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Contents

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Montana Army National Guard Goes Solar Bozeman Green Build Helps the Guard Meet the Challenge

18 22

Switching to a New Mounting System

NABCEP Alternative Experience Pathway for Qualified Electricians A Way for Qualified Electricians to Enter the Market

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Size Does Matter How Larger, More Efficient Solar Modules Can Lead to Big Savings

30 32

KVAR EC™: BEST IN CLASS

Harmonics and Noise in Photovoltaic (PV) Inverter and the Mitigation Strategies

38 40

New Stiebel Eltron SOL 27 Premium Flat Plate Collectors

Advertiser Index

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PRESIDENT/PUBLISHER Glen Hobson - 205-733-1341 SALES DEVELOPMENT MANAGER Hank Underwood - 205-733-1343 NATIONAL SALES MANAGER Rick Harless - 205-733-1324 CIRCULATION DIRECTOR/WEB DESIGN Jacklyn Hobson CREATIVE DIRECTOR Derek Gaylard ART DIRECTOR David Todd Executive and Advertising Offices 2070 Valleydale Rd, Suite # 6 Hoover, AL 35244 toll free: 866.981.4511 phone: 205-733-1341 fax: 205-733-1344 www.theelectriccurrent.com The Electric Current is distributed free to qualified subscribers. U.S. Postage paid at Birmingham, Alabama and additional mailing offices. The Electric Current is distributed to to qualified owners and managers in the electrical industry. Publisher is not liable for all content (including editorial and illustrations provided by advertisers) of advertisements published and does not accept responsibility for any claims made against the publisher. It is the advertiser’s or agency’s responsibility to obtain appropriate releases on any item or individuals pictured in an advertisement. Reproduction of this magazine in whole or in part is prohibited without prior written permission from the publisher. POSTMASTER: Send address changes to The Electric Current 2070 Valleydale Rd., Suite #6 Hoover, AL 35244 PRINTED IN THE USA

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The Electric Current August/September 2011


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Goes Solar

Montana Army National Guard

Feature Story

Bozeman Green Build Helps the Guard Meet the Challenge By: John Palm

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n 2005 President Bush signed Executive Order 13423 Act mandating that federal buildings across the country begin to incorporate renewable energy systems into their physical plants. The mandate laid out a set of goals that have acted as a catalyst for implementation of solar photovoltaic generating systems at Army National Guard facilities across the country. The goals may be unattainable within their original terms, e.g., the conversion to 7.5% renewable energy by 2013, but they provide a necessary target. The Energy Policy Act of 2005, in addition to the 2013 goal, sets the bar for new construction and major renovation at federal buildings at 5% for 2010 to 2012. The Act also allows the agencies to double count production if the power is generated on-site. Montana Army National Guard’s (MTARNG) leadership has embraced this campaign and, in the past couple of years has taken impressive strides toward increasing renewable energy on its bases across the state. Two projects designed and installed by Bozeman Green Build at Fort Harrison, Montana, will produce 2% of the base’s electricity. After double-counting (4%), this level of production comes very close to meeting the 5% goal set out in the Energy Policy Act of 2005. Another federal initiative which is encouraging the implementation of solar PV at Army National Guard facilities is the BRAC Act (Base Realignment and Closure). The 2005 BRAC Act was modified in 2006 to include the added requirement that all federal Army National Guard new construction and major renovation projects from fiscal year 2008 onward be built to meet the requirements of the U.S. Green Building Council’s LEED Silver rating. This requirement has prompted many designers to add renewable energy systems to their projects due to the large number of LEED points that these systems bring. A quick survey of Army National Guard new construction

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The Electric Current August/September 2011

Fort Harrison RTC System, 50KW


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projects underway across the country in August 2011 shows that a large number of these include solar PV systems. (To view these projects go to: https://www.fbo.gov/ index?s= opportunity&mode=list&tab=list, and enter “W912” in the keyword/search bar.) The solar PV project designed and installed by Bozeman Green Build in the spring of 2011 at the Great Falls Armed Forces Reserve Center, Great Falls, MT, is part of a BRAC project. To learn more about the federal government’s renewable energy goals and mandates view this document: http://www1.eere.energy.gov/femp /pdfs/re_programoverview.pdf. At the state level, Montana’s chief executive has also implemented ambitious energy conservation goals for the state’s buildings and facilities. In 2008 Governor Brian Schweitzer initiated his statewide energy conservation plan which called for a 20% reduction in fossil fuel-based energy usage by the end of fiscal year 2010. The Montana Army National Guard rose to the challenge. Three projects highlight their efforts to achieve this goal. They vary in type and size and are installed at two bases near major Montana cities. They were all completed in a 12 month period. The first, commissioned in August 2010, is a 50KW system for the Army National Guard base at Fort Harrison, Montana. This system has brought the building where it is located to a near net zero status. The RTC (Regional Training Center) Building has used 63,810 KWH since the installation date. The utility has only provided 1,336 KWH of that total while the PV array has provided 62,474 KWH representing 97.9% of the building’s load. Across the base this level of renewable energy production represented a little over 1% of the base’s total power consumption. When asked about the RTC system’s performance the MTARNG’s Energy Manager, Clay White, said, “The PV system has been performing well and has made a significant impact on the electric consumption at the RTC Building. PV has proven itself to be a viable renewable resource, and will be incorporated in future projects by the Montana Army National Guard.” The second system, at the Troop Medical Clinic, Fort Harrison, MT, was completed this spring and is contributing an additional annual power production of

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Ballast Blocks in ballast pan

