String Inverters Single-Phase Solutions for the North American Market (2011)

While utility-scale PV plants utilizing high-power central inverters make up the fastest growing solar market sector globally, many SolarPro readers may be surprised by the fact that low-power string inverters accounted for the majority of inverter capacity sold worldwide in 2010. Ash Sharma, a member of IMS Research, a UK-based market research firm, presented some compelling numbers at PHOTON’s PV Inverter Conference in Berlin, Germany, in April 2011—compelling numbers for string inverters, that is. Globally, 21 GW of inverters were sold in 2010. Low-power string inverters represented 57% of this total sales capacity. High-power central inverters accounted for 42% of the sales, with microinverters rounding out the field at 1%. While most leading inverter manufacturers design and produce both string and central inverters, based on the current market share percentages, it is a safe bet to assume that manufacturers are devoting significant resources to the advancement of their string inverter products.

While data that represents string inverter market share in the US in its entirety is not publicly available, the regularly updated California Solar Initiative (CSI) database provides insight into inverter manufacturers’ share of the California market and serves as a general reference point for the US market for these products as a whole. SunCentric, a solar consulting firm based in California and Oregon, generated the data included in Figures 1 and 2 for publication in SolarPro. (SunCentric’s recently released 2011 CSI program analysis can be downloaded from the company’s website at The data included in the two charts was sourced directly from the raw CSI data in mid-May 2011, and was filtered to present a clear snapshot of inverter market share among string inverter manufacturers. Residential and nonresidential projects using single-phase string inverters comprised the dataset. Only systems utilizing grid-direct, single-phase string inverters were included. Private-label inverters from companies including SunPower and Yes! Solar were allocated to the original equipment manufacturer. It is interesting to note that the shift in market share between SMA and Fronius appears to be driven in part by SunPower purchasing and branding. SunCentric reported that SunPower has approximately 10.8 MW of Fronius string inverters in process compared to 8.4 MW of branded SMA products.


As the application space for string inverters grows, manufacturers of these products have been positioning themselves to capture North American market share through expanded product lines and manufacturing capacities, strategic acquisitions and an increased presence in North America in both sales and support services. As a point of reference, SolarPro’s 2010 string inverter specification table lists 48 inverter models from eight manufacturers. The updated accompanying table (Click HERE for .xls version) includes 72 string inverter models from 12 manufacturers. Several existing string inverter manufacturers have added models to their product lines and four additional major manufacturers have released equipment for the US market.

To create a clear differentiation between product classes, only single-phase string inverters are listed in this year’s string inverter specifications table. With the exceptions of a few models that are pending CSI eligibility, all of the inverter products included in the table are listed to UL 1741 and are currently eligible for the CSI program. The decision to make CSI eligibility the criteria for inclusion is based on our perspective that if inverter manufacturers are serious about delivering and supporting products in the US, they are surely eager to meet the incentive eligibility requirements for California, the country’s largest solar market.


While seasoned integrators working in North America are familiar with the system design, installation and performance subtleties of major string inverter brands, the companies behind the products and the evolution of the product lines are less well known. The following profiles present detailed information about the companies behind the products, in an effort to shed some light on exactly who is manufacturing the products you are installing. Information included in the company profiles was sourced from interviews conducted by SolarPro staff with company representatives and from information published directly by these manufacturers in investor profiles, earnings reports, company histories and corporate press releases. It should be noted that the depth and thoroughness of the information provided by the various manufacturers during our interview process varied considerably, as did the availability of company-specific information that was sourced during the online research phase of each profile’s development.

Advanced Energy. Headquartered in Fort Collins, Colorado, Advanced Energy (AE) was founded in 1981. The publicly traded company (NASDAQ: AEIS) reported revenues of $459.4M for the 2010 fiscal year. AE currently has more than 1,600 employees working across a relatively diverse product and services portfolio that, as of January 2011, comprises two primary business units: AE Thin Films and AE Renewables. AE Thin Films develops and manufactures power conversion and control systems for technology markets that include semiconductor, solar, glass and flat-panel displays. AE Renewables develops and manufactures utility- and commercial-scale central inverters, as well as a full line of string inverters for small commercial and residential markets.

AE’s line of Solaron central inverters has been a leading brand in the utility and large commercial application space since the introduction of the Solaron 333 kW central inverter in 2007. With the acquisition of PV Powered in May 2010, AE added several central inverters to its product portfolio, as well as nine string inverter models. PV Powered was founded in 2003 and is located in Bend, Oregon. AE’s line of PV Powered string inverters is manufactured at the Oregon plant to supply the US market. In addition, the company shipped its first units from an Ontario manufacturing partner, Celestica, in December 2010, to serve the Ontario feed-in tariff (FIT) market.

