninterrupted power to maintain pumping and treatment operations. Large event centers and other gathering places employ backup generators out of concern about safely handling crowds of people during an outage.

Whether they serve data centers, arenas, college campuses, business parks, hospitals, or supermarkets, as the region grows, so does the number of generators. In 2001, the Bay Area Air Quality Management District estimated that there were 3,000 to 5,000 backup generators, or BUGs, in the region. Now that estimate is 7,500 BUGs, most of them diesel-powered.

Diesel particulate matter, the fine sooty particles in diesel exhaust, was a growing issue of concern for regulators in 2001. At the same time, the state was in an energy crunch, prompting a proposal to link large emergency diesel generators into the grid to form a distributed energy network. The Air District pushed back against this idea — the agency’s executive officer at the time, Ellen Garvey, warned, “During a rolling blackout situation, firing up those dirty diesels can add up to 10 tons of pollutants in a day.” The Air District took action that summer, eliminating permit exemptions for emergency standby engines while also setting new operating rules.

Currently, stationary generators over 50 horsepower are regulated by the Air District, the California Air Resources Board, and the U.S. Environmental Protection Agency. Generator operators receive Air District permits after an engineer determines compliance with restrictions set by all of these agencies on nitrogen oxides, sulfur compounds, ozone precursors, carbon monoxide, toxic organic compounds, and diesel particulate matter. The permits allow limited hours of use for maintenance and reliability-related activities. Otherwise, the generators may be operated only during emissions tests and for emergencies; all operations must be logged and reported.

To reduce emissions, all generators must use “best available control technology” requirements mandated by the federal Clean Air Act. Diesel particulate matter is considered a toxic air contaminant, so diesel generators are also subject to additional restrictions, and if the levels of emissions run high enough, the Air District conducts a health risk assessment. Permit conditions such as specific hours for maintenance testing may be set based on closeness to hospitals, schools, daycare facilities, or senior housing — those places that serve people more vulnerable to toxic air contaminants. If a proposed generator is unable to meet the restrictions, the permit applicant may need to accept reduced hours of operation for maintenance and reliability-related activities. The addition of abatement devices may also be necessary.

Although data centers use multiple generators, for permitting purposes they are considered as part of a single project. Sanjeev Kamboj, engineering manager for the Air District, explained, “We look at risk levels for the whole project. There is no ‘piecemealing’. In order to discourage circumvention that might be achieved by breaking a project into smaller pieces and submitting more than one permit application over a period of time, we look back two years to be sure we include any previous permits at the same location.” This look-back period applies to all permits. For example, a recent application for a new BUG at Broadway Plaza Shopping Center in Walnut Creek included data for an existing generator as well. In addition to the project level risk, the Air District on an annual basis reviews the BUG emissions data for each facility to ensure that the facility-wide risk stays below regulatory thresholds.

Federal regulations for generators have become increasingly stringent. The EPA started by setting Tier 1 standards in 1994, and now applies Tier 3 standards to stationary diesel BUGs and Tier 4 standards to prime ones. Tier 3 controls reduce nitrogen oxides and particulate matter by about 62 percent over Tier 1 levels, while Tier 4 brings reductions to 90 percent. Kamboj expects that Tier 4 could soon start to apply to diesel BUGs.

The remaining older generators are more than offset by restrictions on the others. Despite the increased number of BUGs, the amount of total particulate matter they add to the Bay Area’s air is still only 16 tons per year, a relatively slight increase over the 2001 estimate. Today, they contribute only .09 percent of the region’s total particulate matter. As Kamboj summed it up, “Overall, the tech has improved, regulatory programs have become more stringent, and the risk has decreased.” Per the Air District’s data, the estimated lifetime cancer risk in the Bay Area from all toxic air contaminants combined declined by 80 percent between 1990 and 2014.

If air pollution is less of a concern now for diesel backup generators on the output end, what about making them “greener” at the input end? A relatively small generator, such as the one at Walnut Creek’s Broadway Plaza that produces about 200 kilowatts of power, uses about 14 gallons of diesel an hour at maximum power. It’s comparable to the engine in a diesel-powered transit bus, while a typical diesel BUG at a data center is like the engine in a switching yard locomotive — it’s 10 times as powerful (2,000 kilowatts) and uses 10 times as much diesel (140 gallons).

Here the potential for improvement may not be as great. Generators fueled by natural gas and propane are used in the Bay Area; both are cleaner than diesel engines, at least before pollution control technology is applied. Unfortunately, natural gas has a downside: automatic cutoffs for gas lines in the case of an earthquake make it useful only for other types of power disruptions. Another option is an alternative fuel such as biodiesel, which has some of the same emissions concerns but is not a fossil fuel. However, a white paper on biodiesel by Erich Plebuch, a consultant with Peterson Power Systems in San Leandro, has cautioned that “its innate properties, as well as inadequate regulations pertaining to its usage, renders its use in standby applications problematic.”

Could renewable sources and new forms of energy storage replace diesel BUGs? “Fueled systems are difficult to replace in this instance,” Haresh Kamath from the Electric Power Research Institute in Palo Alto e-mailed in answer to this question. “It’s unlikely that batteries will ever entirely replace diesel generators for backup, for the simple reason that battery storage is a limited duration technology and most backup systems require a continuous reliable source of power.”

Kamath noted that most backup systems today use a combination of short-duration batteries for 5 to 15 minutes, giving the system enough time to turn on a diesel generator. “In the near future, however,” he added, “we can expect backup batteries to be longer duration, so the backup system will perhaps run on batteries for an hour or longer before turning on the generator. Local renewable energy such as solar can be implemented through a microgrid. Together, these advances can substantially reduce the amount of diesel fuel used, even if it does not entirely eliminate it.”

Leslie Stewart covers air quality and energy for the Monitor.

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