Photovoltaic Energy Program Overview, Fiscal Year 19951 Photovoltaic Energy Program Overview 1995 PV Program Accomplishments Research and Development Refined and continued to transfer

ContentsMessage from the Director . . . . . . . . . . . . . 1

1995 PV Program Accomplishments . . . . . . . . 2

Introduction . . . . . . . . . . . . . . . . . . . . . 3Accomplishments of the PV Program in FY 1995 stem from work planned and carried out in collaboration with the U.S. PV industry.

Research and Development . . . . . . . . . . . . 4Researchers in DOE laboratories, industry, and universities generate new approaches for increasing the efficiency and reducing the cost of PV.

Technology Development . . . . . . . . . . . . . . 12The PV Program sponsors work that applies R&D innovations to tomorrow’s PV products.

Systems Engineering and Applications . . . . . . 19The PV Program supports projects that validate PV technology for world markets.

Program Resources . . . . . . . . . . . . . . . . . 27The PV Program distributes funding within the program elements and supports the U.S. PV industry through the researchers and facilities of the national laboratories.

Cover Photos: On left, the Sacramento Municipal Utility District installed a210-kW PV system at the Hedge substation in California (SMUD/PIX01026).On right, from top to bottom: Large-scale photovoltaic systems can provide gridsupport for electric utilities (William Wallace, NREL/PIX01541). PV systemsare being deployed and evaluated in a variety of applications around theworld (Solar Electric Light Fund/PIX01543). Through the support of the PV Program, Golden Photon, Inc., has improved the efficiency of its cadmium telluride modules and manafacturing process (David Patryas Photo-graphy/PIX01545). One way that DOE researchers at the national labora-tories help the U.S. PV industry is through R&D on deposition of PV materials (Jim Yost Photography/PIX03655).

Message from the DirectorThis year photovoltaic (PV) systems used sunlight alone to generate morethan 800,000,000 kilowatt-hours of electricity throughout the world. Thesesystems installed since 1988 generate enough electricity to power 8 mil-lion homes in the developing world or 150,000 homes in the UnitedStates. This year, worldwide sales of PV systems grew again by more than15 percent. And, for the past 2 years, U.S. industry increased its share ofthis exploding world market. This year, corporate America increased itsinvestments to expand PV manufacturing capacity, while researchers worked to maintainthe technological edge that has fueled our market successes.

We look with pride on the achievements of the fiscal year just ended.While the lion’s share of the credit for our accomplishments goes to indus-try, the government program in cooperative research and development ishelping to turn the tide of dwindling market share by making remarkabletechnical advances. These advances in understanding and improvingmanufacturing technology, PV materials, balance-of-system components,and engineering applications are giving U.S. industry the edge it needsagainst heavily subsidized foreign competition.

We look with hope to our labors ahead. Competing in world markets demands continuous improvements in performance and cost. To reap therewards of our national investment in this technology success story wemust keep the momentum going. The research agenda set forth in the National Photovoltaic Program 5-Year Plan supports high-risk, high-pay-off research that will keep U.S. industry on top. The programs of coopera-tive research that draw on the resources of the national laboratories, universities, and the PV industry provide the feedback loop from the market to the laboratory. This feedback to the laboratory is vital in advancing PV technology to benefit new products. And it is new and bet-ter products that will deliver electricity from the sun to the people of theworld.

James E. Rannels, DirectorPhotovoltaic Technology DivisionU.S. Department of EnergyWashington, D.C.

1 Photovoltaic Energy Program Overview

1995 PV Program Accomplishments

■ Research and Development

Refined and continued to transfer to industry the techniquesfor producing record 17.1%-efficient cells in the laboratorybased on copper indium diselenide.

Supported work leading to two companies bringing proto-type products of cadmium telluride thin-film technology tomarket.

Developed a new production technique—hot-wire deposi-tion—that shows promise of more-efficient amorphous sili-con solar cells.

Verified a record 30.2%-efficient gallium arsenide alloy con-centrator cell at 180 suns.

Developed cells from new high-efficiency material—poly-crystalline gallium arsenide—verified at 16.6% in the firstyear of research.

Demonstrated that rapid thermal processing of silicon can reduce processing time while maintaining high efficiencies.

■ Technology Development

Successfully completed several PV Manufacturing Technol-ogy (PVMaT) contracts having 3-year commitments, exceed-ing cost and production goals of the program. Awarded newcontracts for product-driven system and component technol-ogy and manufacturing technology.

Supported work at AstroPower that led to their winning anR&D 100 award for a PVMaT product.

Supported work at Spire Corporation to develop its auto-mated PV module assembler being marketed this year.

Supported work at Solarex leading to a manufacturing process for the commercial production of 8-ft2 multijunctionamorphous silicon modules.

Supported work with Springborn Materials Science Corpora-tion leading to the development of two new encapsulant formulations for the PV industry.

Developed and tested balance-of-system (BOS) componentsincluding inverters, batteries, and charge controllers underthe BOS project.

Added to laboratory capabilities, including a new outdoortest facility at NREL and a BOS testing laboratory at Sandia.

■ Systems Engineering and Applications

Completed a major step toward creating a domestic certifica-tion program for PV modules and systems.

Assisted Omnion Power Engineering Corporation to achieveUL and FCC approval for their 4-kW inverter.

Supported Utility PhotoVoltaic Group’s efforts in 1995 andplans for 1996.

Demonstrated through an expanded load-matching studythat PV electricity generation matches utility loads in most regions of the United States.

Expanded efforts to promote PV to federal agencies, includ-ing the National Park Service, U.S. Forest Service, Bureau ofLand Management, and the military.

Supported the design and construction of six modularhouses incorporating PV under the PV:BONUS project. Alsoaccelerated development of PV-integrated roofing productsand a module that converts dc power directly to ac power.

Completed international projects in South Africa, Brazil, Mexico, India, and Russia that installed PV hardware andmodule assembly plants.

Fiscal Year 1995 2

IntroductionAccomplishments of the PV Program in FY 1995 stem from work planned and carried out incollaboration with the U.S. PV industry.

The National PhotovoltaicProgram supports efforts tomake PV an important partof our economy through itsthree main program elements:

Research and Development, TechnologyDevelopment, and Systems Engineeringand Applications.

Research and development activitiesgenerate new ideas, test the latest scientific theories, and push the limitsof PV efficiencies in laboratory and prototype materials and devices.

Technology development activities apply laboratory innovations to prod-ucts to improve PV technology and themanufacturing techniques used to pro-duce PV systems for the market.

Systems engineering and applicationsactivities help improve PV systems andvalidate these improvements throughtests, measurements, and deploymentof prototypes. In addition, applicationsresearch validates sales, maintenance,and financing mechanisms worldwide.

All PV Program activities are plannedand executed in close collaboration andpartnership with the U.S. PV industry.

Fiscal Year (FY) 1995 has seen advancesand significant accomplishments ineach of these program elements, expanding the foundation on whichnext year’s activities will build.

This 290-kilowatt PV hybrid system stemming from PV Program activities generates electricity for a military operation in China Lake, California.

“There is no doubt that the costs ofphotovoltaic modules have decreased bya factor of 10 over the past 15 years...Thisdecrease has been as a result of bothtechnological progress and gain in PVproduction experience.”

— Renewable Energy Technologies: A Review of the Status and Costs of Selected Technologies, by the World Bank.


Research and DevelopmentResearchers in DOE laboratories, industry, and universities generate new approaches for increasingthe efficiency and reducing the cost of PV.

U.S. industry markets themost advanced PV tech-nologies in the world. Recent innovations havehelped U.S. industry

regain some of the world market sharelost in the 1980s. An aggressive researchand development program helps main-tain our position of technological leader-ship so we can continue to reap theeconomic rewards of our long-term investments.

Through its cooperative research anddevelopment activities, the PV Programconducts research in thin films, crystal-line silicon, and advanced high-efficiency materials and devices. Thisyear, researchers increased cell efficien-cies through basic research and innova-tive fabrication techniques. PhotovoltaicProgram personnel transferred thesetechniques to industry and expanded research partnerships to further advancethe technology. In addition, work withuniversities yielded valuable results andhelped inspire the next generation of researchers.

■ Thin-Film Materials:Improvingefficiencies,performance, and costs

To compete in world markets for bulkpower generation, the cost of electricityfrom PV systems must decline from today’s 20¢ per kilowatt-hour (kWh) toaround 6¢/kWh. To reduce costs by thismuch we need new technologies thatcan be mass-produced from inexpensivematerials. Thin-film materials are apromising path to very low-cost PV. At

least eight U.S. companies are buildingplants to produce modules made ofthin-film materials for today’s markets.

To supply tomorrow’s markets, the PVProgram’s research addresses technicalissues to raise the efficiencies of thin-film devices to new records. New records are often the result of laboratoryresearch that expands our theoreticalunderstanding of thin-film materials. Inaddition, some technical problems onlyemerge as products are manufacturedfor the first time. When these problemsarise, they must be referred back to thelaboratory for new approaches to thin-film devices.

PV cells and modules are very reliable in space and on the earth. The Hubble space telescope (picturedhere) and virtually all communications satellites are powered by photovoltaic technology. The DOEprogram over the last two decades has worked to bring this technology to earth.

