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4 The Electric Current August/September 2011

Contents +

PRESIDENT/PUBLISHERGlen Hobson - 205-733-1341SALES DEVELOPMENT MANAGERHank Underwood - 205-733-1343NATIONAL SALES MANAGERRick Harless - 205-733-1324CIRCULATION DIRECTOR/WEB DESIGNJacklyn HobsonCREATIVE DIRECTORDerek GaylardART DIRECTORDavid Todd

Executive and Advertising Offices2070 Valleydale Rd,Suite # 6 Hoover, AL 35244toll free: 866.981.4511phone: 205-733-1341fax: 205-733-1344www.theelectriccurrent.com

The Electric Current is distributed free to qualified sub-scribers. U.S. Postage paid at Birmingham, Alabama andadditional mailing offices.

The Electric Current is distributed to to qualified ownersand managers in the electrical industry. Publisher is not li-able for all content (including editorial and illustrationsprovided by advertisers) of advertisements published anddoes not accept responsibility for any claims made againstthe publisher. It is the advertiser’s or agency’s responsi-bility to obtain appropriate releases on any item or indi-viduals pictured in an advertisement. Reproduction ofthis magazine in whole or in part is prohibited withoutprior written permission from the publisher.

POSTMASTER: Send address changes toThe Electric Current 2070 Valleydale Rd.,Suite #6 Hoover, AL 35244

P R I N T E D I N T H E U S A

1806

06Montana Army National Guard Goes SolarBozeman Green Build Helps the Guard Meet the Challenge

18Switching to a NewMounting System

22NABCEP Alternative Experience Pathway for Qualified ElectriciansA Way for Qualified Electricians to Enter the Market

26Size Does MatterHow Larger, More Efficient Solar Modules Can Lead to Big Savings

30KVAR EC™: BEST IN CLASS

32Harmonics and Noise in Photovoltaic (PV)Inverter and the Mitigation Strategies

38New Stiebel Eltron SOL 27 Premium Flat Plate Collectors

40Advertiser Index

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In 2005 President Bush signed Execu-tive Order 13423 Act mandating thatfederal buildings across the country

begin to incorporate renewable energy sys-tems into their physical plants. The man-date laidout a set of goals that have actedasa catalyst for implementation of solar pho-tovoltaic generating systems at Army Na-tional Guard facilities across the country.The goalsmaybeunattainablewithin theiroriginal terms, e.g., the conversion to 7.5%renewable energy by 2013, but they pro-vide a necessary target. The Energy PolicyAct of 2005, in addition to the 2013goal, setsthe bar for new construction and majorrenovation at federal buildings at 5% for2010 to 2012. The Act also allows the agen-cies to double count production if thepower is generated on-site.MontanaArmyNational Guard’s (MTARNG) leadershiphas embraced this campaign and, in thepast couple of years has taken impressivestrides toward increasing renewable energyon its bases across the state. Two projectsdesigned and installed by Bozeman GreenBuild at Fort Harrison, Montana, will pro-duce 2%of the base’s electricity. After dou-ble-counting (4%), this level of productioncomes very close tomeeting the 5%goal setout in the Energy Policy Act of 2005.

Another federal initiative which is en-couraging the implementation of solar PVat Army National Guard facilities is theBRACAct (BaseRealignment andClosure).The 2005BRACActwasmodified in 2006 toinclude the added requirement that all fed-eral Army National Guard new construc-tion and major renovation projects fromfiscal year 2008onwardbebuilt tomeet therequirements of the U.S. Green BuildingCouncil’s LEED Silver rating. This require-ment has promptedmanydesigners to addrenewable energy systems to their projectsdue to the large number of LEED pointsthat these systems bring. A quick survey ofArmy National Guard new construction

Feature Story +Montana Army National Guard

Goes SolarBozeman Green Build Helps the Guard Meet the Challenge

By: John Palm

Fort Harrison RTC System, 50KW

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Feature Story +projects underway across the countryin August 2011 shows that a large num-ber of these include solar PV systems.(To view these projects go to:https://www.fbo.gov/ index?s= oppor-tunity&mode=list&tab=list, and enter“W912” in the keyword/search bar.) Thesolar PV project designed and installedby Bozeman Green Build in the springof 2011 at the Great Falls Armed ForcesReserve Center, Great Falls, MT, is partof a BRAC project. To learn more aboutthe federal government’s renewableenergy goals and mandates view thisdocument:http://www1.eere.energy.gov/femp/pdfs/re_programoverview.pdf.

At the state level, Montana’s chief execu-tive has also implemented ambitious en-ergy conservation goals for the state’sbuildings and facilities. In 2008 GovernorBrian Schweitzer initiated his statewide en-ergy conservation plan which called for a20% reduction in fossil fuel-based energyusage by the end of fiscal year 2010. TheMontana Army National Guard rose to thechallenge. Three projects highlight their ef-forts to achieve this goal. They vary in typeand size and are installed at two bases nearmajor Montana cities. They were all com-pleted in a 12 month period.

The first, commissioned in August 2010,is a 50KW system for the Army NationalGuardbase at FortHarrison,Montana. Thissystem has brought the building where it islocated to a near net zero status. The RTC(Regional Training Center) Building hasused 63,810 KWH since the installationdate. The utility has only provided 1,336KWH of that total while the PV array hasprovided 62,474 KWH representing 97.9%of the building’s load. Across the base thislevel of renewable energy production rep-resented a little over 1% of the base’s totalpower consumption. When asked aboutthe RTC system’s performance theMTARNG’s Energy Manager, Clay White,said, “The PV system has been performingwell and has made a significant impact onthe electric consumption at the RTC Build-ing. PV has proven itself to be a viable re-newable resource, and will be incorporatedin future projects by the Montana ArmyNational Guard.”

