Useful Web Sites - NREL · phous silicon (a-Si) thin film with low defect densities and high...

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U.S. Department of EnergyJames E. Rannels, DirectorOffice of Solar Energy Technologies1000 Independence Ave., SWWashington, DC 20585202-586-SUNS (7867)Fax: 202-586-8148E-mail: [email protected]

Richard King, Team Leader Photovoltaics Program1000 Independence Ave., SWWashington, DC 20585202-586-1693Fax: 202-586-8148E-mail: [email protected]

Useful Web SitesDOE: www.eren.doe.gov/pvNCPV: www.nrel.gov/ncpvSandia: www.sandia.gov/pv

National Renewable Energy LaboratoryLawrence Kazmerski, DirectorNational Center for Photovoltaics1617 Cole BoulevardGolden, CO 80401-3393303-384-6600Fax: 303-384-6481E-mail: [email protected]

Thomas Surek, Technology Manager Photovoltaics Program1617 Cole BoulevardGolden, CO 80401-3393303-384-6471Fax: 303-384-6481E-mail: [email protected]

Sandia National LaboratoriesPaul Klimas, ManagerPhotovoltaics Program P.O. Box 5800Albuquerque, NM 87185-0753505-844-8159Fax: 505-844-6541E-mail: [email protected]

Joe R. Tillerson, ManagerPhotovoltaic Systems R&D P.O. Box 5800Albuquerque, NM 87185-0753505-844-1806Fax: 505-844-6541E-mail: [email protected]

Key Contacts

Produced for theU.S. Department of Energy1000 Independence Avenue, SWWashington, DC 20585

by the National Renewable Energy Laboratory,a DOE national laboratory.

DOE/GO-102001-1168February 2001

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Research and Development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 3

Program Highlights

■ Accomplished rapid deposition of amor-phous silicon (a-Si) thin film with low defectdensities and high efficiencies.

■ Fabricated many copper indium galliumdiselenide (CIGS) thin-film devices with effi-ciencies between 18.1% and 18.8%.

■ Marked first copper indium diselenide(CIS)-based thin-film products entering market.

■ Validated partner BP Solar’s production of10.6%-efficient cadmium telluride (CdTe) modules.

■ Transferred PVScan system to industry.

■ Coordinated meeting of researchers explor-ing transparent conducting oxides (TCOs) toapply their work to PV.

■ Launched High-Performance PV Initiativeresearch contracts to increase efficiency of multijunction thin-films and III-V cells for concentrators.

■ Demonstrated with Spectrolab a 32.3%-effi-cient GaInP/GaAs/Ge cell under 566 suns ofconcentration.

■ Sponsored 10th Workshop on CrystallineSilicon Solar Cell Materials and Processes topromote exchange of research results.

■ Issued four new research contracts explor-ing hydrogen passivation.

■ Marked Sandia’s 12 years of contributionsto research in crystalline silicon.

■ Published World Photovoltaic Scale Recalibra-tion and North American Solar Atlas.

■ Issued PV Technologies Beyond the Horizonresearch solicitation.

Technology Development. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 11

■ Issued new solicitation, PV ManufacturingR&D—In-line diagnostics and intelligent processingin scale-up manufacturing.

■ Evaluated 7 grid-tied inverters and 9 invertersin off-grid configurations.

■ Held workshop with Brookhaven NationalLaboratory on use of lead-free solder in manufacturing.

■ Identified positive features of 20-year-oldmodules that have performed well.

■ Began testing modules from three manufac-turers on the Performance and Energy RatingsTestbed.

■ Documented continued technology improve-ments under the PVMaT contracts that will becompleted in FY 2001.

■ Compared module energy-rating methodsin support of IEEE Module Energy Rating standard under development.

Systems Engineering and Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 16

■ Gained approval from testing and standardsorganizations for “non-islanding inverter.”

■ Continued support for standards develop-ment. Achieved procedure for testing small PV systems; passage of the first standard forinterconnection of PV, IEEE 929-2000 Recom-mended Practice for Utility Interface of PVSystems; and balloting on IEEE RecommendedPractice for Qualification of Concentrator PVReceiver Sections and Modules.

■ Supported development of Solar LoadController to increase the value of PV to cus-tomers on time-of-use tariffs.

■ Supported TEAM-UP project to install 7.2 MW of solar electric systems in 40 states.

■ Worked with Native American tribes toencourage installation of solar electric systems.

■ Recorded accomplishments of partners inMexico that obtained World Bank and GlobalEnvironmental Facility grants and loans basedon successful projects with PV Program.

■ Initiated technology validation activities for thin-film PV technologies in India.

Message from the Director...to offer the world a cost-effective, reliable technology that turns sunlight into electricitywith no pollution, wherever it is needed. Mission of the National Photovoltaics Program

Photovoltaic Energy Program Overview FY 2000 1

This year, concerns about rising fuel costs, energy security, statewidebrownouts, and demand surges that exceeded electrical supplyunderlined the urgency of positioning solar electric systems to meet

a greater share of our energy needs. In response to these problems, thePV Program is poised to take on an increased responsibility to meet theurgent challenges facing the nation. The market for solar electric systemsis steadily increasing as improved products resulting from our researchefforts in collaboration with industry are accepted. Customers in therestructured electricity market are seeking local sources of electricity that are clean, quiet, and reliable.

To meet the demands of a growing market, the solar electric industry hasnew systems both in the marketplace and on the drawing board that pro-duce higher electrical output for lower cost. In fiscal year (FY) 2000, wesaw the first commercial products made from copper indium diselenide,a thin-film material that we have been researching with industry fornearly 20 years. If we apply this development cycle to other promisingtechnologies in our laboratories today, more new products will be intro-duced each year. To keep the pipeline from laboratory to marketplacefilled with innovative approaches to supplying electricity from the sun,we began the process of issuing new contracts for fundamental researchand development (R&D) in 2000.

We cannot overstress the importance of these new R&D efforts in conjunc-tion with our manufacturing R&D and systems development and appli-cation activities. In FY 1999, we saw the solar electric industry develop a roadmap for market development over the next 20 years. Achievingindustry’s goals demands significant reductions in the cost of solar elec-tric systems; cost reductions can only be achieved through aggressivework in fundamental research, manufacturing, and system applications. For our part, the National Photovoltaics Program continues to sponsorhigh risk, potentially high payoff research and development from whichprivate enterprise can choose options for further development and appli-cation in competitive U.S. electrical energy markets.

Taking account of the industry roadmap goal, the National Photovoltaics(PV) Program issued its multiyear plan for 2000 to 2004 last year, com-plete with specific research goals necessary to support the industrial goals.Results are encouraging after the first year of the Program’s 5-year plan.Although the data are not yet in for industry sales, we have met everyR&D milestone of the Program Plan. As described in this report of ouraccomplishments for the year, the National PV Program is providing the R&D necessary to make solar electric systems an ever more signifi-cant contributor to our national energy supply.

James E. RannelsJames E. Rannels, DirectorOffice of Solar Energy TechnologiesU.S. Department of EnergyWashington, D.C.

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PV IndustryRoadmap Goal

“The vision is to provide consumers with competitive andenvironmentally friendly electricity from a thriving United States-based solar electric power industry.”PV Industry Roadmap Vision

2 Photovoltaic Energy Program Overview FY 2000

A solar electric system includes several key components that work together todeliver electricity to the user. Cells are composed of layers of semiconductor and other materials that produce electric current in response to sunlight.Individual cells are connected in strings to make up the PV module that issealed from the weather with encapsulants. Module electrical wires are connected by electrical junction boxes. PV modules generate direct current(dc) electricity that can be stored in batteries. Charge controllers keep batteries from overcharging or undercharging. If alternating current (ac) is needed, such as for conventional appliances or for interconnection to a utility grid, an inverter or power conditioner is necessary.

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IntroductionThe purpose of the U.S. Department of Energy (DOE) Photovoltaics Program is twofold: to accelerate the development of PV as a national and global energy option, and to ensureU.S. technology and global market leadership.The National Photovoltaics Program Plan

In 1839, a French physicist found that certain materials would producesmall amounts of electric current when exposed to light. The first PVdevice to actually generate electric power was made of silicon at Bell

Laboratories in 1954. The proportion of sunlight energy that those earlycells converted to electrical energy was between 1% and 2%. The efficiencyof today’s best solar electric cells is about 32%. Efficiency is an importantbenchmark for PV technology, and it is theoretically possible for solarcells to operate at greater than 40% efficiency.

Commercial use of solar electric cells began in 1958, when the Vanguard 1satellite carried PV cells to power a 5-milliwatt backup transmitter. Today,virtually all satellites and spacecraft use solar cells to generate their elec-trical power. Interest in making PV technology affordable for terrestrialuse was sparked by rising energy costs in the mid-1970s. Since then, thefederal government, working with universities and industry partners,has conducted an aggressive research and development (R&D) program to further develop this promising technology.

Expanded use of solar electric systems depends on lowering the cost ofsystems and ultimately the cost of the energy they produce. System costscome down as we develop new, higher efficiency materials, as weimprove manufacturing processes, and as we engineer greater reliabilityinto all parts of the generating system.

The R&D activities of the National PV Program accelerate the developmentprocess, with fundamental research supporting development of materialsand devices, manufacturing technology, systems engineering, and marketinformation. The PV Program implements these activities through theNational Center for Photovoltaics (NCPV), an alliance of organizationsworking with the U.S. PV industry to maintain our global leadershipposition. The National Renewable Energy Laboratory (NREL) in Golden,Colorado, and Sandia National Laboratories (Sandia) in Albuquerque,New Mexico, are the key national laboratory participants in these efforts.

R&D on thin films, high-performancedevices, silicon materials, characterizationtechniques, and innovative concepts willdeliver low-cost PV and fill the technologypipeline for future progress.The National Photovoltaics Program Plan

The National PV Program, through theNational Center for Photovoltaics (NCPV),coordinates teams of in-house researchers,

industrial partners, and university researchers,all working to increase our understanding ofsolar electric materials and devices. Includingindustrial partners in this work assures thespeedy transfer of research results to industryfor product development and manufacturing.

