www.lesswrong.com/posts/fp3hAkLgnbsnzm8d4
2 corrections found
Unfortunately these aren't allowed anymore for residential rooftop solar.
This overstates the effect of NEC rapid-shutdown rules. SMA’s own documentation shows residential Sunny Boy systems still had NEC-compliant rooftop configurations, including one where Secure Power Supply could be enabled with TS4-R-O devices.
Full reasoning
Saying these systems "aren't allowed anymore" is too strong.
SMA's own compatibility documentation for the Sunny Boy US-41 residential inverter line says it is compatible with multiple rapid-shutdown devices for rooftop systems. In particular, the official SMA technical document "TS4 / JMS-F / RSD-S-PLC – Overview of approved SMA inverters" lists the SBx.x-1SP-US-41 residential models as compatible with TS4-O / TS4-R-O-Duo, and adds that "The secure power supply operation can be enabled if the secure power supply module has been installed according to the technical information 'TECHN_SPS-SwitchwTS4-H-en'".
That directly contradicts the blanket claim that such systems were no longer allowed for residential rooftop solar. NEC 2017 did make rapid-shutdown requirements stricter, and some configurations (for example SunSpec receiver setups like JMS-F) disable SPS. But SMA documents show there were still residential rooftop configurations that remained code-compliant rather than categorically prohibited.
2 sources
- Technical Information - TS4 / JMS-F / RSD-S-PLC: Overview of approved SMA inverters
For SBx.x-1SP-US-41 residential models, SMA lists TS4-O / TS4-R-O-Duo as compatible and states: “The secure power supply operation can be enabled if the secure power supply module has been installed according to the technical information 'TECHN_SPS-SwitchwTS4-H-en'."
- Easy, Reliable and Cost-Effective Rapid Shutdown Compliance Utilizing the SunSpec Standard - SMA Corporate Blog
SMA states it integrated a SunSpec-certified rapid-shutdown transmitter into its residential Sunny Boy US-41 inverter line, describing it as a code-compliant solution for 2017/2020 NEC rapid-shutdown requirements.
The only option now, as far as I can tell, is the recently released Enphase IQ8 Sunlight Backup
Enphase IQ8 was not the only outage-power option. SMA documented a Sunny Boy US-41 + TS4-R-O configuration in which Secure Power Supply could still be enabled on a residential rooftop system.
Full reasoning
By September 2022, Enphase IQ8 was not the only way to get daytime outage power from a residential rooftop solar system without a large battery.
SMA's official compatibility document for the Sunny Boy US-41 residential inverter line says the inverter is compatible with TS4-O / TS4-R-O-Duo devices and that secure power supply operation can be enabled when installed according to SMA's technical instructions. In other words, SMA itself documented a residential rooftop configuration that could still provide its Secure Power Supply function.
SMA's own support discussion also distinguishes between two different NEC-2017-era paths:
- JMS-F / SunSpec receiver setups meet 2017 rapid-shutdown requirements but do not allow SPS.
- A separate TS4-R-O configuration, described in SMA's technical note and quoted back to SMA staff on the company's blog, does allow the inverter to commence operation from the DC inputs during a utility outage.
That means IQ8 was not the sole option; there was at least one documented SMA alternative.
2 sources
- Technical Information - TS4 / JMS-F / RSD-S-PLC: Overview of approved SMA inverters
For the SBx.x-1SP-US-41 line, SMA lists TS4-O / TS4-R-O-Duo as compatible and says: “The secure power supply operation can be enabled if the secure power supply module has been installed according to the technical information 'TECHN_SPS-SwitchwTS4-H-en'."
- JMS-F SunSpec Certified Rapid Shutdown Device Installation - SMA Corporate Blog
In the comments, an SMA technical trainer confirms that SunSpec/JMS-F shutdown prevents SPS, but also says a separate SMA technical note about two 9-volt batteries applies to TS4-R-O units and allows the inverter to commence operation from the DC inputs when the utility grid is disconnected.