Key takeaways
- UL’s pages name UL 1741 as the standard for inverters, converters and controllers. They name UL 9540 as the standard for energy storage systems.
- A California Energy Commission (CEC) sheet, revised 30 March 2022, says an SB certificate must show UL 1741 3rd Edition, IEEE 1547:2018 and IEEE 1547.1:2020.
- UL 9540A is a fire test method. Solar Builder says "There is no certification for UL 9540A."
- UL’s Question Corner (1 July 2025) says IRC Section R328 and NFPA 855 Chapter 15 call for UL 9540 listing and installation to the maker’s instructions.
- One utility example: PG&E’s current interconnection page, checked November 2026, still states that it requires UL1741 SB certified inverters and CSIP conformance, a rule that took effect on 29 August 2023 and remains in force today.
To get listing certificates into a permit packet, see the best solar permitting software. For the storage side, see the best solar battery storage design software.
UL 1741 and UL 9540 at a glance
UL 1741 lists the inverter. UL 9540 lists the storage system. Neither is the interconnection rule. That job is for IEEE 1547, covered on the IEEE 1547 page.
| Item | Detail |
|---|---|
| UL 1741 | Inverters, converters, controllers and interconnection system equipment for use with distributed energy resources (UL page, checked October 2026). Supplement SA and Supplement SB add grid-support testing. |
| UL 9540 | Energy storage systems and equipment. UL says it covers "electrical, electrochemical, mechanical and other types of energy storage technologies". A system listing covers the combination, not only the parts. |
| How it differs from IEEE 1547 | IEEE 1547-2018 sets the interconnection requirements. IEEE 1547.1-2020 sets the test procedures (IEEE SCC21 page). UL 1741 SB is the certification that refers to those tests. A datasheet line naming IEEE 1547 is not a listing. |
| Who certifies | A nationally recognised testing laboratory (NRTL). The CEC wants a certificate from an NRTL. Its OSHA scope of recognition must include UL 1741. |
| In software | Design tools hold model numbers and equipment libraries. The listing itself is a certificate. It still goes in the permit file. |
Why UL 1741 and UL 9540 matter for installers
A missing or wrong listing can stop a permit or a utility approval, because inspectors and utilities ask for the paper. You need the certificate for the exact model, not the datasheet line.
For storage, the rule is now in the model codes. UL’s Question Corner says "All the model installation codes require Certification (Listing) for compliance with UL 9540". It also says IRC Section R328 and NFPA 855 Chapter 15 call for UL 9540 listing and labelling. The details depend on the edition your AHJ has adopted.
Utilities can name the supplement for inverters. PG&E’s interconnection page, checked November 2026, confirms its UL 1741 SB and CSIP requirement has been in force since 29 August 2023. Name the exact inverter model in the design. The listing papers go in the interconnection application and permit plan set.
Figure 1. A UL 9540 listing covers the whole storage system. A listed battery and a listed inverter bought separately do not make a listed system.
How to read a listing
Start with the standard, the edition, the supplement and the model number. Then check the firmware, the inverter type and what the AHJ asked for. Each can differ from the datasheet headline.
- Find the standard. Use UL 1741 for the inverter and UL 9540 for the system. UL 1973 names the battery alone.
- Find the supplement, SA or SB. The CEC accepts either. SB must be on the 3rd Edition.
- Check the model number. The CEC wants the exact models named and any wildcards defined.
- Check the firmware. For SA, the CEC wants a test report that names the firmware.
- Check the inverter type. The CEC wants "Grid Support Utility Interactive" on the certificate.
- Check what the AHJ or utility asked for. Attach the certificate. A datasheet is not enough.
UL 1741 SA and SB differ. Solar Builder says SA certifies grid-support functions of smart inverters. Examples are anti-islanding, ride-through and volt-var modes. It says SB added an interoperability test under IEEE 1547.1-2020. The IEEE SCC21 page says a 3rd Edition of UL 1741 was published 28 September 2021. See anti-islanding for the trip behaviour.
Worked example: what three datasheet lines show
This is a paperwork check. It is not a calculation. Cases A and B are invented sheet wordings. Case C is the line in Tesla’s 2024 Powerwall 3 North America datasheet.
| Case | Printed on the sheet | What it shows | Ask for |
|---|---|---|---|
| A (example inverter) | "UL 1741" | An inverter listing. No supplement is printed. So grid-support testing is not shown. | The certificate with SA or SB and the edition. |
| B (example battery) | "UL 1973, UL 9540A" | A battery component listing and a fire test method. No system listing is printed. | The UL 9540 system listing, or the AHJ’s written route. |
| C (Powerwall 3) | A long line that includes UL 1741, UL 9540, UL 9540A, UL 1741 SB, UL 1973 and IEEE 1547.1, plus others | The maker claims system, inverter and battery listings. The IEEE items are standards. They are not marks. | The certificate for your model and the NRTL listing page. |
A printed line is a claim by the maker. The certificate and the model number prove it.