AE’s Corporate Fact Sheet for the Second Quarter 2011 reported that the company achieved a 22% US solar inverter market share for the first 9 months of 2010 with its Solaron and PV Powered inverter models combined. PV inverters represent 23% of the company’s overall revenue, and the company projects its inverter manufacturing capacity (including string commercial and utility-scale products) to reach approximately 2 GW annually by the end of 2011. While AE does not publicly share manufacturing capacity by market segment, in the press release announcing the acquisition of PV Powered, the company projected the sales of PV Powered inverters would contribute $40–$50M to AE’s 2010 revenue, with $30–$35M from sales in the commercial market and $10–15M from the residential market.

Casey Miller, AE’s director of string inverters and site solutions, comments on the ongoing improvements in reliability of the PV Powered line of inverters. “PV Powered string inverters have been on the market in the US since 2003,” Miller says. “The product has undergone three design revisions, all focused on reliability and installability improvements based on real-word, under-the-sun performance.” He notes that the company has a clear focus on product design details that make the equipment installer-friendly. According to Miller: “We do the little things right to make installation easy. UL 98 listed dc/ac disconnect, ample wire bending and working space, and plug-and-play monitoring save time and money on the job site.”

In addition, Miller highlighted the company’s focus on advances in system monitoring: “We believe that system owners should take an active role in understanding how their system is performing. Adhering to this philosophy, we offer a very low-cost data monitoring card that, through, allows system owners to monitor their inverter anywhere in the world. is a service that is totally free for the life of the inverter and is simple, intuitive and easy to use, yet includes powerful features such as data export and reporting for incentive programs. The optional PVM1010 data monitoring card is installed internally to the inverter and does not require additional external enclosures or power outlets.”

AE’s PV Powered string inverter line includes 2 kW to 5.2 kW units with model-specific output voltage options of 208 Vac and 240 Vac. The inverters are passively cooled and include an integrated dc/ac disconnect listed to the UL 98 standard. The inverters feature a split-chassis design with the disconnect housed within an NEC-compliant raceway that facilitates manufacturer-approved, flush side-by-side mounting of multiple inverters.

Delta Energy Systems. While Delta’s string inverter products are new to the North American market, the company itself is well established. Delta was founded in 1971 and is a $6.6B company with 80,000 employees worldwide. It is also the number one manufacturer of switch-mode power supplies globally. Delta is one example of a power systems technology corporation that has recently directed its sights on the North American solar marketplace. In 2002, Delta acquired the advanced power supply division of the Swiss group ASCOM Energy Systems ( formerly FRAKO, a German power supply manufacturer founded in 1928). The division was renamed Delta Energy Systems. A subsidiary of the global Delta family, Delta Energy Systems manufactures power supply products for computer, telecommunication, medical and industrial industries, as well as products for PV applications.

According to Andreas Schmitt, head of marketing for Delta Energy Systems, Delta began investing in the research and development of solar inverter products at its Teningen, Germany, location in 1999. Delta’s first solar inverter product was a microinverter that was developed for a Belgian OEM customer and released in 1999. Over 30,000 microinverter units were sold up to 2003. In 2002, development and production of string inverters for OEM customers began. In 2005, Delta launched OEM string inverters for the US market. Three years later, it introduced Delta solar inverters for the European market at the annual Intersolar conference in Munich, Germany. In 2010, Delta Energy Systems launched the SOLIVIA brand solar inverters and shipped the first SOLIVIA EU models. Also in 2010, Delta released a 100 kW central inverter, as well as 15 kW and 20 kW transformerless string inverters for European projects.

In 2010 Delta strategically decided to enter the US market with its own SOLIVIA TR String Inverter brand and began building US sales and support. This year, Delta Energy Systems is launching four models of SOLIVIA string inverters for the US and Asian-Pacific markets and a PV monitoring system that is compatible with all the singlephase SOLIVIA string inverters available worldwide. Delta Energy Systems’ design R&D headquarters is located in Teningen, Germany. The SOLIVIA line of inverters is manufactured in Dubnica nad Váhom, Slovakia, and Bangkok, Thailand. The Slovakia factory was opened in May 2007, and has a current production capacity of 600 MW, which the company projects will grow to 2 GW by 2015. Inverters destined for the US and Asia-Pacific markets are manufactured in the Thailand factory that was opened in 2010 with a production capacity of 600 MW. Currently, central inverter solutions represent 10% of Delta Energy Systems’ total inverter revenue, with string inverters accounting for 90% of the company’s inverter revenue.

“There is stability offered in the $6.6 B company behind our products,” says Schmitt. “The PV business, while appearing to be quite mature to many, is just in its early stages. We believe local installers are the most influential group determining what solutions end-users choose, so we continue to focus on working with installers and trying to make their job easier.”

Delta Energy Systems’ current SOLIVIA TR string inverter line for the US market includes four units with rated power specifications ranging from 2.5 kW to 5 kW. The 4.4 kW and 5 kW units were pending CSI eligibility at the time of publication. The inverters are field configurable for 208/240 Vac output and feature NEMA 4X enclosures, a fused string combiner and array dc disconnect standard.

