IEEE 1547-2018 — Distributed Energy Resource Interconnection for Solar

IEEE 1547-2018 — Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces — is the technical standard that governs how solar systems, battery storage, and other distributed energy resources (DERs) connect to and behave on the electric utility grid. If you have submitted an interconnection application to PG&E, Con Edison, PSE&G, Eversource, or any other utility in the past several years, the inverter compliance requirements on that application are traced directly back to IEEE 1547-2018.

For solar permit designers and installers, IEEE 1547-2018 matters in two specific contexts: (1) the inverter must be certified compliant with IEEE 1547-2018 (via UL 1741 SA or SB certification) before the utility will approve interconnection; and (2) the interconnection application must document the inverter’s IEEE 1547-2018 operating settings — particularly voltage ride-through, frequency ride-through, and reactive power capability — which affects how the solar system behaves during grid disturbances.

Direct answer. IEEE 1547-2018 replaced IEEE 1547-2003 with substantially expanded requirements for distributed solar and storage systems. The key changes affecting solar installers: (1) inverters must now support voltage ride-through (the system stays on during grid voltage fluctuations instead of immediately tripping); (2) reactive power capability is now required; (3) two categories of inverters are defined — Category A (default settings suitable for most installations) and Category B (adjustable settings for utility-managed grid support, required by some utilities for larger systems). Inverter certification to IEEE 1547-2018 is denoted as UL 1741 SA (Supplementary Annex, Category A) or UL 1741 SB (Supplement B, Category B).

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Why IEEE 1547-2018 Replaced IEEE 1547-2003

The original IEEE 1547-2003 standard was written when distributed solar was a tiny fraction of total generation. Its core requirement — that DERs disconnect from the grid when voltage or frequency moved outside a narrow window — made sense for a world where rooftop solar was negligible and grid stability depended entirely on large centralized generators.

By the early 2010s, California, Hawaii, and other high-solar-penetration states discovered a serious problem: the IEEE 1547-2003 “trip and disconnect” behavior was causing thousands of solar systems to simultaneously disconnect during minor grid disturbances — the very disturbances that the grid needed DER support to manage. This phenomenon, called nuisance tripping, destabilized the grid rather than helping it.

IEEE 1547-2018 fundamentally reverses this logic. Instead of requiring DERs to disconnect during grid disturbances, IEEE 1547-2018 requires DERs to:

1. Ride through voltage and frequency disturbances within defined ranges
2. Support the grid with reactive power during voltage sags
3. Reconnect automatically after a disturbance clears rather than waiting for manual reset

This shift has profound implications for inverter design, utility interconnection requirements, and what solar permit designers must document.

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The Two IEEE 1547-2018 Categories

IEEE 1547-2018 defines two categories of DER systems with different requirement levels:

Which Category Does Your Installation Need?

For most residential and small commercial solar systems in the USA:

• Category A (UL 1741 SA) is the default requirement
• Most major inverter manufacturers (SMA, SolarEdge, Enphase, Fronius, Sungrow) have achieved UL 1741 SA certification
• Category B (UL 1741 SB) is required by some utilities for specific projects — check the utility’s interconnection application instructions

Key Utilities That Require Category B for Specific Applications:

• California IOUs (PG&E, SCE, SDG&E): Rule 21 requires UL 1741 SA for smart inverter compliance; Category B functionality may be required for advanced DER management programs
• Hawaii (HECO): Advanced inverter requirements in some interconnection tracks
• New Jersey utilities: IEEE 1547-2018 compliance required; Category A typically sufficient for residential

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IEEE 1547-2018 Key Technical Requirements

Voltage Ride-Through

IEEE 1547-2018 defines mandatory voltage ride-through requirements — the DER must remain connected during grid voltage deviations within specified ranges and time windows.