The second system, at the Troop Med-ical Clinic, Fort Harrison, MT, was com-pleted this spring and is contributing anadditional annual power production of


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% ofthe base’s load. The simple, straightforwarddesignof bothof these systemsmade their in-stallation fast and trouble-free. Both systems are flush, roof mount systems installed onsloped, standing seam metal roof panels. Both systems are comprised of a single, large ar-ray. The RTC system uses a “z” shaped stainless bracket attached to the roof deck withscrews. The Troop Medical system uses the “S-5!-U Mini” clamps which attach by setscrew to the standing seamsof the roof panels. By contrast, the third system, locatedat theGreat Falls Armed Forces Reserve Center (GFAFRC), Great Falls, MT, brought unexpectedchallenges that reaffirmed the importance of teamwork during the design phase of anybuilding-mounted solar PV system.

This system, installed on two buildings at the GFAFRC, has a DC nameplate rating of58.19 KW (49.91 KW on the Readiness building and 8.28 KW on the OMS building) andwill produce 63,550 KWH of AC power annually. The system’s placement on an existingbuilding added complexity that can usually be avoided in new construction. BozemanGreen Build led the design team over several siting, shading and structural hurdles to

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Feature Story +


the project’s commissioning on June 20,2011. We will now take a closer look atthe design issues presented by this flat-roof, fully ballasted, non-penetrating sys-tem, and how they were resolved.

The first challenge was to fit 217 mod-ules on a roof (Readiness building) withnumerous mechanical vents, HVACunits and lightning protection already inplace. In addition, the layout of the roofin three elevations causes inter-levelshading that drastically reduces the areaavailable for siting the sub-arrays. Boze-man Green Build selected SunLink, aracking company with the experienceand engineering depth to tackle a fullyballasted, non-penetrating system thatwould have to be distributed across theroof in several sub-arrays. The next step, having arrived at an initialplan to divide the system into three sub-arrays, was to bring in thestructural engineer of record for the project, Thomas Dean andHoskins (TD&H) of Great Falls, MT.

TD&H checked the Readiness Center roof’s capacity to carrythe distributed load of 20.65 tons of modules, racking materialsand concrete ballast blocks (1,030 blocks at 24 pounds each).TD&H’s initial analysis determined that the distributed load aver-aging 7.52 pounds per square foot, would fall within the designparameters of the roof framing. But TD&H also found that a 26-module area would have to be excluded due to the presence of a3,000 pound HVAC unit suspended below the roof. BozemanGreen Build and SunLink then split the single largest sub-array of156 modules into arrays of 60 and 70 modules and repositionedthe 26-module group raising the number of sub-arrays to five. Do-ing this presented a considerable challenge to SunLink’s engineers.Fully ballasted systems rely heavily on the interconnection of as

many modules as possible in order to reduce the overall ballastrequirement. Breaking the system into five sub-arrays meant thatthe distributed load would have to increase. Through additionalwind-tunnel modelling, SunLink was able to keep the load withinTD&H’s prescribed limits, an average of 8.26 PSF per array. TD&Hthen analyzed the new layout and found that while the distributedload passed, the point loads at each tilt bracket were now out oflimits. This development presented another challenge due to theunavailability of engineering data for the roof’s Vulcraft steel webjoists. TD&H suspected that these existing joists could carry addi-tional weight beyond that described in the as-built plans, but Vul-craft does not keep this historical information. To have analyzedthe joists from scratch would have been impossible due to timeand cost constraints.

Bozeman Green Build, TD&H and SunLink considered severalalternatives and finally arrived at a two-fold solution that wouldkeep the point loads within limits. The first adjustment was to

completely re-configure the sub-arrays, switchingfrom groups of 4-module panels to three-modulepanels. This increased the number of brackets by33 percent. The second adjustment was to field-drillthe racking rails to accept an additional four tiltbrackets per 3-module panel, increasing the ratioof brackets to modules by an additional 133 per-cent. This solution was then successfully modeledin SunLink’s wind tunnel testing program to con-firm its viability, and TD&H accepted the new pointload values. The skewing of the additional ballastweight required for the smaller sub-arrays can beseen in Table 1.

TABLE 1Number of PV Modules Per Square Foot

Weight22 9.1626 8.5939 8.2460 7.8070 7.54Readiness Center Sub-Arrays A and B

Readiness Center Sub-Array E, Installation of 3-module panel

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Feature Story +

The layout of the sixth array of 36 modules, located at theOMS building, also required modification to increase thenumber of tilt brackets and decrease the point loads. By thetime the final load compliant system layout was drawn,twenty-one different layouts had been created and tested bythe design team.

The process that was engaged at the GFAFRC brings atten-tion to an often overlooked aspect of commercial PV projectdesign, namely, how to attach the system to the roof.

With any large-scale, ballasted, roof-mounted PV project, thedesign team’s time and resources should be allocated so thatthe compatibility of the existing roof structure and PV rackingloads are checked and confirmed simultaneously. This ap-proach worked well at GFAFRC. At no additional cost and with-out any delay to the project schedule, the design teamwas ableto fit a complex system on an existing roof for which there waslimited structural information.

The Montana Army National Guard is pleased with the en-ergy savings that will be realized from the solar PV system atthe Great Falls Armed Forces Reserve Center. “The PV arrayswill generate roughly 30 percent of the energy needs of the ad-dition once it’s in full use and 40 percent of the needs of theOMS,” said Justin Bailey, the MTARNG’s Project Manager forthe GFAFRC. “In the end, the users are very happy with theproduct they’ve gotten.”

Bozeman Green Build will continue to partner with the ArmyNational Guard in Montana and across the West as it meetsthe goals set out in the Energy Policy Act, the BRAC Act andother federal renewable energy mandates.