Thin-Film PV Research

Using thin films of semiconductor material tomake solar electric devices holds the promise of low-cost manufacturing capitalizing on tech-niques perfected in the glass industry. Whenevaluating our progress with new PV materials,important criteria are material deposition rate,solar cell efficiency, and power output. Poweroutput is related to module size and efficiency.High power output in a single module is desir-able because it reduces other system costs suchas those associated with connectors. Achievinglarge module size is a manufacturing challengebecause it requires both consistent material performance over a larger area and special handling techniques to assemble modules.Deposition rate is important because high rates reduce initial capital costs and lower manufacturing costs.

FY 2000 saw many firsts for thin-film PV tech-nology. In addition to improvement in the per-formance of materials in the laboratory, the first

commercial products using cadmium tellurideand copper indium diselenide materials wenton the market in the United States, andplanned increases to manufacturing capacityare at an all-time high.

Since 1994, the Thin Film PV PartnershipProgram has coordinated research contractswith industry, universities, and governmentresearchers in the NCPV to explore the mostpressing scientific issues that limit the wideruse of this technology. Over the years, severalcompanies have explored using thin films asadditional materials for solar electric devices.In the early years, the market was dominatedby crystalline silicon products with some thin-film amorphous silicon in consumer productssuch as calculators. In 2000, nearly 10 MW ofthin-film modules were produced in the

United States. Manufacturing plants planned orunder construction will boost U.S. capacity toproduce thin-film modules of more than 140 MW per year.

National investment in exploring the fundamen-tals of PV has provided the foundation for thisunprecedented expansion in the market. How-ever, much remains to be done to reach the fullpotential of PV. In FY 2000, the Thin Film PVPartnership’s national research teams exploredsolar electric materials and devices made fromamorphous silicon, copper indium diselenide,and cadmium telluride. Each team is composedof about forty scientists from universities,NCPV, and industry who collaborate on sharedresearch goals important to the future of theirtechnologies. Continued work on fundamentalswill provide the advances that improve deviceperformance and manufacturing processes.


Research and Development

Table 1. Best Large-Area, Thin-Film Modules (standard conditions, aperture area)

Power (W) Company/Date Device Size (ft2) Efficiency (%)

91.5 BP Solar, 5/00 CdS/CdTe 9.5 10.6

70.8 United Solar, 9/97 a-Si/a-SiGe/ 10.2 7.6a-SiGe/SS (stabilized)

61.3 First Solar, 6/96 CdTe/CdS 7.8 9.1

59.0 Matsushita, 6/00 CdS/CdTe 6.0 11.0

56.0 BP Solar, 9/96 a-Si/a-SiGe 8.2 7.6

53.9 BP Solar, 4/00 CdS/CdTe 5.4 10.8

44.3 Siemens Solar, 3/99 CdS/CIS-alloy 4.0 12.1

38.0 Kaneka, 9/00 a-Si/c-Si/glass 4.1 10.0(est.) (est., stable)

35.7 United Solar, 6/97 a-Si triple junction 5.0 7.9(stabilized)

31.0 Golden Photon, 4/97 CdS/CdTe 3.7 9.2

Consequently, one PV Program Plan milestonefor FY 2001 will be the issuing of a new solicita-tion for the Thin Film PV Partnership.

Amorphous Silicon (a-Si)

Amorphous silicon is a growing segment of thesolar electric market, accounting for nearly 10%of PV sales worldwide in 2000. Compared tocrystalline silicon, it can be manufactured atlower cost, is more responsive to indoor light,and has advantages such as flexible or low-costglass substrates. As a result, the PV industry inthe United States is investing in significant newplant capacity.

One of the ways to reduce the cost of solar elec-tricity is to decrease the time it takes to manu-facture PV devices. Increasing deposition ratesof PV materials during manufacturing canreduce industry’s labor and material costs. Toreduce costs of devices made from a-Si, deposi-tion rates must be increased from the current1–3 angstroms/sec levels achieved in manufac-turing to the level of 6–10 angstroms/sec orhigher. However, depositing the a-Si materialsat higher rates can cause changes in the mate-rials, such as increased defect densities, thatadversely affect the performance of solar elec-tric devices. Intense laboratory research isunder way to develop materials and processesthat produce high-performing solar electricdevices in shorter time periods.

For example, in FY 2000, NCPV researchers atNREL achieved low defect density in hydro-genated amorphous silicon (a-Si:H) films thatwere grown at record deposition rates as highas 83 angstroms/sec. Normally, a-Si is depositedusing plasma-enhanced chemical vapor deposi-tion (PECVD). When PECVD rates are increased,the resulting materials have high defect densi-ties, indicating that efficiencies of the resultingdevices would be unacceptably low. The high-deposition-rate a-Si that researchers at NRELgrew using the hot-wire chemical vapor depo-sition technique had much lower defect densi-

ties. Low defect densities are one indicator ofpotentially acceptable efficiency, but the per-formance of the material must still be demon-strated in PV devices. In FY 2001, the a-SiNational Team will apply ultrahigh-deposition-rate materials to solar cells with a-Si:H layersgrown in less than a minute.

Additionally, several subcontractors to the NCPVhave achieved deposition rates higher than theindustry norm, while still preserving acceptableefficiency levels. Energy Conversion Devicesmade an 8.8%-efficient cell from material depo-sited at 10 angstroms/sec, and United Solarmade a 10%-efficient cell from material depo-

sited at 4 angstroms/sec. These results wereconfirmed at NREL by the Measurements andCharacterization group and mark a milestone identified by the National a-Si Team for FY 2000.In addition, BP Solar doubled the depositionrate, while maintaining the efficiencies of itsmultijunction a-Si modules. Higher through-put lowers manufacturing cost and is beingapplied in the BP Solar manufacturing plant.

Copper Indium Diselenide (CIS)

Achieving world-record efficiency for a solarelectric material or device is only the first ofmany steps along the way to industrial produc-


Table 2. Technical Issues: a-Si Technology

Topic Issue

Stability Can we use improved understanding of Staebler-Wronski degradation mechanisms to minimize or eliminate the problem?

Deposition cost Can we increase amorphous silicon deposition rates while maintaining efficiencies to reduce manufacturing costs?

Efficiency Can we improve cell and module efficiencies through greater fundamental understanding of present limitation, and by development of improved component cells and interfaces?

Low-gap bottom cell Can we improve the low-gap bottom cell for use with an amorphous silicon top cell, either by application of micro-crystalline silicon or by improvement of a-SiGe:H alloys?

Using our patented high-speed, hot-wiredeposition technique, NCPV scientists atNREL can accomplish in 2 minutes whatnow takes industry about 35 minutes tocomplete.

United Solar plans to expand its productioncapacity from 5 MW per year to 25 MW per year, applying developments achievedthrough its participation in the National a-Si Research Team.

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tion. One of the very next steps after achievinga world record, as NCPV researchers at NRELdid in FY 1999, is establishing a reproduciblebaseline process for achieving consistent effi-ciency results. In FY 2000, NCPV researchers at NREL demonstrated that its optimized sub-strate allowed repeated fabrication of CIS withadded gallium (CIGS) devices with efficienciesbetween 18.1% and 18.8%. The special plasmavapor deposition (PVD) technique used tosputter molybdenum on the substrate used forCIGS deposition produced these consistentresults for a set of 15 devices fabricated fromseven CIGS samples.

Industry is exploring a new processing systemfor large-area CIS deposition developed at theUniversity of Delaware’s Institute of EnergyConversion (IEC). Using the new systememploying co-evaporation of CdS/Cu(In,Ga)Se2,IEC produced solar cells that reached 14.9%efficiency. The cells were prepared in IEC’slarge-area, in-line deposition system designedto deposit CIGS-based semiconductors on acontinuously moving substrate. The system isdesigned so that it could be adapted to use aweb-type substrate (roll-to-roll deposition). IEC has also used in situ atomic absorptionspectroscopy to control deposition rates. Thismeans that IEC can work with industry inresearch efforts to produce larger sheets ofCIGS materials for solar electric module pro-duction. Two companies planning to manufac-ture CIS-based solar electric modules are devel-oping processes based on co-evaporation thatare very similar to IEC’s.

Meanwhile, Siemens Solar Industries gainedUnderwriters Laboratories (UL) listing for one of the first two commercial products intro-duced in 2000 using CIS-based thin-film mate-rials. UL approval is an important step towardwidespread use of a new solar electric product.

Cadmium Telluride (CdTe)

Cadmium telluride has several features that makeit a promising material for solar electricity gen-eration. These include a bandgap well matchedto the solar spectrum and a high absorptioncoefficient, meaning that even one micron of theabsorber film is sufficient for solar cell fabrica-

tion. To date, more than 10 techniques have beenused to grow CdTe layers, resulting in solar cellsoperating at 10% or greater efficiency. Three ofthese methods are currently used for modulefabrication by industry. The NCPV works bothto improve these methods and to develop alter-native methods that may yield higher efficienciesor hold promise for low-cost manufacture.


This CIS array from Siemens Solar Indus-tries is being tested at the Florida SolarEnergy Center.

Secondary electron microscopy analysisshows this CIGS film (left) is composed offairly large, aligned long grains that have an open structure and are less dense. Thesecharacteristics allow more sodium to diffuseinto the CIGS absorber during the deposi-tion and improves device performance.

Table 3. Technical Issues: CIS Technology

Topic Issue

CdS Can chemical bath-deposited (CBD) CdS be replaced with alternate heterojunction partners without loss in performance?

Gallium What is the optimum distribution of gallium in the absorber for best device performance?

Sulfur Can S content be controlled at the interface to increase bandgap?

Sodium What is the exact role of sodium, and how can we control it?