“I believe that this jointDOE/NREL program with subcontractors infundamental and appliedresearch and development is a very successful model.”

— John Coors, Chief Executive Officer,Golden Photon, Inc., Golden, Colorado

Fiscal Year 1995 4

The Thin-Film PV Partnership Programis designed to ensure that companies aggressively scaling up their new thin-film products have the R&D resourcesto address these issues and to move forward. The PV Program awarded

11 additional contracts in 1995 underthe Thin-Film PV Partnership Program.

Besides their specific research contracts,investigators participate in researchteams that address technological issues

PV technology basics There are many different technical approaches to converting the sun’s energy intoelectricity. The PV Program conducts R&D on several of the most promising concepts.Program resources are invested in innovative new approaches with the potential forhigh efficiencies and low cost like thin-film PV, as well as established technologieslike crystalline silicon PV.

Crystalline silicon (c-Si) is the semiconductor material used most in the manufactureof PV modules today. Silicon wafer technology is similar to that of computer chips.Wafers for each cell are cut from ingots of crystalline material. Modules are made ofindividual cells, electrically connected and sealed in a weatherproof package. Smallc-Si cells can be used with special lenses that concentrate sunlight to achieve higher ef-ficiencies. These concentrator systems have a large collection area composed of low-cost materials and a smaller area of more-ex-pensive solar cells.

Another variant of c-Si used in manufacture of PV modules today is multicrystallineor polycrystalline silicon. These materials are composed of crystal grains up to 1 cmacross bonded together to form a single material.

Polycrystalline thin-film materials are referred to by the chemical composition of their photosensitive materials such as cadmium telluride (CdTe) or copper indium diselenide and its alloys—Cu(In,Ga)(S,Se)2 or (CIGS). To construct thin-filmPV modules, very thin layers of semiconductor material (down to 1 micron thick, about 300 times thinner than conventional c-Si) are applied to a low-cost backing such as glass or stainless-steel foil. Polycrystalline Si and galliumarsenide are other candidate thin-film materials. Thin films demand less semicon-ductor material per device, so the cost of materials is lower. In addition, thin-filmmanufacturers can take advantage of existing industrial processes such as thoseused to manufacture and coat glass. Furthermore, thin-film modules can be con-nected into an electric circuit as a single large piece. They are said to be “mono-lithic.” In contrast, c-Si modules are made from cells that are wired into electriccircuits within the module.

Amorphous silicon (a-Si) materials are made of solid silicon, but like glass, they haveno crystalline structures. Small a-Si modules are commonly used for solar-poweredconsumer devices that have low power requirements. By carefully controlling theformation of thin layers of a-Si, and by modifying their composition, PV cells withhigher efficiencies are being fabricated. To further increase efficiency, a-Si multijunc-tion devices are constructed in layers, each of which absorbs a different portion of the solar spectrum. This makes the devices more effi-cient than single-junction a-Si, but adds complexity and cost to manufacturing. Theefficiency of amorphous silicon cells and modules is expressed as “initial” or “stabilized,” because the efficiency of most a-Si materials—when exposed to light—declines to a stable lower level.

Thin-Film PV Partnership membersAstroPower, Inc.,Newark, DE (Si film)

Colorado School of Mines,Golden, CO (a-Si; CdTe)

Colorado State University, Ft. Collins, CO (CIS)

Energy Conversion Devices, Inc.,Troy, MI (a-Si)

Energy Photovoltaics, Princeton, NJ (CIS)

Florida Solar Energy Center, Cape Canaveral, FL (CdTe; CIS)

Georgia Institute of Technology,Atlanta, GA (CdTe)

Golden Photon, Inc.,Golden, CO (CdTe)

Harvard University, Cambridge, MA (a-Si)

International Solar Electric Technology,Inglewood, CA (CIS)

Iowa State University, Ames, IA (a-Si)

Pennsylvania State University, University Park, PA (a-Si)

Purdue University, West Lafayette, IN (CdTe; CIS)

Siemens Solar Industries, Camarillo, CA (CIS)

Solar Cells, Inc., Toledo, OH (CdTe)

Solarex Corporation, Newtown, PA (a-Si)

Syracuse University, Syracuse, NY (a-Si)

United Solar Systems Corp., Troy, MI (a-Si)

University of California, Los Angeles, CA (a-Si)

University of Central Florida, Orlando, FL (CIS; CdTe)

University of Colorado, Boulder, CO (a-Si)

University of Delaware, Institute of Energy Conversion, Newark, DE (a-Si; CdTe; CIS)

University of Florida-Gainesville,Gainesville, FL (CIS)

University of North Carolina, Chapel Hill, NC (a-Si)

University of Oregon, Eugene, OR (a-Si)

University of South Florida, Tampa, FL (CIS; CdTe)

University of Toledo, Toledo, OH (CIS; CdTe)

Washington State University, Richland, WA (CIS)


affecting the entire industry. This mecha-nism brings industrial problems back tothe laboratory. The industry partnerseach contribute 10%–50% of the value oftheir contract. They are developing pre-commercial prototype products largelybased on copper indium diselenide, cadmium telluride, thin-layer crystallinesilicon, and amorphous silicon.

Copper indium diselenideIn FY 1995, PV Program researchersstudying laboratory devices based oncopper indium diselenide (CIS) pushedthe conversion efficiencies to 17.1 percent(for a 0.4-cm2 cell). This is the highest efficiency recorded for any thin-film celland demonstrates that a thin-film celldesigned for low cost can approximate

the performance of a traditional wafersilicon cell (the best polycrystalline sili-con cell efficiency is 17.8 percent [1 cm2]).

Industrial partners are also developinghigher-efficiency devices that showpromise for large-scale production. Solarex Corporation, working with thePV Program, produced a 40-cm2 mini-module with a record 12.9% efficiency.In another development, InternationalSolar Electric Technology uses a lowercost, non-vacuum method of depositingcopper indium diselenide precursorswith little waste. Using this method—and without adding gallium—they pro-duced copper indium diselenide cellshaving 13% efficiency. By adding gallium, this simpler process shouldyield cells with even higher efficiencies.

Copper indium diselenide alloys are dif-ficult to make. Proper temperature andtiming of process steps are critical toquality results. PV Program researcherswork closely with industry to ensurethat approaches leading to these high-efficiency materials are well understood.To achieve this, the PV Program has assembled 40 researchers nationwide to devise simpler, more-effective fabrica-tion methods. In FY 1995, the NationalRenewable Energy Laboratory (NREL)began to license its deposition technol-ogy used to achieve world-record effi-ciencies for copper indium diselenidematerials.

Cadmium tellurideCadmium telluride technology is thenewest commercial thin-film PV prod-uct. Two U.S. companies are manufac-turing modules for remote applications.Cadmium telluride holds the promiseof low-cost manufacturing, with morethan a dozen methods having beenused to make 10% cells, including high-rate evaporation, spraying, screen print-ing/sintering, and electrodeposition.

The efficiency of small (0.4-cm2) cad-mium telluride devices has increased tonearly 16 percent. Small, high-efficiencycells are made using new techniques inthe laboratory. Achieving high efficien-cies for larger-sized devices is a centralfocus of ongoing PV Program activities.

Increasing the efficiency of modulesmade from this material is challengingbecause, despite our progress in devel-oping and manufacturing cadmium tel-luride, our fundamental understandingof its properties is very limited. Thisyear, under the Thin-Film PV Partner-ship research agreements, teams areworking to understand specific materialproperties important to the companiesdeveloping this technology. One team isexploring stability in cadmium telluridematerials and devices to learn how tobuild consistently stable modules. These two physical vapor deposition systems are used for making various copper indium

diselenide PV cells.

Fiscal Year 1995 6

Producing stable modules requires sophisticated equipment for monitoringproduction. In a cooperative researchand development agreement (CRADA)with Solar Cells, Inc. (SCI), of Toledo,OH, the PV Program developed andbuilt a photoluminescence diagnosticmonitor to the company’s specifica-tions. SCI will use the monitor in theirproduction line to test the quality of devices as they are produced.

In FY 1995 Solar Cells, Inc., and GoldenPhoton, Inc., of Golden, CO, broughtprototype products to market. The performance of these products will becarefully monitored to improve our understanding of this thin-film material.

Amorphous siliconImproving the stability and efficiency of amorphous silicon materials and devices remains an important programtask. This year work continued to improve amorphous silicon cells bymodifying device structure. The Thin-Film PV Partnership research teams areaddressing a dozen issues surroundingthe design and fabrication of multijunc-tion amorphous silicon alloy cells.

For example, one team is working onback reflectors that direct unused sun-light back up through the very thin lay-ers of a multijunction cell. Good back

reflection can increase the efficiency ofthese cells by up to 40 percent. Anotherteam is modeling the effects of using different combinations of alloys in thelayers of multijunction cells. Modelingallows many combinations to be evalu-ated quickly and the best possibilities tobe selected for laboratory experiments.

Other experiments to improve produc-tion techniques for amorphous siliconshow promise. For example, United Solar Systems Corporation foundthat hydrogen dilu-tion during deposi-tion improved boththe initial and thestabilized perform-ance of amorphoussilicon alloy cellswith hydrogen.

