- Load Curve Definition: A load curve is defined as a graph showing energy demand changes over time.
- Daily Load Curve: The daily load curve represents the energy demand over a 24-hour period.
- Load Duration Curve: This curve shows the duration of specific load demands over a period.
- Industrial and Residential Loads: Industrial and residential load curves have different patterns, with industrial peaks during work hours and residential peaks in the evening.
- Power Plant Operations: Load curves help determine the capacity and operational schedule of power plants, ensuring efficient energy production.
Load Curve
A load curve plots electrical demand, measured as power, against chronological time.
A 24-hour plot is a daily load curve. Weekly, monthly and yearly curves use longer periods while retaining the time order.
A load duration curve uses the same demand readings but sorts them from highest to lowest. Its horizontal axis shows the number or percentage of hours for which each electrical power level is met or exceeded. Because sorting removes the original time sequence, a load duration curve shows capacity use but not when a peak or ramp occurred.
Case Study on Daily Industrial Load Curve.
The illustrated industrial daily load curve has a low overnight demand, a morning ramp as machinery starts and a sustained daytime level. It shows a midday reduction, a return to the earlier level and an evening decline as equipment shuts down. These times describe this example only. An actual industrial profile depends on shift patterns, process type, weather, controls and whether the site operates continuously.
Case study on Daily Residential Load Curve.
The illustrated residential daily load curve falls to a low level overnight and has its highest demand in the evening. The summer line is above the winter line for much of this particular example, which may reflect cooling demand in the location represented. That seasonal relationship is specific to the location and data period. Climate, household routines, heating and cooling fuels, appliance use, tariffs and local time all affect the shape and timing of residential demand.
The chronological load curves show when demand rises, peaks and falls, so system operators can study ramps and operating schedules. The load duration curve answers a different question: how many hours each demand level is equalled or exceeded. Its highest point indicates peak demand, its lowest point indicates minimum demand and the area under the curve represents energy over the period. These measures help planners assess capacity and compare the likely use of baseload, intermediate and peaking power plant resources.
Unit commitment and dispatch also depend on generator availability, start-up costs, ramp limits, minimum operating levels, fuel costs, reserves and network constraints. A load duration curve supports capacity and utilisation studies, but it cannot show the chronology needed to decide exactly when a unit should start, stop or ramp. Engineers combine it with chronological demand data and detailed system models.
