Industrial load is great to have in a power system because it's generally steady 24x7 load that results in high utilization of power generating assets. This utilization is important because it spreads fixed costs out over a large number of kilowatt hours and therefore lowers the effective cost per kWh charged to consumers. Load factor is the best way to measure the relative "peakiness" of an individual or a system load. Load factor is simply the ratio between the peak load and the average load. over a time period. A load factor of 50% means that the peak load is double the average load.
Electric grids throughout North America vary significantly in their load factors. Alberta has one of the highest load factors at near 82%. This is due to the significant industrial load associated with the oil and gas industry. New England has a much lower load factor and it has been declining in recent years. This is due to the one-two punch of de-industrialization and increased adoption of central air conditioning. Once upon a time, New England had a thriving industrial economy with many three shift factories and bustling mill complexes. As the New England region lost its industrial competitiveness to places in the Southern U.S. and overseas, the industrial load decreased as a percentage of the total load over the last 25 years. At the same time, central air conditioning systems became widespread during the 1980s and 1990s and resulted in a significant increase in weather driven summer load spikes in the ISO-NE grid.
The graphic below is very telling. It shows how peak summer demands rose throughout the 1990s and early 2000s and have been stable since 2006. Although the summer seasonal load factor has fluctuated from year to year, the general trend is downward. This isn't the annual load factor, but measures the load factor in the period from June - September. When load factor is near 50%, there are a lot of peaking resources sitting idle, waiting for a hot day.
If you look at winter peak demands in ISO-NE, you'll note that the winter peak has been stable over time. Before air conditioning, ISO-NE occasionally peaked during the winter. This was the case in 1992 and a was semi-regular occurrence before the 1990s. You'll note that the winter load factor has also been stable and the long term trend seems to indicate a modest improvement. For this analysis, winter is defined as December through February.
The one thing that jumps out from this review is how much air conditioning has changed the dynamics of the ISO-NE power grid in the last 20 years. It has changed the cost structure of the grid, making it more expensive to operate due to the vast quantity of peaking resources that must be available to serve the summer peaks. There is a huge energy efficiency opportunity to reduce the load attributable to air conditioning and many smart people are working on this problem. Lets hope they are successful.