Readiness Center Sub-Array E Ballast Pans and Tilt Brackets

43,748 KWH, bringing the base’s renewable energy total to 106,222 annual KWH, or 2% of the base’s load. The simple, straightforward design of both of these systems made their installation fast and trouble-free. Both systems are flush, roof mount systems installed on sloped, standing seam metal roof panels. Both systems are comprised of a single, large array. The RTC system uses a “z” shaped stainless bracket attached to the roof deck with screws. The Troop Medical system uses the “S-5!-U Mini” clamps which attach by set screw to the standing seams of the roof panels. By contrast, the third system, located at the Great Falls Armed Forces Reserve Center (GFAFRC), Great Falls, MT, brought unexpected challenges that reaffirmed the importance of teamwork during the design phase of any building-mounted solar PV system. This system, installed on two buildings at the GFAFRC, has a DC nameplate rating of 58.19 KW (49.91 KW on the Readiness building and 8.28 KW on the OMS building) and will produce 63,550 KWH of AC power annually. The system’s placement on an existing building added complexity that can usually be avoided in new construction. Bozeman Green Build led the design team over several siting, shading and structural hurdles to

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the project’s commissioning on June 20, 2011. We will now take a closer look at the design issues presented by this flatroof, fully ballasted, non-penetrating system, and how they were resolved. The first challenge was to fit 217 modules on a roof (Readiness building) with numerous mechanical vents, HVAC units and lightning protection already in place. In addition, the layout of the roof in three elevations causes inter-level shading that drastically reduces the area available for siting the sub-arrays. Bozeman Green Build selected SunLink, a racking company with the experience and engineering depth to tackle a fully Readiness Center Sub-Array E, Installation of 3-module panel ballasted, non-penetrating system that would have to be distributed across the roof in several sub-arrays. The next step, having arrived at an initial many modules as possible in order to reduce the overall ballast plan to divide the system into three sub-arrays, was to bring in the requirement. Breaking the system into five sub-arrays meant that structural engineer of record for the project, Thomas Dean and the distributed load would have to increase. Through additional wind-tunnel modelling, SunLink was able to keep the load within Hoskins (TD&H) of Great Falls, MT. TD&H checked the Readiness Center roof’s capacity to carry TD&H’s prescribed limits, an average of 8.26 PSF per array. TD&H the distributed load of 20.65 tons of modules, racking materials then analyzed the new layout and found that while the distributed and concrete ballast blocks (1,030 blocks at 24 pounds each). load passed, the point loads at each tilt bracket were now out of TD&H’s initial analysis determined that the distributed load aver- limits. This development presented another challenge due to the aging 7.52 pounds per square foot, would fall within the design unavailability of engineering data for the roof’s Vulcraft steel web parameters of the roof framing. But TD&H also found that a 26- joists. TD&H suspected that these existing joists could carry addimodule area would have to be excluded due to the presence of a tional weight beyond that described in the as-built plans, but Vul3,000 pound HVAC unit suspended below the roof. Bozeman craft does not keep this historical information. To have analyzed Green Build and SunLink then split the single largest sub-array of the joists from scratch would have been impossible due to time 156 modules into arrays of 60 and 70 modules and repositioned and cost constraints. Bozeman Green Build, TD&H and SunLink considered several the 26-module group raising the number of sub-arrays to five. Doing this presented a considerable challenge to SunLink’s engineers. alternatives and finally arrived at a two-fold solution that would Fully ballasted systems rely heavily on the interconnection of as keep the point loads within limits. The first adjustment was to completely re-configure the sub-arrays, switching from groups of 4-module panels to three-module panels. This increased the number of brackets by 33 percent. The second adjustment was to field-drill the racking rails to accept an additional four tilt brackets per 3-module panel, increasing the ratio of brackets to modules by an additional 133 percent. This solution was then successfully modeled in SunLink’s wind tunnel testing program to confirm its viability, and TD&H accepted the new point load values. The skewing of the additional ballast weight required for the smaller sub-arrays can be seen in Table 1.

Readiness Center Sub-Arrays A and B

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The Electric Current August/September 2011

TABLE 1 Number of PV Modules Weight 22 26 39 60 70

Per Square Foot 9.16 8.59 8.24 7.80 7.54


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+ these three projects, is the company, SunWize Technologies. Their sourcing, product support and logistical expertise kept costs down and allowed the Army National Guard to install more kilowatts of production for each tax dollar spent. With the right team of integrators, engineers and suppliers, solar PV costs will continue to drop, making it a truly viable alternative to fossil-fuel based energy production.

System Synopsis:

Readiness center, Sub-Array C, 26 modules

The layout of the sixth array of 36 modules, located at the OMS building, also required modification to increase the number of tilt brackets and decrease the point loads. By the time the final load compliant system layout was drawn, twenty-one different layouts had been created and tested by the design team. The process that was engaged at the GFAFRC brings attention to an often overlooked aspect of commercial PV project design, namely, how to attach the system to the roof. With any large-scale, ballasted, roof-mounted PV project, the design team’s time and resources should be allocated so that the compatibility of the existing roof structure and PV racking loads are checked and confirmed simultaneously. This approach worked well at GFAFRC. At no additional cost and without any delay to the project schedule, the design team was able to fit a complex system on an existing roof for which there was limited structural information. The Montana Army National Guard is pleased with the energy savings that will be realized from the solar PV system at the Great Falls Armed Forces Reserve Center. “The PV arrays will generate roughly 30 percent of the energy needs of the addition once it’s in full use and 40 percent of the needs of the OMS,” said Justin Bailey, the MTARNG’s Project Manager for the GFAFRC. “In the end, the users are very happy with the product they’ve gotten.” Bozeman Green Build will continue to partner with the Army National Guard in Montana and across the West as it meets the goals set out in the Energy Policy Act, the BRAC Act and other federal renewable energy mandates. While overcoming unique project design challenges is essential, holding the line on project costs is equally important. The silent partner, largely responsible for the cost viability of