Exeltech. Exeltech is a privately held company headquartered in Fort Worth, Texas. While grid-connected inverters have only recently been added to the company’s product portfolio, Exeltech has been manufacturing inverters for stand-alone, battery-based applications for the telecomm and renewable energy industries since the company was founded in 1990. Veteran installers who were working in the off-grid marketplace in the early 1990s likely remember integrating Exeltech’s SI Series inverters, the first high-frequency pulse width modulation sine wave inverter available on the market, into systems outfitted with (now largely defunct) modified square wave inverters. At the time, it was a technical revelation to have the option of specifying a true sine wave inverter to run sensitive electronic loads in off grid applications. Exeltech also pioneered the redundant, hot-swappable stage inverter concept with its MX Series battery-based inverter product line.

Exeltech recently entered the grid-tied string inverter market with the introduction of its transformerless XLGT18A60 inverter, which received ETL listing to UL 1741 in February 2011. At 14 pounds, the 1.8 kW 120 Vac unit is the lightest inverter listed in the accompanying specifications table. All of Exeltech’s inverters, including all circuit boards, transformers and enclosures, are manufactured at its Fort Worth facilities.

While the XLGT’s transformerless topology is new to Exeltech, senior engineer Dan Lepinski points to Exeltech’s track record of reliability building battery-based inverters for the telecomm industry. He says, “Exeltech has been manufacturing power inverters for over 20 years and markets its products to applications where high-reliability is paramount. This same philosophy went into the design and manufacture of our grid-tied inverters. While it has become accepted in the solar energy industry that inverters may have to be replaced every 8–10 years, Exeltech took the approach that you buy it and install it once. That’s it.”

Fronius. A privately held firm, Fronius was founded by Gu¨nter Fronius in Pettenbach, Austria, in 1945. The company’s initial products included battery chargers and welding transformers. Today, these fields make up two of the three Fronius business divisions. Its third and most recent business division is solar electronics. In 1995, Fronius entered the solar market with the Sunrise grid-direct inverter. According to a 2011 report published by GTM Research, Fronius is currently the fourth-largest global supplier of inverters. Since the company added light commercial central inverters to its product mix only recently, this substantial market share is built primarily on its offering of string inverters. The company currently employs approximately 3,000 people. It has sales representatives in more than 60 countries and 17 foreign subsidiaries. While solar inverter production had been centralized at the company’s Sattledt location in Austria, which opened in 2007, Fronius recently opened a Canadian subsidiary with an initial annual production capacity of 250 MW.

The Fronius IG-series of inverters was first launched in Europe in 2001. Two years later, the company released the Fronius IG 40 and IG 60, its first multiple power stage inverters. By using intelligent control of multiple power stages, Fronius is able to divide, balance and otherwise optimize the operation of individual inverter power stages. The company refers to this as its MIX concept. In addition to the obvious manufacturing efficiencies of having a standard power stage, Fronius touts improved operational efficiency across all power ranges and increased component lifespan as benefits of a multiple power stage inverter design. MIX technology is now ubiquitous across all Fronius product lines, including its light commercial CL inverters.

The first UL-listed multistage Fronius IG string inverters were released to the North American market in 2004. Four years later, the company released updated IG Plus inverters to the US and Canada. This product line currently includes seven single-phase string inverter models, ranging in capacity from 3 kW to 11.4 kW, capable of interconnecting to the grid at 208, 240 or 277 Vac. The UL-listed IG Plus product line also features a pair of 3-phase inverters, rated at 11.4 kW ( for 208 or 240 delta services only) and 12 kW ( for 277 wye service only). IG Plus inverters are housed in NEMA 3R enclosures and actively cooled using variable-speed fans. Source-circuit fuseholders are provided for the ungrounded dc input conductors, as is an inverter-integrated dc disconnect. Fronius uses a highfrequency, transformer-based inverter topology, which means that its products are not as heavy as comparably sized 60 Hz transformer-based inverters.

In reference to increasing the company’s North American market share, Gord Petroski from Fronius USA, reports: “We are proactive with our efforts in the US market, with very aggressive pricing and products in stock and ready for immediate shipping.” He also points out that the company’s product line is both proven and well suited to the market. “Our IG Plus series has a consistently wide MPPT voltage window for maximum energy harvest in diverse weather conditions,” he explains. “This feature is needed in a market that is as varied as the US and Canada.”

Ingeteam. Headquartered in Zamudio, Spain, Ingeteam brings more than 30 years of experience in the power electronics design and manufacturing sector. It began developing products for the renewable energy industry in the 1990s. The company is privately held, with a network of sales offices that includes locations in Brazil, China, the Czech Republic, France, Germany, Italy, Mexico, Spain, and the US. Ingeteam’s global business structure includes six primary units: energy, industry, shipbuilding, railway traction, basic technologies and services. In 1990, Ingeteam Energy, S.A. was founded to develop electrical and control systems for industrial-scale wind power and PV technologies. The 1990s also marked the beginning of the Spanish company’s international expansion. Today, Ingeteam has more than 3,500 employees worldwide and offers a wide range of grid-connected and stand-alone PV inverters, marketed under the Ingecon Sun brand, with rated capacities from 2.5 kW to 625 kW. Manufacturing facilities are located in Spain and the US. String inverters represent approximately 15% of the company’s overall revenue from inverter sales.

