Arizona Public Service, Puget Sound Energy enter the EIM
ISO real-time market is now providing low-cost energy to consumers in eight western states
FOLSOM, Calif. – After months of intensive testing, Phoenix-based Arizona Public Service (APS)
and Puget Sound Energy (PSE) of Washington state successfully began full participation in the
western Energy Imbalance Market (EIM) on Saturday, October 1.
The real-time wholesale power market managed by the California Independent System Operator
(ISO) enables participating utilities to buy low cost energy available across eight western states.
APS and PSE join NV Energy, which serves 90 percent of Nevada, and PacifiCorp, which has
customers in six states, as part of the Energy Imbalance Market.
“Participation by Arizona Public Service and Puget Sound Energy in the EIM will strengthen the
market and yield substantial benefits in the form of access to low cost energy for them and for all
EIM participants,” said Steve Berberich, ISO President and CEO. “I want to thank the utilities for
their hard and collaborative work in preparing for the EIM and appreciate their commitment to the
The EIM uses ISO’s state-of-the-art software to automatically analyze western grid needs and find
the lowest-cost generation to meet demand every five minutes. Participating utilities also can
access low-cost renewable energy in other western states in real time to offset power generated
from local energy plants. From January to June this year, greenhouse gas emissions were
reduced by an estimated 292,000 metric tons because of EIM participation. This is equivalent to
the emissions otherwise generated to power nearly 31,000 homes for one year*.
Since launching in November 2014, the Energy Imbalance Market has produced benefits of more
than $88 million dollars by effectively using the low cost energy available in the region to meet
changes in real-time energy demand. Those savings are projected to increase as more utilities
join the EIM.