There are two types of load diversity—that of different peak loads between customer classes, and that of different peak loads at different hours of the day and days of the year.
From continuously recorded demand data, a number of different demand measures may be derived.The most commonly metered measure of customer demand is individual customer maximum demand.This measure indicates the highest demand level incurred by the customer during any metering interval in a billing period. Due to varying types and uses of electrical equipment across customers, there are broad differences in the times that customers achieve their individual maximum demands.
For example, one customer whose major use of electricity is outdoor light may regularly experience maximum demand in the late evening hours of the day; while a second customer, whose major requirement for electricity is for air conditioning, is more likely to experience a maximum demand during afternoon hours in the summer months.
Furthermore, the electrical load requirements of an industrial process may be closely tied to work shift hours, or may be nearly flat throughout the 24-hour day if the process operates on a continuous basis. These differences in the timing of individual maximum demands are referred to as diversity.
Diversity in load requirements not only exists among individual customers, but also can be observed among rate classes, customer classes, jurisdictional divisions, utility systems, and power pools.
The inverse of diversity is coincidence. Coincident demand measures the maximum amount of load which occurs within a given measurement interval. If a customer has two or more electricity consuming devices at their facility, or residence, the customer’s individual maximum demand will occur at the time at which the requirements of the individual devices are most highly coincident (i.e., demonstrate the least diversity).
The sum of the maximum requirements of the individual devices will always be greater than, or equal to, the customer’s individual maximum demand. Other measures of individual customer demands tend to relate the individual customer’s requirements to rate class, customer class, jurisdictional, or system requirements.
Owing to diversity among customers, each individual customer’s contribution to class, jurisdictional, or system maximum requirements, cannot be greater than, and tends to be less than; the customer’s individual maximum demand.
System, jurisdictional, class, or customer demand are typically measured on an annual, monthly, or daily basis. However, billing data (both demand and energy measures) typically do not correspond directly to calendar month or calendar year measures.
Usage reported on a bill in January, for example, may include substantial amounts of consumption which occurred in December of the previous year. This occurs because cost-effective meter reading and bill processing schedules generally require that not all meters be read on the same day but rather some are read on each working day of each month.
Each customer is billed based on his metered consumption in the prior billing cycle. Measures of actual requirements on a calendar month basis are not available for individual customers, except where expensive continuously recording demand meters are installed.