Ingeteam first introduced a 2.5 kW transformer-based, single-phase string inverter model for the European market in 2000. A 6 kW transformerless string inverter, also destined for the European market, was released in 2005. More recently, Ingeteam developed a new family of 3-phase transformerless string inverters with power outputs from 10 kW to 18 kW, again for the European market. The company’s first string inverter models developed for the US, the transformer-based Ingecon Sun Lite 5 U and transformerless Ingecon Sun Lite 5 TL U, have been listed to UL 1741. CEC eligibility is pending. The two Ingecon Sun Lite inverter models became available to North American customers in July of this year.

Ingeteam solidified its commitment to the US market with the announcement of a new 100,000-square-foot combined production facility and office complex in Milwaukee, Wisconsin, with completion set for some time this summer. The company expects the facility to employ approximately 275 workers by 2015 and is projected to achieve an annual production capacity of 300 MW. In addition, Ingeteam has a business office in Santa Clara, California, focused on developing the company’s presence in the North American PV market.

KACO new energy. Founded under the name Kupfer-Asbest- Company Gustav Bach in 1914, KACO has evolved from a manufacturer of ring gaskets for use in the automotive industry to the third-largest inverter manufacturer worldwide in 2010. The firm is privately held, is based in Neckarsulm, Germany, and currently has 700 employees worldwide. KACO pioneered the development of electromechanical choppers (predecessors of modern inverters) in the 1940s during World War II in response to the destruction of large segments of Germany’s electrical grid. In 1994, the company began developing inverter technology for PV applications. Today, KACO offers a full line of inverters for residential, commercial and utility-scale applications and has produced more than 3 GW of PV inverters since 1999. A secondary business unit is dedicated to the manufacture of power supply systems for rail and industrial applications. More than 15,000 KACO battery-coupled power supply systems have been employed in rail vehicles worldwide. The company was reorganized in 2009 as KACO new energy GmbH.

While the German PV market has traditionally been the primary focus of KACO’s product distribution, international exports currently represent 35% of the company’s inverter sales. KACO has branch offices in locations that include Canada, China, France, Greece, Israel, Italy, South Korea, Spain and the US. The company’s North American headquarters is located in San Francisco. KACO is actively working to increase its presence in the North American market. KACO new energy began producing 60 MW of string inverters at its San Jose, California, facility in January 2011. The 1502xi and 2502xi models manufactured at this location have been available since Q1 2011, and the 3502xi and the 5002xi models assembled there will be available this summer. The revised nameplate for these inverters will make it clear that the products are assembled in the US. According to Svea Jeske, KACO marketing and event manager, the company’s motivation to manufacture in San Jose is twofold: “California remains one of the strongest and most promising US markets for PV. In addition, San Jose’s proximity to major national distribution will make this production development strategically beneficial for the solar market in California and beyond.” In May 2011, KACO announced the opening of a new North American manufacturing facility in London, Ontario, Canada. The plant has more than 30,000 square feet of manufacturing and warehouse space and will produce a projected 1 GW of PV inverters for the Canadian market in 2011. The company plans to employ more than 100 full-time employees at the facility.

In 2006, KACO released its first string inverters in the US, which included the 1501xi, 2901xi and 3601xi models. The first-generation model line was replaced in 2009 with the current 02xi series. The redesigned model line is comprised of 1.5 kW to 5 kW units. The products come standard with an integrated connection box that houses a dc/ ac disconnect. The split-architecture design allows the inverter to be separated from the wiring/switch enclosure to simplify maintenance or repair work. Output can be configured for 208 Vac, 220 Vac (Mexico) and 240 Vac services. The 1.5 kW, 2.5 kW and 3.5 kW models feature passive cooling. Integrators should note that the 5 kW unit’s cooling approach combines passive cooling with internal fan assist. Web-based system monitoring can be enabled via KACO’s optional watchDOG communication card, and KACO offers blueplanet web, a free webhosted monitoring service for residential systems of up to 10 kW in capacity.

Immediately prior to this issue’s publication date, KACO formally announced the availability of two new transformerless inverter models that are competitively priced for the US market. These models were originally announced in 2010. Both of these inverters are listed to UL 1741 and are eligible for the CSI program. The 6400xi and 7600xi inverters have achieved a CEC efficiency rating of 96.5% and are 94% efficient at 10% of rated output power. The introduction of the new transformerless models is a forward-looking move for KACO and a chance to gain early market share in the rapidly evolving transformerless string inverter space in the US.

Motech Industries. Headquartered in Tainan, Taiwan, Motech Industries is a publicly traded company listed on the Taiwan Stock Exchange. Motech was founded in 1981 and has evolved from a test and measurement instruments designer and manufacturer to a full-service global solar company. Motech’s solar division was established in 1997, and the production of photovoltaic cells commenced in 2000. In 2009, Motech acquired GE Energy’s former solar module assembly operation located in Newark, Delaware. In 2010, Motech reported its position as one of the 10 largest solar cell producers worldwide.

