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Declaring Emergencies in California: The Realities of ISO Operation

An independent system operator's view on the energy crisis and the realities of maintaining reliability.
Fortnightly Magazine - October 15 2001

CAISO's perception of a shortage is erratic and unverifiable are inapposite and can only heighten the crisis.

The energy situation has never been so severe compared to previous years. Within the first five months of 2001, the CAISO has already surpassed the number of emergency declarations for the prior three years.

The complexities of the CAISO system grid, its markets, and the magnitude of data captured to analyze certain instances make it difficult to fully understand the emergency declaration process unless you spend a day in the life of a CAISO grid operator. System operators look at many different aspects that contribute to keeping supply and demand in equilibrium. Each relevant aspect involved in the emergency declaration and curtailment decision process is discussed below. Throughout the description of the core elements, we present specific examples on the process the CAISO conducted in declaring emergencies for nine selected days.

Looking into the Future: CAISO Demand Forecast, Scheduled Load, and Actual Load

Not addressing the intricacies of load forecast methodologies, the CAISO's short-term forecast is an important aspect in identifying periods during which supply deficiencies will require electricity demand to be curtailed. The CAISO forecasts demand (including the required operating reserves for that demand) for every hour eight days in advance of the operating hour. It continues to update each hour's forecast up to one hour prior to the operating hour. Overall, the average CAISO forecast accuracy has been within 2 percent of actual load levels.

In evaluating the need for emergency declarations, the CAISO forecast is compared to 1) scheduled load (both day-ahead and hour-ahead), and 2) actual load on an hourly basis. It is important to note that emergency declarations may be made in an effort to preclude an emergency before it occurs. On a typical day, the CAISO faces a 5,000 to 7,000 MW shortfall between scheduled generation and expected load with as high as 16,000 MW over last summer. As the following examples show, the CAISO deals with underscheduled load of a magnitude that is substantially above the 5 percent level that was originally anticipated. The examples present that there were times with up to a 35 percent (11,942 MW) shortfall of scheduled load during our selected case days. The CAISO generally can obtain a little more scheduled load between the day-ahead and hour-ahead, yet scheduled load still falls significantly short of actual load. This underscores the CAISO's reliance on real-time purchases to make up for resource deficiencies.

After the CAISO analyzes expected operating conditions, it takes a more detailed look at the make-up of its internal generating resources and imports it can rely on to cover its load.

Internal Generation Resources: Where's the Power?

There are several factors that contribute to the available generating capacity within the CAISO's control area. 3 These include:

  1. Qualifying Facility Resource Limitations
  2. Hydroelectric Generation Limitations
  3. Transmission Constraints
  4. Generating Unit Outages: Planned and Unplanned (Forced)

The CAISO calculates net dependable capacity, which takes into account 1, 2, and 3 from above. The net dependable capacity is the capacity available during a given operating hour. Furthermore,