3.1.2 General Financial Characteristics of the Generation Mix The demand for electric power from the utilities varies with the time of day, the day of the week, the weather, and the season. The shape and magnitude of these variations will vary from utility to utility. An example of how the demand varied during a particular week for a particular utility is shown in Figure 3.1. During this period, the demand varied from a minimum of 4.9 GW at 2 a.m. Sunday morning to a maximum of 10.3 GW at 2 p.m. on Friday afternoon. Looking at Figure 3.1, one can distinguish three different types of demand for electric power which can be met by different types of equipment. Base Load Demand - a power demand which exists 24 hours a day for several weeks at a time. The base load demand for the sample power pool would be about 5 GW. The equipment used to meet this demand would be characterized by relatively high capital costs and low operating costs such that the total cost of electrical energy from these units, operating between 6,000 and 7,000 hours per year, would be less than that of energy from other types of generators. Fossil-fueled base load equipment operates at temperatures and pressures close to the physical limit of the materials used in its construction. Frequent thermal cycling of this equipment in load following service normally leads to expensive maintenance. Intermediate or Cyclic Demand - a power demand which exists for 10 to 20 hours a day. The intermediate load demand for the sample power pool would be about 3.5 GW. The equipment used to meet this demand would be characterized by moderately high capital and operating costs such that the total cost of electrical energy from these units, operating between 3,000 and 5,000 hours per year, would be less than that of energy from other types of generators. Much of this equipment is older, less efficient base load equipment. However, equipment built to sustain the thermal cycling associated with load following service is used extensively.
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