The number of System Operating Limit exceedances on Western Electricity Coordinating Council transmission paths continued to decline in 2016, with a decrease of 55 percent from 2015, according to the recently published “State of the Interconnection” report, which WECC said is a snapshot of evolving trends in the Western Interconnection.
Key transmission lines in the Western Interconnection are grouped into numbered paths for planning and operational purposes, the report said. A WECC path SOL indicates the maximum flow possible on the path that ensures reliable operations, the report said, adding that thermal, voltage, or stability criteria performance may be impacted if flow exceeds the prevailing path SOL.
The decrease in exceedances over the last two years has been primarily driven by infrastructure improvements and load composition changes in the Pacific Northwest and Canada, the report said, adding that 83 percent of exceedances in 2016 lasted less than one minute and were less than 50 MW above SOL.
As noted in the report, the report gathers data from various sources to provide a comprehensive summary of information related to the reliability of the bulk-power system, which consists of the generating resources and high-voltage transmission equipment that comprise those networks.
The Western Interconnection serves a population of more than 80 million, and spans more than 1.8 million square miles in all or part of 14 states, the Canadian provinces of British Columbia and Alberta, as well as the northern portion of Baja California in Mexico, the report said.
The Interconnection is made up of about 136,000 circuit-miles of transmission lines that carry power long distances, from remote areas where generating resources are located to populated areas where load is located, primarily along the West Coast, the report noted.
The Western Interconnection relies less on coal and nuclear resources than the Eastern Interconnection, according to the report, which also noted that while the generation capacity of the Western Interconnection makes up about 20 percent of all capacity in the United States and Canada, the Interconnection has 35 percent of all wind and solar capacity, and 40 percent of all hydro capacity.
Discussing disturbances, the report noted that between 2014 and 2016, there were eight loss-of-load events in the West, with loss of load being the loss of firm load for 15 minutes or more exceeding 300 MW for entities with previous year’s demand â‰¥ 3,000 MW, or 200 MW for all other entities.
“While there was an increase in the number reported in 2016 compared to 2014 and 2015, more years of data will be necessary to determine whether this signifies an increasing trend and potential concern, a statistical anomaly, or normal variation between years,” the report said.
The largest loss-of-load event occurred on Aug. 7, 2016, with 665 MW lost, the report said, noting that that represents 0.5 percent of the day’s peak system demand of 126,800 MW.
Of demand, the report said that the Western Interconnection has a diverse load composition, adding that the majority is concentrated along the West Coast, with pockets in the Southwest and Rocky Mountains. Overall, the Interconnection is summer-peaking, though the Northwest is winter-peaking, the report said. Over the last several years, annual energy consumption has changed in response to various factors driving demand, including fluctuations in weather patterns and economic conditions, the report said.
While energy consumption was 0.6 percent lower in 2016 than in 2015, peak demand was 4 percent higher, the report said, noting that the decrease in consumption may be related to the increasing prevalence of rooftop solar in California.
Installed capacity of rooftop solar in the Western Interconnection increased by 130 percent between Jan. 1, 2014, and Dec. 31, 2016, the report said, adding that capacity generally grows linearly, averaging a net increase of 3 percent per month. Three quarters of rooftop solar capacity in the West is in California, where lots of sun, electricity prices and incentives make rooftop solar a viable option for many consumers, according to the report. Other states may see a similar impact if economic, environmental, technical, and policy factors make rooftop solar more cost effective, the report said.
North America will experience a solar eclipse on Aug. 21 that will impact solar irradiance levels across the Western Interconnection, the report said, noting that more than 9,000 MW of solar generation capacity will be impacted in California alone.
Discussing resource portfolio, the report said that the combined nameplate capacity of all utility-scale resources in the Western Interconnection in 2016 was 267,000 MW, or a 1 percent increase from 2015. Retirement of coal and steam-turbine gas units led to slight decreases in capacity from those fuel types, while the installed capacity of utility-scale solar increased by more than 6,000 MW, the report noted.
While hydro units are dominant in the Northwest, California and the Southwest rely heavily on natural gas, the report said, adding that solar units have become increasingly prevalent, especially in California, as wind capacity has grown in the Rocky Mountains, as well as along the Columbia River.
Of renewables, the report noted that the growth of wind and solar resources is driven by political, economic, and social factors. The West is characterized by a high degree of renewable potential, the report said, noting that the Southwest has the highest solar potential in the United States, and it is the only region in the country with areas of significant geothermal potential.
Among other things, the report noted that there are more than 54,000 miles of natural gas pipeline in the Western United States. Natural gas is the primary fuel source for electric power generation in California, as well as in Nevada, the report said. While the amount of natural gas consumed for generation in California is expected to be steady or decrease in future years as the penetration of variable energy resources increases, natural gas and other conventional technologies that provide essential reliability services remain critical for the reliability of the Western Interconnection, the report said.