While overcoming unique project design challenges is es-sential, holding the line on project costs is equally important.The silent partner, largely responsible for the cost viability of

these three projects, is the company,SunWize Technologies. Their sourcing,product support and logistical expertisekept costs down and allowed the ArmyNational Guard to installmore kilowatts ofproduction for each tax dollar spent. Withthe right teamof integrators, engineers andsuppliers, solar PV costs will continue todrop,making it a truly viable alternative tofossil-fuel based energy production.

System Synopsis:Fort Harrison, MontanaRTC Building, July 2010- 49.8 KWDCNameplate Rating- SanyoHIT 215N, (231) 215wattmodules- Solectria Renewables, (3) PV1 15KWInverters

-Unirac SunframeRacking- CommissioningDate: 7-30-10- Energy Policy Act project- Equipment Supplier: SunWizeTechnologies, www.sunwize.com

-Design/InstallationContractor:BozemanGreenBuild,www.bozemangreenbuild.com

Fort Harrison, MontanaTroop Medical Clinic- 35.88 KWDCNameplate Rating- Trina 230WTSL-PA05, (156) 230wattmodules- SMA Inverters, (6) Sunny Boy 6000US-Unirac SolarMount Racking- CommissioningDate: 6-01-11- Energy Policy Act project- Equipment Supplier: SunWize Technologies,www.sunwize.com

-Design/InstallationContractor: BozemanGreenBuild,www.bozemangreenbuild.com

Great Falls Armed Forces Reserve CenterGreat Falls, MT- 49.91 KWDCNameplate Rating, Readiness Center building- 8.28 KWDCNameplate Rating, OperationalMaintenanceShop building

- Solon 220/01, (253) 230wattmodules- SMA Inverters, (5) Sunny Boy 8000US, (1) Sunny Boy7000US, (1) Sunny Boy 5000US

- SunLink Ballasted RoofMount System-CommissioningDate: 6-20-11- BRACproject- Equipment Supplier: SunWize Technologies,www.sunwize.com

-Design/InstallationContractor: BozemanGreenBuild,www.bozemangreenbuild.com �

Author, John Palm, holds both the NABCEP Certified PV Installerand NABCEP Certified Solar Thermal Installer Certifications.

Readiness center, Sub-Array C, 26 modules

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Zeke Yewdall, PV Engineer at MileHi Solar in Boulder, CO, has nearly20 years of experience in solar en-ergy installations and has designedsystems as large as 200 kW. His firstexperience in solar energy was as a child,when he helped to install the off-grid PVsystem on his childhood home. This expe-rience ignited his passion for solar energy.HoldingNABCEPandCoSEIA certificationsfor PV installations and as an instructor forSEI courses in Photovoltaic’s, he is contin-ually striving to increase efficiencies, de-crease costs and implement best practices.When faced with the option to switch

fromhis currentmounting system toCon-ergy’s SunTop IV, Zeke was hesitant, butattracted by the system’s advancementsthat simplified installation and improvedthe system durability. “I’ve used a num-ber of common mounting systems andhave found them to be complicated withtoo many parts, not durable enough andlacking flexibility,” stated Zeke. “I agreedto try Conergy’s SunTop IV system be-cause it promised to fix the problems Iwas experiencing with my previous

racking systems.”At the time that Zeke de-cided to switch to Con-ergy’s SunTop IV, hewasworking with a crewthat included two ap-prentices, himselfandmaster PV tech-nician, Ben Friesen,M.A., the owner ofMile Hi Solar whoinstructs on solarenergy for variousagencies and organi-zations and has de-

signed, installed orserviced over a thousand

solar systems in his career.The two apprentices, who had

just begun training on solar energy


Switching to aNewMounting System

Case Study +

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installations, had already installed a competitor systemona fewpreviousprojects.Despite their apprenticeship status,they were able to quickly learn the SunTop IV mountingsystem in less than one installation. “My crew loved theSunTop system. They no longer had to do the pre-assem-bly of the bolts on the tailgate of the truck, sinceConergy’sQuickStones arrive pre-assembled,” Zeke enthusiasticallypointed out. “Itwas also nice to be able to insert theQuick-Stone bolts anywhere along the rail, instead of needing topre-position everything. It took a lot of hassle out to just beable to put them in where and when we needed one. Ontop of that, the QuickStones are stronger than the com-petitor’s T-bolts.”The splices of Conergy SunTop IV also proved to help

simplify and speed installations. “With the other splicestherewas somuchdrilling,whichmade it hard to align andof course there were a lot of mistakes,” Zeke continued.“Since the SunTop IV splices slide oneasilywithnodrilling,it really increased our speed and completely removed ourchance of error.”With the crewof twoapprentices and twomaster techni-

cians, it took about 5 hours to install their first 10 kW sys-tem with SunTop, but Zeke estimates that if it had been afully seasoned crew itwouldhave taken1 – 2hours off thattime.Zeke stated thatwith theSunTop IV,his crew isable tocut installationdownby25–30%compared to theprevioussystem. There a number of aspects that Zeke says con-tribute to the time savings, “Thenumberof parts and toolsin competitor systemsdrastically increases the installationtime. But, with Conergy’s SunTop IV, there is only the 6mmAllenWrench and the parts are all standard across allrail types. It is really nice to have that consistency.”However, Zeke’s experienced eyepickeduponanother

key advantage of the SunTop IV system. “It was great thatthe 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 crewon anew system. “Afteronly one installation, my inexperienced crew was able tostandardize on the system. A veteran crew could proba-bly learn the system in less than half that time. So, theswitching cost is very low,” stated Zeke. �

Case Study +

The splices of Conergy SunTopIV also proved to help simplify

and speed installations.

