Load factor is the ratio of average demand to peak demand, typically measured in megawatts (MW) on a system wide level. It is a useful metric to show how much of the entire electric delivery system capacity is being used on average over a given period. For example, in 2006, SDG&E system wide peak demand was about 4,224 MW and the average demand was about 2,384 MW. Dividing 2,384 by 4,224 yields a load factor of 55%.This means that on average about 55% of the entire system capacity was used during that year. This is because there are times during the year when demand is higher, typically short durations during hot summer months in Southern California. The electric delivery system must have the capacity to accommodate those peaks. The chart below shows peak demand, average demand, and load factor trends for the San Diego Gas & Electric service territory since 1990. In general, it is advantageous to lower peak demand to a level closer to average demand, thus increasing the load factor. Demand response and other demand reduction programs seek to lower demand during peak times.