Interconnection Standards

March 11, 2016


Note: The California Public Utilities Commission (CPUC) approved a proposed settlement in September 2012, enacting the first fundamental redesign of Rule 21 since 2000. The complete revised Rule 21 Tariff, as described at a high level below, can be found beginning on page 136 of CPUC Decision 12-09-018. The individual tariffs adopted by the utilities can be found on the CPUC web site above.

California's "Rule 21" generally applies to systems connecting to an investor-owned utility’s distribution grid, non-export generating facilities connecting to an investor-owned utility’s transmission grid and all net metered facilities in an investor-owned utility’s service territory. Systems connecting to an investor-owned utility’s distribution grid for the purpose of participating in a wholesale transaction must apply under the investor-owned utility’s Wholesale Distribution Access Tariff. Systems connecting to the transmission grid must apply to the California Independent System Operator for interconnection. Systems connecting to the grid of a municipal or cooperative utility must follow the interconnection procedures adopted by that utility.

Rule 21 clearly defines a series of screens meant to filter applicants into the study path most suited for their project. It also establishes fixed timelines for the screens intended to speed the process of approval. Also defined in the tariff are a variety of fees and deposits required at various stages of the interconnection process. Net metered facilities are exempt from most of these fees.

Fast Track Eligibility
Non-exporting systems (sized and designed so that the electricity is only used on-site and will never deliver electricity to the grid) and all net metered systems, regardless of nameplate capacity, can qualify for Fast Track. Exporting facilities may also be considered for Fast Track if they meet certain size restrictions or if the owner agrees to certain utility-approved protective devices.

After a customer applies for interconnection, the utility performs an Initial Review. If the applicant passes through Initial Review, the system will be able to interconnect without a Supplemental Review. If Supplemental Review is required, the applicant will be notified and can elect to have their application withdrawn, or proceed through the next layer of screens.

Detailed Study Eligibility
Systems not eligible for Fast Track may apply for interconnection through a detailed study process. The detailed study options include an Independent Study Process, a Distribution Group Study Process or a Transmission Cluster Study Process. The parameters for each process are provided in Rule 21.

Program Overview

Implementing Sector: State
Category: Regulatory Policy
State: California
Incentive Type: Interconnection
Web Site:
Start Date:
Eligible Renewable/Other Technologies:
  • Geothermal Electric
  • Solar Thermal Electric
  • Solar Photovoltaics
  • Wind (All)
  • Biomass
  • Hydroelectric
  • Municipal Solid Waste
  • Combined Heat & Power
  • Fuel Cells using Non-Renewable Fuels
  • Landfill Gas
  • Wind (Small)
  • Fuel Cells using Renewable Fuels
  • Other Distributed Generation Technologies
  • Microturbines
Applicable Utilities: Investor-owned utilities
System Capacity Limit: No limit specified
Standard Agreement: Yes
Insurance Requirements: Vary by system size and/or type; levels established by CPUC
External Disconnect Switch: Varies by utility and system size
Net Metering Required: No


Name: CPUC decision 12-09-018
Date Enacted: 09/13/2012
Effective Date: 09/13/2012


Name: Marc Monbouquette
Organization: CPUC, Energy Division
Phone: (415) 355-5504

This information is sourced from DSIRE; the most comprehensive source of information on incentives and policies that support renewables and energy efficiency in the United States. Established in 1995, DSIRE is operated by the N.C. Clean Energy Technology Center at N.C. State University.