• Electric Rule 21 is a tariff that describes the interconnection, operating and metering requirements for generation facilities to be connected to a utility’s distribution system. The tariff provides customers wishing to install generating or storage facilities on their premises with access to the electric grid while protecting the safety and reliability of the distribution and transmission systems at the local and system levels.
  • Interconnected distributed generation99 within the three investor-owned utilities service territories totaled 1,399 megawatts (in alternate current) in 2020, a 5.4 percent increase from 2019.100 Residential continues to be the largest sector, accounting for 62 percent of the interconnected distributed generation installed (864 MW) in 2020. The vast majority of the interconnected distributed generations are for net energy metering photovoltaic, accounting or 88.0 percent of interconnections. So far, it does not appear that the COVID-19 pandemic has significantly prevented installations in California, given that 2020’s interconnections were slightly higher than 2019’s.

99 Any electricity generating technology that is installed by a customer or independent energy producer and connected to the electricity distribution system.

100 Utility interconnections governed by Rule 21. Available at:

  • Interconnected distributed generation has been on a slow decline in the commercial sector after peaking in 2016. In August 2021, California Energy Commission voted to mandate rooftop solar PV and storage on new commercial buildings. If approved for the 2022 California Energy Code, the new mandate would become effective beginning in 2023.101 This could lead to a rebound in installations from the commercial sector as well as accelerating energy storage.

101 Scully, J. California agency backs solar and storage mandate for new commercial buildings. PVTech; Solar Media Ltd. August 16, 2021. Retrieved from: