Timber Mill Substation
CORE Electric Cooperative has sought the approval of Douglas County to build, operate and maintain a new substation and linked battery energy storage system (BESS) near the western end of Timber Mill Parkway in Castle Rock.
The new substation, dubbed Timber Mill, will increase capacity to meet anticipated growth and development in the area, while the BESS will offset peak electric load times to keep rates competitive for CORE members.
Need
CORE’s existing Plum Creek and Sedalia substations currently run at near-maximum capacity. Timber Mill Substation will introduce 100 MW of additional capacity and take load off the existing substations, both of which will eventually be decommissioned.
The proposed BESS will allow CORE to store power during off-peak hours for distribution in periods in which demand is high, which helps members avoid additional fees during on-peak hours.
Location
Expansion of the existing Plum Creek and Sedalia substations is not possible because of a lack of suitable and/or available land at either site. The proposed location for Timber Mill Substation is ideal because it is adjacent to an existing 115-kilovolt transmission line between the Plum Creek and Sedalia substations.
Timeline
Construction of Timber Mill Substation and its BESS will begin in Spring 2026 and be completed by the end of 2026.
Size
The proposed site is within a 41-acre, parcel owned by CORE Electric Cooperative and zoned for Agricultural use. The substation and its yard will have a footprint of approximately 390 feet by 370 feet. The BESS and its yard will be approximately 360 feet by 370 feet.
Aesthetics
Current landscape views near the project site will not change significantly.
Transmission lines already exist in the immediate area, and the project is consistent with the Douglas County Comprehensive Master Plan 2040, which protects, where appropriate, views to and from significant natural features.
A 7-foot perimeter fence will surround the substation and BESS.
Lighting at the substation will be night-sky compliant, downcast and used only during emergencies such as unplanned outages.
Safety
Timber Mill Substation will not generate fumes, odors or particulates.
Substations emit low-frequency EMF radiation, which is non-ionizing. EMF levels decrease rapidly as it gets further from the source, mainly the transformers, and normally you will find that the EMF outside of a substation is no greater than what is inside a typical residence. Modern substations are also designed to emit lower levels of EMF and follow strict safety standards.
The BESS includes many safety features that minimize the risk of fire. Each battery unit within the BESS is continuously monitored by an on-site system to automatically detect abnormal conditions and stop operations, if needed. An off-site, 24-hour control room with trained technicians also constantly monitors the site and can remotely shut down the facility, if needed.
Additional resources
Activity
CORE anticipates just 20 vehicles will enter and exit the proposed site each average workday throughout construction.
After construction is completed, personnel will access the substation only occasionally for inspection and maintenance.