Motech embarked on the development of solar inverters in 2004 and began shipping inverters into the European marketplace in 2006. In 2008, Motech inverters received UL 1741 listing for use in the US and began shipping to the North American market via a distribution agreement with groSolar, a US-based solar solutions provider and equipment wholesaler. Motech’s current PVMate inverter line includes six models with power outputs that range from 2.7 kW to 7.5 kW and feature an integrated dc/ac disconnect. The inverter can be physically separated from the lower wiring box that houses the disconnect, if servicing is required.

Power-One. Headquartered in Camarillo, California, with design, manufacturing, sales and service operations in Asia, Europe and throughout the Americas, Power-One is currently the world’s second largest designer and manufacturer of solar inverters. Over the past 40 years, the company has evolved from a family-owned power supply manufacturing business that was incorporated as Power CA in 1973 to a publicly traded company (NASDAQ: PWER) with net revenues of $1,074M for its fiscal year ending January 2011. Power-One currently has approximately 3,400 employees at facilities worldwide.

Power-One’s initial public offering took place in 1997, raising more than $80M. In 2006, the company acquired the Power Electronics Group of Magnetek for a purchase price of approximately $69.4M, according to Power-One’s most recent annual report. The Power Electronics Group included operations in China, Hungary, Italy and the US, with approximately 500,000 square feet of manufacturing facilities and 1,200 employees. This transaction included dc-to-dc converter products and power supplies and, notably, the Aurora line of PV and small wind inverters with capacities ranging from 3 kW to 6 kW. Power-One’s more recent purchase of Fat Spaniel Technologies in 2010 was another notable acquisition.

In 2010, the company was reorganized into two business units: Renewable Energy Solutions and Power Solutions. The Renewable Energy division designs and manufactures power conversion products for both PV and wind power applications. The Power division is focused on power management solutions used in computer servers, data storage, networking, telecomm and industrial applications.

Power-One has been capturing global inverter market share at an unmatched pace, moving from the number nine position in 2009 to the number two position in 2010. Power- One reports inverter shipments reached 2.6 GW in 2010, and more than 4 GW of inverter capacity has been installed globally to date. Manufacturing facilities are located in Valdarno, Italy, for Africa, Europe and the Middle East (4 GW); Gongming, China, for Asia-Pacific (1 GW); Phoenix, Arizona, for North America (1 GW); and Scarborough, Ontario, for Canada (500 MW).

According to Kent Sheldon, vice president of sales, Renewable Energy Solutions, North America: “The Aurora product family of 2 kW to 6 kW transformerless inverters has been continuously developed in Europe over the past 6 years, as well as in North America over the past 3 years. Our string inverters have evolved into our third generation of TL inverters that have improved features, reliability and price with each update.”

Power-One’s current lineup for the US market includes seven single-phase models. Product highlights include a transformerless topology; dual, isolated MPPT stages that allow different string configurations, lengths and orientations; the widest PV voltage input range specification listed in the accompanying table; and fan-free passive cooling. Later in 2011, Power-One will be launching a redesigned full line of inverter products in North America, to include microinverters, dc optimizers, string inverters, and commercial and utility-scale inverters for PV and wind power applications.

Schneider Electric. Founded in 1836 and incorporated in 1981, Schneider Electric is a global leader in active energy management solutions headquartered in Rueil-Malmaison, France. The company has more than 110,000 employees in more than 100 countries. Publicly traded on Euronext, a pan- European stock exchange, the company reported sales revenues of 19.6B euros for 2010, 24% of which were generated in North America. Schneider Electric acquired Square D, a leading US electrical equipment manufacturer, in 1991. Since 2011, activities at Schneider Electric have been organized into five operating segments: power, energy, buildings, industry and IT. Renewable energy solutions and services are grouped within Schneider Electric’s power portfolio. In 2010, this operating segment of the company accounted for 53% of total revenue, or 10.3B euros. According to the company’s annual report, Schneider Electric’s power business is currently number one in the world in low-voltage markets and number two worldwide in installation and control systems. The report also describes renewable energy as a “lever for growth” within this operating segment. It notes: “Solutions and services (in the power business) are seeing growth again thanks to renewable energy solutions.”

Emphasis on the renewable energy sector is part of a transformation stratagem initiated at Schneider Electric in 2002. Strategic acquisitions in the 1980s and 1990s helped the company transition from being a family-owned steel business to a publicly traded world leader in electrical products. Management at Schneider Electric has recently sought to diversify and enhance its portfolio of solutions to anticipate changing energy requirements in the future. In July 2008, as part of this strategic realignment, the company acquired Xantrex Technology in an all-cash transaction valued at approximately $500M. In addition to portable power products for mobile applications, the Xantrex product portfolio includes battery-backup and grid-direct inverters for residential applications, as well as an extensive line of commercial and industrial inverters.