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Fort Harrison, Montana RTC Building, July 2010 - 49.8 KW DC Nameplate Rating - Sanyo HIT 215N, (231) 215 watt modules - Solectria Renewables, (3) PV1 15KW Inverters - Unirac Sunframe Racking - Commissioning Date: 7-30-10 - Energy Policy Act project - Equipment Supplier: SunWize Technologies, www.sunwize.com - Design/Installation Contractor: Bozeman Green Build, www.bozemangreenbuild.com

Fort Harrison, Montana Troop Medical Clinic - 35.88 KW DC Nameplate Rating - Trina 230W TSL-PA05, (156) 230 watt modules - SMA Inverters, (6) Sunny Boy 6000US - Unirac SolarMount Racking - Commissioning Date: 6-01-11 - Energy Policy Act project - Equipment Supplier: SunWize Technologies, www.sunwize.com - Design/Installation Contractor: Bozeman Green Build, www.bozemangreenbuild.com Great Falls Armed Forces Reserve Center Great Falls, MT - 49.91 KW DC Nameplate Rating, Readiness Center building - 8.28 KW DC Nameplate Rating, Operational Maintenance Shop building - Solon 220/01, (253) 230 watt modules - SMA Inverters, (5) Sunny Boy 8000US, (1) Sunny Boy 7000US, (1) Sunny Boy 5000US - SunLink Ballasted Roof Mount System - Commissioning Date: 6-20-11 - BRAC project - Equipment Supplier: SunWize Technologies, www.sunwize.com - Design/Installation Contractor: Bozeman Green Build, www.bozemangreenbuild.com ❑ Author, John Palm, holds both the NABCEP Certified PV Installer and NABCEP Certified Solar Thermal Installer Certifications.

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Switching to a New Mounting System Zeke Yewdall, PV Engineer at Mile Hi Solar in Boulder, CO, has nearly 20 years of experience in solar energy installations and has designed systems as large as 200 kW. His first experience in solar energy was as a child, when he helped to install the off-grid PV system on his childhood home. This experience ignited his passion for solar energy. Holding NABCEP and CoSEIA certifications for PV installations and as an instructor for SEI courses in Photovoltaic’s, he is continually striving to increase efficiencies, decrease costs and implement best practices. When faced with the option to switch from his current mounting system to Conergy’s SunTop IV, Zeke was hesitant, but attracted by the system’s advancements that simplified installation and improved the system durability. “I’ve used a number of common mounting systems and have found them to be complicated with too many parts, not durable enough and lacking flexibility,” stated Zeke. “I agreed to try Conergy’s SunTop IV system because it promised to fix the problems I was experiencing with my previous racking systems.” At the time that Zeke decided to switch to Conergy’s SunTop IV, he was working with a crew that included two apprentices, himself and master PV technician, Ben Friesen, M.A., the owner of Mile Hi Solar who instructs on solar energy for various agencies and organizations and has designed, installed or serviced over a thousand solar systems in his career. The two apprentices, who had just begun training on solar energy

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installations, had already installed a competitor system on a few previous projects. Despite their apprenticeship status, they were able to quickly learn the SunTop IV mounting system in less than one installation. “My crew loved the SunTop system. They no longer had to do the pre-assembly of the bolts on the tailgate of the truck, since Conergy’s QuickStones arrive pre-assembled,” Zeke enthusiastically pointed out. “It was also nice to be able to insert the QuickStone bolts anywhere along the rail, instead of needing to pre-position everything. It took a lot of hassle out to just be able to put them in where and when we needed one. On top of that, the QuickStones are stronger than the competitor’s T-bolts.” The splices of Conergy SunTop IV also proved to help simplify and speed installations. “With the other splices there was so much drilling, which made it hard to align and of course there were a lot of mistakes,” Zeke continued. “Since the SunTop IV splices slide on easily with no drilling, it really increased our speed and completely removed our chance of error.” With the crew of two apprentices and two master technicians, it took about 5 hours to install their first 10 kW system with SunTop, but Zeke estimates that if it had been a fully seasoned crew it would have taken 1 – 2 hours off that time. Zeke stated that with the SunTop IV, his crew is able to cut installation down by 25 – 30% compared to the previous system. There a number of aspects that Zeke says contribute to the time savings, “The number of parts and tools in competitor systems drastically increases the installation time. But, with Conergy’s SunTop IV, there is only the 6 mm Allen Wrench and the parts are all standard across all rail types. It is really nice to have that consistency.” However, Zeke’s experienced eye picked up on another key advantage of the SunTop IV system. “It was great that the height was adjustable to account for an uneven roof – customers always appreciate an aesthetic system.” However, the biggest concern for any installer is the switching cost of training its crew on a new system. “After only one installation, my inexperienced crew was able to standardize on the system. A veteran crew could probably learn the system in less than half that time. So, the switching cost is very low,” stated Zeke. ❑

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IV also proved to help simplify and speed installations.