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Feature Story +

InAugust of 2009 NAB-CEP announced a newprogram thatwould en-

able journeymenelectriciansto gain the experience re-quired to sit for the NABCEPexam. This program wascalled the Alternative Experi-encePathway (AEP). Its guid-ing principle recognizes theextensiveknowledgeandskillthat it takes to earn journey-man electrician recognitionandprovidesa“fast track”ap-proach to these individualsgaining their PV installationexperience.In brief, this newpathway

allows teams of up to fourqualified electricians (jour-neymen) towork together ona PV installation that is doneunder the supervision of aproctor. Each of the teammembers will get installation credit forthese installs that is unique in the NABCEP Eligibility Require-ments – in all other cases only a single individual can get credit forany given installation.At first the programmet with some resistance,many seasoned

PV installers felt that the AEPwould water down the eligibility re-quirements to take the exam. This is in fact no way the case. Theonly peoplewhoevenqualify for this installation experiencepath-waymust be journeymenormaster electricians (or be recognizedas a qualified electricianby their AHJ) and theymust have amini-mumof 40hours of PV specific training that includes thehands-oninstallationof twodistinctly different PV systems, plus the two sys-tem installs that are part of this Alternative Experience Pathway.Thismeans that candidates qualifying to sit for this examwill haveparticipated in aminimumof four PV installs.Don Warfield, Chairperson of NABCEP says, “The Alternative

Experience Pathway program enables a large block of otherwisequalified craftsmen to qualify for certification and increase thesupply of Certified workers inmarkets which place high value oncertification”Chris LaForge, a veteran solar installer, electrician andadvanced

PV trainer who works with the non profit solar training organiza-tion theMidWest Renewable Energy Association (MREA) agrees,he says; “At theMREAwe find that qualified electricians are build-ing their skill sets quickly and fully meeting the goals outlined in

NABCEP’s task analysis. Thenewpathwaywill allowus toprovide the opportunity formore of our most qualifiedstudents tomeet the experi-ence requirements to sit forthe PVCertification Exam. ”Over past two years Alter-

native Experience Pathwayinstallations have takenplace inTexas andMontana.The first roundof candidateswho completed their train-ing and installations at theAustinElectric JATC took theNABCEP Certified PV In-staller Exam in September2010– and their passingscore percentagewas higherthan the average.InTexas theAEPprogram

has been used in conjunc-tion with a Department of

Labor grant to train electricians to work in senior roles on PVinstallation projects. The project is a joint effort between theAustin Electric JATC (Joint Apprenticeship and Training Com-mittee) and ImagineSolar – a private PV and smart grid trainingcompany. This unique partnership brings together the com-bined strengths of a nationally recognized PV centric trainingorganization and the outstanding facilities of a JATC.Response to this program fromElectrical Contractors has been

equally positive. “ImagineSolar provided not only a pathway totheNABCEPCertification Exambut also in-depth installation ex-perience on cutting edge solar.” said Jack Payne,Owner, B.J. Elec-tric, and a member of the AEJATC Board of Trustees. Jack is aNABCEP Certified PV Installer who achieved his eligibility to takethe NABCEP exam through the Alternative Experience Pathwayprogramoffered at the AEJATC.ImagineSolar starts their students out in an extensive classroom

and laboratory based trainingprogram that runs 128hours. In ad-dition to theoretical learning the students participate in group in-stallations that includes a wide variety of system types including;AC-coupledbimodal systems,micro-inverters, dual-axis trackers,and cylindrical CIGSmodules as well as traditional solar technol-ogy. In short the students are exposed to a very wide range ofequipment and installation types. After completing the classroomandhands on training the students are broken into teams of four,as a team they complete two installations at the JATC.

NABCEP Alternative ExperiencePathway for Qualified Electricians

A Way for Qualified Electricians to Enter the MarketBy – Ezra Auerbach

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Richard Stovall, ISPQ CertifiedMaster Trainer and Director ofOperations of ImagineSolar says, “The Alternative ExperiencePathway has been hugely successful, and very well received. Todate over 60 electricians have gone through the program. Whatthey get from the AEP is an opportunity to test their skills andknowledge andapply them to two significant installations that arerequired to be fully commissioned and code-compliant. Outsideof this program,manyof these electricianswouldnot have accessto the installs required to sit for the exam. They understand thisand therefore take the activity very seriously.”

In Austin, incentive payments for PV installations are tied to arequirement to haveNABCEPCertified Installers on the job. Thisproject is helping ensure that there is a ready supply ofwell trainedand fully qualifiedworkers available as solar electric installationsbecome increasingly prevalent. “Many of our alumni are nowworking for electrical contractors on PV projects,” said MichaelKuhn, CEO of ImagineSolar, “Their NABCEP Certification allowstheir contractors to participate in the PV incentive programs aswell as providing the necessary expertise to do the job.”

TheMontanaElectrical JointApprenticeshipandTrainingCom-mittee took a different approach to their implementation of theAEPprogram. Thanks to the doggeddetermination ofMitchHeg-man, the Assistant Training Director at the JATC a community-based installation was located. A team of four electricians, whoadvanced PV training at the JATC, worked together to install a PVsystemon the East ValleyMiddle School in East Helena,MT. Thisjobprovided the electriciansworking on theprojectwith valuablereal-world PV installation experience, which, of course, entailedthe odd bit of difficulty – the wrong fasteners for the mountingframe slowed down progress while someone was dispatched tothe nearest hardware supplier for the correct length screw.

The “realworld” intervened in the installationa second time.Anissuewith cabling arosewhen installing themonitoring system– toaddress theproblemoneof the installers had to interfacewith theIT person at the school. Mitch Hegman says; “This issue is illus-

trative of the technical problems that can ‘haunt’ installers andlead to unanticipated expenditures of time. In that regard thisproblem was almost fortuitous with respect to the intent of thisprogram to present some obstacles for the installers to solve.”