In another devel-opment, a new pro-duction techniqueshows promise forincreasing the effi-ciency of amor-phous silicon.Amorphous sili-con produced bytoday’s glow-discharge methodexperiences

permanent losses in conversion effi-ciency when exposed to sunlight—aphenomenon known as the Staebler-Wronski Effect. A potentially more sta-ble amorphous silicon material wasproduced at NREL last year using a hot-wire technique. The extremely high tem-perature near the wire causes the liquidmixture of material to separate into lay-ers and deposit on the cell surface up to10 times faster than the glow-dischargemethod used by industry today. In addi-tion, the material contains less poorlybonded hydrogen, the agent suspectedto cause instability in amorphous siliconmaterial.

Tests in 1995 confirm that material cre-ated with the hot-wire method is morestable, and further tests show that effi-ciency can be increased as well. InFY 1996, researchers plan to incorporatematerial made with the hot-wire tech-nique into devices with higher efficien-cies, such as tandem or triple-junctioncells. In addition, this technique will be used to deposit other alloys of amorphous silicon, such as amorphoussilicon germanium.

This prototype PV system is made with cadmium telluride thin-film technology pioneered inDOE laboratories and developed in conjunction with Solar Cells, Inc. The modules feed enoughelectricity into the utility grid each year to meet the energy needs of four typical American homes.

The new hot-wire deposition process being developed in the PV Programproduces amorphous silicon material that is more stable and does so inabout one-tenth the time of other methods.


Meanwhile, the U.S. PV industry is ex-panding its production capacity foramorphous silicon PV systems. DuringFY 1995 United Solar Systems Corpora-tion/Energy Conversion Devices ofTroy, MI, and Solarex, of Newtown, PA,began major scale-ups of their amor-phous silicon manufacturing capabili-ties. These new facilities will have animportant impact on the U.S. produc-tion capacity for amorphous silicon PV.

■ Crystalline SiliconMaterials:Advancing theindustry’s workhorse

Crystalline silicon dominates the domestic and international PV marketstoday because of its relatively high effi-ciency, stability, competitive cost, anddurability in the field. In 1994, crystal-line silicon materials accounted for 83% of the total world sales of PV. Yet,as laboratory achievements in efficiencyare reproduced in industry, crystallinesilicon devices will become even morecompetitive with other forms of energy

generation. To make crystalline silicondevices more competitive, cooperativeresearch sponsored by the PV Programfocuses on adapting laboratory tech-niques to make larger cells morequickly and increasing the efficiency oflow-cost materials.

For example, rapid thermal processingis an important step toward continuousautomated production of silicon solarcells. This process reduces the time toprocess silicon solar cells by using opti-cal lamps to heat samples very quickly.Speeding up processing time reducesthe amount of chemicals and energyused and can achieve better perform-ance from low-cost, solar-grade, crystal-line silicon materials.

This year the program’s work with theGeorgia Institute of Technology—one ofDOE’s University Centers of Excellencein Photovoltaic Technology—made sili-con cells by rapid thermal processing.These cells have measured efficienciesof 17.1% on semiconductor-grade float-zone silicon, 16.4% on solar-grade sili-con, and 14.8% on cast-multicrystallinesilicon. These efficiencies, comparableto those of cells produced using conven-tional processes, demonstrate that rapidthermal processing can produce accept-able cells more quickly. This laboratorywork is being applied by Solarex Corpo-ration, Frederick, MD, using high-throughput production equipment.

For several years, the program’s Multi-crystalline Silicon Research Cooperativehas provided a framework for industryto benefit from and guide work at thenational laboratories in multicrystallinematerials and devices. For example, onetask under the cooperative was process-ing material manufactured by CrystalSystems, Boston, MA, and producing amulticrystalline module with 15.3% effi-ciency. The task was identified, con-firmed, and monitored by the team inFY 1994. This activity demonstrated thepotential of large-area multicrystallinecells to have such a high efficiency.

Crystalline silicon modules produced in the U.S. dominate the world market for PV. The Sacramento Municipal Utility District (SMUD) installed this 210-kilowatt crystalline siliconsystem at its Hedge substation in California.

Fiscal Year 1995 8

This year the research cooperative expanded its membership (and changedits name) to include those working insingle-crystal silicon materials and devices. Researchers from U.S. crystal-line silicon manufacturers—ASE Americas, Billerica, MA; AstroPower,Newark, DE; Crystal Systems; Solarex;and Siemens Solar Industries—NREL,and Sandia work together to specifyand direct work in areas likely to havean impact on future products. Someeight universities also conduct related research in cooperation with the PV Program.

Future products will also benefit fromresearch results presented at the FifthWorkshop on Silicon Point Defects andDefect Processes. Defects related to theboundaries between the crystals in mul-ticrystalline materials provide places forfree electrons to recombine, reducingthe energy production of the PV cell.The PV Program sponsors research toidentify and compensate for defects toimprove the efficiency of PV materialsand cells.

Engineering higher efficiency solar cellsfrom multicrystalline silicon has beenhampered by the enigma of excessiveloss of minority carrier lifetime in low-resistivity materials. The poor lifetimeof charge carriers appears to be due tothe level of iron impurity, according towork performed for DOE this year at the Massachusetts Institute of Technology.

Understanding the role of iron, as wellas boron, in these materials is an impor-tant step for improving the efficiency of multicrystalline materials. Now researchers can explore ways to overcomeor compensate for these interactions toincrease the efficiency of PV cells.

Another approach to increasing the efficiency of PV devices is controlling reflectance. The surface of a solar cell, if left untreated, can act as a mirror, reflecting the sun’s energy rather than

converting it to electricity. Crystallinesilicon manufacturers use an inexpen-sive chemical process to etch the surfaceof the cell. But this process is not suit-able for most multicrystalline materials.

A promising approach to reducing reflec-tance is being developed and tested incooperation with the Crystalline SiliconResearch Cooperative and Harvard University. Textured dielectric films(first developed for use in amorphoussilicon cells) are deposited on the sur-face of silicon cells. This year the processproduced devices matching the perfor-mance of conventionally producedcells. And applying a coating should bequicker and less expensive than the mechanical reflectance texturing usedin production today.

Meanwhile, the crystalline silicon indus-try is also moving to larger cells. Compa-nies have found that by eliminating thecost of sawing wafers into squares theydo not pay much more for the glass andframing of larger modules containing

voids between the cells. The integratedcircuit industry is producing silicon wafers up to 500 cm2 in area, and sev-eral PV companies now use 250-cm2

cells, rather than 100-cm2 cells, in theirmodules.

Module manufacturing capacity for the crystalline silicon industry will beexpanding in 1996. Solarex Corporation,Siemens Solar Industries, and Solechave all announced plans that signifi-cantly increase the U.S. manufacturingcapacity for this technology.

■ Advanced Conceptsfor High Efficiency:Tomorrow’stechnology inprocess

High-efficiency gallium arsenide cellsdeveloped in the PV Program hold theworld-record efficiency at 30.2% underconcentrated sunlight. Specifically, these

cells are monolithic,two-terminalGaInP/GaAs devices.In 1995, researchersmade remarkable progress on the nextstep to develop low-cost, high-efficiencysolar cells for tomor-row. They appliedtheir understandingof high-efficiency materials to developnew 16.6%-efficientpolycrystalline cells.

Researchers designedthis new galliumarsenide polycrystal-line cell from the bottom up, based onthe physical under-standing of what ittakes to achieve high

Research Triangle Institute, North Carolina, produced polycrystallinegallium arsenide solar cells with conversion efficiencies of 16.6% dur-ing their first year of work to apply high-efficiency technology in low-cost materials. Thin films of gallium arsenide are deposited ongermanium substrates having millimeter-size grains.


efficiency. In addition researchers designed production processes to yieldthe types of materials needed, ratherthan beginning with a process to seewhat it produces.

The production method leading to thishigh-efficiency device shows promisefor manufacturing. The 16.6% cell wasmade using chemical vapor depositiontechniques similar to the way amor-phous silicon is made, thus having thepotential for large-scale manufacturing.Related projects sponsored by the pro-gram are tackling the materials chal-lenge of producing gallium arsenidefilms of this morphology on glass orother low-cost substrates.

This year improvements in the PV Pro-gram’s laboratory equipment shouldhelp make even more-efficient cells. Byusing a linear transfer line, a molecular-beam epitaxy growth chamber is beingcombined with a metal-organic chemicalvapor deposition unit—a combinationthat will allow careful analysis of mate-rials as they are grown. Using scanningtunneling microscopy, atomic force microscopy, and low-energy electrondiffraction, researchers can study theatomic structure and microscopic features of a material’s surface as itemerges from the growth chamber. Ultimately, this ability will lead to a bet-ter understanding of growth processesand improved high-efficiency cells.

Advanced concepts can take manyforms. This year a university researchcontract with Johns Hopkins Universityyielded a photoelectrochemical solar cellthat was 10% efficient. This approachtakes advantage of organic dye mole-cules bonded to the large surface area ofthe cell. When light is absorbed into thetitanium dioxide (a pigment used in or-dinary paint), energy is transferred intothe semiconductor and collected between the electrolyte-semiconductorjunction. Although this novel technol-ogy is highly experimental, it has thepotential for very low-cost production.

