Extreme Heat Wave: Seattle City Light’s System Capability and Response

As our region grapples with a historic heat wave, Seattle City Light is carefully monitoring external conditions and our systems to maintain reliable power to our customers in Seattle and our surrounding communities. We have brought in extra crews to respond to unplanned outages and we have postponed planned outages at least through Tuesday, June 29 to minimize the impact on customers.  

It takes three things to create the magic that happens when we flip the light switch (or the AC, if you’re among the fortunate 44% in Seattle): 

  1. Adequate supply of power – We are participating in daily calls with the Northwest Power Pool (NWPP), which manages resource adequacy across the region. While utilities in the Northwest typically see their highest demand in the winter, not the summer, the NWPP continues to report adequate resources to meet the demands of this sustained heat wave. Great news for us and our customers! The fact that we are a hydropower region, not overly dependent on intermittent resources like solar and wind, is very helpful in this situation. Today, we’re expecting to see a peak load about 30% higher than a typical June day that hits around 70 degrees, or about 20% higher than past historically hot June days that reach the 90s.
  2. A grid capable of bringing the power supply to City Light’s service territory – The grid refers to the interconnected transmission system. City Light owns some transmission, particularly the high voltage lines that bring power from our Skagit Hydroelectric Project to the city of Seattle. Most of the transmission we utilize is owned by the Bonneville Power Administration and it is BPA’s transmission lines that deliver BPA power to City Light (hydro power produced on the federal Columbia River Power System) as well as power produced at our Boundary Hydroelectric Project in northeastern Washington. The grid is currently operating without issue. The biggest risk is around wildfires and BPA’s potential need to activate a public safety power shut-off (PSPS) protocol to prevent wildfires. We are actively monitoring BPA’s situation and the good news is, as of right now, we are not experiencing the kind of winds that would increase wildfire risk.
  3. A distribution system capable of delivering power to our customers – The bulk of City Light’s distribution system is overhead, although we do have parts of the system served via underground conduit and we also operate a network serving downtown and parts of South Lake Union. The heat is especially hard on underground infrastructure and the majority of outages over the past few days have been heat-related. Unfortunately, it takes more time to locate and repair underground equipment failures and our restoration speed is also impacted by excessive heat in the vaults that house that equipment – we are working hard to restore service quickly while keeping our employees safe.

    At the peak on Sunday, June 27, we had about 1,700 customer meters out of ~480,000 without power at one time. We expect we could see similar outages with the heat continuing through today and we are prepared to respond as quickly as is safely possible. 

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