Substrates Can high-efficiency devices be achieved on alternative substrates? (e.g., foils, polymer, or stainless steel)

Transients Can transient effects in modules be eliminated or minimized?

Mfg. process Can we develop a process that gives compositional uniformity, high efficiency, and high yields?

Moisture Can the effect of moisture ingress be eliminated?

Siemens Solar Industries/PIX09100

Siemens Solar Industries/PIX09742

In FY 2000, BP Solar, a participant in the NationalCdTe R&D Team, began production of a CdTemodule with verified world-record aperture-area efficiency of 10.6% and power output of91.5 W. These improvements to performance

came from changes in the electro-deposition bathand reduction in the thickness of the CdS film.The BP Solar results demonstrate that high effi-ciency and good electrical properties (short-circuit current density, open-circuit voltage, and

fill factor) can be achieved in a pilot line andeventually in large-scale manufacturing. Theseresults further the Thin Film PV Partnership’sprogress toward an important PV ProgramPlan milestone for 2004—a 10%-efficient com-mercial thin-film CdTe module.

Transparent Conductors

Thin-film solar cells are composed of layers ofmaterials that serve specific functions in theprocess of converting sunlight into usable elec-trical energy. An important layer in thin-filmsolar cells is the transparent conducting oxide(TCO) layer that serves as the top contact andcollects electrical current. The structural, opti-cal, and electrical properties of various TCOmaterials are the subject of active research within the Thin Film PV Partnership Program.

In FY 2000, researchers from the NCPV andDOE’s Basic Sciences Center collaborated todevelop new conducting oxides by chemicalvapor deposition. The characteristics of thismaterial could facilitate the use of cadmiumstannate in commercial applications such asthose of BP Solar and First Solar. The switch to cadmium stannate, if feasible in commercialproduction, could increase module efficienciesover those achieved today with tin oxide.

TCOs are a critical and frequently limiting com-ponent of advanced electronic devices, such asflat-panel displays, architectural coatings, andinnovative lighting using light-emitting diodes.Pulling together researchers from the variousindustries working on TCOs could reduceresearch costs and speed progress in all of theseapplications, including solar electric modules.To keep PV applications visible to otherresearchers and to learn of their progress, NCPVresearchers at NREL organized a workshop toattract researchers working in other applicationsof TCOs. This kind of coordination ensures that the PV industry benefits from the latestresearch being conducted for other purposes.


This new manufacturing plant (right) inToledo, Ohio, was built by First Solar toproduce glass substrate PV plates coatedwith thin-film CdTe at the rate of 8 platesper minute. When fully operational, thisplant can produce 100 MW per year of thin-film solar electric modules. First Solar hasbrought a technology to market that hasbeen under development in cooperation withthe DOE program for more than 10 years.

NCPV research at NREL led to this anneal-ing technique for heat treating CdTe solarcells to improve performance and manufacturing.

Table 4. Technical Issues: CdTe Technology

Topic Issue

Copper What is the exact role of Cu?

Contacts Can contacts be improved and stabilized, or alternative structures be developed?

CdCl2 What is the exact role of the CdCl2 treatment? Can the wet process be replaced by a vapor process?

Interface What is the role of interdiffusion at the CdS/CdTe interface?

Module design Can large-area modules be as efficient as small cells?

Encapsulation Are edge sealants required for stable modules? Can the effect of moisture ingress be eliminated?

Cd usage Can Cd be used safely in the environment and workplace? Can modules be recycled at the end of their useful life?

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High Performance and ConcentratorResearch

The attraction of high-performance solar cells isthe possibility of using small, highly efficientcells with inexpensive concentrating lenses toproduce large amounts of low-cost electricity.The NCPV and Spectrolab are working towarda goal of cells with 40% efficiency under con-centrated sunlight.

In FY 2000, NCPV researchers collaborated withENTECH Corporation to produce a 28%-efficientminimodule using NREL’s triple-junction high-performance solar cell in ENTECH’s linearFresnel-lens (10 suns) concentrator system.

Meanwhile, work continues to develop materialsthat perform well at very high concentrationsof sunlight. Such materials would produce elec-tricity in commercial-sized systems by using avery small amount of highly efficient PV mate-rial operating under powerful lenses. In 1999, a special concentrator cell operated at 32.3%efficiency under 47-sun concentration. Efficiencyfell off at higher concentration levels because of unexpected decreases in open-circuit voltage.In 2000, NCPV researchers at NREL and scien-

tists at Spectrolab identified the cause of theproblem and demonstrated an improvedGaInP/GaAs/Ge cell that operated at 32.3%efficiency under 566 suns of concentration.Record efficiency at this level of concentrationmeans that this cell is fully compatible with the high concentration levels expected in com-mercial applications. Work continues on achiev-ing even higher efficiencies at concentrationsup to 1000 suns.

The National Photovoltaics Program Plan con-tains a 10-year program goal to double the efficiency of multijunction thin-film modules(to 20% efficiency). An additional goal is todemonstrate high-efficiency III-V cells in a precommercial concentrator module (to 33%efficiency). To help achieve this objective, the High Performance PV Initiative was launched in FY 2000. When contracts are awarded in2001, university and industry contractors willbegin work in two general areas—thin-filmmultijunction cells and high-efficiency III-Vmultijunction cells and concentrators. Thissolicitation complements work being plannedby the NCPV for NREL in-house researchers.It also will begin identifying critical pathwaysto the 10-year efficiency goals.

Crystalline Silicon Research

Crystalline silicon was the first material used tomake commercial solar electric devices, and itcontinues to be used in 90% of the PV systemsbeing installed today. The NCPV strives toimprove the performance of this durable mate-rial, while helping industry develop faster waysof manufacturing modules.

Among five research needs identified by indus-try participants in the 10th NREL Silicon Work-shop, one was to replace the screen-print processused to apply contact metallizations in siliconsolar cells. NCPV researchers at NREL haddemonstrated nano-particle metallic inks thatinclude metalorganic sources for deliveringmetal elements to “glue” the particles, resultingin conductivities comparable to electrodepositedmetals. A cooperative research and develop-ment agreement (CRADA) has been establishedwith Evergreen Solar to develop the new direct-writing approaches for contact metallizations in its silicon solar cells.

NCPV researchers also developed a techniquefor fast screening of single-crystal silicon wafersprior to solar-cell processing, using Fourier-transform infrared spectroscopy. This diagnostictechnique could improve production yields andlower manufacturing costs.

Another industry-identified need at the work-shop was a new understanding of hydrogenpassivation of impurities and defects to bettercontrol their processes for high-efficiency crys-talline silicon PV modules. NCPV researchersat Sandia and NREL have expanded under-standing in this area. In FY 2000, four univer-sities worked on these issues under contracts of the new Hydrogen Passivation of Impurities and Defects in Silicon Solar Cells solicitation. All five research needs identified by industry at the workshop will be topics in next year'ssolicitation for university research on crystal-line silicon.


Arizona Public Service is installing a largeintegrated high-concentration PV systemfrom Amonix, Inc., totaling 300 kW.

High-performance solar cells produced withthis kind of equipment could double thepower output of terrestrial PV systems inoperation today.

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Measurements and Characterization

The Measurements and Characterization Divi-sion at the NCPV provides invaluable servicesto the research and industrial community intheir detailed measurements from the atomiclevel to the systems level. For example, in FY 2000, researchers successfully analyzed CdTe and CIGS thin-film devices in cross sec-tion using atomic force microscopy. This tech-nique provides, for the first time, three-dimen-sional information with a spatial resolution inthe nanometer range.

In FY 1997, the NCPV developed PVScan, a specialized diagnostic tool to characterize crystalline silicon materials. In FY 2000, the PV Program met a planning goal by transfer-ring this defect mapping system to industry. At AstroPower Corporation, it will be used

to characterize the company’s commercialproduct. The version delivered to AstroPowerhas a resolution of 50 microns and can scan atrates up to 10 cm/sec. A version of PVScan isalso being used at the Georgia Institute ofTechnology to develop dislocation and grain-boundary maps, reflectance, and minority-carrier lifetime for PV devices up to 20 cm by 20 cm.

To serve collaborators in the NCPV’s manypartnership R&D efforts, the Measurementsand Characterization Division uses the latestanalytical tools to help solve important mate-rials and device problems. In FY 2000, Web-based data delivery techniques were enhancedso that, for example, collaborators could receivereal-time images of their materials from theNCPV’s scanning electron microscope. These

data are available to customers on their desk-top computers anywhere in the world. Thisefficient delivery of data is one more way theNCPV works to accelerate development oftechnology for solar electric systems.

To provide the best measurement and charac-terization support to the U.S. PV industry forcells and modules, the NCPV strives to main-tain leadership and compatibility of measure-ment with other laboratories around the world.In FY 2000, the World Photovoltaic Scale Recalibra-tion project report was published, meeting akey milestone for the measurements program.This study, involving the leading measurementlaboratories in the United States, Japan, France,Germany, China, and India, ensures that meas-urements conducted in any of these countriesare comparable to those conducted by any ofthe other countries.

Basic and University Research

Many researchers assert that science will be theforce that moves solar electric systems fromtoday’s prices to those required to meet the PVIndustry Roadmap goals. To tap into the latest


Solar Resource Assessment

To help system engineers accurately assessthe value and design of PV electric systemsacross North America, NCPV researchers at NREL completed the North American Solar Atlas. This atlas contains a new database that allows a wide range of users to determine monthly and annualsolar resources for any spatial grid and forvarious solar electric module orientations.Reliable resource data allow increased confidence in power output projections.Installed systems designed according toaccurate resource data result in systemsthat perform as advertised and that satisfycustomers.

