ERCOT tries to keep the electric power grid in Texas operating at 60 Hertz (i.e., 60 cycles per second, Hertz is abbreviated “Hz”), like the rest of North America, and a few other places in the world. If electrical load grows faster than power supply, the system frequency will fall below 60 Hz; if the load drops off faster than supply, the frequency will rise above 60 Hz. ERCOT tends to have more of a problem with frequency control than elsewhere in the United States because the area does not have strong interconnections with utilities outside ERCOT.
As the system frequency deviates from the ideal, ERCOT sends out signals to selected controllable generators to increase or decrease output to bring the system back into balance. Also, most existing non-wind generators in ERCOT have automated “governor” systems that help maintain system frequency. In certain emergency conditions ERCOT can call on interruptible load to help maintain system frequency.
Increased wind power capacity is adding to the challenges of frequency control in ERCOT, and in response, as Platt’s reports, ERCOT is considering how wind power generators can help contribute to frequency control. An ERCOT stakeholder committee is meeting tomorrow (March 31, 2009) to discuss the issue, and under consideration is a proposal to require new wind power generators to add the control equipment necessary to enable the wind generators to respond to frequency control instructions from the grid.
The urge to make new wind power generators add control equipment simply because wind power capacity additions will increase the need for frequency control services is a mistake. Rather, ERCOT should pay the generators (or controllable consumer loads!) for the frequency control services it needs and allocate these costs to the consumers and generators that create the need for frequency control services.
If wind power generators are the least cost source of additional frequency control services in ERCOT, they will respond by adding the necessary equipment to their generators. However, as may be likely, if other generators or responsive consumers can offer frequency control more cheaply, then consumers will be better off paying these other market participants for additional frequency control service.