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The Western Interconnection serves a population of over 80 million. It spans more than 1.8 million square miles in all or part of 14 states, the Canadian provinces of British Columbia and Alberta, and the northern portion of Baja California in Mexico. Because of its unique geography, demography, and history, the Western Interconnection is distinct from the other North American interconnections in many ways.

Geography and Land Use

The Western Interconnection is diverse in climate, topography and terrain. It experiences weather extremes that affect how the system is operated. For instance, daily temperature swings of over 50°F occur throughout much of the West. Changes in climate, coupled with increases in weather-dependent resources, pose further short- and long-term planning and operational challenges.

A large part of the Western Interconnection is public land. This presents challenges when planning the system, including:

  • Protection of vulnerable species, habitats, and vegetation;
  • Preservation of game rangeland, migration corridors, and critical rivers and streams; and
  • Cultural considerations, including National Parks and Monuments, and Native American tribal lands and sacred sites.

Operations and Planning

The Western Interconnection is operationally distinctive. Historically, there has been less reliance on market structures than in the rest of North America. There are relatively more Balancing Authorities, and multiple Reliability Coordinators. As a result, operations and planning activities in the West are unique.

Resource Portfolio

The Western Interconnection has a diverse mix of resources that vary widely by subregion. Generation in the Western Interconnection makes up just under 20 percent of the North American total.  A large proportion of generation comes from hydroelectric and variable (wind and solar) resources.


Transmission System

The Western Interconnection is made up of about 136,000 miles of transmission lines. Two features distinguish the flow of electricity in the West from that in the East:

  • Long high-voltage lines were built to connect remote generating resources with population centers, primarily along the West Coast.
  • Other lines carry power from hydroelectric resources in the Pacific Northwest to California and other states. These resources have the greatest capacity during the spring and summer, when demand in the Northwest is relatively low.

Because of these unique supply-and-demand patterns, utilities in the West rely more heavily on electricity transported over long distances than utilities in the East. Electricity generally flows south and west in a "doughnut" pattern, in contrast to a spiderweb configuration in the East.