Mr. Hegman says. “I am very pleased with the performance ofthe installers. I think we can all agree that these candidates longago achieved ‘expert’ status in skills such as interpretation of theNEC, raceway installations, conductor sizing, etc. The trainingthroughout this venturehowever, hasbeen remarkablyproductivein bringing them to the front edge of PV design and installation.”He continues; “The Middle School was actually the third site se-lected for thePV system.Bothprevious locations failed toprogressbeyond the permitting process due to structural loading beyondexisting roof design – all of this made for valuable lessons in sitesurveys, permitting and systemdesign.”

This 4.48 kW installation of two strings of ten 224Watts SharpPVmodules is a virtually letter perfect example of the intent of theAEP program because it provided value multiple stakeholders.Not only did the candidates get the experience they needed to sitfor the NABCEP exam they also made a lasting contribution totheir community. East Valley students, parents and school staffwill long see the benefits offered by solar electricity thanks to thisproject.

TheAlternative Experience Pathway installation opportunity isopen to all Joint Apprenticeship TrainingCenters. It offers a greatway for qualified electricians who take advanced training basedon the NABCEP PV Installer Job Task Analysis to get the experi-ence they need to take the Certification Exam. It also presents agreat opportunity for training centers toworkwith their commu-nity andmake a positive contribution to the greening of the localelectrical grid. NABCEP strongly encourages collaboration be-tween contractors, JATCs, utilities and community groups to uselasting, real-world projects for Alternative ExperiencePathway in-stallations. Formore information on this program readers shouldcontact the author at [email protected]. �

Feature Story +

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in installation time, racking or BOS costs.The module often requires the same lengthof rails, the same effort to mount to the rack,the same number of connections, the samesingle grounding lug or WEEB, etc. Simi-larly, the forklift doesn’t care if the palletweighs 1300 or 1400 lbs but wouldn’t it benice to get an extra 1200-1500 watts out ofthat same pallet.

Case StudyThe table below shows a comparison of

several modules. Modules of course havevarying efficiencies, varying sizes and vary-ing prices. The example here shows theeconomics behind a 50kw system. It isbased on a real case study comparing mod-ules from different manufacturers and theirvarying costs. Here we have normalized themodules with respect to cost and cell effi-ciency by using the same manufacturer.The result is an analysis of efficiency, sizeand the combination of the two without theclutter of varying pricing and module con-struction. It breaks out the factors that areaffected by module choice and illustratesthe efficiencies gained by needing fewermodules. As the industry has narrowed itsfocus on dollar-per-watt some, may haveneglected the bigger picture. Asking

E very day, the sun rises inthe east and sets in thewest, showering the

earth with its warming rays in arelatively predictable manner.Harvesting those rays and theenergy they contain can be ac-complished in a number ofways.

In the PV world there are asmany different applications asthere are solar module options,from large to small, thin-film tocrystalline, tried-and-true tocutting edge - no one modulesatisfies all needs. One oftenoverlooked module character-istic is power-per-module.Understanding the economics behind thenumber of watts a single module producesis a key to generating significant competi-tive advantages.

The amount of watts a module can pro-duce is a function of several factors. Thewattage of the solar cell determines a max-imum threshold of power for a given sizedmodule. The other factor is, of course, themodule’s dimensions. Crystalline modulesare sized in increments based on cell di-mension. For instance, a module using six-inch cells must be built in increments ofsix-inches in both length and height. Sim-ply adding more cells means more power.

So what does this have to do withmodule choice?

Most designers understand the value ofhigher-wattage modules and the corre-sponding reduction in the number of mod-ules needed. This allows the system tosqueeze more power out of a space-con-strained area, often referred to as powerdensity. Selecting more powerful cells withtighter build-specs increases power densityeven further. A similar analysis should bedone regarding module size because largermodules can save on installation costs sim-ply by being large.

A 72-cell module may be able to produce50 additional watts with little or no increase

“what’s the price” is certainlya valid question but, unlessthose numbers are fully ana-lyzed they may lead to a de-sign that leaves money onthe table or, worse yet, getsbeat out by a better design.

Using the 235 watt mod-ule as a baseline, we can seethat 213 units are needed topower the system. Simplyincreasing module output(not footprint) to 255 wattsreduces themodulecount to197. Moving to a 72-cell,305-watt module cuts thecount to 164 and a 96-cell410-watt module requiresjust122units. Eachmodule

requires the same mounting procedure,same grounding procedure, the same con-nectionprocedure, thesametwo-manteamto set and connect, etc.

A multiplier was inserted into the laborcalculation to adjust for increased difficultyin handling larger modules – 5% increasefor 72-cell and 20% for the 96-cell module.Installation labor was also adjusted in themodel between length of the module andthe number of modules. This particular ex-ample is of a portrait-oriented array so thewidth of the modules was used to calculatewire length, racking length, etc. For the pur-poses of this study the labor ratio was split:33% based on number of modules, 67%based on system length. To illustrate thispoint, consider the 60-cell versus the 96-cellcomparison. Thirty-three percent of the la-bor equation is derived by the number ofmodules, in this case 213 for the 60-cell (or197 for 255 Wp module) and 122 for the 96-cell unit (including the 20% labor increasefor the 96-cell module’s larger size). Thismeans 91 fewer modules to move and in-stall. As for length (in portrait orientation),we get 8,264 inches for the 60-cell and 6,244for the 96-cell, a difference of over 168 feet.

