• Home
  • -
  • Rule 21: Three Utilities, Three Phases

Last Updated undefined NaN, NaN

Rule 21: Three Utilities, Three Phases



California’s Rule 21 moderates the interconnection of new distributed generation systems to the grid. System owners/end users must work within the guidelines set by their utility service. As noted on the following linked page, “Each investor-owned utility is responsible for administration of Rule 21 in its service territory and maintains its own version of the rule.”

Furthermore, Rule 21 has been split into three phases of implementation, the first of which has already been enacted. As a whole, Phase 1 established a baseline for advanced grid function requirements of smart inverters. More information is available on each utility’s Rule 21 website. The CPUC resolution discussed below adds an additional requirement to Phase 1 and is in effect at the time of this article.



Phase 1 Update Effective July 26, 2018


CPUC Resolution E-4920 states that solar PV interconnection applications submitted after July 26, 2018 must activate the reactive power priority (RPP) setting as the default Volt/Var function. Most California-approved Rule 21 compliant inverters can meet this additional phase 1 requirement by applying a new grid profile (CA Rule21 201807 VV w/RPP) application (software).


We at Renvu have compiled a list of the primary inverter brands we offer and compiled their respective Rule 21 information below:

Enphase: The IQ6, IQ6+, IQ7, and IQ7+ can be properly configured before, during, or after the installation. For Enphase’s statement advisory on Rule 21, read here.

APsystems: The YC600 features reactive power control and is Rule 21 compliant in California.

SolarEdge: SolarEdge supplies a proprietary SD or microSD card with its inverters which can be loaded with firmware upgrades. Per this Rule 21 installation guide, inverters may need to be visibly labeled to reflect Rule 21 compliance.

SMA: “SMA’s residential inverter lines, the Sunny Boy US-40 and Sunny Boy Storage US-10, and commercial string inverter lines, the Sunny Tripower TL-US-10 and Sunny Tripower CORE1-US, will prioritize reactive power when you correctlyenable the required CA Rule 21 Phase 1 settings.”



What About the Next Phases?

Phase 2 will standardize a common language for inverters and utility systems to communicate. Systems will eventually be required to communicate over the internet, although California has to decide who should pay for internet connection - the utility or the homeowner. Phase 2 is to be activated nine (9) months after the release of an industry-recognized communication protocol certification standard for inverters. The release of this certification standard has not been determined at the time of this article.

Phase 3 will cover additional inverter functions, like data monitoring, remote connection and disconnection, and maximum power controls. The timeline for adopting Phase 3 has not been settled yet.