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+ NABCEP Alternative Experience Pathway for Qualified Electricians

Feature Story

A Way for Qualified Electricians to Enter the Market By – Ezra Auerbach

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n August of 2009 NABCEP announced a new program that would enable journeymen electricians to gain the experience required to sit for the NABCEP exam. This program was called the Alternative Experience Pathway (AEP). Its guiding principle recognizes the extensive knowledge and skill that it takes to earn journeyman electrician recognition and provides a “fast track” approach to these individuals gaining their PV installation experience. In brief, this new pathway allows teams of up to four qualified electricians (journeymen) to work together on a PV installation that is done under the supervision of a proctor. Each of the team members will get installation credit for these installs that is unique in the NABCEP Eligibility Requirements – in all other cases only a single individual can get credit for any given installation. At first the program met with some resistance, many seasoned PV installers felt that the AEP would water down the eligibility requirements to take the exam. This is in fact no way the case. The only people who even qualify for this installation experience pathway must be journeymen or master electricians (or be recognized as a qualified electrician by their AHJ) and they must have a minimum of 40 hours of PV specific training that includes the hands-on installation of two distinctly different PV systems, plus the two system installs that are part of this Alternative Experience Pathway. This means that candidates qualifying to sit for this exam will have participated in a minimum of four PV installs. Don Warfield, Chairperson of NABCEP says, “The Alternative Experience Pathway program enables a large block of otherwise qualified craftsmen to qualify for certification and increase the supply of Certified workers in markets which place high value on certification” Chris LaForge, a veteran solar installer, electrician and advanced PV trainer who works with the non profit solar training organization the Mid West Renewable Energy Association (MREA) agrees, he says; “At the MREA we find that qualified electricians are building their skill sets quickly and fully meeting the goals outlined in

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NABCEP’s task analysis. The new pathway will allow us to provide the opportunity for more of our most qualified students to meet the experience requirements to sit for the PV Certification Exam. ” Over past two years Alternative Experience Pathway installations have taken place in Texas and Montana. The first round of candidates who completed their training and installations at the Austin Electric JATC took the NABCEP Certified PV Installer Exam in September 2010– and their passing score percentage was higher than the average. In Texas the AEP program has been used in conjunction with a Department of Labor grant to train electricians to work in senior roles on PV installation projects. The project is a joint effort between the Austin Electric JATC (Joint Apprenticeship and Training Committee) and ImagineSolar – a private PV and smart grid training company. This unique partnership brings together the combined strengths of a nationally recognized PV centric training organization and the outstanding facilities of a JATC. Response to this program from Electrical Contractors has been equally positive. “ImagineSolar provided not only a pathway to the NABCEP Certification Exam but also in-depth installation experience on cutting edge solar.” said Jack Payne, Owner, B.J. Electric, and a member of the AEJATC Board of Trustees. Jack is a NABCEP Certified PV Installer who achieved his eligibility to take the NABCEP exam through the Alternative Experience Pathway program offered at the AEJATC. ImagineSolar starts their students out in an extensive classroom and laboratory based training program that runs 128 hours. In addition to theoretical learning the students participate in group installations that includes a wide variety of system types including; AC-coupled bimodal systems, micro-inverters, dual-axis trackers, and cylindrical CIGS modules as well as traditional solar technology. In short the students are exposed to a very wide range of equipment and installation types. After completing the classroom and hands on training the students are broken into teams of four, as a team they complete two installations at the JATC.

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Richard Stovall, ISPQ Certified Master Trainer and Director of Operations of ImagineSolar says, “The Alternative Experience Pathway has been hugely successful, and very well received. To date over 60 electricians have gone through the program. What they get from the AEP is an opportunity to test their skills and knowledge and apply them to two significant installations that are required to be fully commissioned and code-compliant. Outside of this program, many of these electricians would not have access to the installs required to sit for the exam. They understand this and therefore take the activity very seriously.” In Austin, incentive payments for PV installations are tied to a requirement to have NABCEP Certified Installers on the job. This project is helping ensure that there is a ready supply of well trained and fully qualified workers available as solar electric installations become increasingly prevalent. “Many of our alumni are now working for electrical contractors on PV projects,” said Michael Kuhn, CEO of ImagineSolar, “Their NABCEP Certification allows their contractors to participate in the PV incentive programs as well as providing the necessary expertise to do the job.” The Montana Electrical Joint Apprenticeship and Training Committee took a different approach to their implementation of the AEP program. Thanks to the dogged determination of Mitch Hegman, the Assistant Training Director at the JATC a communitybased installation was located. A team of four electricians, who advanced PV training at the JATC, worked together to install a PV system on the East Valley Middle School in East Helena, MT. This job provided the electricians working on the project with valuable real-world PV installation experience, which, of course, entailed the odd bit of difficulty – the wrong fasteners for the mounting frame slowed down progress while someone was dispatched to the nearest hardware supplier for the correct length screw. The “real world” intervened in the installation a second time. An issue with cabling arose when installing the monitoring system – to address the problem one of the installers had to interface with the IT person at the school. Mitch Hegman says; “This issue is illus-

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trative of the technical problems that can ‘haunt’ installers and lead to unanticipated expenditures of time. In that regard this problem was almost fortuitous with respect to the intent of this program to present some obstacles for the installers to solve.” Mr. Hegman says. “I am very pleased with the performance of the installers. I think we can all agree that these candidates long ago achieved ‘expert’ status in skills such as interpretation of the NEC, raceway installations, conductor sizing, etc. The training throughout this venture however, has been remarkably productive in bringing them to the front edge of PV design and installation.” He continues; “The Middle School was actually the third site selected for the PV system. Both previous locations failed to progress beyond the permitting process due to structural loading beyond existing roof design – all of this made for valuable lessons in site surveys, permitting and system design.” This 4.48 kW installation of two strings of ten 224 Watts Sharp PV modules is a virtually letter perfect example of the intent of the AEP program because it provided value multiple stakeholders. Not only did the candidates get the experience they needed to sit for the NABCEP exam they also made a lasting contribution to their community. East Valley students, parents and school staff will long see the benefits offered by solar electricity thanks to this project. The Alternative Experience Pathway installation opportunity is open to all Joint Apprenticeship Training Centers. It offers a great way for qualified electricians who take advanced training based on the NABCEP PV Installer Job Task Analysis to get the experience they need to take the Certification Exam. It also presents a great opportunity for training centers to work with their community and make a positive contribution to the greening of the local electrical grid. NABCEP strongly encourages collaboration between contractors, JATCs, utilities and community groups to use lasting, real-world projects for Alternative Experience Pathway installations. For more information on this program readers should contact the author at eauerbach@nabcep.org. ❑