Freight savings can also be reaped. Mod-ules are produced all over the world, but

Case Study +

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

Brent Brucker, Helios Solar Works

08-0911TECp06-40:08-0911TECp06-40 9/16/11 10:16 AM Page 26

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responding increase in skid shipping rates,more often than not, the reduced numberof skids more than compensates for anyunit increases.

The FutureThere aremany reasonswhy systemde-

signers are not specifying larger modules.Often a “system”begins to be standardizedand humans have a tendency to go withwhatworks. If youwon the last jobona 60-cell module design it wouldn’t be a stretchto think that that was a design worth re-peating. The truth is that as the solar in-dustry gathers steam it will become morecompetitive across all facets of thebusiness.

any manufacturer who wants to competein the U.S. must find routes that save theircustomer money. In an apples-to-applescomparison, reducing the number of skidsor truckloads will markedly cut shippingcosts. Savings are often reaped when thenumber of skids can be reduced due to theefficiency of the module. Simply goingfromnine to eight skids of 60-cell modulesin our example saves $225. Imagine thesavings on a MW project when the metricis fewer truckloads. Higher efficiencyequates directly to fewer modules whilelarger, more powerful modules equate tofewer skids, fewer forklift drops, etc. Whilelargermodulesmean larger skids anda cor-

More people are looking seriously at an in-dustry that continues to growwhile othersaround it are shrinking. Competition is get-ting tougher and the days of getting the jobsimply because youwere there are over.More powerfulmodules are a combina-

tion of higher efficiency cells and havingmore cells per unit – being bigger. Whilelargermodules are slightlymore difficult tohandle,weighmore and canbemore cum-bersome (in this case a 96-cell moduleweighs asmuch as 19 poundsmore than a72-cellmodule and 23poundsmore than a60-cell module), the economic benefits ofutilizing thesemodules clearly justify adap-tation and ingenuity.As the construction industry flourished

in previous decades, many successful in-novations incorporated scale: 12’ sheetrockreduced thenumber of joints to finish; pre-made trusses saved time and producedmore consistent results; structural insulatedpanels (SIPs) saved multiple constructionsteps; precast foundation walls allowedfoundations to be built a fraction of thetime of more traditional systems. Wherethere is value, designers and contractorswill find away to extract it.

SummarySavings aredramatic in the examplepro-

vided. Using the 235 watt module as thebaseline, total systemsavings of 2%, 7%and10%canbe realized for the 255, 305 and410watt modules, respectively. On a dollar-per-watt basis the savings are $.09, $.25 and$.37 for the same three module choices.These numbers reveal just how importantsize -an often under-considered factor inmodule selection - can be. This type ofanalysis can also lay the framework for bet-ter designs, more job wins and increasedmargins.This comparison tool was originally de-

veloped to analyzemodules fromdifferentvendors. The example here holds priceconstant across all modules, allowing for aclearer picture of the effect of module se-lectionon system factors such as labor, bal-ance-of-system (BOS) costs and freight.There are many factors to consider whenchoosing a module and price-per-watt isusually at or near the top of that list. It isclear, though, that price-per-watt needs tobe just one of the data points in a thoroughanalysis ofwhole-systemoptions. Anythingless andyouare riskingbeingout-designed.An analysis of this nature will help weedthrough the choices and help expose thereal value of “cheap”modules. �

[email protected]

Example System - 50,000 Watts

Case Study +

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been in business since 1992 and has along running reputation of support andstanding behind its product, the KVAREC™, with great success stories.KVAR ECs™ are power factor (PF) op-

timization devices designed for electricutility customers to reduce their energyconsumption (kWh), lower KVA demand,optimizePF for inductive loads, reduceelec-tric losses and decrease carbon footprints.KVARECs™areamost effectiveenergyeffi-cient measure and a wise investment thatwillpreserveournatural resourcesand fostera sustainable environment.

WHY ARE KVAR ECS™THE BEST IN THEIR CLASS?Without KVAR’s patented method,

there is absolutely no reason why any-one should buy, sell or install a devicelike the KVAR EC™ in their electricalsystem. The use of KVAR’s sizing appa-ratus, procedure, and specified energycontrollers is the only PF optimizationdevice technology solution able to opti-mize PF on-site by tuning the electricalsystem in real time, from the inductiveequipment back through the electricutility meter so that demand on the elec-tric grid, energy consumption, electricalsystem losses and carbon footprints arereduced, and operations are stream-lined. This KVAR patented apparatusand procedure provides real time on-site100% PF correction to the unity level, i.e.1.0 PF.KVAR ECs™ reduce electric bills by

6% to 10% for residential, commercialand industrial loads, depending on howyour electricity is billed and your type ofelectrical maintenance program.Through sales channels spanning

multiple business sectors, KVAR ECs™are making a real difference in reducingenergy costs in national and interna-tional markets. The KVAR ECs™ are UL,

CSA and CE listed, as well as RoHScertified.KVAR ECs™ are not one size fits

all devices. Each unit is properlysized and custom units are built tosuit each consumer’s needs and tomeet and exceed the National Elec-tric Code (NEC). Also, 100% of theunits sold in America are built withpride and tested in KVAR’s DaytonaBeach, FL manufacturing plant.KVAR Distributors are the only dis-

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Industry News +

Harmonics andNoise in Photovoltaic(PV) Inverter and theMitigation Strategies

PV inverters use semiconductor devices to transform the DC power intocontrolled AC power by using Pulse Width Modulation (PWM) switch-ing. PWM switching is the most efficient way to generate AC power, al-

lowing for flexible control of the outputmagnitude and frequency. However, allPWMmethods inherently generate harmonics andnoise originating in thehighdv/dt and di/dt semiconductor switching transients. In order to reduce har-monics and switching noise, external filtering needs to be added.ThePWMwaveform is generatedby comparing a reference signal (sinusoidal

red trace) anda carrierwaveform (triangular blue trace). ThePWMwaveformcon-trols the Insulated Gate Bipolar Transistor (IGBT) switches to generate the AC output.When the reference signal is bigger than the carrierwaveform, theupper IGBT is triggered

Example of aPVI 82KW-480VAC inverter

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08-0911TECp06-40:08-0911TECp06-40 9/9/11 2:45 PM Page 32

The Electric Current August/September 2011 33

dards. To present the theoretical and ex-perimental analysis of this phenomenon, aSolectria Renewables PVI 82KW - 480VACPV inverter system is beingused. However,since most PV inverters have similar typesof component configurations, the informa-tion in this article can be used to under-stand the harmonics and EMI issues in avariety of inverter systems.