It is worth noting that Xantrex, which was founded in 1983, had its own history of strategic acquisitions in renewable energy and power conversion technology. Over a 2-year period, starting in 1999, Xantrex acquired three inverter companies: Heart, Statpower and Trace Engineering. While Xantrex used the products and technologies acquired from Heart and Statpower primarily in mobile and consumer electronic solutions, the assets acquired from Trace were used in both grid-direct and utility-interactive battery-backup solutions. Xantrex’s early grid-tied experiences using Trace technology were not without challenges. The Trace Sun Tie inverter, Xantrex’s only residential grid-direct inverter when it was released in July 2001, suffered from multiple problems with its MPPT algorithm, which the company was slow to address until these issues became well publicized. Around the same time, in November 2001, Xantrex received notification that UL was decertifying its battery-based Trace SW series inverters for utility-interactive operation. While Xantrex fixed this problem relatively quickly with the release of an add-on gridtied interface, the company’s responsiveness was once again called into question.

Given the rapid rate of change in the solar industry, these decade-old bumps in the road for Xantrex were ancient history—until January 18, 2011, when Schneider Electric announced a recall of approximately 25,000 Xantrex GT series and private-labeled inverters. Whatever memories this announcement may have brought back for industry veterans, Schneider Electric’s management of the Xantrex recall is a marked departure from the past. First, it was the company’s own quality control processes and procedures that identified the potential problem—prior to any reports of injury or property damage. Second, in initiating a voluntary recall, the company was adhering to its own internal quality control standards. The Schneider Electric annual report states: “Despite its testing and quality control procedures, the company’s products might not operate properly or might contain design faults or defects, which could give rise to disputes in respect to its liability as a seller or manufacturer.... To prevent or limit these risks, the company recalls products if there are any doubts whatsoever that a product or one of its components is not 100% safe in respect of people and/or equipment.”

“Schneider Electric takes product safety and quality very seriously,” explains Ron Catanzaro, vice president of marketing. “We identified a potential safety issue in the North American single-phase Xantrex GT series grid-tied inverter related to a component on the circuit board. We reported this to the Consumer Product Safety Commission and agreed to a voluntary field repair upgrade, which involved a kit to replace the component and further strengthen the enclosure. As the solar industry matures, Schneider Electric and other global suppliers will support events like this with well-established processes, policies and actions that are commonplace in other industries.”

This ability to leverage the backing of a 19.6B euro company— one that is also a leading supplier of electrical distribution equipment—is one of the things that sets Schneider Electric apart. Catanzaro notes: “We not only offer inverters, but also a full line of dc and ac circuit protection products and disconnects from Square D.” While the company uses a mixture of in-house and contracted manufacturing plants in Asia and North America, its new single-phase line of Conext series inverters for North America will be produced in Bangalore, India, where a subsidiary, American Power Corporation, has manufacturing plants. Catanzaro explains: “This allows the product line to take advantage of world-class manufacturing and global supply chain capabilities within the Schneider Electric group.”

The redesigned Conext series of string inverters from Schneider Electric consists of four models designed for 208 Vac or 240 Vac interconnection, ranging in capacity from 2.7 kW to 5 kW. The high-frequency, transformer-based inverters are housed in NEMA 3R enclosures. Each unit includes an integrated Square D disconnect that opens both the dc and ac inputs to the inverter. The inverters are passively cooled, which allows them to be installed side-by-side with no side clearance. The Conext series inverters feature Fast Sweep technology, a shade-tolerant MPPT algorithm. Schneider reports that performance is comparable to microinverter systems.

SMA. Founded in 1981 when it was spun off from the University of Kassel, SMA has been headquartered in Niestetal, Germany, since 1982. Since 2008, shares in SMA Solar Technology have been listed in both the Prime Standard of the Frankfurt Stock Exchange (S92) and the TecDAX. Sales of 1.9B euros were reported in 2010, making SMA the world market leader for solar inverters. The company currently employs approximately 5,000 people worldwide and has 17 foreign subsidiaries on four continents (Asia, Australia, Europe and North America), including four subsidiaries in the US and Canada. While SMA does not release subsidiary sales figures, David Wojciechowski, senior director of sales for SMA America and SMA Canada, reports: “About 80% of SMA’s 2010 global sales were generated by its medium-power solutions, which include residential and light commercial inverters.”

A longtime leader in residential inverter technology, SMA released its first solar inverter, the PV-WR, to the European market in 1990. Subsequent European product releases include a long list of industry firsts: the first highvoltage string inverter (the Sunny Boy 700) in 1995; the first transformerless inverter (the Sunny Boy 1500) in 1998; and the first multistring inverter (the Sunny Boy 5000TL) in 2002. Similarly, the first high-voltage string inverters available to the North American market were a pair of UL-listed, 60 Hz transformer-based Sunny Boy string inverters—the SWR 1800 and SWR 2500—released in 2001.