How solar software handles UL 1741 and UL 9540
We checked two tools, and neither states a listing check. SolarAPP+ lists UL equipment types on its help page, while Aurora’s pages do not mention UL 1741 or UL 9540.
| Software | Does it check the UL listing? |
|---|---|
| SolarAPP+ | Lists UL 1741 and UL 9540 equipment types. A certificate check is not stated |
| Aurora Solar | Not stated |
Not stated: the company page we cite does not say.
- SolarAPP+: The help page "Is my Energy Equipment Supported on SolarAPP+?" lists "UL 1741 / Inverters" and "UL 9540 & 9540A Batteries". It says the tool "uses the CEC database to populate its Module/Inverter/Battery fields". It does not say the tool reads a UL certificate. Page last updated 6 July 2026. A second page, last updated 29 April 2026, says the SolarAPP Foundation keeps a database of reviewed UL 9540A reports. An AHJ may approve per product.
- Aurora Solar: The Components help page and the article on approved company lists for third-party-ownership financiers do not mention UL 1741, UL 9540 or certification. Both pages are undated and were read in October 2026. The list shows only what those two pages print.
Common mistakes with UL 1741 and UL 9540
UL 1741 and UL 9540 rules by jurisdiction
The local code or utility sets the listing rule. UL does not. Each example comes from a page that names its jurisdiction.
- California (CEC). The sheet, revised 30 March 2022, asks for an NRTL certificate to UL 1741 with SA or SB. SolarAPP+ says it fills equipment fields from the CEC database.
- PG&E (California utility). Its interconnection page, checked November 2026, says PG&E "will require interconnection applicants to use UL1741 SB Certified inverters" and CSIP conformance "starting on August 29, 2023". That date has long passed and the page still carries the requirement, so it is now a live rule, not a future one. PG&E’s Rule 21 advice letter 6635-E-C (May 2023) revised Section Hh to add UL 1741 SB and IEEE 1547-2018 voltage and ride-through values alongside the existing text, confirming the earlier footnote that Section Hh "will also be revised".
- Massachusetts. The town of Brookline’s page quotes NFPA 855 (2020) Chapter 15, which is part of the Massachusetts fire code (527 CMR 1.00). Section 15.2.1 says an ESS of 1 kWh or more "shall be listed and labeled in accordance with UL 9540". Section 15.8.1 says inverters must be listed to UL 1741 "or provided as part of the UL 9540 listing".
- Washington State. MyBuildingPermit.com’s Construction Tip Sheet 26 (24 April 2025) cites the 2021 IRC R328 with Washington amendments. It says an ESS "shall be listed and labeled in accordance with UL 9540". A UL 9540A report can support smaller separation distances.
FAQs
Is UL 1741 the same as IEEE 1547?
No. IEEE 1547-2018 sets interconnection requirements. IEEE 1547.1-2020 sets the test procedures. UL 1741 SB is the listing that uses those tests. Read the IEEE 1547 page for the requirements.
What is the difference between UL 1741 SA and SB?
SA certifies grid-support functions, and SB adds an interoperability test, says Solar Builder. The test is under IEEE 1547.1-2020, and it uses DNP3, IEEE 2030.5 or SunSpec Modbus. The CEC asks an SB certificate to show the 3rd Edition. Check which one your utility names.
Does UL 9540A certify a battery?
No. UL calls UL 9540A a test method for thermal runaway fire propagation. Solar Builder says it cannot be listed. A UL 9540 listing is a separate document.
Is a UL 1973 battery plus a UL 1741 inverter enough?
Not by UL’s account. UL’s Question Corner says: "Simply combining individual, independently certified products in the field does not result in a certified (Listed) system." Ask your AHJ which route it accepts.
Where do I find the certificate?
Ask the maker for the certificate. Give your exact model. An EPRI Q&A says certified products will be on the NRTLs’ websites. In California, SolarAPP+ says it uses the CEC database.
Related terms
- IEEE 1547: the interconnection standard UL 1741 SB tests against.
- Anti-islanding: the trip function that grid-support listings test.
- Hybrid inverter: an inverter that also handles a battery.
- Battery management system: the controller inside a battery.
- Arc-fault protection: covered by a separate product standard, UL 1699B.
Next step: get the certificate for each exact model, with supplement and edition. Then see the best solar permitting software list, or the best solar battery storage design software.
Sources
All pages below were checked in October 2026, except the two PG&E items re-checked in November 2026. Where no date is shown, the page printed none.
- UL: PV inverter page.
- UL: energy storage system page.
- IAEI: UL Question Corner, 1 July 2025.
- CEC: Inverter Listing Request Instructions (30 March 2022).
- EPRI: questions and answers on IEEE 1547-2018.
- IEEE SCC21: IEEE 1547-2018 page.
- Solar Builder: smart inverter overview and UL 9540 versus 9540A.
- PG&E: UL 1741 SB requirements and PG&E: interconnections and renewables (checked November 2026).
- Brookline, Massachusetts: ESS permits.
- MyBuildingPermit.com: Tip Sheet 26 (24 April 2025).
- SolarAPP+ help: equipment (6 July 2026) and UL 9540A (29 April 2026).
- Aurora help: Components and AVL selection.
- Tesla: Powerwall 3 datasheet, 2024.
Last updated 3 November 2026. Next scheduled review: 30 January 2027.