Project Overview
Selected by Eolian as the engineering, procurement, and construction (EPC) contractor, Mortenson delivered the Seaside Energy Storage Project in northwest Portland, Oregon.
The project included a 200 MW/800 MWh battery energy storage system (BESS), a new 230 kV/34.5 kV substation, transmission and distribution infrastructure improvements, and interconnection to Portland General Electric's Rivergate Substation. Completed in June 2025, the facility provides large-scale energy storage capacity that supports grid reliability and clean energy infrastructure in Oregon.
Customer Impact
Eolian required both utility-scale energy storage infrastructure and the supporting electrical facilities needed to connect the project to the regional power system. Mortenson delivered an integrated solution that combined battery storage, substation construction, transmission improvements, and distribution upgrades into a single project.
The completed project provides substantial energy storage capacity and when combined with Portland General Electric's existing generation assets, can provide enough stored energy to power nearly 125,000 homes at peak demand for four hours.
Key Takeaways
- Delivered a 200 MW/800 MWh battery energy storage system.
- Supports grid reliability and clean energy infrastructure in Oregon.
- Provides enough stored energy to power nearly 125,000 homes at peak demand for four hours when combined with Portland General Electric's existing generation assets.
- Constructed a new 230/34.5kV substation that included a 240 MVA main power transformer supplied by the owner.
- Engineered and constructed a new 230kV transmission line using three dead-end and five direct-embed steel structures.
- Rebuilt an existing 115kV transmission line and relocated two overhead 12kV distribution circuits.
- Connected the facility to Portland General Electric's Rivergate Substation.
- Completion Date
June 2025
- Delivery Method
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Engineer, Procure and Construct
- Additional Project Facts
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200MW / 800MWh Energy Storage
230kV Substation
230kV Transmission Line
Rebuild 115kV Transmission Line
Relocate 12kV Overhead Distribution Circuits
Delivering Utility-Scale Energy Storage and Grid Integration
As EPC contractor and system integrator, Mortenson delivered a utility-scale battery energy storage facility and the supporting infrastructure required for interconnection to Portland General Electric's Rivergate Substation. The project combined energy storage, transmission, distribution, and substation work to support integration with the regional electrical system.
Building the Infrastructure Required for Interconnection
To support operation of the facility, Mortenson constructed a new 230 kV/34.5 kV substation that included a 240 MVA main power transformer supplied by the owner.
The transmission and distribution scope included engineering and construction of a 230 kV transmission line utilizing three dead-end and five direct-embed steel structures. To connect the facility to the regional power system, Mortenson engineered and constructed a 230kV transmission line, rebuilt an existing 115kV transmission line, and relocated two overhead 12kV distribution circuits.
Overcoming Challenging Site Conditions
The project team encountered challenging weather and poor soil conditions during construction. To address site constraints, the PCS units and battery energy storage system were installed on concrete foundations supported by 100-foot-deep rigid inclusions.
During commissioning, Mortenson implemented temporary weather protection measures to maintain project progress despite environmental challenges.