Voltage Ride-Through Table (Category A — Default):

Voltage Range (% of nominal)	Maximum Trip Time Allowed
≥ 110%	0.16 seconds (immediate disconnect)
100–110%	12 seconds (must ride through for 12 sec)
88–100%	Continuous (must ride through indefinitely)
70–88%	20 seconds (must ride through for 20 sec)
50–70%	10 seconds (must ride through for 10 sec)
< 50%	0.16 seconds (immediate disconnect)

Under IEEE 1547-2003, the threshold was much narrower — systems would trip at voltages slightly outside the 88–110% range. IEEE 1547-2018’s wider ride-through band means solar systems no longer mass-trip during normal grid voltage fluctuations.

Frequency Ride-Through:

Frequency Range	Maximum Trip Time
> 62.0 Hz	0.16 seconds
61.2–62.0 Hz	300 seconds
60.5–61.2 Hz	300 seconds
59.0–60.5 Hz	Continuous
57.0–59.0 Hz	300 seconds
< 57.0 Hz	0.16 seconds

Reactive Power Capability

One of the significant departures from IEEE 1547-2003: IEEE 1547-2018 requires DERs to have reactive power (VAR) capability.

Category A Default: ≥ 44% reactive power capability at full active power (approximately 0.9 power factor)

Category B: Adjustable volt-VAR settings; can be configured by the utility for dynamic voltage support on specific feeders

Volt-VAR Control Mode: The DER adjusts its reactive power output in response to local voltage measurements — providing VAR support when voltage is low (voltage sag) and absorbing VARs when voltage is high (overvoltage). This is the “smart inverter” functionality that utilities use to manage distribution system voltage.

Permit Documentation: For interconnection applications that request advanced inverter functionality, the smart inverter settings (volt-VAR curve, V/Hz setpoints) must be documented in the interconnection application. Default settings are pre-programmed per IEEE 1547-2018 and utilities generally do not require custom configuration for standard residential interconnection.

Anti-Islanding

IEEE 1547-2018 maintains the requirement that DERs must not sustain energization of a portion of the distribution system (island) when the utility has de-energized that section for maintenance or fault isolation. The anti-islanding requirement protects utility workers who may be working on a de-energized line from inadvertent re-energization by the DER.

IEEE 1547-2018 updates the anti-islanding testing methodology to align with UL 1741 SA certification testing, which uses a more rigorous test circuit than the original IEEE 1547-2003 test.

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UL 1741 SA vs SB — What Goes on Your Permit Package

The most practical impact of IEEE 1547-2018 for permit designers is ensuring the correct inverter certification appears in the permit package.

UL 1741 SA (Supplementary Annex — Category A):

• Confirms the inverter meets IEEE 1547-2018 Category A requirements
• Required for interconnection under California Rule 21 smart inverter mandate
• Required for many state interconnection programs (New Jersey, New York, Massachusetts, others)
• Found on the inverter cut sheet as “UL 1741 SA Listed” or similar language

UL 1741 SB (Supplement B — Category B):

• Confirms the inverter meets IEEE 1547-2018 Category B requirements including adjustable settings
• Required by specific utilities for advanced DER programs
• Less commonly required for standard residential interconnection

UL 1741 (without SA or SB):

• The original UL 1741 certification to IEEE 1547-2003
• Still valid for jurisdictions that have not adopted IEEE 1547-2018 requirements
• Not sufficient for California Rule 21, New Jersey BPU, or other IEEE 1547-2018 mandating utilities

CEC Inverter List: California also requires inverters to be on the California Energy Commission (CEC) Eligible Inverter List in addition to UL 1741 SA certification. The CEC list is accessed at: energy.ca.gov/programs-and-topics/programs/solar-equipment-lists.