A Dozen Years: Sandia's Contributions to Crystalline Silicon Research

Since 1988, researchers at Sandia have been conducting in-house research and supportingcontracted research to advance the technology of crystalline silicon. They supported earlyresearch for dendritic web and silicon sheets that are now entering commercial production. They also supported development at Stanford University of ultrahigh-efficiency, one-sun silicon solar cells that have been incorporated into commercial products. Sandia helped found the University Center of Excellence in Photovoltaics program at the Georgia Institute of Technology. This work resulted in world-record efficiencies for cells made with novel processes and has contributed to the fundamental understanding of commercial processes.Sandia pioneered the teamed research approach within the DOE Program with the Crystalline-Silicon Research Cooperative, which includes industry, laboratory, and university researchers.

Sandia’s in-house activities developed the first PC-based program for numerical simulation ofPV devices (PC1D). Their new device-characterization techniques have become standards inthe PV community. In-house researchers demonstrated a record 15.3%-efficient multicrystallinesilicon module, explored plasma processing for solar-cell fabrication, investigated reactive ionetching for texturing crystalline-silicon substrates, and developed the Emitter Wrap-Throughcell with back-contact cell design.

Sandia’s PV Program has been restructured to emphasize PV system research, but will continueto provide some support to crystalline silicon PV research. In cooperation with industrial part-ners, NCPV researchers at Sandia will continue to investigate plasma-texturization of multicrys-talline silicon cells. They will also continue to apply their years of experience to supporting con-tracted research and participating in the R&D cooperatives they were instrumental in founding.

ideas and provide support to develop promisingcreative approaches, the PV Program funded 18 proposals from the nation’s universities toexplore unconventional ideas in FY 1999.

These Future Generation PV contracts havealready yielded some interesting results. Forexample, crystalline silicon is known for itshigh efficiency and stability, but traditional silicon growth methods are expensive and can only produce substrates of limited size.Using a deposition technique similar to thatused to produce a-Si, researchers at the Cali-fornia Institute of Technology are growing nonconventional silicon. This thin-layer siliconconsists of large crystalline grains. So far, theyhave been able to grow 10–50 microns of sili-con on glass. They are working to increasegrain size and lower defect density, as well as to improve growth rates at low temperaturesand to develop a surface with enhancedoptical absorption.

In other work to understand thin polycrystallinesilicon films, Cornell University is using anelastic measuring technique to explore themolecular order in thin-film silicon. Yet anothergroup, at Pennsylvania State University, isapplying novel spectroscopic probes to studyoptical absorption in textured thin-silicon films.

While these Future Generation PV contracts wereunder way, another solicitation for proposalsfrom universities, colleges, and U.S. companieswas issued in 2000. The Photovoltaic TechnologiesBeyond the Horizon solicitation encourages basicresearch to explore nonconventional technolo-gies that could lead to new options for gener-ating inexpensive electricity from sunlight.

When awards are made in FY 2001, contractorswill begin exploring technologies such as liquidcrystal-organic solar cells, novel group IV solarcells, polymer solar cells, microcrystalline sili-con cells, tandem organic cells, innovative Si

substrates for III-V solar cells, low-temperature CIGS deposition, and nanoscale silicon theory.Scientists will also explore optical rectennasolar cells, nonvacuum CIGS processing, dye-sensitized solar cells, molecular array solarcells, ultrahigh-efficiency heterostructures,GaInNAs nanoscale characterization for high-efficiency cells, optical filter concentrators formultiple bandgap solar cells, and solid-stateelectrolytes for dye-sensitized solar cells.

In FY 2000, three researchers had their worksponsored by the PV Program published in the prestigious international journal Nature.Such honors ensure the widest possible appli-cation of our research results and indicate thegroundbreaking nature of this work.


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University Partners

In a totally new type of solar cell based on nano-crystal composites, University of California,Berkeley researchers discovered nanocrystal rodsthat may lead to improved photovoltaic perform-ance compared with that of nanocrystal spheres dispersed in a polymer medium.

Future Researchers

The purpose of the PV Research Programwith Historically Black Colleges and Uni-versities (HBCUs) is to advance under-graduate knowledge of PV through research investigations and to encourage a diverse group of students to learn aboutPV. In FY 2000, each of the eight partici-pating universities had a subcontract withthe NCPV to perform specific PV research.Each project has a principal investigator(professor) and several research associ-ates (undergraduates) performing the work.Some of the associates have stayed withthe project to the graduate level. Since1995, about 30 college students have participated in the program for one or more years.

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Additional Achievements in R&D

Organization Achievement Why it is important

Washington State Observed a change in the defect state A step toward understanding theUniversity of a-Si after light soaking with the help Staebler-Wronski effect that could

of positron annihilation spectroscopy. lead to eliminating its reduction of efficiency.

Siemens Solar Improved efficiency in CIS cell to 15% Measurements show reducedIndustries, by applying a cyanide treatment to magnitude of transients. This Colorado State remove contaminants and binary points to further work to University, and impurity phases and by post annealing compare the transient effect in NREL in air at 200°C for 2–10 minutes. NREL devices and to analyze

the compositional properties of the interface region.

University of Improved electron mobility by a factor This is a key 1-eV material neededCalifornia, of two in GaInNAs material by using for the structure of a 40%-efficientSan Diego GaInAs/GaNAs superlattice structure. solar cell.

NREL Reduced bias errors in outdoor solar Improve the accuracy of outdoor radiometers by about one half. calibrations of PV cell technologies.

University of Discovered new nanoparticles and Exploratory research that could California, fabricated quantum rods instead of lead to new high-efficiency, low-Berkeley quantum dots, boosting the efficiency cost solar-cell technologies.

of nanoparticle solar cells.

NREL Researchers demonstrated >3 µm/min Progress at these high growth rates direct deposition of ~20 µm polycrys- has stimulated commercial interesttalline silicon layers on LGA-139 glass for further development of the IVT ceramic, mullite, glass, and tantalum process. at ~900°C by the atmospheric-pressure iodine vapor transport (IVT) process.

Vanderbilt Fabricated a polymer nanocrystal Exploratory research that could University composite solar cell with good lead to high-efficiency, low-cost

open-circuit voltage. solar cells.

NREL and Conducted the PV Performance and Such workshops promote improved PV industry Reliability Workshop. test methods, evaluation, and stan-

dards for PV modules and systems.

NREL Secondary-ion mass spectroscopy Cu impurities resulting from depo- (SIMS) measurements of CdS/CdTe sition and processing conditionssamples revealed high concentrations have been tied to device degra- of Cu located in the CdS layer far dation issues. SIMS measurements from the back contact. can give clues for improving device

stability.

Sandia Patent application—metal catalyst Patent protection will aid licensing process for reactive ion etch (RIE) for this approach that could texturing of multicrystalline silicon improve efficiency and reduce cost. cells.

Sandia Patent award—self-aligned, selective Allows further development andemitter, plasma-etchback and passi- licensing to industry of this poten-vation technique. tially beneficial cell design.


In 1992, two universities were awarded “Centers ofExcellence in Photovoltaic Research and Education”by the U.S. Department of Energy. The GeorgiaInstitute of Technology (top) researches the funda-mentals of crystalline silicon materials and themodeling and design of high-efficiency cells.Researchers have developed rapid thermal process-ing technologies and are working on fabricatinglow-cost, high-efficiency cells. Georgia Tech alsoprovides high-quality research and education oppor-tunities for student scientists. The University ofDelaware's Institute of Energy Conversion (IEC)(bottom) researches thin-film PV cells. IEC worksclosely with the NCPV, PV manufacturers, andother government entities, thus allowing under-graduate and graduate students to obtain degreeswhile working with professionals in solar cellresearch.

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The Program and industry work togetherto move technology from the laboratory to manufacturing, and to increase the reliability and performance of modules. The National Photovoltaics Program Plan

Annual increases in U.S. module productioncapacity of 15% to 20% and reductions inmodule production costs exceeding 35%

can be largely attributed to the PV Program’scost-shared R&D projects with industry overthe past ten years. During this decade, in addi-tion to continuing fundamental research dis-cussed earlier in this document, 40 subcontractswith industry have been awarded for high-riskmanufacturing research and development.Twenty-five subcontracts improved modulemanufacturing. The other 15 addressed prob-lems with components other than modules,such as power conditioning and system designs,as well as generic issues applicable to the entireindustry. Twelve active subcontracts will becompleted in FY 2001.

In 2000, the U.S. Photovoltaics Industry RoadmapWorkshop set ambitious goals demanding amove to large-scale manufacturing in all tech-nologies. Large-scale manufacturing for ourmost promising new technologies requires resolution of many issues due to the complexityof the processes involved. In addition, therequired manufacturing equipment demandsfundamental research and engineering work toensure proper operation and reasonable costs.

In response to these realities, the PV Programissued a new solicitation in August 2000, PVManufacturing R&D—In-line diagnostics andintelligent processing in scale-up manufacturing.This solicitation encourages teams to share

the cost of high-risk research to develop intelli-gent processing for larger-scale manufacturingthat will be the foundation for achieving the PV Industry Roadmap goals.

Manufacturing Research andDevelopment

Since Congressional funding began in 1991, the Photovoltaic Manufacturing Technology(PVMaT) Project has conducted manufacturingresearch and development in partnership withindustry. The contracts have reduced costs ofmanufacturing PV modules, balance-of-systemscomponents, and integrated systems and haveimproved the performance and reliability ofcommercial products. These activities have led to increased investment by industry forsubstantial scale-ups of U.S.-based PV manu-facturing plant capacities.

Module Manufacturing Processes

Each manufacturer of solar electric moduleshas a unique approach to producing high-performance, competitively priced products.Under PVMaT contracts, manufacturers per-form high-risk research to improve their ownprocesses and technologies.

ASE Americas cuts wafers from silicon materialproduced in the unique edge-defined, film-fedgrowth (EFG) system, which produces a thin-walled cylinder of crystalline silicon materialthat is cut into wafers for cell and module man-ufacture. In FY 2000, the company integratedlasers for high-speed wafer-cutting. Faster cutting can decrease labor costs by 75% andreduce the capital costs of production by 50%.The company also used Rapid Thermal Annealprocessing developed at Georgia Tech for


Technology Development

This year, the ASE Americas EFG system produced larger, 50-cm-diameter, 1.2-meter-long cylinders withwalls of crystalline silicon as thin as 100 microns. Growing larger cylinders with thin walls reduces material waste and increases the speed of silicon production.