SMA currently offers 14 grid-direct string inverters in North America, many of which operate at multiple output voltages. The original 60 Hz transformer-based inverter line has been updated and expanded over the past decade; the US series of Sunny Boy inverters currently includes eight models ranging in capacity from 700 W to 8,000 W. SMA also offers a series of three high-frequency string inverters, ranging in capacity from 2 kW to 3 kW; inverters in the HF-US series are designed to fit between studs, making them ideal for new construction or space-constrained retrofit applications. In 2010, SMA introduced its TL-US series of inverters in North America; ranging in capacity from 8 kW to 10 kW, these are the first transformerless inverters ever to receive UL certification.

SMA’s annual manufacturing capacity is 11 GW, the highest of all solar inverter manufacturers; this includes 500 MW of capacity in Ontario, Canada, and 1 GW in Denver, Colorado, which is reportedly the western hemisphere’s largest inverter assembly site. ARRA-compliant string inverter models being assembled in Denver include SB 3000-US, SB 4000-US, SB 5000-US, SB 6000-US, SB 7000-US and SB 8000-US. These same Sunny Boy models are also being assembled in Ontario, initially by Celestica, to meet the province’s microFIT requirements for domestic content.

According to Wojciechowski, SMA’s commitment to regional production sites is just one of the strategies that the company employs in order to protect its leadership position in the North American market. The other way is through continued innovation of its products and technology. “SMA’s Sunny Boy TL-US series of transformerless inverters offers significant improvement in a range of key criteria when compared to traditional galvanically isolated PV inverters,” he explains. “Eliminating the transformer has allowed SMA to improve the efficiency of the system and, therefore, energy yields. At the same time, weight has been reduced by nearly half, allowing for easier installation. Integrators have been quick to recognize the benefits of transformerless inverters and have rapidly adopted these new models for their projects.”

When asked about potential permitting or inspection obstacles, Wojciechowski reports that the company has experienced “little to no push-back.” He credits the company’s strong service, support and education programs for the smooth rollout. “SMA America took care to educate integrators, utilities, AHJs and other stakeholders,” he notes. “SMA believes that the imperative to reduce PV system costs and improve energy yields will continue to drive manufacturers to introduce transformerless inverters to the US market.”

SolarEdge Technologies. A group of professional technologists with experience in solar, semiconductor and missioncritical power systems established SolarEdge Technologies as a private company in 2006. Widely recognized for its technological innovation, the company’s global investors include GE Energy Financial Services and several top-tier venture capital firms. With offices in Germany, Israel, Japan and the US, the company has more than 100 employees involved in R&D, marketing, sales, and technical and logistical support. Since early 2009, Flextronics, a global provider of electronics manufacturing services, has mass-manufactured SolarEdge products in Israel; in April 2011, the two companies announced the opening of a new production line for North America, located in Newmarket, Ontario, Canada. The scheduled production capacity in both plants is 250 MW for 2011, but this capacity can be doubled if needed to meet market demands.

The SolarEdge system consists of module-level, dc-to-dc power optimizers and proprietary transformerless inverters. The optimizer is available both as a module-embedded and a module add-on solution. The company’s first products were released in 2009. In 2010, product shipments exceeded 50 MW and went primarily to the European market. Because its product line had to be adapted for North American requirements, SolarEdge did not begin its US and Canadian product rollout until August 2010. The company currently offers four singlephase string inverters in North America—ranging from 3.3 kW to 6 kW in capacity—that interconnect to the grid at either 208 Vac or 240 Vac. The company is currently shipping secondgeneration optimizers and inverters. Third-generation products, offering additional features and improved energy yield, are expected to begin shipping later this year.

The proprietary transformerless inverters from SolarEdge were developed in cooperation with the Franhoffer Institute in Germany. Recognized as a leader in inverter technology, Franhoffer currently holds the world record for PV inverter efficiency, with a 99% efficient 5 kW transformerless 3-phase inverter. The CEC efficiency rating for SolarEdge string inverters is 97.5% at 240 Vac and 97% at 208 Vac. SolarEdge believes that module-level optimization can further increase energy yield by 2% to 3% compared to an ideal unshaded array, with greater gains possible on shaded arrays.

In addition to improving energy yields, the main SolarEdge system differentiators, according to John Berdner, general manager for North America, are design flexibility and improved safety. “The combination of module-level optimizers coupled with our own transformerless inverters frees system designers from nearly all the constraints of traditional string inverters,” he explains. “String lengths of eight to 25 modules are possible, regardless of temperature. Strings can be of dissimilar lengths, modules within the same string can be mounted in different orientations and different types of modules can be used in the same string.”

Module-level optimization also means that the system includes module-level safety and fault monitoring. “During installation and service, the output voltage of individual power optimizers is reduced to a safety voltage of 1 Vdc,” Berdner points out. “The system also automatically reverts to safety mode in response to any grid faults or array ground faults, or if an excessively high temperature is detected, such as during a fire. Fault messages are reported by email, and system performance is verified with web-based module-level monitoring that is included with every inverter.”