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IEEE 1547-2018 Adoption by State and Utility

State / Utility	IEEE 1547-2018 Status	UL 1741 SA Required?	Notes
California (PG&E/SCE/SDG&E)	Adopted via Rule 21	Yes	Smart inverter mandate Phase 1 (2017) and Phase 2 ongoing
New Jersey (PSE&G, JCP&L, RECO)	Adopted	Yes	IEEE 1547-2018 compliance required for all DER interconnection
New York (Con Edison, NYSEG, etc.)	In process / partially adopted	Required for advanced DER programs	NYS DPS advancing IEEE 1547-2018 implementation
Massachusetts (Eversource, National Grid)	Adopted	Yes	DOER-EDERC interconnection rules reference IEEE 1547-2018
Hawaii (HECO)	Adopted	Yes	Advanced inverter requirements in DG Fast Track
Texas (TDU varies)	Partially adopted	Varies by TDU	Oncor, AEP, Entergy Texas have different requirements
Colorado (Xcel Energy)	Adopted	Yes	Solar*Connect program requires IEEE 1547-2018 inverters
Illinois (ComEd)	Adopted	Yes	Illinois Shines program (Adjustable Block) requires IEEE 1547-2018
Arizona (APS, SRP)	APS: adopted; SRP: not standard	APS: Yes; SRP: No	SRP E-27 has separate interconnection process

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Interconnection Application Documentation

For utilities that require IEEE 1547-2018 compliance documentation, the interconnection application typically requires:

1. Inverter make, model, and serial number — used to verify the inverter is on the utility’s approved inverter list (many utilities maintain their own list of pre-approved IEEE 1547-2018 inverters)

2. UL 1741 SA or SB certification confirmation — either from the cut sheet or from the inverter manufacturer’s certification letter

3. Default operating settings — for Category A inverters, confirmation that default IEEE 1547-2018 settings are used (no custom configuration required for most residential systems)

4. Volt-VAR settings (if requested) — some utilities request documentation of the default volt-VAR curve programmed into the inverter per IEEE 1547-2018 Table 8

5. Anti-islanding confirmation — typically addressed by UL 1741 SA listing; the listing confirmation is sufficient for most utilities

Utilities with Approved Inverter Lists:

Rather than reviewing individual inverter certifications, many utilities maintain approved inverter lists that pre-screen for IEEE 1547-2018 / UL 1741 SA compliance:

• California Rule 21 Approved Inverter List (maintained by CPUC/utilities jointly)
• CEC Eligible Inverter List (separate from Rule 21 list)
• Xcel Energy Solar*Connect approved inverter list
• ComEd DG approved inverter list

For permit packages, verifying the inverter appears on the utility’s approved list is often more efficient than documenting the full certification chain.

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IEEE 1547-2018 and BESS Interconnection

Battery energy storage systems connected to the grid are also DERs subject to IEEE 1547-2018. For solar+BESS systems, the BESS inverter (or the combined solar+BESS inverter) must also meet IEEE 1547-2018 requirements.

AC-Coupled BESS: For AC-coupled storage (separate BESS inverter connected at the AC side), the BESS inverter independently must meet IEEE 1547-2018 if it operates in grid-tied mode.

DC-Coupled BESS: For DC-coupled storage (shared inverter for solar and storage), the combined system is tested as a single DER against IEEE 1547-2018.

Revenue-Grade Metering and IEEE 1547-2018: Some state incentive programs (Massachusetts SMART, New Jersey TI) require IEEE 1547-2018 smart inverter functionality as a prerequisite for the incentive application. This requirement is documented in the state-specific interconnection rules but traces back to IEEE 1547-2018 as the underlying standard.

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How IEEE 1547-2018 Affects Permit Design in Practice

For day-to-day permit design work, IEEE 1547-2018 appears in three specific places:

1. Inverter specification on the SLD — include the UL 1741 SA or SB certification notation for all grid-tied inverters. This single documentation step addresses anti-islanding, ride-through, and reactive power capability in one line.

2. Interconnection application support — when helping clients complete interconnection applications for IEEE 1547-2018-enforcing utilities, confirm the inverter appears on the utility’s approved inverter list or document the UL 1741 SA listing.

3. State incentive program compliance — for SMART (Massachusetts), Illinois Shines (IL), or other programs that require IEEE 1547-2018 inverters, verify compliance before specifying equipment.