The Electric Current August/September 2011


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Size Does Matter How Larger, More Efficient Solar Modules Can Lead to Big Savings Brent Brucker, Helios Solar Works

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very day, the sun rises in the east and sets in the west, showering the earth with its warming rays in a relatively predictable manner. Harvesting those rays and the energy they contain can be accomplished in a number of ways. In the PV world there are as many different applications as there are solar module options, from large to small, thin-film to crystalline, tried-and-true to cutting edge - no one module satisfies all needs. One often overlooked module characteristic is power-per-module. Understanding the economics behind the number of watts a single module produces is a key to generating significant competitive advantages. The amount of watts a module can produce is a function of several factors. The wattage of the solar cell determines a maximum threshold of power for a given sized module. The other factor is, of course, the module’s dimensions. Crystalline modules are sized in increments based on cell dimension. For instance, a module using sixinch cells must be built in increments of six-inches in both length and height. Simply adding more cells means more power. So what does this have to do with module choice? Most designers understand the value of higher-wattage modules and the corresponding reduction in the number of modules needed. This allows the system to squeeze more power out of a space-constrained area, often referred to as power density. Selecting more powerful cells with tighter build-specs increases power density even further. A similar analysis should be done regarding module size because larger modules can save on installation costs simply by being large. A 72-cell module may be able to produce 50 additional watts with little or no increase

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in installation time, racking or BOS costs. The module often requires the same length of rails, the same effort to mount to the rack, the same number of connections, the same single grounding lug or WEEB, etc. Similarly, the forklift doesn’t care if the pallet weighs 1300 or 1400 lbs but wouldn’t it be nice to get an extra 1200-1500 watts out of that same pallet.

Case Study The table below shows a comparison of several modules. Modules of course have varying efficiencies, varying sizes and varying prices. The example here shows the economics behind a 50kw system. It is based on a real case study comparing modules from different manufacturers and their varying costs. Here we have normalized the modules with respect to cost and cell efficiency by using the same manufacturer. The result is an analysis of efficiency, size and the combination of the two without the clutter of varying pricing and module construction. It breaks out the factors that are affected by module choice and illustrates the efficiencies gained by needing fewer modules. As the industry has narrowed its focus on dollar-per-watt some, may have neglected the bigger picture. Asking

The Electric Current August/September 2011

“what’s the price” is certainly a valid question but, unless those numbers are fully analyzed they may lead to a design that leaves money on the table or, worse yet, gets beat out by a better design. Using the 235 watt module as a baseline, we can see that 213 units are needed to power the system. Simply increasing module output (not footprint) to 255 watts reduces the module count to 197. Moving to a 72-cell, 305-watt module cuts the count to 164 and a 96-cell 410-watt module requires just 122 units. Each module requires the same mounting procedure, same grounding procedure, the same connection procedure, the same two-man team to set and connect, etc. A multiplier was inserted into the labor calculation to adjust for increased difficulty in handling larger modules – 5% increase for 72-cell and 20% for the 96-cell module. Installation labor was also adjusted in the model between length of the module and the number of modules. This particular example is of a portrait-oriented array so the width of the modules was used to calculate wire length, racking length, etc. For the purposes of this study the labor ratio was split: 33% based on number of modules, 67% based on system length. To illustrate this point, consider the 60-cell versus the 96-cell comparison. Thirty-three percent of the labor equation is derived by the number of modules, in this case 213 for the 60-cell (or 197 for 255 Wp module) and 122 for the 96cell unit (including the 20% labor increase for the 96-cell module’s larger size). This means 91 fewer modules to move and install. As for length (in portrait orientation), we get 8,264 inches for the 60-cell and 6,244 for the 96-cell, a difference of over 168 feet. Freight savings can also be reaped. Modules are produced all over the world, but


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+ Example System - 50,000 Watts

More people are looking seriously at an industry that continues to grow while others around it are shrinking. Competition is getting tougher and the days of getting the job simply because you were there are over. More powerful modules are a combination of higher efficiency cells and having more cells per unit – being bigger. While larger modules are slightly more difficult to handle, weigh more and can be more cumbersome (in this case a 96-cell module weighs as much as 19 pounds more than a 72-cell module and 23 pounds more than a 60-cell module), the economic benefits of utilizing these modules clearly justify adaptation and ingenuity. As the construction industry flourished in previous decades, many successful innovations incorporated scale: 12’ sheetrock reduced the number of joints to finish; premade trusses saved time and produced more consistent results; structural insulated panels (SIPs) saved multiple construction steps; precast foundation walls allowed foundations to be built a fraction of the time of more traditional systems. Where there is value, designers and contractors will find a way to extract it.

