All of the electricity consumed on Mercer Island is provided by Puget Sound Energy (PSE) under a franchise agreement with the City of Mercer Island. An agreement was approved in early 1994 that is valid until a new agreement is reached. PSE’s rates are set by the Washington Utilities and Transportation Commission (WUTC).
In 1999, PSE had 9,169 customers on Mercer Island, compared to 8,971 in 1992.
In 2004, PSE served 9,300 customers, and 9,562 customers in 2014.
PSE builds, operates and maintains the electrical system serving Mercer Island. The system includes 6.2 miles of transmission lines (115 kV), three substations and two submarine cable termination stations.