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ELECTRICAL DEMAND AND ENERGY  FEBRUARY 1994

Background:

The amount of electricity that is being used at any given time and the length of time that electricity is being used are both critical components in the electrical power system. The relationship between these components is also important.

Discussion:

Demand: The amount of electricity that is used at any given time is called the "demand" for electricity. In small quantities electrical demand is measured in watts (W), and in larger quantities it is measured in kilowatts (kW = 1,000 W) of megawatts (MW =1,000 kW or 1,000,000 W). Although demand may vary from moment to moment, for reporting purposes, demand is usually averaged over 15 minute, 30 minute, or one-hour periods. For sizing of generation and transmission facilities, the electrical load carrying capability is referred to as the "capacity" of the facility and the highest demand which occurs is generally referred to as the "peak" demand.

Energy: The use of electricity over a longer period of time is generally referred to as energy and is measured in watt hours (WH) or for larger quantities kilowatthours (kWH = 1,000 WH), megawatthours (MWH = 1,000 kWH or 1,000,000 WH), or gigawatthours (GWH =1,000 MWH).

Load Factor: The relationship between energy and capacity is generally referred to a "load factor." In the case of generation facilities, it is referred to as "capacity factor." This relationship can be calculated as follows:

Load factor graphic

The Load Factor relationship is an indication of the percentage of time that the system is being fully utilized and in Colorado, a typical annual load factor is about 65-70%. The other 30-35% represents the unused capacity during the night time when everyone is asleep, weekends when industries are not operating, and the lighter loaded seasons such as spring and fall when air conditioning and heating are not required.

Source: Colorado Association of Municipal Utilities (CAMU)

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