An abundance of inverter headlines were released around Solar Power International this year, many revolving around the SunSpec Alliance’s new rapid-shutdown communication standard.
The “communication signal for rapid shutdown interoperability specification” may seem like a mouthful, but it addresses a key, and somewhat controversial, part of the 2017 NEC code that requires all rooftop PV modules installed after December 2018 to stop electricity generation within 30 seconds. Supporters say the move will increase safety for first responders.
However debatable, NEC 2017 rapid-shutdown requirements have been published but won’t be enforced until January 2019, giving the industry time to develop technology to meet them. The new SunSpec standard is part of this development.
SunSpec is a trade alliance that develops and publishes free, open interoperability specifications that software developers and hardware manufacturers use to ensure their solutions communicate. This takes the guesswork out of a project and makes it easier and cheaper to build projects, therefore accelerating the deployment of solar.
SunSpec’s rapid-shutdown specification is a communication protocol that defines how the modules, inverters and other control systems interact to get the job done. In more technical terms, modules and a master control device (sold through the inverter manufacturer) use solar array cabling to transmit messages over DC power lines. Module manufacturers implement the protocol within the junction box of each panel. The inverter’s master control device (often referred to as a rapid-shutdown “box”) then communicates with the PV modules.
So if contractors see that a module or inverter is compliant to the SunSpec standard, they know the components will be able to work together to comply with NEC 2017 rapid-shutdown. This plug-and-play interoperability makes it simple to meet requirements at a low cost.
“After nearly two years of intense technical collaboration amongst competitors and business partners within the Alliance, the SunSpec communication signal for rapid shutdown specification is now ready for implementation,” said Tom Tansy, chairman of the SunSpec Alliance, in a news release. “This open standard delivers multiple benefits to the distributed energy industry, most notably lower integration costs and the freedom to choose from an array of interoperable products.”
Many manufacturers—including ABB, Fronius, Maxim Integrated, Omron, Outback, SMA and Texas Instruments—announced plans at SPI to incorporate the protocol. Microinverters inherently meet rapid-shutdown codes because they attach to each panel, and string inverter manufacturers are starting to offer SunSpec-certified solutions to also achieve module-level rapid shutdown.
Fronius announced its new Symo Advanced string inverter actually integrates communications compliant with the SunSpec protocol directly inside the inverter, so no extra box is needed. It also offers a box solution for the rest of its inverters.
“Fronius strongly believes in industry standards and innovation to drive down cost and allow customer choice,” said Michael Mendik, head of Fronius solution management USA, in a news release. “We strive to provide our customers state-of-the-art open systems that offer freedom of choice in components. There will be a lot of SunSpec-based smart modules in the future.”
SMA achieves module-level shutdown with its string inverters through a partnership with Tigo. Both SMA and Tigo will incorporate the SunSpec communication protocol into their technology, saying that SMA’s partnership with Tigo, and Tigo’s relationships with most module suppliers, maximizes system safety and reliability.
“The solar industry is experiencing significant growth with new requirements, so we welcome the vendor coordination efforts and the wide adoption by many vendors working to improve the safety of clean energy production,” said Danny Eizips, VP of engineering at Tigo, in a press release. “This is a great opportunity for multi-vendor support.”
Like all SunSpec standards, the communications protocol was established by a working group of manufacturers and other industry participants.
It’s a beautiful example of how competing companies can come together to further the industry.