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New generators help California meet summer challenges to electric reliability

Update: Shortly after this article was published, Southern California Edison, the principal plant owner and operator, announced its plan to permanently retire both units at the San Onofre Nuclear Generating Station.

map of CAISO capacity additions and transmission upgrades, as explained in the article text.

Source: U.S. Energy Information Administration, based on the California Independent System Operator's 2013 Summer Loads and Resources Assessment.
Note: Capacity values are derated, or adjusted, for resource constraints typical of summer weather patterns. This includes derates for intermittent resources like hydroelectric, wind, and solar capacity.

Update: Shortly after this article was published, Southern California Edison, the principal plant owner and operator, announced its plan to permanently retire both units at the San Onofre Nuclear Generating Station.

Southern California's electric power system is facing a number of challenges heading into the summer peak demand season, largely because of the prolonged outage of the two units at the San Onofre Nuclear Generating Station (SONGS), which have been offline since January 2012. A combination of recent capacity additions and electric system upgrades made since June 2012 will help meet peak electric demand this summer.

Why do grid planners adjust capacity?

Generation capacity is counted differently for planning purposes (like CAISO’s summer reliability assessment) than for operational purposes. Planners use an adjusted capacity number to represent how much of a particular generator’s capacity may be available to meet peak demand for electricity, based on historic or projected availability. This number will differ from the generator’s tested capacity, especially if the fuel–like wind, solar, or hydro–is intermittent or the generator is not fully dispatchable by the power system operator.

The California Independent System Operator (CAISO), the grid operator for most of the state, noted in its Summer Loads and Resources Assessment that 2,502 megawatts (MW) of capacity (capacity adjusted for planning purposes) have been added since June 2012, with an additional 891 MW slated to come online by June 1, 2013. The two off-line SONGS units, in comparison, total 2,246 MW.

This new capacity will help make up for the loss of the generation from SONGS, but the reliability issue is more complicated than simply providing replacement generation. Geographically, SONGS is in a localized pocket of electric power demand near San Diego and Los Angeles. Given the characteristics of the electric transmission system, the loss of SONGS limits the amount of power that can be brought into the area over the transmission grid—rather than generated locally—under some conditions. Much of the new capacity lies outside of the San Diego-Los Angeles area, meaning that additional transmission upgrades are needed to supply that area.

The local grid will be bolstered at strategic locations in the Los Angeles basin and northern San Diego County. Southern California Edison also plans to reconfigure the existing 220-kilovolt Barre-Ellis transmission line from two circuits to four by June 15, increasing the amount of electricity that transmission path can move. However, the region also needs local sources of reactive power (a portion of generated electricity which is lost in large quantities when transmitting power over long distances, i.e. importing power from some of the new generating capacity to Southern California). Capacitors will be added to several substations (see map above) by June 1, and two natural gas-fired generators at the Huntington Beach facility will be converted to synchronous condensers by June 28. Capacitors and synchronous condensers are commonly used to provide voltage support in the form of reactive power to the transmission grid. All of these system upgrades are designed to allow the system to bring more power into the region.

The two units at SONGS have been offline since January 31, 2012 as a result of mechanical problems currently being evaluated by Southern California Edison and the Nuclear Regulatory Commission. Replacing the power from a low-cost source of generation like SONGS already has changed wholesale electricity prices in the state. Rising natural gas prices are likely to increase that effect in 2013. In its annual report, CAISO noted that 2012 wholesale power prices were higher than prices in the previous three years even when adjusted for the lower 2012 natural gas prices. In addition, the unusually large spread in wholesale electricity prices between the northern and southern portions of the state indicates system congestion.

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