By Hudson Sangree
FERC on Thursday approved changes to CAISO’s Tariff that describe practices already employed by the ISO’s system operators to balance supply and demand in the day-ahead and real-time markets (ER19-538).
The day-ahead market encompasses CAISO’s balancing authority area, primarily in California, while the real-time market extends to seven entities across the West that participate in the ISO’s Western Energy Imbalance Market.
The “load conformance” practices approved by FERC allow CAISO operators to manually adjust for conditions that the ISO’s automated load-forecast system do not anticipate. In addition, a “load conformance limiter” automatically makes sure the operators’ adjustments don’t exceed the ramping capability of generators available at a given time.
FERC noted that the ISO’s system operators balance of supply and demand to maintain system reliability and comply with NERC reliability standards “primarily through CAISO’s market systems.”
At times, however, “the automated load forecast used in clearing supply bids against forecasted load and exports for CAISO’s real-time market does not match actual system conditions” because of load forecast error, significant deviations in predicted wind and solar supply, and “unpredictable events like outages or weather changes,” FERC said.
When operators see a mismatch between the load forecast and actual conditions in the real-time market, they can manually adjust the forecast, before the market runs, in a practice known as load conformance, FERC explained. The CAISO Tariff does not specifically describe load conformance but will include it after the revisions take effect Feb. 27, the commission said.
The revisions will also include a description of CAISO’s load conformance limiter, currently absent from the Tariff. The automated system corrects for manual adjustments that are “often ‘coarse’ in nature because they represent operators’ imprecise approximation of what they perceive to be the system need at the time based on best estimates and judgment,” FERC wrote.
The third Tariff change approved by FERC is similar to the load conformance adjustments in the real-time market but applies to the residual unit commitment process in the day-ahead market.
Commenters generally supported allowing CAISO operators to make adjustments in the real-time and day-ahead markets, FERC noted. However, one commenter, Powerex, argued that frequent load conformance may be “masking” systemwide shortcomings that could impair the efficient operation of CAISO’s real-time markets.
Powerex said CAISO should hold a stakeholder process to identify why the ISO is using load conformances so frequently and develop automated tools that ensure real-time conditions are accurately reflected in market processes.