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    Understanding Rule 21 in California & Beyond

    Rule 21 Solar: What Is It?

    Rule 21 Solar is an interconnection tariff that was originally adopted in 1982 by the CPUC (California Public Utilities Commission), as a means of controlling distributed generators that are hooked up to the electric grid.  The CPUC is the regulatory body that regulates utilities like electric service, water, natural gas, and telecommunications providers.

    Rule 21 for Solar is not new. It has, however, been updated, and the new rule has some implications for solar energy installations. 

    Whether it’s a solar system, a wind turbine, or a diesel generator, Rule 21 sets some guidelines for what type of equipment can be used and how it needs to be set up. These distributed generators are known as DER’s (distributed energy resources). 

    One of Rule 21’s functions is to optimize the way these DER’s interact with the existing electricity grid infrastructure. The goal of the updated California Rule 21 is to ensure the safety of the electric grid and to prevent disturbances. By increasing the control capabilities of DER’s, the grid can be operated with greater ease and efficiency. 

    What are the changes to California Rule 21?

    The changes to Rule 21 are essentially aimed at increased grid safety and reliability. 

    The new rule dictates that all solar inverters installed in California must be “Smart” Inverters. These are inverters with a wider range of operational capabilities.

    These additional operational capabilities allow the inverters to work more smoothly with the power grid and to communicate with the utility. These functions can decrease stress on the grid by utilizing a suite of communications and electrical monitoring technologies.

    Here’s a good summation of the spirit of the changes, as told by Ben Ealey, senior project manager at the Electric Power Research Institute: 

    DERs (Distributated Energy Resources) are developing rapidly to provide new capabilities in serving customers and the grid. Yet without a standard way for utilities to communicate with new technologies, they cannot reach their full interactive potential. We closed gaps in older communication models, which didn’t have the ‘words’ to command new capabilities of smart inverters and battery storage. We’ve added ‘new words’ for utility grid operators to use that can unlock emerging capabilities of DER, most specifically within the storage domain.”

    Ben Ealey | Sr Project Manager | Electric Power Research Institute

    Rollout Schedule for California Rule 21 Solar Updates

    buildings with solar and wind energy integrated

    Rule 21 Solar Updates in 3 Phases 

    Phase 1

    Requires Installation of Compliant Solar Inverters

    The first phase of the Rule 21 update was put in place in the Fall of 2017. Specifically, the update stated that inverters for all new solar projects must comply with UL 1741–SA or anything inverter approved and listed on California Energy Commission’s database of compliant solar inverters

    The features of acceptable inverters include;

    • soft start reconnection
    • ramp rate controls
    • fixed power factor
    • volt–VAR management, and
    • updated anti-islanding requirements (among other things). 

    Phase 2

    Requires All Inverters to Have Internet Communication

    The 2nd phase went into effect in 2018, and it largely deals with inverter communication requirements. Most inverters already communicate over the internet, for the purpose of monitoring system production. Phase 2 of Rule 21 mandates some more advanced communication capabilities so that the utilities can use the inverters as data points as they assess the grid as a whole. 

    Phase 3: Not Yet Determined

    The final phase of the CA Rule 21 update will require new inverters to have some additional functions. The list of approved PV inverters may change in the future.

    Expect Rule 21 to Spread Beyond California

    As solar continues to become more prevalent in other states beyond California, it will be important for the stability of the grid to require smart inverters on all new solar installations. This will prevent states from forcing solar customers from requiring them to retrofit their existing systems. 

    Given California leads the nation in solar energy, it is likely that any smart inverters approved by the California Energy Commission will meet future standards in other states. Currently, the other states considering requiring smart inverters are Arizona, Massachusetts, Nevada, Vermont, and Hawaii. 

    rows of rule 21 solar complaint equipment

    Working With Rule 21 – Avila Solar Can Help

     It will be important for your company to keep an eye out for upcoming inverter regulations in the states and municipalities where you work. This is where we can help. At Avila Solar, our professional solar PV designers will build your solar permits that meet all local, state, and national safety regulations. We 100% guarantee our work or your money back! Contact us today to learn more about or solar permit services.

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