■University Programs: Inspiring researchersof tomorrow

The PV Program has several activities toattract the next generation of researchersand technicians to the PV industry. Forexample, the Georgia Institute of Tech-nology and the University of DelawareInstitute of Energy Conversion are Cen-ters of Excellence that operate state-of-the-art laboratories and offer courses inphotovoltaic technology to engineeringstudents.

In addition, the PV Program is commit-ted to providing hands-on experience in photovoltaic science to students

Two years of work ended for 38 teams as the latest Sunrayce solar car race was completed. DOE, General Motors, and others support the race to help college students become experts in photovoltaics and automotive technology. The race route ran from Indianapolis, Indiana, to Golden, Colorado. The next Sunrayce will take place in June 1997.

High-efficiency cells madefrom gallium arsenide alloysbeing developed in the PVprogram hold world-recordefficiencies at 29.5% for aone-sun cell and 30.2% for aconcentrator cell at 180 suns.

Fiscal Year 1995 10

attending historically black colleges and universities. This year, six studentsadvanced their interest and skills inphotovoltaics through summer intern-ships, sponsored by the PV Program, atSolar Cells, Inc., the Institute of EnergyConversion (University of Delaware),the University of South Florida, andNREL.

University students at architecturalschools will have the opportunity tostudy how to incorporate PV into building design thanks to a curriculum developed under the PV Program. The American Institute of Architects developed materials on PV and build-ing design. This year the course was distributed to universities across thecountry.

■Measurements andCharacterization

Each year the PV Program test laborato-ries at NREL and Sandia evaluate morethan 20,000 components, devices, andPV materials for more than 200 differentresearch and industry groups.

Careful testing, characterization, andevaluation is an important part of theprocess to improve PV systems. Tests establish benchmarks against which improvements are measured. They pro-vide important diagnostic information

to industry and researchers trying outnew concepts. The world-class testingand evaluation laboratories of the PVProgram provide unbiased, third-partytest results against which the PV indus-try can validate its own measurementsand measuring equipment.

As an example of the value derivedfrom these laboratories, in FY 1995 theaccumulated test results for various PVmaterials based on copper indium dise-lenide alloys were published in a refer-ence book for the research communityin that technology.

Researchers use this X-ray photoemission spectroscopy system to obtain information on chemi-cal bonding and molecular structure of solid-state materials.

The PV Program sponsors research at sevenhistorically black colleges and universitiesacross the country. Sixteen students willsolve problems in photovoltaic science during the 1995-96 academic year.


Technology DevelopmentThe PV Program sponsors work that applies R&D innovations to tomorrow’s PV products.

Through its collaborative tech-nology development workwith industry the PV Pro-gram modifies successfullaboratory techniques to

enhance the competitiveness of U.S. PV products. This year the nation’s PVindustry expanded production capacity,launched new products, and increasedmarket share.

■ PhotovoltaicManufacturingTechnology Program:From prototypes to advancedmanufacturingtechnology

DOE initiated the Photovoltaic Manu-facturing Technology (PVMaT) pro-gram in 1990 to help the domestic PVindustry extend its world leadershiprole. This cost-shared project, con-ducted in several phases, supports in-dustry to optimize manufacturing andreduce costs, thereby leading to the de-velopment of commercial PV modulesand systems.

Industry accomplishmentsunder PVMaT this yearThis year several companies workingunder subcontracts awarded in 1992completed their final year of research.Each company’s accomplishments areunique, demonstrating that there aremany ways to approach the manufac-ture of PV devices. In each case, the industrial partner achieved or exceededtheir objectives in the project and are actively marketing products that are a

“The PVMaT program is making apositive contribution to the U.S. PVindustry. Companies like Solarex arebeing assisted in the development ofimproved manufacturing technologies,taking those advances made in thelaboratory and developing themanufacturing processes to increaseproduction and lower the cost of PVproducts.”

— Harvey Forest, President and Chief Operating Officer, Solarex Corporation

Fiscal Year 1995 12

direct result of their PVMaT researchand development efforts.

AstroPower, Inc., Newark, DE, manufac-tures PV modules made with its proprie-tary polycrystalline Silicon-FilmTM

process. Under its Phase 2A (see box on page 15) subcontract completed this year, AstroPower developed the machine to generate sheets of a thin active-layer for the multicrystalline sili-con solar cell on a low-cost substrate.The company also developed the proc-esses for fabricating the sheets into cellsand modules. AstroPower developedtheir laboratory-scale process into con-tinuous sheet production capacity of 3.7 MW/year, exceeding their PVMaTgoal.

Energy Conversion Devices, Inc. (ECD),Troy, MI, produces modules made fromthin-film amorphous silicon. Under itsPhase 2A subcontract, ECD developed a deposition chamber to continuouslymanufacture rolls of films made frommultijunction amorphous silicon alloys.The chamber produces a uniform prod-uct, reduces gas utilization, improves

module throughput, and reduces theamount of floor space needed in manu-facturing plants.

ECD’s 4-ft2 modules have a stabilized efficiency of 8% (compared to 6% beforePVMaT), whereas a triple-junction cellusing this amorphous silicon technologydemonstrated a 9.5% efficiency this year.

ENTECH, Inc., Dallas, TX, manufacturesPV modules that focus sunlight ontolines of solar cells made from single-crystal silicon. Under its PVMaTPhase 2A contract, ENTECH completedfourth-generation improvements inmodule design begun under the pro-gram’s Concentrator Initiative. The company also improved productionprocesses to reduce material and laborcosts. ENTECH now offers fully testedand economically competitive concen-trator PV modules for small- and large-scale applications.

Mobil Solar Energy Corporation (nowASE Americas), Siemens Solar Indus-tries, Solarex Corporation, and UtilityPower Group completed their Phase 2Acost-shared projects in FY 1994.

The companies working under Phase 2Bimproved their manufacturing tech-niques and expanded capacity.

Golden Photon, Inc., Golden, CO, is devel-oping a new PV product based on mod-ules made from cadmium telluridematerial. Under its Phase 2B subcon-tract, the company is scaling up its advanced production techniques for its 2-MW manufacturing facility, whichbegan pilot operation this year.

AstroPower, Inc., received the prestigious R&D 100 award this year for its AP-225 solar cell,conceived and manufactured under PVMaT. The award was given because the AP-225 com-bines the performance and stability of conventional crystalline-silicon-based solar cells with thelow cost of sheet-material production. This Silicon-FilmTM product is nearly twice as large andtwice as powerful as conventional solar cells.

ENTECH’s concentrating PV system modified under PVMaT operates reliably for the Centraland Southwest Services utility in Ft. Davis, Texas.


Solar Cells, Inc. (SCI), Toledo, OH, is test-ing a high-volume manufacturing linefor PV modules made from cadmiumtelluride. Under its Phase 2B subcon-tract, SCI achieved a two-fold increasein the total module batch throughputduring the last year. These are 60-cm by120-cm pilot production modules. Theresearch results are being incorporatedinto the design of a 20-MW manufactur-ing line.

Solarex Corporation, Frederick, MD, increased the size of ingots and wafersunder its PVMaT contracts resulting ina 73% increase in capacity. A new wiresaw for cutting wafers from cast ingotssaves on material costs by reducing theamount of wafer that ends up as “sawdust.”

The two companies working underPhase 3A subcontracts made importantcontributions to the PV industry as awhole.

Spire Corporation, Bedford, MA, designs,fabricates, and markets automatedequipment for PV manufacturers. Underits Phase 3A subcontract, Spire devel-oped a machine that assembles and solders silicon solar cells into strings.Making cell strings is an important andtime-consuming step in producing PVmodules. The equipment can be pro-grammed to accommodate the moduledesigns of various manufacturers.

Springborn Materials Science Corporation,Enfield, CT, conducts chemical researchto develop new industrial products. Under a Phase 3A subcontract, Springborn scientists sought to under-stand the yellowing of ethylene vinylacetate (EVA), a substance used to encapsulate PV modules. Springbornalso developed two new encapsulantformulations that have resisted all visible yellowing. After 18 weeks intheir Xenon-Arc Weatherometer,

The SPI-Assembler 5000, developed under PVMaT by Spire Corporation, can reduce the costto assemble PV modules by a factor of 5 over manual assembly methods. Two U.S. manufactur-ers ordered this equipment in FY 1995.

The 1996 Summer Olympics aquatic center incorporates a 340-kilowatt PV system made by Solarex, as well as 9 kilowatts of ac modules in the visitors center. The project is cost-sharedevenly among the DOE, Georgia Institute of Technology, and Georgia Power.

Fiscal Year 1995 14

modules encapsulated in the new formulas showed no signs of yellowing,while modules enclosed in the standardEVA showed visible yellowing.

In FY 1996 Springborn will test their twonew formulations with PVMaT partici-pants. Ten manufacturers will preparetwo modules for each new formulationand one control module with the oldformula for a total of 50 modules. Thesemodules will be sent to Arizona StateUniversity for indoor and outdoor test-ing at the Arizona Public Service STARfacility.

