Electrical Power Systems Technology

Electrical Power Production Systems 85

Supply and Demand

The supply and demand situation for electrical energy is much differ-

ent from that of other products that are produced by an organization and

later sold to consumers. Electrical energy must be supplied at the same

time that it is demanded by consumers. There is no simple storage sys-

tem that may be used to supply additional electrical energy at peak demand

times. This situation is unique, and it necessitates the production of suf-

ficient quantities of electrical energy to meet the demand of the consum-

ers at any time. Accurate forecasting of load requirements at various given

times must be maintained by utility companies in order that they may

recommend the necessary power plant output for a particular time of the

year, week, or day.

Plant Load and Capacity Factors

There is a significant variation in the load requirements that must be

met at different times. Thus, the power plant generating capacity utiliza-

tion is subject to continual change. For this reason, much of the generat-

ing capacity of a power plant may be idle during low demand times. This

means that not all the generators at the plant will be in operation.

There are two mathematical ratios with which power plants are con-

cerned. These ratios are called load factor (demand factor) and capacity fac-

tor. They are expressed as:

Average load for a time period

Load (demand) factor = ——————————————

Peak load for a time period

Sample Problem:

Given: a power plant has an average load of 220 MW and a peak load

of 295 MW over a 24-hour period.

Find: the load factor of the power plant during the 24 hour period.

Solution:

Average Load

Load factor = ———————

Peak Load

220 MW

= ————

295 MW

Load factor = 0.745