PV Inverter System Configuration

ASolectria PVI 82KW inverter include fil-ters used for attenuating thehigh frequencynoise on the inverter output voltages andcurrents. There are two main sources ofhigh frequency noise generated by thePWM inverters. The first one is the PWMmodulation frequency (2 ~ 20kHz). This

on (lower IGBT being off) and positive DCvoltage is applied to the inverter outputphase (A). In the other case, when the ref-erence signal is smaller than the triangularcarrierwaveform, the lower IGBT is turnedon (upper IGBTbeing off) andnegativeDCvoltage is applied to the inverter output.The reference signal magnitude and fre-quency determine the amplitude and thefrequency of the output voltage. The fre-quencyof the carrierwaveform is called themodulation frequency. Inorder to generatemore precise sinusoidal AC voltage wave-forms and keeping the size of the LC filtersmall, high modulation frequencies aregenerally used.

There aremany industrial standards thatcontrol the noise and harmonic contentsfor ACmotor drives, Uninterrupted PowerSupplies (UPS) or other AC power applica-tions. In the case of grid-tied PV inverters,the Institute of Electrical and ElectronicsEngineers (IEEE) 1547, Underwriters Lab-oratories (UL) 1741 andFCCPart 15B stan-dards specify the guidelines to control theharmonic contents of the output currentand the Electro Magnetic Interference(EMI) generation in the inverter. Theguidelines guarantee that:

The inverters do not generate exces-sive noise and harmonics, which cancontaminate the AC grid voltage.

The inverters are immune to electricaland magnetic noise from other sourcesand provide reliable operation in an envi-ronment of high electromagnetic noise.

The inverters do not generate unwantedradiated or conducted noise, which candisturb the stable operation of otherequipment coupled either electrically ormagnetically.

Most of the PV inverters manufacturedin the United States are designed to meetUL 1741 and IEEE 1547 standards. As thecapacity of PV generation in power distrib-ution systems grows, utility companies be-come increasingly concerned that thenoiseand harmonics from the PV inverter sys-tems might adversely impact the powerquality or affect the operation of otherequipment and cause it to malfunction orotherwise disrupt the stable operation ofthe power distribution system.

This article lists the possible sources ofthe harmonics and switching noise gener-ated by the PV inverter and describes howthey canbe controlled tomeet customer re-quirements and relevant industrial stan-

Visit us at: www.americantech.net

08-0911TECp06-40:08-0911TECp06-40 9/9/11 1:06 PM Page 33


component ismainly attenuated by the LCfilter and the transformer. The secondsource originates from the switching tran-sients of the power electronics switchingdevices (IGBTs). The frequency of theswitching transients is dependent on thedevice switching characteristics, gate drivecircuit and the snubber circuit in the in-verter, and ranges from several hundredkHz to 100MHz. The series filter and theshunt filter are designed to attenuate thefrequency components caused by theseswitching transients and also the harmon-ics fromother subsystemcomponents suchas the switchedmodepower supply (SMPS)and other inverter control circuitry.Most of theharmonic components in the

voltage and current waveforms are filteredout by the LC, series and shunt filters. Theinverter output current is in phasewith thevoltage (unity power factor) and the totalharmonic distortion (THD) is less than 5%at rated operation, which is far better thanthe current THD of most industrial loads,and is comparable to the output currentwaveforms of an Uninterruptable Power

Supply (UPS).

PWM Frequency and LC FilterAnLC filter is used to attenuate thePWM

modulation frequency and its harmonics inthe inverter system. The leakage induc-tance of the integrated isolation trans-former further attenuates the highfrequency component so that the outputcurrentwill be sinusoidal andmeet the de-sired THD limit. A symmetrical PWMscheme is generally preferred to reduce theripple in the inverter output current. Asymmetrical PWMschemecompared to anasymmetrical PWM reduces the effectivepeak-to-peak ripple current by half whenusing the same switching frequency.An inverter’s power stage output volt-

age waveform is composed of a series ofsquare waveforms and includes high fre-quency components. The current wave-form is relatively smooth and sinusoidalas the inverter output current flows intothe inductor such that it cannot changeinstantaneously.In the time domain, the waveforms do

not look very different. However, the FastFourier Transformation (FFT) results showthat the inverter current after the LC filterhasmuch less high frequency componentsthan the unfiltered power stage outputcurrent.This filtering effect can be illustrated in

a Bode Plot. The LC filter frequency char-acteristics use the theoretical frequencyanalysis and measured harmonic compo-nents with a frequency analyzer when theinverter operates at full power.