Product-driven system andcomponent technologyPV modules represent about one half of the cost of a complete PV system. Sothe cost of electricity generated by PVcan be reduced by improving the otherelements of the system such as powerconditioning units and trackers.Phase 4A1 of PVMaT addresses the entire PV product and the integration of system components.

Selected from the more than 30 propos-als submitted to DOE for this phase ofPVMaT, the following companies and

their lower-tier contractors began workthis year.

Advanced Energy Systems, Inc., Wilton,NH, will design, develop, produce, and test prototype 10-kW and 50-kWinverters for stand-alone, hybrid, or utility-interactive applications. The company will then plan for pilot manu-facturing of these new products.

Ascension Technology, Inc., Billerica, MA,has been developing a module-scale inverter to convert the dc electricityfrom the PV module to ac at the module,allowing ac power to be used immedi-ately at the site or fed into the grid. Under its Phase 4A1 subcontract, Ascension Technology will work withASE Americas, also of Billerica, MA, to design, assemble, test, and certify acomplete system package for the acmodule.

Evergreen Solar, Inc., Sommerville, MA,will improve PV module materials andassembly methods to reduce costs asso-ciated with interconnection, moduleframing, and mounting the PV array.

Omnion Power Engineering Corporation,East Troy, MI, will develop a prototype

50-kW, three-phase power conversionsystem to specifications developed by a team of utility representatives. Reli-ability, conversion efficiency, and cost reductions will be achieved.

Solar Design Associates, Inc., Harvard,MA, has been developing an inverterfor the ac PV module under DOE’sPV:BONUS program. In Phase 4A1, the company will create a standard, certified, modular, ac PV system usingSolarex Corporation’s ac module.

Solar Electric Specialties, Inc., Willits, CA,will develop, test, and gain certificationfor two different system packages under its Phase 4A1 subcontract. Onepackage will be a pole-mounted stand-alone PV system without a generatorfor backup. The second will be a 1-kWPV system with a backup generator suit-able for off-grid applications.

Trace Engineering, Arlington, WA, willdevelop a 2-kW inverter to be used inparallel or in series, which will behighly efficient and low in price.

Utility Power Group, Chatsworth, CA,will design, fabricate, and test a track-ing PV panel with an integrated powerprocessing unit. These panels will thenbe incorporated into a 20-kW ac trackingarray that can be expanded in 20-kW increments.

Manufacturing researchand developmentFollowing Phases 2A, 2B, and 3A, theseadditional contracts for PV modulemanufacturing research and develop-ment were issued this year underPhase 4A2.

ASE Americas, Inc. (formerly Mobil Solar), Billerica, MA, will advance themanufacturing technology for the edge-defined, film-fed growth process devel-oped at Mobil Solar. The companyshould reduce wafer, cell, and modulecosts by at least 25 percent.

Phases of the PVMaT ProgramPhase 1A: Twenty-two companies identified projects to improve PV module manu-facturing. All subcontracts were completed in 1991.

Phase 2A: Beginning in 1992, seven companies carried out their recommenda-tionsfrom Phase 1 to make proprietary improvements and increase their manufacturingcapabilities.

Phase 2B: Four companies continue with projects similar to those of Phase 2A. These3-year subcontracts began in FY 1994.

Phase 3A: Two companies are addressing issues common to the PV industry as awhole. These subcontracts began in FY 1993.

Phase 4A1: This year eight companies began 2-year subcontracts to develop systemand component technology for PV products.

Phase 4A2: This year five companies began 3-year contracts to address proprietarymanufacturing issues to reduce costs and increase capacity of their module produc-tion facilities.


AstroPower, Inc., Newark, DE, will focuson each process component to manu-facture its large-area modules and solar cells made from Silicon-FilmTM

technology.

Iowa Thin Film Technologies, Inc., Ames,IA, will alter its manufacturing pro-cesses to increase throughput of amor-phous silicon deposition, laser-scribing,and welding processes to reduce costs.

Siemens Solar Industries, Camarillo, CA,will reduce crystalline silicon modulecosts with changes in module designs,material sources, and processes.

Solar Engineering Applications (SEA) Cor-poration, Santa Clara, CA, will reducemanufacturing costs through automat-ion and expanded production capacityof their line-focus concentrator modules.

■ModuleDevelopment:Improving thedurability of today’sand tomorrow’sproducts

The laboratories and personnel of thePV Program work with industry to develop better modules through testingand evaluation. Module testing at theDOE laboratories supports in-house research, as well as contracts for R&D,manufacturing, and system develop-ment. In addition, manufacturers sendtheir prototype modules scheduled forcommercial production to the laborato-ries to confirm their own test resultsand receive confidential test reports.

The durability of PV modules has increased over the years. Today, manu-facturers of crystalline silicon modulesoffer warranties up to 20 years on theirproducts, while some thin-film modulescarry 10-year warranties. This is a sig-nificant improvement over earlier gen-erations of PV products.

With megawatts of crystalline siliconPV systems in the field for more than adecade, inevitable signs of wear haveappeared on these earlier products. ThePV Program works directly with manu-facturers and with cooperative groupsin industry to understand the mecha-nisms of wear. They work to devisenew techniques and materials to pro-long the life of PV systems and improvenew products.

After crystalline modules are assembledthey are sealed against moisture anddust using a coating called an encapsu-lant. The encapsulant must withstandprolonged exposure to the sun’s ultra-violet radiation and the mechanicalstresses of temperature changes andprecipitation.

The PV Program is working with indus-try to understand and avoid problemsthat appear in about 2% of earlier gen-eration modules. The first problem—delamination—is partial separation ofthe encapsulant from the solar cells underneath. Performance can decline asmuch as 5% in delaminated modules,and if moisture accumulates inside themodule this could cause other problemsas well. The second problem—discolora-tion—can also reduce module perform-ance if the encapsulant allows less ofthe sun’s energy to pass through to thesolar cells.

When developing new encapsulants,both issues must be addressed. The PVProgram, through in-house analysesand cooperative research with PV com-panies, universities, and SpringbornMaterials Science Corporation, has beenevaluating the discoloration of the encapsulant ethylene vinyl acetate. Pro-gram researchers demonstrated thatchromophores generated during curingare a principal cause of the prematureyellowing of EVA. New curing tech-niques and new chemical formulas thatwill not discolor were developed. In FY1995 several new formulations for en-capsulants underwent accelerated test-

ing and have resisted yellowing. Thesewill be available to the PV industry inFY 1996.

The PV industry is also working coop-eratively to make modules more dura-ble. Delamination in crystalline siliconmodules is being explored by programresearchers, the Florida Solar EnergyCenter, Siemens Solar Industries, andSpringborn Materials Science Corpora-tion. For example, Sandia and the Florida Solar Energy Center measuredhow strongly the encapsulant adheredto cell interfaces on modules taken fromthe field. These adhesion tests were alsoperformed on small sections of modulessupplied by Siemens right off the assem-bly line. These and similar tests shouldhelp ensure that new encapsulant formu-lations have good adhering properties.

Another durability issue is the long-term integrity of solder bonds. Evalu-ations of old modules taken from thefield showed that solder bonds on thebacks of modules were cracking and becoming more resistive. As bondsslowly degrade, module performancedeclines until the circuit opens up andoutput stops. Metallurgy specialists areevaluating this failure mechanism—common in all electronic equipment exposed to temperature fluctuations—for recommendations in FY 1996 to improve durability.

The long-term durability of thin-filmmodules is being explored at the pro-gram’s outdoor test facility in Golden,CO, and by members of the PV industry.Program researchers have monitoredthe performance of prototype thin-filmtechnologies for up to 10 years. InFY 1995 temperature coefficients andtheir effect on output were explored andreported at the program’s PhotovoltaicPerformance and Reliability Workshop.In addition, research contracts with Solarex, Siemens Solar Industries, Colorado State University, and othershelp clarify durability issues and develop solutions.

Fiscal Year 1995 16

■ Balance-of-systems(BOS): Addressingthe other half of the PV system

Through a combination of in-houseR&D, testing, and cooperative researchcontracts, the PV Program is working toreduce the costs and increase the reliabil-ity of the non-module components ofthe PV system.

This year, the PV Program awarded several new contracts for balance-of-system (BOS) research and development,in addition to the work under PVMaTdirected at non-module components.The program also conducted tests onBOS components destined for projectsin federal agencies.

An important part of PV systems ispower processors and system controlhardware. PV Program testing of thesecomponents supports the industry in

general and several projects in particu-lar such as military installations, utilityprojects, and international projects. For specific projects, acceptance testingin the program’s unique laboratory ensures that power processors meetmanufacturers specifications. Once relevant specifications are met, the

hardware is shipped to the project forinstallation. Over the years programpersonnel will assess the reliability ofthe systems.

Hybrid systems—those containing twoor more electric-generating technolo-gies—are an important market for PVsystems. Integrating the components ofhybrid systems so that they work welltogether is a complex activity with littleoperating experience for designers todraw on.

The PV Program set up a test bed thatsimulates a small village. The test bed isused to test inverter performance andto develop control logic based on actualoperation. The set-up has lead-acid stor-age batteries, a diesel generator, and aPV array that feeds the system. The loadbank is programmed to simulate theweekly load profile of a small village.During tests, researchers work collabo-ratively with industry to evaluate resis-tive, reactive, non-linear, and transientloads (such as motors).

