Load Curve in a Power Plant – Daily, Monthly and Annual

A load curve is a plot of the load demand (on the y-axis) versus the time (on the x-axis) in the chronological order.

It is a curve showing the variation of load on the power station with respect to (w.r.t) time.

Daily Load Curve in a Power Plant
Daily Load Curve in a Power Plant

From out of the load connected, a consumer uses different fractions of the total load at various times of the day as per his/her requirements.  

Since a power system has to supply load to all such consumers, the load to be supplied varies continuously with time and does not remain constant. 

If the load is measured (in units of power) at regular intervals of time, say, once in an hour (or half-an-hour) and recorded, we can draw a curve known as the load curve.

Daily Load Curve

A time period of only 24 hours is considered, and the resulting load curve, which is called a Daily load curve, is shown in the figure. 

Monthly Load Curve

The monthly load curve can be obtained from the daily load curves of that month.

For this purpose, average values of power over a month at different times of the day are calculated and then plotted on the graph.

The monthly load curve is generally used to fix the rates of energy.

Yearly/Annual Load Curve

The yearly load curve is obtained by considering the monthly load curves of that particular year.

The yearly load curve is generally used to determine the annual load factor.

However, to predict the annual requirements of energy, the occurrence of the load at different hours and days in a year and in the power supply economics, ‘Annual load curves’ are used.

An annual load curve is a plot of the load demand of the consumer against time in hours of the year (1 year: 8,760 hours).

Daily Load Curve in which Load is measured in an hour


The significance of Load Curve

From the daily load curve shown above, the following information can be obtained.
  • Observe the variation of load on the power system during different hours of the day.
  • The area under this curve gives the number of units generated in a day.
  • The highest point on that curve indicates the maximum demand on the power station on that day.
  • The area of this curve divided by 24 hours gives the average load on the power station in the day.
  • It helps in the selection of the rating and number of generating units required.

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