Solectria Renewables. Headquartered in Lawrence, Massachusetts, Solectria Renewables is a privately held corporation that manufactures and supports a full range of inverter products for utility, commercial and residential projects. The US company has an interesting history. In 1989, James Worden and Anita Rajan Worden founded Solectria Corporation. At the time, their design and manufacturing focus was on energy management components for automotive, power generation and other industrial applications. From 1989 to 2005, Solectria Corporation manufactured over 4,000 electric vehicles that relied on the proprietary drive system technology it had developed. Solectria Corporation also manufactured power electronics and controls for high-power systems, including inverters, dc-to-dc converters, energy storage and related technologies. In 2005, Solectria Renewables was founded with the sole focus of developing PV inverters, and Solectria Corporation was sold to Azure Dynamics. Solectria Renewables went from EV to PV, carrying the inverter technology utilized in the Solectria Corporation’s electric vehicles to the manufacture of PV inverters.

Today, Solectria Renewables’ wide range of products includes 1.8 kW to 500 kW grid-tied inverters. Solectria Renewables’ marketing manager, Natalie Wiener, reports that the company’s current inverter sales revenue distribution is approximately 35% string inverters and 65% central inverters. In addition to PV inverters, Solectria Renewables also manufactures string combiners and offers a variety of online system monitoring options via its SolrenView webbased monitoring system.

Solectria Renewables launched its line of PVI 1.8 kW and 2.5 kW single-phase string inverters in 2005. In 2008, the company partnered with Taiwanese inverter manufacturer Motech to release the PVI 3000–5300 series string inverter line to the US market. Mike Kelly, engineering manager for Solectria Renewables, emphasizes the strength of the relationship as well as his company’s ownership of the PVI inverter line. “The PVI 3000–5300 series is our inverter, and we treat it as such,” Kelly says. “We’re responsible for the product line’s distribution, support and warranty. Our investment in the product is much deeper than simple branding.” This summer, two additional PVI models, the PVI 6500 and PVI 7500, will be released. These inverters have been ETL listed to UL 1741 and are currently eligible for the CSI program. The new units can be field-configured for 277 Vac output for commercial applications and will fill out Solectria Renewables’ overall inverter line. The company’s commercial and utility-scale PV inverters are manufactured in the US and are ARRA compliant as well as Ontario FIT Content Compliant. Solectria’s PVI 3000–5300 series Ontario FIT compliant single-phase string inverters are assembled in Ontario, Canada.

Solectria Renewables has been developing smart grid features for its high-power 3-phase inverters. While bringing these advanced capabilities to the string inverter product class is possible, Kelly does not feel that this transition will occur in the near future. He says, “There are no real technical obstacles to porting the smart grid features we have been developing for our large commercial and utility-scale inverters over to string inverter products. However, in most cases, string inverter systems do not tend to be aggregated to a degree that would justify advanced grid features like remote command and control or VAR support.”

In March, Solectria Renewables completed an expansion at its manufacturing facility in Lawrence, Massachusetts. The company expanded its California sales office and opened new offices in Florida and Colorado to increase its presence in the US. Scott Bowden, business development manager for Solectria Renewables, commented: “Solectria Renewables’ business is growing extremely quickly, and we see a need for regional support. We’ve strategically located our new offices in Florida and Colorado in part to serve existing customers, but also to reach the growing number of new customers. The expansion of our California facility is also very exciting. We’ve expanded our sales office to include customer service and application engineering. We are pleased to be well positioned to serve the PV market nationwide.”


When you consider that high-voltage string inverters were a new-to-market technology in the US in 2001, the product class has clearly experienced extraordinary growth and innovation. New products from manufacturers like Eltek Valere are on the immediate horizon, and we expect to see additional models from the current market leaders as well.

SolarEdge’s Berdner believes that string inverter developments over the next few years will take three directions. First, he expects the US PV industry to transition to transformerless inverters, noting: “There is a growing acknowledgement that ungrounded arrays offer a number of safety benefits compared to grounded arrays.” Second, he expects the adoption of module-level power electronics in rooftop systems to become more widespread. Third, Berdner expects more inverter systems to incorporate bidirectional communication and control. “Once some changes are made to the UL and IEEE standards, inverters can easily provide improved low voltage ride through and enable remote utility control of power level and power factor. In order to allow widespread adoption of PV, inverters will need to become better citizens of the grid.”


David Brearley / SolarPro magazine / Ashland, OR /

Joe Schwartz / SolarPro magazine / Ashland, OR /


Advanced Energy / 800.446.9167 /

Delta Energy Systems / 520.326.8401 /

Exeltech / 800.886.4683 /

Fronius USA / 810.220.4414 /

Ingeteam / 262.240.9850 /

KACO new energy / 415.931.2046 /

Motech Industries / 302.451.7500 /

Power-One / 805.987.8741 /

SMA America / 916.625.0870 /

Schneider Electric / 847.397.2600 /

SolarEdge / 530.273.3096 /

Solectria Renewables / 978.683.9700 /

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