In FY 1995 tests were completed onlarge hybrid inverters from Abacus Controls and Omnion Power Engineer-ing Corporation, as well as on a numberof smaller grid-tied, hybrid, and stand-alone inverters.

Battery tests sponsored by the PV Program at Sandia Laboratories helped define appropriatecharge and set points and predict battery maintenance intervals in PV systems.

An array structure that moves the PV modules to follow the sun can increase annual energycapture by 30 percent. This microprocessor-based controller called SolarTrak was developed bythe PV Program and is licensed for use in several commercial PV products.


The PV Program is also working to coordinate information among makersof charge controllers and batteries to improve reliability and lower costs.Charge controllers are electronic devicesthat control how the battery in a PV sys-tem is charged. The way charge control-lers operate has a significant effect onthe life of batteries. Charge controllersmust be durable and responsive, andthey must integrate a controller logic appropriate to the unique operating environment of the PV application. Thisyear the program completed the secondround of testing with Digital Solar Tech-nologies for a microprocessor-based PV charge controller destined for use in large PV telecommunications sys-tems. In another project, Morning StarCorporation developed a pulse-widthmodulated charge controller that willcost less than $30 for use in small PVsystems up to 10 amps at 12 volts.

The PV Program works with manufac-turers of charge controllers to improvehow they operate. In addition to severalresearch contracts, the program testscharge controllers with equipment thatmost manufacturers do not have. Theprogram documents the behavior of batteries when they are charged by PV.Test results should help improve thisimportant part of the balance of systemsfor PV.

Other BOS products were developed forthe program under contract this year.For example, Trojan Battery in conjunc-tion with Sandia designed a deep-cyclebattery with 40% more electrolyte. Moreelectrolyte means less frequent batterymaintenance in PV applications. In another project, Mor Lite designed amore-efficient ballast and fixture for PV lighting systems. Lighting systemsdesigned specifically for PV-poweredbatteries perform better than those designed for other applications.

Fiscal Year 1995 18

Systems Engineering and ApplicationsThe PV Program supports projects that validate PV technology for world markets.

Through systems engineeringactivities, the PV Program works with industry to address design issues, meas-ure the performance of emerg-

ing technologies, and develop standardsand certification programs. Applicationsresearch deploys prototype PV tech-nologies to validate their performancein specific applications.

■ SystemsEngineering:Objectivemeasurements and standards

Systems engineers and analysts in thePV Program evaluate power and energyproduction, to support industry andDOE cooperative research and technol-ogy development contracts.

This year, a major addition to the pro-gram’s laboratory capabilities went intooperation—the Outdoor Test Facility(OTF). This building is designed specifi-cally to serve the testing needs of PVProgram researchers and industry. Thefacility has state-of-the-art equipmentfor controlled indoor testing and meas-urements. In addition, researchers in theOTF monitor module and system experi-ments conducted at the adjacent fieldsite. Underground cables for data acqui-sition connect the test area to the OTFcontrol room. Researchers can performaccelerated and exploratory tests andmeasurements.

The OTF has several new capabilitiesfor the program. For example, bettermodule diagnostics and failure analysisare possible with all the tests performedunder one roof. The OTF also has large-area simulators that apply pulse or continuous light sources to modules.Modules up to 6-ft by 8-ft, small panels,and even arrays can be operated undersimulated conditions and their perform-ance evaluated.

The amount of energy a PV module generates during a period of time atvarying conditions may be more impor-tant to the user than the peak power ratings currently furnished. The PV Pro-gram has subcontracts with EndeconEngineering of San Ramon, CA, to help

develop a module energy-rating methodthat will lead the industry to consensuson this issue.

Measuring the output of commercialmodules at Sandia’s outdoor test facilityhas led to a system characterizationmethod of potential use to owners oflarge PV systems. The new system char-acterization model, which began valida-tion testing in FY 1995, can predictenergy output for a specific PV systemat a specific site, using inputs for timeof day, measured temperature, andmeasured irradiance. After further vali-dation testing in FY 1996, this tool willbe used by the military to monitor theirPV systems installed under the Strate-gic Environmental Research and

At NREL’s Outdoor Test Facility, photovoltaic modules and systems made by various manufac-turers and using various technologies are tested and monitored under actual weather condi-tions, as well as under controlled laboratory and accelerated weathering conditions.


Development Project and by utilities installing systems with the Utility PhotoVoltaic Group.

Standards of performance for PV sys-tems can help establish consumer confi-dence. The experts in the PV Programare an important resource to organiza-tions developing standards and codes.DOE’s Third Photovoltaic Standardsand Codes Forum brought together com-mittees from several standards groups,enabling them to complete several important projects. For example, repre-sentatives from PV manufacturers, utilities, and research and testing labora-tories reached consensus on standardprocedures for module qualification test-ing. This standard, when approved bythe Institute of Electrical and ElectronicsEngineers (IEEE), will serve the PV industry as the U.S. standard. Otherworkshop attendees completed a majorrevision of the American Society forTesting and Materials standard for meas-uring module and array performance.

The PV Program staff developed a draftprocedure for determining system rat-ings and acceptance this year. At presentthere is no U.S. laboratory accredited tocertify the performance of PV systems.U.S. manufacturers have had to go over-seas for this service.

In addition, the PV Program supportedArizona State University to developguidelines for accrediting laboratoriesto certify PV module performance. Theeffort also generated criteria for certify-ing PV modules. The report publishedthis year, Photovoltaic Module Certifica-tion/Laboratory Accreditation Criteria Development, recommends the testing required for a module design to be certi-fied, the criteria for accrediting a testlaboratory, and a model for a U.S. PVcertification program.

Another form of certification, Under-writers Laboratories (UL) listing, of PV

products is an importantstep in an expanding market-place. The PV Programworked with Omnion PowerEngineering Corporation togain UL approval for its 4-kW inverter. UL does notcurrently have a standard for testing PV concentratortechnologies. Sandia, manu-facturers, and UL staff areworking to develop a teststandard based on UL’sstandard for flat-plate mod-ules and Sandia’s concentra-tor test document.

PV Program specialists arealso working with variousstandards groups. For example, the IEEE Guide forTerrestrial PV Power Systems Safety is being written for single-phase and three-phase systems up to 50 kW in size. Others include IEEE Recommended Prac-tice for Determining Performance Charac-teristics and Suitability of Lead-AcidBatteries in PV Systems, IEEE Recom-mended Practice for Field Test Methods andProcedures for Grid-Connected Photovoltaic Systems, and National Electrical Code.Consensus standards will help PV com-panies demonstrate product perform-ance and durability, especially for utilitymarkets. The National Electrical Codefor acceptance of systems is importantfor building inspectors and electrical inspectors to approve PV system installations.

■ PhotovoltaicApplications:Validating PVtechnologyworldwide

The PV Program works with industryand potential users of PV systems tovalidate the benefits of PV in specific applications. This year projects withutilities, federal agencies, the buildings

industry, and foreign governments generated information neccessary toexpand these markets for U.S. PV prod-ucts. Several follow-on projects promiseadditional benefits for the domestic PVindustry.

PV for utility applicationsElectric utilities represent a large exist-ing market for PV systems, and the potential for future utility applicationsfor lower-cost systems is tremendous.

Activities continued in FY 1995 aimed atdeveloping sustainable markets for bothgrid-connected and grid-independentPV applications of benefit to electricutilities and their customers. In one ofthese activities, Southern CaliforniaEdison installed PV to relieve the stresson overburdened circuits in residentialneighborhoods.

To avoid upgrading an overloaded circuit, Southern California Edison installed a pilot project on MontereyHills Elementary School this year. In FY1996, the utility plans to install PV at three other public buildings. In all,the utility expects to install 500 kW ofPV under its Solar Neighborhood

Utility planners were surprised that PV made the mostsense in certain older residential areas with overloaded underground circuits. Installing PV at Monterey Hills Elementary school made digging up and replacing overburdened circuits unneccessary.

Fiscal Year 1995 20

Program, with support from DOE. Theprojects will all be monitored and asses-sed so that the benefits of this applica-tion can be evaluated by other utilities.

Another California utility, the SacramentoMunicipal Utility District, installed PVprojects totalling 934 kW in FY 1995 aspart of a multiyear DOE commercializa-tion effort for grid-connected PV. Threerooftop PV projects and three systemsat utility substations began operationsthis year. A project review committee ensures that information on the systemis collected and eventually dissemi-nated to other utilities.

Utility PhotoVoltaic Group (UPVG)

In 1992, a group of utilities particularlyinterested in PV and its potential forlarge-scale power generation formedUPVG to accelerate cost-effective PV applications to benefit electric utilitiesand their customers. Its members nowinclude nearly 90 utilities, the ElectricPower Research Institute of Palo Alto,CA, as well as the American PublicPower Association, the Edison ElectricInstitute, and the National Rural Electric Cooperative Association, all ofWashington, D.C. Collectively, the mem-ber utilities of UPVG represent morethan 40% of total U.S. electricity sales.The activities of UPVG are fundedthrough membership fees and a grantfrom DOE’s PV Program.

