Load duration curves are a handy way to visualise how often different levels of load (demand) are exceeded over a period of time, usually a year. They are easily plotted, by plotting load values in order of size rather than in time sequence – for a fuller explanation, I’d recommend reading this article.
Here are a couple of examples, plotting data from the South Australian power system in 2017. The top chart is a full year load duration curve. If the x-axis looks confusing, that’s because the data is plotted using half-hourly periods, of which there are 17,520 in a year (365 days x 24 hrs x 2 half-hours). The bottom chart focuses in on the left-hand side of the topic one, showing just the highest 480 half-hourly levels of power demand.
The takeaway is clear though: the highest levels of demand don’t happen very often at all!