Across the United States, but most pronounced in New England, the ratio of annual peak-hour electric demand to average hourly demand has risen over the past 20 years. In New England, the peak-to-average demand ratio has increased from 1.52 in 1993 to 1.78 in 2012. In other words, the highest peak-hour electric demand for the year in 1993 was 52% above the hourly average level while in 2012 peak-hour demand had risen to 78% above the hourly average level.

This higher ratio translates into decreasing average utilization levels for generators in New England and other regions. Electric systems maintain sufficient capacity to meet expected peak loads plus a reserve margin. As the peak-to-average ratio rises, generators called on to meet peak-hour demand are running fewer hours and/or at lower output levels the rest of the year. Because energy payments are generator’s primary source of revenue in regional transmission organization (RTO) systems such as New England’s Independent Systems Operator (ISO), the rising ratio of peak-to-average hourly demand is likely cutting into generator revenues and increasing the importance of capacity market payments to generators.

via Peak-to-average electricity demand ratio rising in New England and many other U.S. regions – Today in Energy – U.S. Energy Information Administration (EIA).