For FY 1996, UPVG plans to supportthirteen grid-connected PV applicationsprojects. These projects are designed tovalidate PV in a variety of utility appli-cations. Data from the projects will bewidely circulated to promote furtherinstallations of PV by utilities.

Several other activities, supported inpart by DOE, are promoting deploy-ment of photovoltaics. The National Association of State Utility ConsumerAdvocates directs a Photovoltaic Education Project. The Pace UniversityLaw School conducts Renewable EnergyTechnology Analysis aimed at quantify-ing the indirect benefits of PV such asavoiding harmful emissions and increas-ing utility system reliability. And thePV4U state working groups bring together diverse organizations within astate to influence legislation, encourageutilities to consider PV, and provide information to decision makers.

PV for Utility-Scale Applications(PVUSA)

Early in 1986, several utilities, DOE, astate government, and some local gov-ernments joined together to install, oper-ate, and monitor PV systems connectedto a utility grid. So far, the PVUSA pro-gram has purchased and installed morethan 1,700 kW of PV at test sites aroundthe country. PVUSA operates a maindemonstration site in Davis, CA, wheresystems using state-of-the-art moduletechnologies and utility-scale systemsfeed electricity into the grid. Several additional PVUSA systems are operatedat host utilities across the country.PVUSA also cooperatively monitorsother PV systems of utility interest.

In 1995 the PVUSA project continued todemonstrate new module technologyfor utility-grade PV generating systems.A new 10.8-kW system using cadmium

A 6-year program to install PV at these locations has been proposed by the Utility PhotoVoltaicGroup for cost-sharing with the U.S. Department of Energy. TEAM-UP stands for TechnologyExperience to Accelerate Markets in Utility Photovoltaics.

“The utility industry ischanging and utilities arelooking for new businessopportunities in this morecompetitive environment.Photovoltaics provides oneof these opportunities.”

— Christine A. Ervin, Assistant Secretary for Energy Efficiency and RenewableEnergy, U.S. DOE.


telluride thin-film technology was sup-plied by Solar Cells, Inc., to the Davisdemonstration site. In addition, two sys-tems incorporating concentrator tech-nologies were installed in 1995 underPVUSA. A high-concentration (260x) PV array nominally rated at 19 kW wasinstalled at Davis by Amonix Corporation,Torrance, CA. Central and SouthwestServices, a utility in Ft. Davis, TX, alsopurchased a 21x linear concentrator system from ENTECH Corporation ofDallas. The nominal 83-kW system willbe monitored as a PVUSA system.

PVUSA installed the first PV system tovalidate grid-support at the Kermansubstation near Fresno, CA, in 1993.Electricity from the nominal 498-kW PVsystem helps offset afternoon peaks inelectrical demand at the substation andeffectively reduces the load on the sub-station. The data from this test havebeen combined with later grid-supportapplications of PV to show utilities howthis application could benefit their activities.

Developing tools for utilities

In FY 1994, PV Program analysts concluded a five-utility study on the potential for distributed PV. From theirextensive calculations, the analysts developed a simplified technique to determine where PV has value in a dis-tributed application such as grid sup-port or preventing voltage sag at theend of long lines. Whereas each of the

original studies required months of effort from several experts, the newQuickScreen technique can be per-formed by one person (with access tothe utility’s basic economics) in half aday. An experienced user can performa QuickScreen analysis in less than anhour.

The simplified analysis was performedfor the original utilities studied, and theresults varied by less than 10% from the

original analyses. About 40 utilities arenow using the prototype version ofQuickScreen. After fine-tuning in lightof utility comments, QuickScreen willbe available in FY 1996 to utilities inter-ested in distributed applications of PV.

PV for federal agenciesBy assisting other federal agencies intheir PV projects, DOE effectively lever-ages its funding to achieve wider oppor-tunities for validating PV technology.Technical assistance from the PV Pro-gram promoted 25 projects this year,paid for with funds from other govern-ment agencies.

In FY 1994 , the National Park Serviceand DOE collaborated to assess how PVwas being used in the parks, how wellit was performing, and where more PVmade sense. In FY 1995, several projectsidentified during the study as havinghigh value and low obstacles were well

Two new PV arrays from Solar Cells, Inc., and Amonix Corp., were added to the PVUSA test facility at Davis, CA, this year.

The PV Program evaluated the match between actual utility load and the projected output of aPV system for more than 40 utilities across the United States. This map shows the distribution ofthe effective capacity of PV in the United States, assuming a 2-axis tracking system and 2% PVpenetration into the utility grid.

Fiscal Year 1995 22

under way. For example, PV Programpersonnel assessed the Chaparral areaof Pinnacles National Monument inCalifornia. They recommended a hybridPV system, high-efficiency loads, andconservation to reduce existing electricalloads. DOE then assisted in specifying a10-kW PV-engine hybrid system, whichincludes a 20-kW propane generatorthat will replace two 100-kW diesel gen-erators and eliminate the use of dieselfuel at Chaparral.

In FY 1996, twelve more pilot projectsare planned for parks, including GrandCanyon, Rocky Mountain, and YosemiteNational Parks.

The U.S. Forest Service also has manyPV systems operating at its facilitiesacross the country. After a survey simi-lar to the one conducted for the parks iscompleted, pilot projects to expand theuse of PV by the Forest Service will getunder way in FY 1996.

The U.S. Bureau of Land Management,an agency that administers 12% of thetotal U.S. land area, is expanding recreational facilities on its lands. These

facilities will require power. To help ensure that some of that power is gener-ated with the sun, PV Program person-nel will survey more than 60 districts in13 state offices. As withthe parks and forests, the project with the Bureau of Land Man-agement aims for pilotprojects that expand theways in which PV isused in the agency.

The military, as anagency with a potentialof more than 3000 MW ofpossible projects, is ahuge market for PV sys-tems. Sandia engineers,who also work in the PV Program, are assist-ing the military in install-ing PV systems for theStrategic Environmental Research and Develop-ment Project (SERDP).This project, which hasidentified cost-effectiveapplications of PV within

the military, is funded cooperatively bythe Environmental Protection Agencyand the Department of Defense.Through SERDP, Sandia is helping theU.S. Marine Corps, Navy, and Air Forceto specify, design, and install large (75-kW to 300-kW) PV systems at mili-tary bases around the country.

PV integrated intobuildings Buildings consume nearly two-thirds ofthe electricity generated in the UnitedStates, and there are many ways thatPV technology can provide some of thiselectricity. In addition to large generat-ing stations located in rural areas, PVcan be incorporated right into buildingstructures to generate electricity for usein the same buildings. Promoting the interaction of industries to develop PVbuilding products is the goal of DOE’sBuilding Opportunities in the U.S. forPV, or PV:BONUS.

PV Program personnel, working with several other agencies and U.S. PV companies, arrangedfor this PV array to help power the National Christmas Tree during the Pageant of Peace in FY1995. Thousands of visitors witnessed the system’s operation during the festival.

The shingle modules developed under PV:BONUS by EnergyConversion Devices, Inc., blend so well with conventional roof-ing that they can be used on new homes where covenants would prohibit more typical PV modules.


Under PV:BONUS, teams are workingto develop PV products for buildings.Each team contains several organizationsrepresenting groups like building materials manufacturers, building con-tractors, PV suppliers, utilities, colleges,system designers, architecture and engi-neering firms, and building owners.The objective of these efforts is to develop products that will introduce PVinto markets other than conventionalground- or roof-mounted systems.

For example, PV systems that double as electrical generators and roofing material have extra value to the buildingowner. One PV:BONUS team, led by Energy Conversion Devices, Inc. (ECD),is developing flexible, lightweight roof-ing materials and has tested a PV shin-gle that can replace asphalt shingles.The shingle module is being installedon a house being built for the 1996 SummerOlympics in Atlanta, GA, by United Solar Systems Corp., ECD’s joint ven-ture partner.

Another project, led by Fully Indepen-dent Residential Solar Technology, Inc.(FIRST), of Hopewell, NJ, focuses on incorporating PV products into the increasingly popular modular, manu-factured house. Modular houses areconstructed in a factory and assembled

at the building site. The PV:BONUSteam incorporated PV systems into twoprototype modular homes in FY 1994.In FY 1995, the first six PV modularhomes were built and sold, each locatedin a different utility service area innortheastern states. In FY 1996, ninetownhomes will be designed and con-structed in a low-income housing project in Philadelphia. Work also con-tinues to develop new roof-integratedmodules for this application.

Today’s PV modules produce direct current (dc) electricity, which must beconverted to alternating current (ac) forbuildings connected to utility power.The need for this conversion compli-cates building design and adds cost.Therefore, a PV:BONUS team, led by Solar Design Associates, is applying advances in power electronics and inte-grated circuits to deliver utility-gradeac power from the back of individualPV modules. The team tested five ofthese prototype PV devices in FY 1995.In FY 1996, 9 kW of ac modules will beinstalled at the entrance to the aquaticcenter for the 1996 Summer Olympics.The ac module team will continue itswork to reduce the cost of the productunder a PVMaT manufacturing contract.

