Data Center

EPIC maintains regional energy and greenhouse gas data.

Featured Data

This page provides a brief explanation of some of the data included in the EPIC Data Center. A new data topic is presented every month.

Load Duration Curve

A load duration curve (LDC) shows the level of demand (megawatts) sorted from highest to lowest for each hour of the year. Peak demand is the highest level of demand on the left-hand side of the chart. LDCs are useful to track trends in demand, particularly peak demand. A flatter LDC means that more of the total system capacity is being used more of the time. A steeper curve (higher on the left, lower on the right) means the opposite. Theoretically, it would be preferable to have a nearly flat curve, but this is difficult to achieve in practice.

Load duration curves also help to understand the effects of demand reduction measures. For example, the chart below shows the LDC for SDG&E territory for 2008. The left-hand most portion of the curve rises steeply the axis. In this case, a significant amount of capacity is required to serve the top 100 hours of demand.

This concept is clearer in the chart below, which only shows the top 100 hours of demand. In 2008, 672 MW of capacity (including a 15% required reserve margin) was required to serve 100 hours of the year. Put another way, 15% of the total electric capacity of the system was required to serve 1% of the hours in the year. Capacity to serve these hours can be expensive, so reducing these high demand hours can reduce costs for the entire system.

Updated 1-3-11