Summary

any manufacturer who wants to compete in the U.S. must find routes that save their customer money. In an apples-to-apples comparison, reducing the number of skids or truckloads will markedly cut shipping costs. Savings are often reaped when the number of skids can be reduced due to the efficiency of the module. Simply going from nine to eight skids of 60-cell modules in our example saves $225. Imagine the savings on a MW project when the metric is fewer truckloads. Higher efficiency equates directly to fewer modules while larger, more powerful modules equate to fewer skids, fewer forklift drops, etc. While larger modules mean larger skids and a cor-

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Savings are dramatic in the example provided. Using the 235 watt module as the baseline, total system savings of 2%, 7% and 10% can be realized for the 255, 305 and 410 watt modules, respectively. On a dollarper-watt basis the savings are $.09, $.25 and $.37 for the same three module choices. These numbers reveal just how important size -an often under-considered factor in module selection - can be. This type of analysis can also lay the framework for better designs, more job wins and increased margins. This comparison tool was originally developed to analyze modules from different vendors. The example here holds price responding increase in skid shipping rates, constant across all modules, allowing for a more often than not, the reduced number clearer picture of the effect of module seof skids more than compensates for any lection on system factors such as labor, balance-of-system (BOS) costs and freight. unit increases. There are many factors to consider when The Future choosing a module and price-per-watt is There are many reasons why system de- usually at or near the top of that list. It is signers are not specifying larger modules. clear, though, that price-per-watt needs to Often a “system” begins to be standardized be just one of the data points in a thorough and humans have a tendency to go with analysis of whole-system options. Anything what works. If you won the last job on a 60- less and you are risking being out-designed. cell module design it wouldn’t be a stretch An analysis of this nature will help weed to think that that was a design worth re- through the choices and help expose the peating. The truth is that as the solar in- real value of “cheap” modules. ❑ dustry gathers steam it will become more bbrucker@helios-usa.com competitive across all facets of the business. www.TheHeliosPicture.com

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KVAR EC™: BEST IN CLASS WHEN IT COMES TO ENERGY EFFICIENCY AND POWER FACTOR OPTIMIZATION DEVICES, KVAR ENERGY CONTROLLERS (KVAR ECS™) ARE THE BEST IN THEIR CLASS. KVAR Energy Savings, Inc. (KVAR) has been in business since 1992 and has a long running reputation of support and standing behind its product, the KVAR EC™, with great success stories. KVAR ECs™ are power factor (PF) optimization devices designed for electric utility customers to reduce their energy consumption (kWh), lower KVA demand, optimize PF for inductive loads, reduce electric losses and decrease carbon footprints. KVAR ECs™ are a most effective energy efficient measure and a wise investment that will preserve our natural resources and foster a sustainable environment.

WHY ARE KVAR ECS™ THE BEST IN THEIR CLASS? Without KVAR’s patented method, there is absolutely no reason why anyone should buy, sell or install a device like the KVAR EC™ in their electrical system. The use of KVAR’s sizing apparatus, procedure, and specified energy controllers is the only PF optimization device technology solution able to optimize PF on-site by tuning the electrical system in real time, from the inductive equipment back through the electric utility meter so that demand on the electric grid, energy consumption, electrical system losses and carbon footprints are reduced, and operations are streamlined. This KVAR patented apparatus and procedure provides real time on-site 100% PF correction to the unity level, i.e. 1.0 PF. KVAR ECs™ reduce electric bills by 6% to 10% for residential, commercial and industrial loads, depending on how your electricity is billed and your type of electrical maintenance program. Through sales channels spanning multiple business sectors, KVAR ECs™ are making a real difference in reducing energy costs in national and international markets. The KVAR ECs™ are UL,

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CSA and CE listed, as well as RoHS certified. KVAR ECs™ are not one size fits all devices. Each unit is properly sized and custom units are built to suit each consumer’s needs and to meet and exceed the National Electric Code (NEC). Also, 100% of the units sold in America are built with pride and tested in KVAR’s Daytona Beach, FL manufacturing plant. KVAR Distributors are the only distributors authorized to use the patented method and apparatus to determine the exact amount of capacitance for what is needed to optimize PF in homes, businesses and individual motors. Today, there are several knock-offs and counterfeit products in the market attempting to mirror the success of KVAR ECs™, but those imitation products only confirm the effectiveness of KVAR ECs™ because only products that work are copied. However, the KVAR EC™ is the original, quality energy controller, and KVAR holds the related

The Electric Current August/September 2011

Through sales channels spanning multiple business sectors, KVAR ECs™ are making a real difference in reducing energy costs in national and

international markets. patented technology. Finally, by using KVAR ECs™ or becoming a part of KVAR, one can become part of the global “green” movement by decreasing electrical consumption and carbon footprints. ❑ For more information on our products and services or how to become a part of KVAR, please view our website at www.kvar.com, or contact our office at (386) 767-0048.


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Industry News

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Harmonics and Noise in Photovoltaic (PV) Inverter and the Mitigation Strategies

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V inverters use semiconductor devices to transform the DC power into controlled AC power by using Pulse Width Modulation (PWM) switching. PWM switching is the most efficient way to generate AC power, allowing for flexible control of the output magnitude and frequency. However, all PWM methods inherently generate harmonics and noise originating in the high dv/dt and di/dt semiconductor switching transients. In order to reduce harmonics and switching noise, external filtering needs to be added. The PWM waveform is generated by comparing a reference signal (sinusoidal red trace) and a carrier waveform (triangular blue trace). The PWM waveform controls the Insulated Gate Bipolar Transistor (IGBT) switches to generate the AC output. When the reference signal is bigger than the carrier waveform, the upper IGBT is triggered

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The Electric Current August/September 2011