High Frequency Noise Generatedby Switching TransientsWhen the switching devices are turned

on and off, high dv/dt and di/dt cause os-cillations during the transients,which con-tain high frequency noise in the range of100kHz or higher.By using a slow switching transient, the

oscillation can be reduced but switchinglosses are increasing due to longer opera-tion of IGBTs in the active region. With afaster switching speed, the switching lossescan be kept lower but oscillations in volt-

Industry News +

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08-0911TECp06-40:08-0911TECp06-40 9/9/11 1:36 PM Page 34

The Electric Current August/September 2011 35

quency range between 50kHz and 5MHz.This filter is added to further reduce theswitching noise from the power stage aswell as from the switch mode power sup-ply in the inverter control system. Theshunt filter also provides a protection cir-cuit against surges of atmospheric origin tothe grid, typically caused by lightning andcharacterized by high current levels of shortduration. The filter reacts in a few mi-croseconds to current spikes of a few kA,and protects the system against impulsesurges of up to 1000 volts.

System Wide EMI ControlSome of the EMI reduction strategies

that are used in a PVI 82KW inverterinclude:• Solid Grounding• Controlled Wire Routing• Board level filtering and EMIreduction layout

• Wire twisting• Stack configuration for reducedstray inductance

• Power electronics for EMI shielding• Analog signal conditioning usingferrite beads

• DC side high power wiring for EMIshielding

Harmonics Generatedby Firmware Control

Conventional PV inverters firmware runsat least two nested control loops. One is theAC current control loop to control the in-verter output current, purely sinusoidal andin phase with the grid voltage, generatingactive power. The other is the DC voltagecontrol loop in conjunction with a Maxi-mum Power Point Tracking (MPPT) algo-rithm to most efficiently harvest the DCpower generated by the solar panels.

When grid conditions change due topower grid transients, power line faults orload based voltage fluctuations in the dis-tribution line, the inverter output current iscontrolled to balance the power transferfrom the PV array to the grid. The currentcontrol loop gains need to be tuned prop-erly, so that the firmware does not gener-ate frequency oscillations, which in turn

age and current are being generated due tothe parasitic inductance and capacitancein the inverter stack. This high frequencyoscillation may fall into the frequency bandregulated by FCC. In order to increase theoverall efficiency of the inverter and at thesame time to minimize EMI, the IGBTswitching speed and noise filter designmust be carefully coordinated.

There are other sources of switchingnoise in the inverter system caused by theSwitch Mode Power Supplies (SMPS) andthe digital control logic circuits. The noisefrom these components can reduce the sys-tem performance by contaminating inter-nal analog feedback signals, resulting inlogic level or communication errors andcould also cause EMI interference with theoutside world.

The high frequency noise can be classi-fied into radiated noise and conductednoise. The radiated noise can be controlledin many ways at the board level and at thesystem level such as shielding, componentlayout, wiring routing, and signal group-ing. Theconductednoise canbecontrolledby grounding or the use of proper filters,carefully designed to eliminate specific fre-quency components. In Solectria’s PVI82KW inverter, excellent noise levels wereachievedby implementing a robust printedcircuit board (PCB) layout in combinationwithhardware and software filters. Noise insignal circuits is controlled by ferrite beadsand proper grounding. The PVI 82KW in-verter also features series and shunt filtersin the final output stage of the system.These filters areband limiting anddesignedto filter out switching transient frequencies.

Series FilterThe series filter in the PVI 82KW at-

tenuates both common mode and dif-ferential mode noise. It provides 80dBcommon mode attenuation for the fre-quencies between 100kHz and 1MHz,and 70dB differential mode attenuationfor the frequencies between 200kHz and3MHz. The filter is selected to eliminatethe system specific dominant frequencycomponents, and is not active in thelower PWM modulation frequency range.

Shunt FilterThe selected shunt filter for the PVI

82KW inverter has a resonance pointaround 150kHz and provides a reductionofnoise interference particularly in the fre-

would generate harmonics in the 100 ~1kHz range. The DC voltage control loop isaround the current control loop and is usu-ally controlled at a lower sampling rate. Ifthe DC voltage fluctuates due to suddenchanges inweather conditions, theDCvolt-age control loop has a certain bandwidth toreact and stabilize the system output. Dur-ing sunlight transients, the system mightgenerate even slower oscillations in the DCbus and output AC currents.

Since the DC voltage control loop band-width is low, it does not cause any harmon-ics or EMI issues. However, if the voltagecontrol loop were not tuned properly, thegeneration efficiency would decrease dueto failure to track the maximum powerpoint of the PV panels.

Solectria Renewables’ inverters havebeen fully testedat different loadconditionsto have excellent dynamic characteristicsfor both the AC current and DC voltagecontrol loops. The AC current controlbandwidth is about 2kHz and the DC volt-age control bandwidth is less than 100Hz.

ConclusionThis article described how the current

harmonics and EMI are controlled in PV in-verters. IEEE 1547, UL 1741 and FCC Part15B standards impose strong guidelines forgrid-tiedPV inverters to reduce currenthar-monics and eliminate electromagneticnoise. Extra attention is given by the PV in-vertermanufacturer todesign inverters thatare immune to EMI problems and guaran-tee reliable operation of the inverter in allworst case operating conditions.

Different types of practical harmonicsand noise reduction strategies for a com-mercial three-phase PV inverter were intro-duced in this article. The filtering ofharmonics and EMI needs to be carefullydesigned to maintain the control band-width of the inverter and to provide cleanand reliable control signals in both analogand digital electronic circuits. The PVI82KW inverter system is equipped with sev-eral levels of harmonics and EMI filteringand its effectiveness and reliability havebeen proven in harshest commercial andutility scale applications. �

ArticlewrittenbyDr. Soonwook Hong, Se-nior Electronic Power Systems Engineer andMichael Zuercher-Martinson, Chief Tech-nologyOfficer of SolectriaRenewables, LLC.For more information, please go to

www.solren.com.

Since the DC voltagecontrol loop bandwidth islow, it does not causeany harmonics or EMIissues.

08-0911TECp06-40:08-0911TECp06-40 9/9/11 1:08 PM Page 35

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TEC 9.11

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