PV Goes USB

Print PDF

Photon: The Photovoltaic Magazine (April 2012) - by Michael D. Matz - The Universal PV Interface Alliance (UPVI) is a consortium of eight companies trying to develop an interface standard for the integration of modules with panel-level power electronics devices like microinverters and power optimizers. Despite challenges attracting module manufacturers to the initiative and the absence of microinverter market leader Enphase Energy on the member roster, UPVI is forging ahead with its plans and expects a standard and certifi cation program to be ready later this year.

Greg Madianos wants the photovoltaics (PV) industry to learn from past mistakes. Speaking at PHOTON’s 3rd PV SAFETY Conference in February in San Francisco, California, the product line director at microinverter producer Solarbridge Technologies Inc. opened his presentation with a PV history lesson. As PV module connectors became common in the late 1990s, explained Madianos, there was no attempt to develop a standard design for the gadgets used to connect modules in
strings. After Multi-Contact introduced its MC4 connector in 2002, this system became a de facto industry standard. Many manufacturers developed products that were mechanically compatible with the MC4, said Madianos, but vendor-specific tools are required to attach each device to cables. Today, none of these products are tested or certified for interoperability – a situation that Madianos believes is a significant safety problem and a major headache for manufacturers and installers.

Madianos was not giving this history refresher as a lead-in to a product pitch on a new connector. Rather, he was using it to promote the Universal PV Interface Alliance (UPVI), an industry consortium founded last October to establish an open interface standard for the integration of modules with panel-level power electronics devices, like microinverters and power optimizers. As the number of power electronics companies grows, so too does the number of proprietary connection schemes for these devices. An open standard, says Madianos, is needed now to help the industry avoid another connector debacle.

Madianos says that a universal open PV interface would be analogous to the Universal Serial Bus (USB) standard in the personal computer industry. With USB, compliant peripheral devices, like thumb drives, plug into computers. He points to several benefits to having a standard PV interface: improved safety, lower costs through streamlined product development, and reduced risk for manufacturers who would otherwise have had to bet on one winning technology. UPVI’s vision is to have PV products certified according to a single interface standard.

Gaining industry support
To achieve industry buy-in on the universal interface concept, UPVI is lobbying manufacturers to become members and contribute to developing the standard. The group’s eight-member roster includes microinverter makers Enecsys Ltd. and Solarbridge, as well as power optimizer producers Tigo Energy Inc. and Solaredge Technologies Inc. Only one module manufacturer has joined the consortium so far – Sunpower Corp. UPVI Executive Director Stan Moyer explains that the current industry slowdown has made it difficult to attract panel makers. Many have expressed strong interest but have admitted that their bandwidth for [standards development] activities is limited at the moment, he notes.

Nevertheless, the consortium is moving forward with the development of the electrical and mechanical aspects of the standard now, such as the dimensions and materials. According to Moyer, it’s a three-step process: the first release of the specification will be finalized in the third quarter of this year, a certification program will be in place by the end of the same quarter and UPVI-compliant
products will hit the market in the first half of 2013. Some key details have yet to be hashed out. In particular, UPVI has not yet selected a laboratory to conduct the certification. Madianos says it’s still an open question as to what entities will govern this standard, adding, Our expectation is to have the Nationally Recognized Testing Laboratories play an active role.

Where’s Enphase?
Conspicuously missing from the UPVI member list is market-leading microinverter producer Enphase Energy Inc., which turned down an invitation to UPVI and has continued to focus on a proprietary interface solution. Enphase’s Raghu Belur says that his company is not joining UPVI because its technology is 3 to 4 years ahead of the current members, so it would be a big leap backward. Belur expresses concern that most of the UPVI members are not experienced enough in a technology sense to drive a high-quality standard.

Moyer counters that UPVI members include companies and individuals with decades of experience on the Underwriters Laboratories (UL) and International
Electrotechnical Commission (IEC) module and inverter standards development committees, as well as in the PV industry advisory group to the National Electrical Code (NEC). He is confident that UPVI’s open interface will succeed without Enphase, pointing to the plug-in electrical socket as a successful open interface example. In the area of electrical interfaces, the market has repeatedly rewarded open standards and punished proprietary ones, says Moyer.

Ultimately, it will be up to the module manufacturers to decide whether open or proprietary is the way to go. Both Solarbridge and Enphase have already partnered with several major module manufacturers on frame-attached AC modules, and some of these module companies are collaborating with both microinverter firms. Assuming Enphase continues down its proprietary path, it remains to be seen whether the panel makers will stick with the company on future-generation AC modules in which the microinverter is attached directly to the backsheet.

While Enphase and other power electronics companies can debate whose technology is more advanced, the combined expertise of several PV manufacturers on the UPVI roster clearly lends weight to the open interface initiative. According to Moyer, The development of an open standard cannot be a step backward for any of the members, since it takes the best thinking of all members and applies it for the mutual benefit of all members.