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increasing EFG solar cell efficiency and usedoxide formation, back-surface fields, siliconnitride, and gettering in their processing.

AstroPower produces solar cells from sheets ofSilicon-Film™ material. This large-area sheetmaterial is produced in a continuous mannerthat could be compatible with in-line process-ing. In FY 2000, the company continued itsprogress toward eliminating all batch processsteps, from material growth to solar cell fabri-cation. The company fabricated cells processedwith an in-line, water-based cleaning system. Itevaluated a prototype in-line chemical etchingsystem to prepare the silicon surface prior tothe diffusion step and to remove post-diffusionoxides. AstroPower designed and purchased a prototype in-line diffusion-oxide etch systemfor processing Silicon-Film™ sheets. Continu-ous, in-line processing will increase productionspeed and reduce costs. In FY 2001, the companywill demonstrate production of Silicon-Film™sheets at 3.0 m/minute and will complete thedesign of a 50-MW/year Silicon-Film™ manufacturing line.

BP Solar is working to reduce the costs of pro-ducing its polycrystalline silicon PV modulesand to increase the capacity of its manufactur-ing plant. In FY 2000, BP Solar completed apilot facility to produce solar-grade silicon from SiF4, an important step for reducing thecosts of its silicon material. The company isusing an optimized wire-saw process and hasincorporated the recycling of SiC and oil. BPSolar has also begun environmental testing ofthe cells resulting from a new ultrasonic doperand a silicon-nitride deposition system. In FY2000, the company studied methods for detect-ing cracks in wafers and finished cells, ana-lyzed ways to reduce the cost of consumables,developed a prototype ultrasonic doper, selecteda candidate method for in-line, nondestructivetesting of cell interconnects, and selected twocandidate fast-cure encapsulant formulations

for environmental and outdoor testing. In FY 2001, BP Solar will continue incorporatingthe results of the research activities into its production line.

Crystal Systems has developed an effective andsimple approach to removing impurities frominexpensive metallurgical-grade silicon to makeit comparable to commercially available solar-grade silicon. In FY 2000, the company con-ducted refining experiments that producedcharges of 150 kilogram. Hot loading proce-dures for adding feedstock to molten siliconwere developed and demonstrated for chargesup to 300 kg. With an appropriate crucible,charge sizes up to 500 kg can be refined usingthe current HEM™ (Heat Exchanger Method)furnace. Impurities have been removed toacceptable levels so that the approach is consis-tent with producing solar-grade silicon at aproduction cost of less than $20/kg. In FY 2001,the company will work on accelerating theremoval of impurities to reduce refining times.Crystal Systems will also distribute its refinedmaterial to the photovoltaic industry for evaluation.

Energy Conversion Devices (ECD) works withUnited Solar Systems Corporation to improvethe continuous manufacture of a-Si alloy PVmodules in the United Solar manufacturingplant. ECD designed, fabricated, and installeda new substrate heating system in United

Solar’s 5-MW production facility, to decreaseproduction downtime. Other ECD improve-ments include in-line diagnostic systems, a new process for depositing the back-reflectorlayer, improved cathode hardware, and newtechnology for changing substrate rolls. Theseimprovements will be incorporated into equip-ment for United Solar's 25-MW productionfacility and should reduce module costs by 25% to 30% over 1997 levels and increase pro-duction capacity 60% over previous plans forthis production line.

Evergreen Solar produces silicon material calledstring ribbon to make PV modules. In a contin-uous process, each machine grows a single ribbon 24 hours a day. For its 10-MW plant,Evergreen plans to install 120 of the newmachines it developed in FY 2000. In FY 2000,Evergreen also began using an automated con-tact machine for soldering individual cells andfor forming cell strings for modules. The com-pany developed a new string material and edgemeniscus control method and applied forpatent protection of these innovations. Thesechanges in manufacturing have increased runlength by 200%, increased cell efficiency by 5%,improved factory yield by 20%, reduced costsof consumables by 60%, and reduced the costof the new furnace by a projected 20%.

First Solar continued its work on its CdTe thin-film module manufacturing processes. Thecompany adopted a new UL-listed mountingmethod and developed a new “cord-plate” contact termination method, replacing pottedpolyurethane termination “pigtails.” Testingwas completed for an improved module lami-nation process and for a high-throughput solarfinishing line that will be used in the First Solarproduction line. Another production-lineimprovement is an automated, single-laserscribing system that is up to 10 times faster andshows a 15-fold improvement in registration ofconsecutive laser-scribe lines over existing sys-tems. First Solar’s improved modules passedUL 1703 qualification testing, and the compa-ny’s Environmental, Health and Safety pro-gram continued work to ensure the safety ofmanufacturing its modules.

Global Solar Energy worked to increase thethroughput of their manufacturing processesfor CIGS thin-film PV modules. A new high-speed scribing process in its manufacturingequipment demonstrated robust and repeatablescribing. Engineers completed analyses andinstalled production equipment to integrate


industrial ink-jet hardware and accomplish highCIS deposition rates. An alternative back-con-tact material and process for deposition on flexible polymer and stainless-steel substratesincreased productivity without reducing prod-uct performance. In FY 2001, the company willincorporate these and other improvements intothe manufacture of 27-W modules.

Most of the PV modules manufactured bySiemens Solar Industries are made withCzochralski crystalline silicon. The company is working to produce solar cells that are thin-ner and larger in surface area and that haveback-surface field processes to increase effi-ciency. These changes should reduce modulemanufacturing costs by 30%. To produce thenew 17%-efficient thin cells, the company hasdeveloped a pilot crystal-growth process for silicon ingots, which will be sliced into 150-micron-thick wafers and then processed into125-micron-thick cells. Siemens has also devel-oped a pilot process for fabricating the thincells so that they have a back-surface field. InFY 2000, the company demonstrated prototype

125-micron-thick cells that were 16.5% efficient.To produce larger-area cells, Siemens grew a200-mm-diameter ingot and developed a newprocess for fabricating these cells.

Spire Corporation sells production equipmentfor crystalline silicon or thin-film PV modulemanufacturers. It is developing automated sys-tems that process the edge of modules, installjunction boxes, test final modules, and storemodules between processing steps. In FY 2000,Spire demonstrated the SPI-BUFFER™ 350,which stacks modules on a cart where they canbe stored safely and moved to the next step onthe production line. This buffer storage com-pensates for the batched steps of PV modulemanufacture. Spire also introduced the SPI-MODULE QA™ 350, a system for transporting,probing, and testing modules for electrical iso-lation, ground continuity, and performance inthe form of current-voltage measurements. In FY 2001, two additional systems will be perfected: an edge trimmer for removing excess encapsulant and back-cover film frommodule edges after lamination, and an edge

sealer and framer for trimmed modules. Devel-opment of automated processes for junction-box installation is planned.

System and Component Technology

Research contracts to improve system and com-ponent technology address specific problemsfor manufacturing steps and include materialdevelopment. Some of the research partner-ships to improve manufacturing of the balance-of-system (BOS) components and completedesign of solar electric systems began in 1995.Research aims to develop innovative, low-cost,high-return, high-impact PV products. Thework addressed improvements to componentssuch as inverters, efficient integration of com-ponents into the system, and improvement inthe design of systems.

Advanced Energy, Omnion Power Engineering(a division of S&C Electric Company), andTrace Engineering worked to improve theinverters that convert the dc electricity fromsolar electric cells and modules into ac powerfor utility interconnection. The companies used advanced electronics, new approaches to power bridge design, and complex softwareto improve performance, reduce costs, andinclude monitoring and improved communica-tions options in the inverters they supply to the PV systems industry.

Applied Power Corporation (formerly Ascen-sion Technology) manufactures an ac solar elec-tric module that makes PV truly modular andsimplifies installation of systems that are fullycompatible with ac appliances and with theutility grid. In FY 2000, the first prototypeSunSine® ac module delivered to NREL foroutdoor testing showed that inverter efficiencymet the project target of 91%. Refining theproduct’s design, the company designed andbuilt prototypes, and began production of a die-cast aluminum enclosure. Applied Powerfiled two patent applications, one relating to


This 2.8-kW flexible solar array made of CIGS thin-film material was used in the U.S. Army’s OperationStrong Angel training exercise in Hawaii. In FY 2000, Global Solar and Siemens Solar sold the first commercial products made from CIS-based thin-film materials.

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the design of the die-cast enclosure, and theother relating to the power electronics designand a factory calibration procedure. AppliedPower also improved the reliability of its acmodules by incorporating its proprietary ZeroVoltage Switching soft-switching into theSunSine® inverter. The company reduced production costs by cutting the number of parts by 57%. To make components smaller,Applied Power reduced the footprint area ofthe inverter by 45%. The SunSine® AC 325module passed FCC tests of electromagneticemissions and underwent the PV Program’sHighly Accel-erated Life Testing. Near the endof FY 2000, Applied Power began production of 110 units of this new version of its ac mod-ule. Of these, 28 were installed at the Univer-sity of Texas, Houston Science Center.

PowerLight Corporation produces Power-Guard® tiles for rooftop solar electric systems.The company’s process mounts PV modules(crystalline silicon or thin-film) on 3-inch-thickboards of extruded polystyrene foam covered with a cementlike coating. In FY 2000, Power-Light increased production from 200 to 400 tilesper day. The company improved handling and application of the cement coating by designing a new hopper that included pneumatic mixing,

easy cleaning, and an electronic motion-controlcircuit, and it eliminated the need to handlelaminates twice by integrating a spacer attach-ment process into the production line. Otherimprovements include incorporating electronicsensors to monitor and control steps in theprocess line, better edge trimmers, and a betterhydraulic tool for moving finished tiles to pal-lets for shipment. In FY 2000, the company esti-mated an overall cost reduction per board footof tile of nearly 60% compared with costs in1999. PowerLight has increased productioncapacity from 5 MW to 20 MW per year.