Example of a PVI 82KW-480 VAC inverter

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on (lower IGBT being off) and positive DC voltage is applied to the inverter output phase (A). In the other case, when the reference signal is smaller than the triangular carrier waveform, the lower IGBT is turned on (upper IGBT being off) and negative DC voltage is applied to the inverter output. The reference signal magnitude and frequency determine the amplitude and the frequency of the output voltage. The frequency of the carrier waveform is called the modulation frequency. In order to generate more precise sinusoidal AC voltage waveforms and keeping the size of the LC filter small, high modulation frequencies are generally used. There are many industrial standards that control the noise and harmonic contents for AC motor drives, Uninterrupted Power Supplies (UPS) or other AC power applications. In the case of grid-tied PV inverters, the Institute of Electrical and Electronics Engineers (IEEE) 1547, Underwriters Laboratories (UL) 1741 and FCC Part 15B standards specify the guidelines to control the harmonic contents of the output current and the Electro Magnetic Interference (EMI) generation in the inverter. The guidelines guarantee that: The inverters do not generate excessive noise and harmonics, which can contaminate the AC grid voltage. The inverters are immune to electrical and magnetic noise from other sources and provide reliable operation in an environment of high electromagnetic noise. The inverters do not generate unwanted radiated or conducted noise, which can disturb the stable operation of other equipment coupled either electrically or magnetically. Most of the PV inverters manufactured in the United States are designed to meet UL 1741 and IEEE 1547 standards. As the capacity of PV generation in power distribution systems grows, utility companies become increasingly concerned that the noise and harmonics from the PV inverter systems might adversely impact the power quality or affect the operation of other equipment and cause it to malfunction or otherwise disrupt the stable operation of the power distribution system. This article lists the possible sources of the harmonics and switching noise generated by the PV inverter and describes how they can be controlled to meet customer requirements and relevant industrial stan-

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dards. To present the theoretical and experimental analysis of this phenomenon, a Solectria Renewables PVI 82KW - 480VAC PV inverter system is being used. However, since most PV inverters have similar types of component configurations, the information in this article can be used to understand the harmonics and EMI issues in a variety of inverter systems.

PV Inverter System Configuration A Solectria PVI 82KW inverter include filters used for attenuating the high frequency noise on the inverter output voltages and currents. There are two main sources of high frequency noise generated by the PWM inverters. The first one is the PWM modulation frequency (2 ~ 20kHz). This

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+

component is mainly attenuated by the LC filter and the transformer. The second source originates from the switching transients of the power electronics switching devices (IGBTs). The frequency of the switching transients is dependent on the device switching characteristics, gate drive circuit and the snubber circuit in the inverter, and ranges from several hundred kHz to 100MHz. The series filter and the shunt filter are designed to attenuate the frequency components caused by these switching transients and also the harmonics from other subsystem components such as the switched mode power supply (SMPS) and other inverter control circuitry. Most of the harmonic components in the voltage and current waveforms are filtered out by the LC, series and shunt filters. The inverter output current is in phase with the voltage (unity power factor) and the total harmonic distortion (THD) is less than 5% at rated operation, which is far better than the current THD of most industrial loads, and is comparable to the output current waveforms of an Uninterruptable Power

Supply (UPS).

not look very different. However, the Fast Fourier Transformation (FFT) results show PWM Frequency and LC Filter that the inverter current after the LC filter An LC filter is used to attenuate the PWM has much less high frequency components modulation frequency and its harmonics in than the unfiltered power stage output the inverter system. The leakage induc- current. This filtering effect can be illustrated in tance of the integrated isolation transformer further attenuates the high a Bode Plot. The LC filter frequency charfrequency component so that the output acteristics use the theoretical frequency current will be sinusoidal and meet the de- analysis and measured harmonic composired THD limit. A symmetrical PWM nents with a frequency analyzer when the scheme is generally preferred to reduce the inverter operates at full power. ripple in the inverter output current. A High Frequency Noise Generated symmetrical PWM scheme compared to an asymmetrical PWM reduces the effective by Switching Transients peak-to-peak ripple current by half when When the switching devices are turned using the same switching frequency. on and off, high dv/dt and di/dt cause osAn inverter’s power stage output volt- cillations during the transients, which conage waveform is composed of a series of tain high frequency noise in the range of square waveforms and includes high fre- 100kHz or higher. quency components. The current waveBy using a slow switching transient, the form is relatively smooth and sinusoidal oscillation can be reduced but switching as the inverter output current flows into losses are increasing due to longer operathe inductor such that it cannot change tion of IGBTs in the active region. With a instantaneously. faster switching speed, the switching losses In the time domain, the waveforms do can be kept lower but oscillations in volt-

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The Electric Current August/September 2011

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age and current are being generated due to the parasitic inductance and capacitance in the inverter stack. This high frequency oscillation may fall into the frequency band regulated by FCC. In order to increase the overall efficiency of the inverter and at the same time to minimize EMI, the IGBT switching speed and noise filter design must be carefully coordinated. There are other sources of switching noise in the inverter system caused by the Switch Mode Power Supplies (SMPS) and the digital control logic circuits. The noise from these components can reduce the system performance by contaminating internal analog feedback signals, resulting in logic level or communication errors and could also cause EMI interference with the outside world. The high frequency noise can be classified into radiated noise and conducted noise. The radiated noise can be controlled in many ways at the board level and at the system level such as shielding, component layout, wiring routing, and signal grouping. The conducted noise can be controlled by grounding or the use of proper filters, carefully designed to eliminate specific frequency components. In Solectria’s PVI 82KW inverter, excellent noise levels were achieved by implementing a robust printed circuit board (PCB) layout in combination with hardware and software filters. Noise in signal circuits is controlled by ferrite beads and proper grounding. The PVI 82KW inverter also features series and shunt filters in the final output stage of the system. These filters are band limiting and designed to filter out switching transient frequencies.

