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King County Washington home

Battery energy storage systems (BESS)

These systems store electricity from the grid or on-site generation sources, including solar and wind. Some energy sources don’t produce power continuously, and a BESS can store electricity when it’s available and release it when it’s needed. At different scales, BESS may be used to support electrical grid operations or to provide backup power for homes and businesses.

Depending on size, location, and design, BESS projects may raise considerations related to safety, environmental impacts, and land use compatibility. These factors are evaluated through applicable codes, permitting processes, and, in some cases, public review.

Battery energy storage systems vary in size, ranging from small residential units of a few kilowatts to large utility-scale systems of 100 megawatts or more.

Battery systems are allowed in most of King County’s unincorporated areas, subject to zoning and permitting requirements. In agricultural areas, they may be allowed as an accessory use, with size limits and other conditions defined in code.

What King County evaluates

When reviewing BESS proposals, King County evaluates compliance with applicable codes and regulations. Depending on the project, this may include considerations such as…

  • Fire and life safety requirements
  • Environmental impacts (including SEPA requirements, when applicable)
  • Site design, landscaping, and stormwater management
  • Closeness to critical areas and sensitive uses
  • Noise and operational standards
  • Infrastructure and access requirements

Permit application process

Permits and reviews that may be required

There are several permits and reviews that could be required for a larger BESS project, including the following.

  • Land use: Conditional use permit/special use permit if in forestry or residential zones.
  • Zoning review for projects not subject to a conditional or special use permit.
  • Clearing and grading permits or site development permits.
  • State Environmental Policy Act (SEPA) review may be required depending on project characteristics and applicable exemption thresholds. This review includes environmental checklists, impact analysis, mitigation, and public comment periods.
  • Building/Electrical: For buildings, structural and building code standards. Electrical system compliance; electrical permits permitted through State Department of Labor and Industries.
  • Fire/system safety: Fire permit required for fire suppression systems, storage of hazardous materials, and compliance with updated International Fire Code (thermal runaway protections, ventilation, spill control).
  • Site development related reviews that might include surface water management, erosion control, land clearing and grading, flood development, critical areas compliance, landscaping.
  • Certain projects may need a National Pollutant Discharge Elimination System (NPDES) permit. These are administered by the Washington State Department of Ecology.

King County permitting process

  • Pre-application meeting (optional): Applicants may request a pre-application meeting to discuss the project scope, development, and related regulations, and the application process and requirements.
  • Application process: The application process depends on the location of the project, the presence and impact to critical areas, and the size and scope of the proposal.

    Once an application is filed, the Permitting Division will screen it for completeness. Customers are notified if any information is missing and have an opportunity to respond within 30 days from request for information. This screening process can take weeks or months.

    After the application is determined to be complete and the applicant has paid the application review fees, the application moves into the official review process.

    If a public notice is required, the notice is usually given within 14 days after the application is determined to be complete.

    Depending on permit type, King County review times range between 60 and 170 county review days. Plan review is a collaborative process among applicants, county staff, and outside agencies. This does not include the time when the applicant is responding to questions, corrections, or clarifications, or when the county is waiting for payment. Times can vary for other reasons as well.

  • Public notice if required: If the project triggers review under the State Environmental Policy Act (SEPA) or requires a Conditional Use or Special Use permit, public notice will be provided in accordance with King County code. King County typically publishes this notice in the Seattle Times and on the King County Permits website; requires the applicant to post at the property; and mails a notice to property owners within 500 feet consistent with King County code. This process provides an opportunity for community members to submit written comments regarding environmental impacts and potential mitigation for those impacts.

    If the project does not trigger review under SEPA or requires a Conditional Use or Special Use permit, there likely will not be a public notice.

  • Decision and post-approval: We issue permits after all reviews are satisfied, and the applicant has demonstrated compliance with applicable codes and regulations. Where the project requires a Conditional Use Permit or Special Use Permit, a separate decision on that permit will be issued.
  • Inspections: Various inspections may need to occur after a permit has been issued, including site development, building, fire or ecological inspections. Other agencies such as Washington state Labor and Industries and Public Health – Seattle and King County may also inspect for electrical permits or septic systems, respectively.

Rules and regulations

Battery energy storage systems of all scales are allowed on nearly 97% of King County’s unincorporated land area. For the remaining 3% of the land—primarily agriculture land—battery energy storage systems are allowed as an accessory use, up to 2 megawatts on-site. This leaves flexibility for farmers to store energy for their own use and to participate in energy sharing with their neighbors, subject to size limits and use restrictions defined in code.

Ordinance 19824 establishes regulations for such systems under the King County Code, covering zoning, safety, insurance, environmental protection, and financial responsibility. Many of the standards are found in King County Code 21A.08.100.

Size and complexity will make a difference to the scope of standards. BESS installations would still be subject to compliance with critical areas protection, stormwater, landscaping, site development standards, noise standards, and potential review under SEPA, depending on scope and size.

Other standards may include:

  • Washington State adopted Building, Fire and Electrical Codes and standards
  • Seattle-King County Public Health standards for facilities that necessitate sewer and/or water service

Resources

Related legislation

King County: In October 2024, King County enacted Ordinance 19824, establishing regulations for BESS installations under the King County Code covering zoning, safety, insurance, environmental protection, and financial responsibility.

County codes that may be relevant include Title 20, Title 21A, Title 9, and Title 16.

Washington state resource

Battery energy storage system (BESS) (Washington State Energy Facility Site Evaluation Council)

Building code resources

King County Code definitions

Battery energy storage system – A system consisting of one or more rechargeable batteries assembled together, capable of storing energy to supply electrical energy at a future time. Such systems typically include battery chargers, controls, power conditioning systems, and associated electrical equipment, and are typically used to provide standby or emergency power, uninterruptable power supply, load shedding, load sharing, smoothing and dispatching of intermittent renewable energy sources, or similar capabilities.

BESS accessory to commercial or industrial use – Battery energy storage systems are considered a commercial/industrial accessory use when the total system capacity is two megawatts or less, and…

  1. the system provides electricity for on-site use only, including net metering as well as charging of vehicles on-site or in the right-of-way immediately adjacent to the site; or
  2. the system is intended primarily for on-site use, but also participates in load sharing or another grid-connected electricity-sharing arrangement.

Information about active applications

Public comment

When a public notice or comment period is required, comments may be submitted to the contact identified on the notice.