Utility Power Group (UPG) is completing afactory-assembled PV array, and Trace Engi-neering is developing companion 12-kW power conversion and energy storage units.The power conversion unit can operate in agrid-tied or stand-alone configuration whencoupled with the 13-kW/h capacity energystorage unit. This fully integrated residentialPV system will incorporate advanced powermanagement and storage. UPG’s PV arraydesign can accommodate PV modules fromseveral different manufacturers, either framedor frameless. Its design uses bolts and a railassembly to attach the factory-assembled pan-els to the roof. In a test for planned projects for

the Sacramento Municipal Utility District, UPGreported a crew of two people installed a 1-kWPV system on a test roof in less than 1 hour. InFY 2001, UPG will complete field testing of thePV array, and Trace will complete developmentof the power unit’s management control soft-ware and field test the system with storage.

Work continues on improving the performanceand reducing the cost of other BOS components,such as batteries, materials, and packaging. Forexample, tests of a hybrid system being devel-oped for the Navajo Nation by NCPV engi-neers at Sandia revealed that battery life wouldbe adversely affected by the way the chargecontroller was directing electricity from the PV modules. Replacing batteries is expensive,increasing the cost of solar electricity. Changingthe charge controller set points in response tothese test results resolved the issue before thesystems were installed in the field.

Module Performance and Reliability R&D

To demonstrate the performance of differentsolar electric technologies, the NCPV conductstests in the laboratory and in the field of bothprototype and commercially available modules.The sophisticated monitoring equipment andanalysis methods of the NCPV laboratoriesprovide information that would be difficult for manufacturers to obtain and virtuallyimpossible for end users to get.

In FY 2000, results of a field test begun in 1997show that one technology, a-Si triple-junctionPV modules from United Solar System Corpo-ration, is living up to its ratings. After threeyears of continuous outdoor exposure, the two1.01-square-meter (about 10-square-ft), 64-wattmodules were placed in the NREL Large-AreaContinuous Solar Simulator, which revealedthat their efficiencies were 7.26% and 7.18% and that their output powers at standard reporting conditions were 67.3 and 66.6 watts.


Applied Power Corporation’s power modules serve as an awning for the University of Texas Houston HealthScience Center. The ac modules will produce nearly 10,000 kWh of electricity each year.

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To help understand and characterize the outdoorperformance of polycrystalline silicon moduletechnologies, the NCPV began a test of six newPV modules on its Performance and EnergyRatings Testbed (PERT). This outdoor test ofcommercially available polycrystalline siliconmodules, which could last up to four years,will determine the actual power and energyproduction capacities of these modules underfield conditions. The six 40-W modules, twofrom each of three manufacturers, are mountedon the roof of the Outdoor Test Facility atNREL and connected to data acquisition systems that monitor their current-voltage characteristics once every 30 minutes during all daylight hours. The test system also main-tains the modules at their peak-power-pointload at all other times, which allows derivationof the total energy produced by each moduleevery day. The first results should be availablein FY 2001.

In FY 2000, work by NCPV researchers at Sandiacontinued using high-resolution infrared cam-eras to detect and characterize defects in PVmodules. This is a quick and inexpensive wayto identify module defects that could reduceperformance and reliability.

Researchers at Sandia are also studying the suc-cessful manufacturing techniques used to pro-duce the modules that have operated effectivelyfor more than two decades at Natural BridgesNational Monument, Utah. After more than 20 years in the field, the crystalline silicon modules manufactured by Spectrolab still per-form close to original specifications. Detailedanalysis in FY 2000 identified several positivefeatures, including the use of polyvinyl-butyralencapsulant, expanded metal interconnects, silicon oxide antireflective coating, and excel-lent solder/substrate solderability. This infor-mation will help manufacturers improve thedurability of current and future products.

An important tool to design solar electric systemsis the model used to predict PV module perform-ance for the complete range of outdoor operat-ing conditions expected at a specific site. NCPVengineers at Sandia and NREL have made sig-nificant progress in developing, validating, anddocumenting performance models to simulatethe total energy production (daily and yearly)of the commercial PV modules available today.The performance of modules is characterizedunder actual outdoor operating conditions at outdoor test facilities and in the laboratoryusing solar simulators. In FY 2000, NCPVresearchers completed a comparison of twocandidate PV module energy-rating methodsand published the results to support ongoingefforts to develop a new Module Energy Ratingstandard through the Institute of Electrical andElectronics Engineers (IEEE).


Addressing Environment, Safety,and Health Issues

The NCPV works to identify and solveenvironmental health and safety issues in the manufacture, use, and disposal ofsolar electric systems. In FY 2000, theNCPV and Brookhaven National Labora-tories held a workshop on the use of lead-free solder in the manufacture of PV modules. The technology was devel-oped under contract to the PV Manufac-turing R&D effort of the program by ASEAmericas. ASE Americas shared itspatents and technical details with work-shop participants from the PV industry.Making PV modules without leaded solder ensures that PV modules can bedisposed of at the end of their 30-year life without violating EPA landfill restric-tions on lead.

In FY 2000, NCPV engineers at Sandia evaluated 7 grid-tied inverters and 9 inverters in off-grid configurations. These evaluations helped manufac-turers, including those in the PV manufacturingR&D project, develop new products.

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The Program—with industry, governments,national and international organizations—improves performance and reliability ofsystems and introduces technology todomestic and foreign markets.The National Photovoltaics Program Plan

An important part of the Program’s devel-opment strategy is to monitor solar elec-tric technology performance to provide

feedback to system engineering and R&Defforts. This iterative process from basicresearch to commercial operation will ulti-mately reduce the cost of producing, installing,and operating solar electric systems.

Systems Engineering

When customers calculate the cost of solar elec-tricity, the equation includes the PV modules,all the related or balance-of-system (BOS) com-ponents, and the costs of operation and mainte-nance over a specified equipment lifetime.System engineering support activities at theNCPV work to estimate and reduce all of these costs through testing, modeling, stan-dards development, and technical assistance to initial users.

Non-Islanding Inverters

For solar electric systems to power standard acappliances, a necessary system component is aninverter. The inverter converts the dc electricityfrom the PV modules to ac current. This ac cur-rent can be sent into the power line if the solarelectric system is connected to the utility grid.If the power line is shut down for any reason,the utility must be confident that no PV or dis-tributed generation source continues to ener-gize the grid. This electricity-flow restriction

is to ensure the safety of line workers or otherpeople coming into contact with the line. Elec-tric utilities have been reluctant to connect dis-tributed electric generation systems to the gridbecause of this potential risk to personnel andequipment during such “islanding” events.

In FY 2000, a new control method for invertersdeveloped over two years by NCPV engineersat Sandia has been approved by testing andstandards organizations. The “non-islandinginverter” automatically diverts or turns off electricity flow from grid-connected solar electric systems when an electric distributionline shuts down. Several manufacturers havealready adapted their inverters to include thenew control method.

StandardsSmall-systems test procedures

The PV Program has been working to developa single test that will be accepted anywhere inthe world. This is important for enabling orga-nizations like the World Bank to determinehow well a small stand-alone PV system willperform in the field. NCPV researchers atNREL, Sandia, the Florida Solar Energy Center,the Southwest Technology DevelopmentInstitute, and PVUSA have developed a proce-dure for outdoor testing based on two small PV lighting kits. This testing procedure hasbeen incorporated by the IEEE SCC 21 WorkingGroup on Small Systems Testing into a newdraft of IEEE PAR 1526, Recommended Practicefor Testing Stand-Alone PV Systems. Additionaltesting to validate the procedure is under wayin a collaboration between the GENEC PV test-ing group in France and the NREL Outdoor Test Facility in Colorado. Meanwhile, the

European Solar Test Installation (ESTI) hasdeveloped an indoor test procedure for smallstand-alone PV systems. A new draft documentby the International Electrotechnical Commis-sion (IEC) combines both the indoor and out-door test into one procedure that can be con-ducted almost anywhere in the world. Oncethis procedure is approved, a significant obsta-cle to programs promoting solar electricity foroff-grid applications will be removed.

IEEE interconnection standard

For the solar electric systems market to reachthe goals of the PV Industry Roadmap work-shop, the procedure for connecting these sys-tems to the utility grid must be simple andacceptable to utilities and system installers.This requires that the procedure guarantee thesafety of all personnel and ensure delivery ofhigh-quality electricity to all customers. In FY2000, more than three years of work by utilities,the NCPV, and many other engineers achieveda very important step toward safe, widespreaduse of solar electricity. The IEEE standardsboard passed IEEE Standard 929-2000, Recom-mended Practice for Utility Interface of Photovol-taic Systems, the first standard of its kind allow-ing utility interconnection of distributed gener-ation equipment (including PV) not owned bythe utility. Two things that make this standardunique are its definition of a non-islandinginverter and of a procedure to test inverters forthe non-islanding features. This standard sim-plifies the process of interconnecting a solarelectric system to the grid, while includingtightly defined requirements for the intercon-necting hardware. These hardware require-ments can be tested at an independent labora-tory, such as Underwriters Laboratories, thanks


Systems Engineering and Applications

to a parallel effort to develop the appropriatetest procedure. The test procedure included in UL 1741 determines if inverters meet therequirements of IEEE 929, which specifies operating voltage, frequency windows, triptimes for excursions outside these windows,requirements for wave-form distortion, anddefinition of a non-islanding inverter.

IEEE standard for concentrator PV modules

A milestone of the National PV Program Planwas met in FY 2000 when balloting began on a new IEEE Standard, titled RecommendedPractice for Qualification of Concentrator Photo-voltaic (PV) Receiver Sections and Modules. TheNCPV has led the three-year development ofthis standard because concentrating PV sys-tems could be a key terrestrial application ofthe high-efficiency solar cells now being usedin space. An accepted method to identify anyweakness in concentrating systems that couldcause problems in the field will increase salesof concentrating PV systems.

