1,000 Vdc Utilization Voltages
Inside this Article
While 1,000 Vdc PV systems are common in Europe and the rest of the world, they have traditionally been relegated to large free-field solar power plant applications in North America. Back in 2007 and 2008, this was truly a niche market. Fast-forward to 2013, and the utility sector not only is the largest market segment for PV in the US, but also exceeds the cumulative capacity of the residential and nonresidential market segments—a trend that analysts like GTM Research expect to continue in the near term.
It should come as no surprise, then, that the needs of the utility-market segment are increasingly driving PV product development in North America. For example, prior to 2010, very few PV system components were tested and listed to UL standards at 1,000 Vdc. Today, however, designers and installers have access to 1,000 Vdc–listed PV modules, utility-interactive inverters, fuses, disconnects, combiner boxes, PV wire and so on—in short, everything needed to design and deploy a 1,000 Vdc PV system in applications covered by the National Electrical Code.
Here we explore the reasons why 1,000 Vdc utilization voltages have not been more widely adopted in North America to date and why many in the industry expect that the design and deployment of 1,000 Vdc PV systems will become routine in the future, no longer unique to utility applications but a standard practice in nonresidential settings. In addition to presenting a brief history of PV utilization voltages in North America, we include a survey of Code considerations for designing and deploying 1,000 Vdc PV systems. We also consider the advantages to and limitations of 1,000 Vdc designs in nonresidential applications.
PV Utilization Voltages in North America
The maximum utilization voltage for a PV system is limited by several interrelated factors, including electrical codes, equipment standards, equipment availability and cost. Over the last decade, 600 Vdc PV utilization voltages have been the norm in North America. Both code considerations and market conditions maintained the status quo.
Code considerations. The two main electrical codes that apply to PV systems in North America are the NEC and the National Electrical Safety Code (NESC). In broad terms, the NEC applies to public and private premises wiring, both indoor and outdoor, and the NESC applies to power generation, transmission and distribution wiring that is under the exclusive control of an electric utility.
Within the context of the NEC, Section 690.7(B) specifically limits PV utilization voltages in one- and two-family dwellings to 600 Vdc or less. However, it also contains provisions for higher utilization voltages, stating, “Other installations with a maximum system voltage over 600 volts shall comply with Article 690, Part IX.” Titled “Systems over 600 Volts,” Part IX of Article 690 was added in 1999 in anticipation of higher-voltage PV systems. As described in Section 690.80, Part IX generally refers back to Article 490 (“Equipment, over 600 Volts, Nominal”) and “other requirements applicable to installations over 600 volts.”
While Article 690 does not specifically preclude utilization of voltages above 600 Vdc in nonresidential applications, for most of the past decade it was either impossible or impractical to design and deploy 1,000 Vdc PV systems in applications covered by the NEC. These applications require the use of listed equipment. Until recently, designers and installers simply did not have access to PV system components listed to applicable UL standards, such as UL 1703 or 1741, at 1,000 Vdc. This had less to do with equipment standards than with a lack of market demand.
Brian Grenko, the director of operations for Yingli Green Energy, points out: “There is a common misunderstanding in the PV industry that the UL 1703 standard limits PV module suppliers to a 600 Vdc maximum system voltage rating. While a maximum limit of 1,000 Vdc is clearly stated in the scope of the UL 1703 standard, it also specifies conformance with the National Electric Code as a general requirement. Of course, Article 690 of the NEC specifies a limit of 600 Vdc for residential dwellings. Given the abundance of electrical components rated for 600 Vdc, and the fact that the North American PV market was originally comprised primarily of residential and off-grid applications, it made sense for PV manufacturers to design their products to 600 Vdc.”