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How Heaven Designs Documents IEEE 1547-2018 in Permit Packages

• Solar Permit Design (USA) — All SLDs include UL 1741 SA/SB certification documentation for inverters in states with IEEE 1547-2018 requirements. Interconnection application support included.
• NEC 2023 vs NEC 2020 Solar Change Log — NEC 2023 changes that interact with IEEE 1547-2018 requirements.
• Massachusetts SMART Program Solar Design — SMART program engineering guide with IEEE 1547-2018 inverter requirement documentation.
• New Jersey Solar Permit Guide — PSE&G/JCP&L interconnection requirements including IEEE 1547-2018 compliance documentation.

The IEEE 1547-2018 standard page is the authoritative source. The NREL IEEE 1547-2018 technical review provides a detailed explanation of the standard changes and their grid impact. The CPUC Rule 21 interconnection page documents California’s implementation of IEEE 1547-2018 requirements. The FERC distributed energy resources policy page covers the federal interconnection policy context for IEEE 1547-2018 adoption.

Glossary: AHJ, NEC 705, SolarApp+.

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FAQ

What is IEEE 1547-2018 and why does it matter for solar installers?

IEEE 1547-2018 is the standard that defines how solar systems and other distributed energy resources connect to and behave on the electric utility grid. It matters for solar installers because: (1) most major utilities now require inverters to be certified compliant with IEEE 1547-2018 (via UL 1741 SA or SB) before approving interconnection; and (2) the interconnection application for states like California, New Jersey, Massachusetts, and others requires documentation of IEEE 1547-2018 inverter compliance. Specifying a non-compliant inverter is the fastest way to have an interconnection application rejected.

What does UL 1741 SA mean on an inverter data sheet?

UL 1741 SA (Supplementary Annex) indicates that the inverter has been tested and certified to meet IEEE 1547-2018 Category A requirements. This includes voltage ride-through, frequency ride-through, reactive power capability, and anti-islanding detection per the updated IEEE 1547-2018 test methods. UL 1741 SA is the certification mark that California Rule 21, New Jersey BPU, and other IEEE 1547-2018-mandating utilities require for interconnection approval. UL 1741 SB indicates Category B compliance — adjustable settings for utility-managed grid support.

Is my SMA, SolarEdge, or Enphase inverter IEEE 1547-2018 compliant?

All major inverter manufacturers (SMA, SolarEdge, Enphase, Fronius, Sungrow, Huawei, Delta) have achieved UL 1741 SA certification for their current-generation product lines. However, certification is model-specific — confirm the exact model and firmware version is certified, as earlier firmware versions may not be. The inverter cut sheet or manufacturer’s certification page will list the UL 1741 SA certification. When in doubt, check the California Rule 21 approved inverter list or the utility’s approved inverter list for the specific state.

Does IEEE 1547-2018 apply to battery storage systems?

Yes. Battery energy storage systems (BESS) that connect to the utility grid are DERs subject to IEEE 1547-2018. For AC-coupled storage (independent BESS inverter at AC side), the BESS inverter must independently meet IEEE 1547-2018 requirements. For DC-coupled storage (shared inverter for PV and storage), the combined system is tested as a single DER. All Tier-1 residential BESS products (Tesla Powerwall, Enphase IQ Battery, Franklin WH, SolarEdge Home Battery) have UL 1741 SA certification for their inverter/power conversion components.

What is the difference between IEEE 1547-2003 and IEEE 1547-2018?

The fundamental difference is how DERs behave during grid disturbances. IEEE 1547-2003 required DERs to immediately disconnect during voltage or frequency excursions outside a narrow range — a behavior that caused mass solar tripping during grid events. IEEE 1547-2018 requires DERs to ride through disturbances within defined windows (staying connected for up to 20 seconds during voltage sags, for example) and to support the grid with reactive power. This “grid-supportive” behavior is the key innovation of IEEE 1547-2018, enabling high penetrations of distributed solar without the grid stability risks that high-penetration 2003-standard systems created.