Battery Energy Storage System (BESS)

Project Overview

The Bainbridge Island battery energy storage system (BESS) is a part of PSE’s hybrid solution to meet Bainbridge Island’s energy needs. The hybrid solution is designed to address Bainbridge Island’s electric reliability, capacity and aging infrastructure.  

The BESS will primarily store energy. It will then deliver this energy to Bainbridge Island customers for a short time when demand for power is high (also known as peak demand). For example, the BESS could provide more electricity when residents turn up the heat in the winter mornings and evenings. By providing this extra energy, the BESS allows customers to keep using their electricity as normal, keeping the lights on and homes and businesses warm during times of high power use.


PSE plans to install a 3.3 MW battery energy storage system (BESS) in the existing Murden Cove Substation site. To accommodate the BESS, we will expand the substation’s fenced area to install the battery and related equipment.   


Currently, the BESS is in the design phase. The Murden Cove Substation improvements for the Murden Cove – Winslow 115 kV transmission line and the BESS work are scheduled for 2025/26. This schedule could change, depending on the status of permit approvals and the progress of construction. We will keep you updated as the project progresses.

About the BESS 

The proposed Bainbridge Island BESS is a lithium-ion battery. Utilities commonly use lithium-ion batteries to help ensure a reliable supply of energy. Lithium-ion batteries also power common devices you use daily such as mobile phones, laptops, electric vehicles, and many other consumer electronics. 

PSE has selected a battery system manufactured by Contemporary Amperex Technology Co. Limited, also known as CATL. CATL is one of the largest lithium-ion battery manufacturers in the world. The battery selected for this project has a preferred modular design, is highly reliable, and has a comprehensive set of safety measures within its design. 

The BESS will include all the components to charge and discharge energy storage, including the connection to the substation, the energy storage reservoir, controls, monitoring, diagnostics, communications and more.  

This BESS project will be PSE’s largest utility-scale battery to date. As part of the hybrid solution, it could serve as a model for future projects in our service area.  

Engaging with the community 

We’re in the early stage of the BESS project and will keep the community informed of our progress. We plan to engage the community through written materials, in-person meetings and more. Please contact us if you have questions or would like us to speak with your community group. 

Hybrid solution for Bainbridge Island

The BESS is one part of PSE’s hybrid solution to improve electric reliability and capacity on Bainbridge Island. PSE is committed to considering new technology and incorporating non-wire alternatives into the electric system. Other projects in the hybrid solution include the new Murden Cove – Winslow 115kV transmission line, the Winslow Tap Rebuild project, substation improvements, a demand response program called Peak Energy Rewards, and energy efficiency programs. 


Project phase: design

Construction: 2025/26