Update: California Installers - Are Your Inverters Ready for the Rule 21 Mandate?

Jul 16, 2018

Update: California Installers - Are Your Inverters Ready for the Rule 21 Mandate?

It is important to note that Rule 21 governs interconnections made to California's investor-owned utilities (IOUs), those regulated by the California Public Utilities Commission (PUC), like Pacific Gas & Electric Co. (PG&E), Southern California Edison (SCE), and San Diego Gas & Electric Co. (SDG&E). Other municipal utilities in the state, like SMUD or LADWP, are likely to voluntarily comply with or adopt similar standards.

Haven’t been following along? Have no fear. We’ve got you covered. In this post, we’ll discuss all the most timely and relevant details.


OK, so what is California Rule 21?

California Rule 21 governs the interconnection agreement that homeowners and utilities sign before new solar energy systems can send electricity to the grid. Starting Sept. 8, 2017, California utilities including PG&E, SDG&E, and SCE require additional functionality from the inverters that are allowed to connect to the grid. Smart inverters may proceed.

Many states often follow the lead of California, so installers around the country might want to pay attention as well.


Why crack down on dumb inverters?

According to Governor Brown’s “Goals for Adding Renewable Capacity in California,” the state is on the path to installing 12,000 megawatts of rooftop solar systems and other distributed energy resources (DERs) by 2020. These resources have great potential to reduce energy costs and improve grid reliability, but first they require some upgrades to the grid. Namely, the grid must be able to handle two-way power flows and it must be able to better handle intermittent resources like solar energy.

Before the solar industry started adding huge amounts of generating capacity to the grid, solar inverters were instructed to switch off at the first sign of a grid disturbance. This approach backfires when there’s a lot of solar on the grid, because the sudden loss of generating capacity can set off a cascading effect that inadvertently increases grid volatility.

This is why Enphase has often said that a solar inverter needs to be smart to be a good citizen of the grid.


Rule 21 will take effect in three phases.

Phase 1 covers an initial set of AGF requirements, including voltage and frequency ride-through, extending the times that solar energy systems can continue to operate while grid conditions are in flux, as well as methods of reactive power control to help regulate grid voltage. For more information about how solar inverters handle reactive power, check out this article from IEEE Spectrum.

Update July 9, 2018

Recently CPUC Resolution E-4920 was circulated by the IOUs, outlining that PV interconnection applications submitted after July 26, 2018 will need to have the reactive power priority (RPP) setting activated as the default Volt/Var function. Reactive power Volt/Var capability was implemented in all Enphase Rule 21 compliant inverters as of September 8, 2017. This additional phase 1 requirement is met with the application of a new grid profile (CA Rule21 201807 VV w/RPP) application (software). Installers, homeowner and third-party system owners can learn more about the latest requirements here.

Phase 2 will set a common language for how inverters, solar energy systems, and utility systems talk to one another. Systems must also be able to communicate over the internet, although they can’t yet be required to have an internet connection because California has yet to decide who should pay for internet connection—the utility or the homeowner.

Phase 3 will cover additional inverter functions, like data monitoring, remote connection and disconnection, and maximum power controls.

The timelines for adopting Phases 2 and 3 have not been settled yet.


What does this mean for Enphase installers?

All Enphase S-Series and IQ-Series Microinverters already perform all the advanced grid functions (AGF) required by Rule 21. In addition, Enphase’s cloud-based infrastructure ensures that our microinverters will be able to keep up with changing requirements in the future.

For an example of how Enphase can remotely upgrade large numbers of microinverters to promote grid stability, have a look at our groundbreaking collaboration with Hawaiian Electric Company.

The trendlines are clear. State policymakers are nudging utilities and homeowners to adopt smart technologies like energy storage and home energy management systems to pave the way toward a more stable grid that can support more solar and other DERs. Enphase has built the technology platform to help realize California’s vision—one that increasingly resembles our own vision of what’s possible with smart energy.

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