Partnerships for TechnologyIntroduction

DOE's Domestic PV Applications and Develop-ment Project reaches out to more than 500,000people each year—consumers, architects,builders, engineers, emergency managementpersonnel, utilities, and farmers—to provideinformation about solar electric systems.

Utilities and Solar Electricity

NCPV engineers support standards efforts andconduct studies to document the value of solarelectric systems as a distributed generationsource for utilities. Solar electric systems can be installed at both residential and commercialsites where the electricity will be used. Solargeneration can be sized to reduce peak demandat these locations, which can reduce the utility’sneed to build new capacity and the amount itspends for new conventional generation facili-ties to meet the peak.

NCPV researchers at NREL, the State Universityof New York, and the New York Solar EnergyResearch and Development Association(NYSERDA) are working to increase the valueof solar electricity to commercial customers.They have developed a new solar load con-troller for customers on time-of-use tariffs inutilities with peak demand driven by air condi-tioning loads. The solar load controller works by shedding loads when the PV system cannotreach its full peak target. Tests so far show thatthe controller can shave peak loads, makingthem match the output of the PV system.Avoiding peak energy charges will translate to significant savings to commercial customers.

The NCPV also works with the SacramentoMunicipal Utility District (SMUD). With morethan 7,000 kW of solar generating capacity,SMUD has the largest utility-owned distributedsolar energy system in the United States.


Success of the TEAM-UP Project

TEAM-UP (Technology Experience toAccelerate Markets for Utility Photovol-taics) was a partnership between the U.S. Department of Energy and the utilityindustry to help develop commercial mar-kets for a wide range of solar photovoltaictechnologies. TEAM-UP awarded matchinggrants on a competitive basis to solar elec-tricity projects across the United States.Those awards resulted in 7.2 MW in gen-erating capacity from solar power installa-tions in 40 states. From 1994 to 2000, theSolar Electric Power Association (formerlythe Utility Photovoltaic Group or UPVG)managed the TEAM-UP project.

This solar electric system in Sacramento, California, generates enough electricity to meet the needs of about180 homes. While providing electricity, it also shades part of the Cal Expo parking lot. The largest parking-lot solar system in the world, this project was a joint effort of the Sacramento Municipal Utility District and DOE through the TEAM-UP program.

Kyocera Solar/PIX09435

PV in Buildings

The buildings sector in the United States con-sumes about two-thirds of the nation’s total annual electricity production. Reducing the electricity demands of buildings on the utility grid would have a significant impact on energyconsumption. The Million Solar Roofs Initiative,spearheaded by DOE, promotes the use of solarthermal and solar electric technologies to reducethe energy demands of buildings. In FY 2000,DOE had 50 partners that had made commit-ments for one million solar roofs by 2010. Ofthe total installations in FY 2000, 750 were solar electric systems equal to about 3 MW of capacity.

One of the Million Solar Roofs partners, theFlorida Photovoltaic Buildings program, hasthe goal of contributing 20,000 of the nation’smillion solar roofs. This state program is a col-laboration among the Florida Energy Office ofthe Department of Community Affairs, the U.S.DOE through Sandia, the photovoltaic industry,

the Florida Solar Energy Center, and nine end-user groups. These important end-user groupsinclude municipal utilities, commercial buildingowners and operators, government agencies,school and church organizations, manufacturedbuilding corporations, roofing companies,builders and developers, and homeowners.

This many-faceted program relies heavily ontraining, certification, and careful administra-tion of incentives to avoid problems with hard-ware and installations that have plagued otherdeployment projects in the past. Partnerships,especially with utilities, lead to many of theinstallations. Revenue for subsidies to reducethe cost of PV systems comes from a variety ofsources including state funds, matching fundsfrom partners, contracts, grants, financing, andTEAM-UP awards from DOE. Distribution offunds is linked to quality of the PV systems,which is determined through design review,module rating tests, and system acceptancetesting. Training conducted by the Florida Solar

Energy Center, with support from the PV Pro-gram, gives installers the certification they need to participate in the Florida PV BuildingsProgram. The Florida program requires systemsto meet standards for safety and electrical quali-ty. High-quality, reduced-cost systems have ledto good customer satisfaction, as monitored bythe careful administration of the program.

One way to expand the market for PV is toincorporate products right into buildings. To develop technologies and foster businessarrangements to integrate PV or hybrid prod-ucts into buildings, DOE initiated the BuildingOpportunities in the United States for PV(PV:BONUS) in 1993. Several of the productsdeveloped under the program were commer-cially available in FY 2000. For example,Advanced Energy Systems received UL listingfor its 1-kW grid-interactive PV inverter and isinstalling the units for PV applications through-out the United States. Models meeting Euro-pean specifications will be available soon.Another team, led by BP Solar and Kawneer, a leading manufacturer of architectural alu-minum products, received a design award atthe 16th Annual European Photovoltaic SolarEnergy Conference. Its winning design was abuilding-integrated sun shade incorporating a-Si PV modules manufactured by BP Solar.And a team with United Solar Systems Corpo-ration received UL listing for its flexible PVmembrane that can be applied in the field.

In FY 2001, five contractors will continue theirwork to install prototype products on build-ings, gain UL listings for these products, andmove to large-scale manufacturing. These prod-ucts include powered electrochromic windows,combination opaque curtain wall and PV a-Simodules, hybrid PV and solar thermal systems,and flexible PV roofing membranes.


Training at the Florida Solar Energy Center qualifies installers for the Florida PV Buildings Program, amodel for the widespread commercialization of grid-tied, rooftop PV systems. FSEC also conducts applica-tions experiments and field testing of PV systems for the National PV Program.

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Remote Systems

In addition to some 200,000 homes in the UnitedStates that are not connected to a utility grid,there are countless other off-grid applicationsfor solar electricity. Farms and ranches, com-munications, pumping, water flow control, andhomes in remote areas can be provided electric-ity more economically using solar electric sys-tems on site than by having grid electricitybrought to each application.

In FY 2000, many of the possible applications ofsolar electricity were presented at the Photo-voltaics in Alaska Workshop. Experts in thetechnology and its many applications spoke to 60 assembled representatives from Alaska’sutilities, Native villages, telecommunicationscompanies, the Alaska Railroad, governmentalagencies, Alaska’s newly formed Million SolarRoofs coalition, and the University of Alaska.The one-day workshop, co-sponsored by DOEand the Alaska Energy Authority, was coordi-nated by the NCPV.

Stand-alone solar electric systems can be veryuseful to emergency management personnel.The NCPV hosted the Federal EmergencyManagement Agency’s (FEMA) 5th AnnualTechnology Partnership for Emergency Man-agement Workshop and Exhibition. More than500 emergency-management professionals dis-covered the versatility of solar electric systemsin both surviving disasters and quickly replac-ing damaged power supplies for critical loads.

Native American Lands

When developing applications for solar elec-tricity, the PV Program tries to move fromgranting subsidies to purchase hardware to providing technical assistance and document-ing successful applications. The Program hasworked in FY 2000 with tribal authorities to install solar electric systems for people of theLaguna Pueblo, the Yurok tribes, and theNavajo Nation.

The Navajo Tribal Utility Authority (NTUA)estimates that, in FY 2000, between 10,000 and30,000 Navajos lived without electric power on

the reservations. Because these homes arespread out over a wide area, it would be pro-hibitively expensive to construct and maintainpower lines to each home. Providing homeswith solar electric systems in the early 1990sdemonstrated the benefits of PV on the reserva-tion. The NTUA, with technical assistance fromNCPV researchers at Sandia and subsidies forhardware from DOE, the State, and local utili-ties, purchased and installed 71 home systemsof 250 watts each . These systems proved sosuccessful that, in FY 2000, NTUA invested $2 million of its own money to install another200 PV systems on private homes. The utilityasked only for technical assistance to imple-ment their project. NCPV engineers fromSandia helped conduct system acceptance testing, train electricians, and determine recommended maintenance procedures.

The lands belonging to the Yurok tribes in North-ern California also offer many opportunities touse renewable energy to supply the population’selectrical needs. NCPV engineers at Sandiajoined a team to evaluate the tribe’s options forusing renewable energy to supply electricity toabout 70% of the inhabited land that does notyet have electrical service. The resulting reportwill help the tribe set priorities and apply forgrants to develop some of these renewableenergy options.

Engineers from the NCPV supported the installa-tion of PV systems at Zion National Park in Utah(left) and the BigHorn Center in Colorado (below). These highly visible, attractive projectspublicize the feasibility of roof-mounted and build-ing-integrated PV systems.

The Bureau of Reclamationuses PV to power motors thatoperate automatic gates forwater flow control in irrigationcanals. These systems improvethe efficiency of water use andeliminate the need for Bureau personnel to manually operatethe gates each day. NCPVresearchers at Sandia are working with the Bureau todevelop system diagnostics and communications systems.

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Susan Masten, the chairperson of the YurokTribal Council, states: “I hope that this collabo-ration represents the beginning of a relation-ship between the Yurok Tribe and DOE thatwill result in significant improvements to con-ditions on the Yurok Reservation.”

Solar Electricity for Developing Countries

India

To validate performance of U.S. thin-film tech-nologies and compare these technologies withthose of international competitors, the NCPVcollaborated with the Solar Energy Center (SEC)in New Delhi, India, to install PV systems fromU.S. module manufacturers. In a 50-50 cost-shared program, the NCPV purchased themodules and the SEC paid for the BOS andinstallation costs. The 5-kW systems will becharacterized at NREL prior to shipment, andtheir performance in outdoor conditions inIndia will subsequently be compared to thesemeasurements. Once this is done for the fivethin-film technologies (a-Si/a-SiGe, dual-junc-

tion a-Si, triple-junction a-Si, CIS, and CdTe),U.S. products could be introduced into the sizable market for solar electricity in India.

