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Utility Applications Case Study: Power for a Utility Substation in California

Photo of PV panels that are installed at the PG&E's Kerman substation in California.

PG&E's Kerman substation in California uses the electricity produced by this 500-kilowatt PV system to help meet peak demand on sunny summer afternoons. Researchers are measuring the value of this system to PG&E in hopes of demonstrating yet another use of PV in utility systems.

Pacific Gas and Electric Company's (PG&E) Kerman substation near Fresno, California, was becoming overloaded on hot summer days. That happened especially when air-conditioning and water-pumping needs were greatest, and the utility experienced its peak demand. Overloading heats up substation components, and that in turn shortens the life of expensive transformers, reduces power quality for customers, and increases line losses during transmission. Analysts in PG&E's research group looked to a PV array to meet the extra demand at Kerman, because it happened on the sunny days when solar cells would be producing power very well.

Analysts at PG&E believed that using PV to support a substation during times of peak electrical demand might make economic sense for their utility, But no one knew how much the PV grid support would be worth. Because upgrading the Kerman substation would cost several million dollars, PG&E decided to install a PV system as a research project (as part of the PV for Utility-Scale Applications project) to evaluate the benefits of grid support.

They found that the PV system installed at Kerman in 1993 produces the most power on sunny summer afternoons, when PG&E experiences its peak demand and electricity has the highest value to the utility. The system maintains its electrical output close to its rated capacity by having the PV modules mounted on trackers that change the modules' tilt as the sun moves across the sky.

The Kerman substation experiment is designed to measure the value to the utility of a 500-kilowatt generating plant that can be quickly (within 6 months) placed where extra power is needed. Monitors record electrical output throughout the day and yield detailed information on system output.

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