Series Filter The series filter in the PVI 82KW attenuates both common mode and differential mode noise. It provides 80dB common mode attenuation for the frequencies between 100kHz and 1MHz, and 70dB differential mode attenuation for the frequencies between 200kHz and 3MHz. The filter is selected to eliminate the system specific dominant frequency components, and is not active in the lower PWM modulation frequency range.

Shunt Filter The selected shunt filter for the PVI 82KW inverter has a resonance point around 150kHz and provides a reduction of noise interference particularly in the fre-

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Since the DC voltage control loop bandwidth is low, it does not cause any harmonics or EMI issues.

would generate harmonics in the 100 ~ 1kHz range. The DC voltage control loop is around the current control loop and is usually controlled at a lower sampling rate. If the DC voltage fluctuates due to sudden changes in weather conditions, the DC voltquency range between 50kHz and 5MHz. age control loop has a certain bandwidth to This filter is added to further reduce the react and stabilize the system output. Durswitching noise from the power stage as ing sunlight transients, the system might well as from the switch mode power sup- generate even slower oscillations in the DC ply in the inverter control system. The bus and output AC currents. Since the DC voltage control loop bandshunt filter also provides a protection circuit against surges of atmospheric origin to width is low, it does not cause any harmonthe grid, typically caused by lightning and ics or EMI issues. However, if the voltage characterized by high current levels of short control loop were not tuned properly, the duration. The filter reacts in a few mi- generation efficiency would decrease due croseconds to current spikes of a few kA, to failure to track the maximum power and protects the system against impulse point of the PV panels. Solectria Renewables’ inverters have surges of up to 1000 volts. been fully tested at different load conditions System Wide EMI Control to have excellent dynamic characteristics Some of the EMI reduction strategies for both the AC current and DC voltage that are used in a PVI 82KW inverter control loops. The AC current control bandwidth is about 2kHz and the DC voltinclude: age control bandwidth is less than 100Hz. • Solid Grounding • Controlled Wire Routing Conclusion • Board level filtering and EMI reduction layout This article described how the current • Wire twisting harmonics and EMI are controlled in PV in• Stack configuration for reduced verters. IEEE 1547, UL 1741 and FCC Part stray inductance 15B standards impose strong guidelines for • Power electronics for EMI shielding grid-tied PV inverters to reduce current har• Analog signal conditioning using monics and eliminate electromagnetic ferrite beads noise. Extra attention is given by the PV in• DC side high power wiring for EMI verter manufacturer to design inverters that shielding are immune to EMI problems and guarantee reliable operation of the inverter in all Harmonics Generated worst case operating conditions. by Firmware Control Different types of practical harmonics Conventional PV inverters firmware runs and noise reduction strategies for a comat least two nested control loops. One is the mercial three-phase PV inverter were introAC current control loop to control the in- duced in this article. The filtering of verter output current, purely sinusoidal and harmonics and EMI needs to be carefully in phase with the grid voltage, generating designed to maintain the control bandactive power. The other is the DC voltage width of the inverter and to provide clean control loop in conjunction with a Maxi- and reliable control signals in both analog mum Power Point Tracking (MPPT) algo- and digital electronic circuits. The PVI rithm to most efficiently harvest the DC 82KW inverter system is equipped with several levels of harmonics and EMI filtering power generated by the solar panels. When grid conditions change due to and its effectiveness and reliability have power grid transients, power line faults or been proven in harshest commercial and load based voltage fluctuations in the dis- utility scale applications. ❑ tribution line, the inverter output current is Article written by Dr. Soonwook Hong, Secontrolled to balance the power transfer nior Electronic Power Systems Engineer and from the PV array to the grid. The current Michael Zuercher-Martinson, Chief Techcontrol loop gains need to be tuned prop- nology Officer of Solectria Renewables, LLC. erly, so that the firmware does not generFor more information, please go to ate frequency oscillations, which in turn www.solren.com.

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New Stiebel Eltron SOL 27 Premium Flat Plate Collectors

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esigned for residential or commercial water and radiant floor space heating, the new SOL 27 PREMIUM low-profile flat plate collectors offer all the latest industry features. The SOL 27 Premium is a highly efficient thermal solar collector. The net absorber surface of over 25 square feet results in a maximum output of 31,300 btu/day per panel (SRCC clear day rating). The SOL 27 Premium also offers: high selective absorber coating, low-iron, tempered solar glazing, and very effective insulation around the absorber plate. The internal fluid tubes are copper and the absorber plate is aluminum. Installation is quick and easy with push nipple plumbing connections and versatile mounting rack kits. Stiebel Eltron thermal solar equipment is the culmination of over 40 years of experience in the thermal solar business. There is an industry leading 10-year warranty on Stiebel Eltron solar panels and tanks. For more information please visit our website at www.stiebel-eltronUSA.com or call us at (800) 582-8423. For more information, visit: www.stiebel-eltron-USA.com Visit us at: www.surgepure.com

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Company Name

Alcan American Technical Publishers ARPI Bierer & Assocates, Inc. California Turbo Cementex Dexter + Chaney EZ Connector Future Lighting Solutions HatiCon Solar, LLC Helios Solar Works Hercules Industries, Inc. Hioki USA Industrial Control & Supply Inc. Jonas Software Krenz-Vent KVAR Lapp USA LEDtronics NABCEP Pelsue Phase- A- Matic Rud Chain, Inc. SMA America Solectria Renewables Springer Controls, Inc. Steelman Industries SunWize Sunwize SurgePure Underground Devices, Inc. Utility Metals

Page Number

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16 33 32 12 29 39 7 40 13 2 9 34 5 21 25 34 31 1 3 36 19 23 IFC IBC 37 27 32 17 BC 38 15 11

Website

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