Mexico

After six years of installing cost-shared pilotsystems in Mexico, one of the PV Program’s in-country partners succeeded in obtainingWorld Bank and Global Environmental Facility(GEF) grants and loans contributing to a $31 million Renewable Energy for AgricultureProgram. The Director of Fideicomiso deRiesgo Compartido (FIRCO) is receiving fundsfor the first World Bank/GEF program usingrenewable energy in the agricultural sector. Forfour years or longer, this program will deploymore than 1200 PV and 55 wind systems topump water for agriculture. Sandia has signeda collaborative agreement with FIRCO to pro-vide technical training and assistance for theirnew program.

China

NCPV engineers at NREL have been workingwith partners in the utility, government, andnon-government sectors to open the Chinesemarket to the products of U.S. PV manufactur-ers. More than 200 solar electric systems have


This solar electric system installed in FY 1999 delivered about 23 megawatt-hours of electricity to the IndianPueblo Cultural Center in Albuquerque, New Mexico, in its first year of operation. NCPV engineers atSandia conducted the project’s electrical design review and monitor system performance.

Local technicians install solar electric modules on a village clinic as part of a collaboration between theNCPV and the Solar Energy Center in New Delhi, India, to test U.S. thin-film solar modules.

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been installed on homes in Tibet, and 243PV/wind hybrid systems have been installed in Inner Mongolia. The Brightness Program,China’s largest rural electrification program,will install solar electric systems in 500 villagesand on about 450,000 homes during the firstphase of the project. National-level policy-makers from China attended a workshop coordinated by NCPV personnel at NREL toaddress renewable energy technologies, distri-bution networks, policies, and business models.

OutreachThe NCPV distributes information to facilitatethe use of solar electric systems in diverseapplications. In FY 2000, publications, includ-ing Making the Most of Residential PhotovoltaicSystems, Photovoltaics and Solar Thermal Tech-nologies in Residential Building Codes, and PowerWhere You Need It, were distributed by mail, atworkshops, conferences, and exhibits. They arealso posted on the popular NCPV Web site (www.nrel.gov/ncpv). The Web site, with links

to useful sites about DOE, NREL, Sandia, andelsewhere, is proving to be an effective way todeliver information about solar electric systemsto audiences with varying levels of technicalexpertise. In addition, the Solar Energy ShowcaseCD-ROM contains 120 high-resolution photoswith extended captions on PV, concentratingsolar power, and solar buildings. This CD-ROMis popular with the news media. Volume 2 willcontain at least 10 photos of solar technologiesfrom each of the 50 states.


Siemens Solar’s earthsafe™ systems, like this one inSacramento, California, are complete solar electricpackages. They are connected to the utility grid and allow the user to produce green power andlower their electric bill. The package includes solar electric modules, mounting hardware designed for any roof surface, and an inverter toprovide the ac power. These earthsafe™ systems are UL listed, and they come in sizes to producefrom 250 watts to 2000 watts of ac power.

Siemens Solar/PIX09826

The National Photovoltaics Program, asdescribed in the 2000 to 2004 ProgramPlan, conducts its business using the

National Center for Photovoltaics (NCPV), an alliance of organizations working to help the U.S. PV industry maintain its global leader-ship position. To reach the milestones listed inthe NCPV’s Five-Year and Annual Operatingplans, the PV Program relies on the core exper-tise of the National Renewable Energy Labora-tory and Sandia National Laboratories to create, develop, and deploy PV and relatedtechnologies. The NCPV also draws upon theresources of Brookhaven National Laboratory,two Regional Experiment Stations (the FloridaSolar Energy Center and the Southwest Tech-nology Development Institute), and DOE'sCenters of Excellence in PV at the GeorgiaInstitute of Technology and the University ofDelaware (the Institute of Energy Conversion).In addition, more than a hundred universityand industry research partners across the country are linked to function in a unified way. The PV Program ensures the widest possible distribution of key scientific and technical material relating to the develop-ment and use of PV systems.

The Program maintains world-class facilitiesand researchers at the national laboratories toserve industry. The national laboratories of theProgram include the following capabilities.

• Solid-state spectroscopic analysis, experimentswith photoelectrochemical processes, and applications of advanced theoretical and computational tools for predicting the behavior of PV materials;

• Analytical microscopy, electro-optical charac-terization, surface and interface analysis of materials, analysis of cell and device opera-

tion, computer modeling of system and com-ponent performance, and development of special measurement techniques and instruments;

• User-accessible laboratories for fabricating and evaluating solar electric technologies and for developing and characterizing balance-of-systems components such as charge controllers and inverters;

• Outdoor test beds, indoor laboratories, and field trials for simulated, accelerated, and actual outdoor test conditions, and under varying temperature, humidity, precipitation (including hail), voltage, and radiation levels;

• Measurement systems traceable to world standards to characterize solar resources, including electronic data sets, maps, and models; satellite imagery, meteorological data, and models.


Program Resources

02897603

Research andDevelopment

52% SystemsEngineering and

Applications24%

TechnologyDevelopment

24%

40%

1%

59%

35%

11%

54%

GovernmentUniversityIndustry

50%

25% 25%

The NCPV awards most of its federal funds through competitive procurement to industry, universities, andother research centers around the country. The federal funds for FY 2000 totalled $65.9 million.


The product of a national solar design competition sponsored by DOE and the American Institute of Architects (AIA), the Solar Wall (pictured here as an artist’sconcept) will cover the currently windowless south wall of the Forrestal Building, DOE’s headquarters in Washington, D.C. In summer, when the sun is high in the sky and building electrical demands are at their peak, PV panels in the lower part of the wall will generate electricity for the building (about 100 kW peak). In fall and winter, when the sun is lower in the sky, solar thermal collectors in the upper part of the wall will also use the sun’s energy to heat water for the building’s heating systems. Designers estimate that the Solar Wall will cut DOE’s energy costs by between $30,000 and $50,000 per year.

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Front cover photos

Fundamental research in photovoltaics leads toadvancements in the technology. The squarephotos show, clockwise from top left:

• PV module framing and manufacturing at Siemens Solar Industries. Siemens Solar/ PIX07832

• The Williams Building in downtown Boston, Massachusetts, has a 37-kW dc and a 28-kW ac PV system integrated into the roof consist-ing of 372 solar panels. Roman Piaskoski/PIX07172

• The Department of Environmental Protection building in Ebensburg, Pennsylvania, was selected as one of the top 10 environmental buildings in the United States by the Ameri-can Institute of Architects on Earth Day 2000. “Green” highlights include a 16-kW PV array,the second largest in Pennsylvania. FIRST, Inc./PIX09437

• NREL's Ron Judkoff inspects a 7.2-kW photo-voltaic array on the south roof of the new Visitor Center at Zion National Park, Utah. Robb Williamson/PIX09264

Center circle photos (left to right): 03525 and03524• A vacuum system at Sandia used to investi-

gate metallization systems for crystalline-silicon solar cells. Researchers use Sandia's PV Device Fabrication Laboratory to design, make, and test crystalline silicon solar cells. Jim Yost/PIX03525

• NREL's Kannan Ramanathan inspects the growth chamber of a physical vapor deposi-tion system used for making solar cells from copper indium diselenide. Jim Yost/PIX03524

Inside cover: A 75-kilowatt photovoltaic systemon the roof of the Mauna Lani Bay Resort Hotelin Hawaii. PowerLight Corporation/PIX06430


UN

ITED

STATES OF AMER

ICA

•DEP

ARTMENT OF ENERGY

•

U.S. Department of EnergyJames E. Rannels, DirectorOffice of Solar Energy Technologies1000 Independence Ave., SWWashington, DC 20585202-586-SUNS (7867)Fax: 202-586-8148E-mail: [email protected]

Richard King, Team Leader Photovoltaics Program1000 Independence Ave., SWWashington, DC 20585202-586-1693Fax: 202-586-8148E-mail: [email protected]

Useful Web SitesDOE: www.eren.doe.gov/pvNCPV: www.nrel.gov/ncpvSandia: www.sandia.gov/pv

National Renewable Energy LaboratoryLawrence Kazmerski, DirectorNational Center for Photovoltaics1617 Cole BoulevardGolden, CO 80401-3393303-384-6600Fax: 303-384-6481E-mail: [email protected]

Thomas Surek, Technology Manager Photovoltaics Program1617 Cole BoulevardGolden, CO 80401-3393303-384-6471Fax: 303-384-6481E-mail: [email protected]

Sandia National LaboratoriesPaul Klimas, ManagerPhotovoltaics Program P.O. Box 5800Albuquerque, NM 87185-0753505-844-8159Fax: 505-844-6541E-mail: [email protected]

Joe R. Tillerson, ManagerPhotovoltaic Systems R&D P.O. Box 5800Albuquerque, NM 87185-0753505-844-1806Fax: 505-844-6541E-mail: [email protected]

Key Contacts

Produced for theU.S. Department of Energy1000 Independence Avenue, SWWashington, DC 20585

by the National Renewable Energy Laboratory,a DOE national laboratory.

DOE/GO-102001-1168February 2001

Printed with a biodegradable ink on paper containing atleast 50% wastepaper, including 20% postconsumer waste.

NOTICEThis report was prepared as an account of work sponsored by an agency of the United States govern-ment. Neither the United States government nor any agency thereof, nor any of their employees,makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specificcommercial product, process, or service by trade name, trademark, manufacturer, or otherwise doesnot necessarily constitute or imply its endorsement, recommendation, or favoring by the UnitedStates government or any agency thereof. The views and opinions of authors expressed herein donot necessarily state or reflect those of the United States government or any agency thereof.

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Available electronically at http://www.doe.gov/bridge

Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from:U.S. Department of EnergyOffice of Scientific and Technical InformationP.O. Box 62Oak Ridge, TN 37831-0062phone: 865-576-8401fax: 865-576-5728email: [email protected]

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