PV for internationalapplicationsIn 1994, more than 75% of this country’sPV production was exported. The export market, mostly in developingcountries, is the fastest-growing PV mar-ket today. And much of this market willbe for the more than 2 billion peoplecurrently living without electricity.Often these people require only smallamounts of power for indoor lighting,water pumping, and refrigeration.Building or extending the electric gridor providing power by other meanssuch as with diesel generators is not eco-nomical in these cases. Even at today’sprices, PV can be the most cost-effectivesource of electricity, once organizationsfor its sale, installation, and mainte-nance are in place. The PV Programsponsors activities to validate PV tech-nology and to establish the organiza-tional and institutional connections forthe sale, installation, and maintenanceof U.S. PV products.

South Africa

South Africa has been identified as oneof the 10 largest emerging markets forU.S. PV exports. Because a main obsta-cle to development in South Africa is energy distribution to remote regions,and because sunshine is the area’s mostabundant resource,photovoltaics has abright future there. In 1995, that futureseemed closer than ever as Energy

This manufactured home, designed by FIRST, Inc., was assembled at the site with all features inplace to accommodate the PV system.

“[This PV module assemblyplant] means jobs for South Africans as well asAmericans who are a part of these joint ventures.”

— Energy Secretary Hazel O’Leary,at the dedication of Suncorp Manufacturing in Johannesburg, South Africa.

Fiscal Year 1995 24

Secretary Hazel O’Leary helped dedi-cate a PV module assembly plant in Johannesburg.

The joint venture will begin by produc-ing almost 5,000 modules in its firstyear, using solar cells manufactured inthe United States. And besides themanufacturing jobs, the venture will create 250 jobs in marketing, sales, installation, and maintenance in SouthAfrica. The PV Program played a keyrole in bringing this PV module assem-bly plant on line by providing projectmanagement, logistical support, andtechnical guidance to the project.

Brazil

The Federal Republic of Brazil and DOEbegan working together in 1993 to bringelectricity to rural communities in Brazil by installing PV systems. In thefirst phase of this pilot project, Brazilianutilities in two states and the nationalministry of energy (known as CEPEL)installed PV lighting systems in 750homes and 14 schools in rural northeastBrazil. The local utilities maintain andevaluate the systems.

After utilities in five additional statesasked to participate in the project, DOEand CEPEL expanded the electrification

program into the northeast and Amazonregions of Brazil. Phase 2 projects include additional applications such aswater pumping, telecommunications,and refrigeration. Furthermore, two vil-lage power systems are being installedthat use more than one source of power,from PV, wind, and diesel fuel, for example. The village power systemshave a large enough capacity to supply the minimal electrical needs of a smallvillage.

Mexico

Studies suggest that within the next12 years Mexico will require 28 giga-watts of new electric power generation.Today, some 100,000 rural villages in Mexico have no electricity, and extend-ing the electric grid to these villageswould be very costly. The PV Programis working with the U.S. Agency for International Development and severalMexican states to share the cost of PV pilot projects for important applications.For example, in the state of Sonora, the PV Program will provide technicalassistance for agricultural water pump-ing projects. In the state of Chihuahua,DOE will share the cost of projects forwater pumping, irrigation, refrigeration,ice making, communications, and facil-ity power. In addition, Sandia is work-ing with the World Wildlife Fund,Conservation International, the NatureConservancy, and local Mexican organi-zations on pilot projects to demonstraterenewable energy in environmentallysensitive areas and for the buffer-zonecommunities around them.

In a joint venture between Spire Corporation of Bedford, MA, and Suncorp Manufacturing, ablack-owned South African business, an assembly plant was constructed that produces enoughPV modules in one year to light 30,000 homes in South Africa.

In Cacimbas, Ceará, Brazil, 50-watt PV systems provide homes with electricity for fluorescentlighting.


India

Last year, a presidential mission to India resulted in more than $1 billion incommercial deals for the U.S. PV indus-try and several major governmentalagreements. This year, two follow-onmissions boosted the number of agree-ments between U.S. and Indian compa-nies even more.

In addition to commercial agreements,DOE and the Indian Ministry of Non-Conventional Energy Sources (MNES)identified several rural electrification initiatives for PV use. The first two gotunder way in FY 1995. DOE is procur-ing PV systems from U.S. vendors for water pumping, street lighting, homelighting, and solar lanterns headed forDhanawas, Haryana. In the second pro-ject, DOE will buy more than 300 PVlighting systems, as well as systems forrefrigeration, spice grinding, waterpumping, and battery charging to be deployed in Sudarbans, West Bengal. In Sudarbans DOE is working with theRamakrishna Mission—a well-respectedhumanitarian organization—that willsupport the installation and mainte-nance of the systems.

These projects will validate U.S. PV tech-nology to provide electrical power tovillages. For these applications, the tech-nology, structures for installing andmaintaining systems, and methods ofcollecting revenues from users will allbe validated. Information on the projectwill be presented to agencies, such asthe World Bank, that are in a position tofinance additional projects.

Russia

A new partnership got under way in1995 between the U.S. government, U.S. private industry, and a Russianstate enterprise. The partnership willsoon have Russian scientists and engi-neers using their talents to make solarmodules instead of military equipment.The PV Program is providing technicalassistance to help start up a photovoltaic

manufacturing plant in Moscow. TheSovlux facility, owned jointly by EnergyConversion Devices of Troy, MI, and Scientific and Industrial EnterpriseKVANT of Moscow, will make thin-filmamorphous silicon modules.

The project is part of a joint DOE andU.S. Department of State program tohelp Russian scientists and engineersapply their expertise to non-military applications having commercial benefit.With financing from KVANT, EnergyConversion Devices designed and builtthe plant in Michigan, then shipped itto Moscow for construction in 1993.However, when the Soviet Union wasdisbanded, funding ran out before thefacility became operational.

To get the facility on line, the PV Pro-gram awarded KVANT a 7-month contract in FY 1995 and signed a coop-erative research and development agree-ment (CRADA) with Energy ConversionDevices, with funding from the jointDOE/Department of State program. Under the CRADA, PV Program person-nel will provide technical assistance forthe start-up. For example, the first mate-rials, cells, and modules to be producedwill be sent to the United States andsubjected to the sophisticated testingavailable only in the national laborato-ries. Results will help factory engineersadjust the equipment to produce thehighest-quality product possible.

By 1996, the factory should be able toproduce up to 2 MW of solar modulesannually for sale in Russia and the surrounding republics. And EnergyConversion Devices, a U.S. company,will reap 50% of the benefit of this potentially huge market, thanks to a little push from DOE and the State Department.

The above examples highlight some of the PV Program efforts to facilitateoverseas markets for U.S. PV products.Various efforts are also under way topromote PV projects in China, Egypt, Indonesia, and Central and South America.

These activities—aimed at improving PV systems and enhancing the marketsfor PV in utilities, federal agencies, andinternational applications—are part ofDOE’s balanced strategy to make PV animportant part of the U.S. economy.

Program activities continue to advancethe technology base through researchand development. Advances and inno-vations are incorporated into new prod-ucts through technology development.And systems engineering and applica-tions activities help validate PV technol-ogy for expanding markets. Continuingefforts in FY 1996 will maintain the momentum and continue progress oneach of these fronts.

The World Bank Many energy projects have been financed in developing countries and, increas-ingly, renewable energy projects are gaining the attention of lenders at the World Bank organizations. The International Bank for Reconstruction and Development (World Bank) has issued loans in excess of $300 billion to govern-ments and government agencies, supporting more than 6000 development pro-jects in about 140 countries. The International Finance Corporation, a member of the World Bank group, finances private-sector projects in developing countriesthrough syndication and equity investments in projects.

Information is a valuable asset for lenders and borrowers alike, and the PV Pro-gram works with units of the World Bank and organizations within borrowingcountries to clarify the technical status, costs, and benefits of U.S. photovoltaictechnology. For example, PV Program personnel are contributing to a study of renewable energy in China conducted by the World Bank in partnership with the State Economic and Trade Commission and the Energy Research Institute of the State Planning Commission in Beijing. Meanwhile, a Memorandum of Understanding is being developed between DOE and the World Bank for analy-ses of many renewable energy technologies being considered for developingcountries.

Fiscal Year 1995 26

Program ResourcesThe PV Program distributes funding within theprogram elements and supports the U.S. PV industry through the researchers and facilities of the national laboratories.

The resources of the federal PV Program are available to the U.S. PV industry to advance its products. The PV Program directs research

at the National Renewable Energy Laboratory and at Sandia NationalLaboratories. Brookhaven NationalLaboratory in Upton, NY, supports theprogram in environmental, safety, andhealth research, while DOE field officeshelp manage research contracts.

■NationalRenewable EnergyLaboratory

The National Renewable Energy Laboratory (NREL) in Golden, CO, wasestablished by Congress as the nation’sprimary center for renewable energy research and development. NREL staffmembers are responsible for most of thefundamental, supporting, and materialsresearch conducted under the program.Module and systems engineering anddevelopment, in collaboration with industry, and applications and marketdevelopment are other important activities.

NREL manages PV-related R&D activi-ties conducted in house and throughsubcontracts with universities, other research centers, and both small andlarge businesses. These activities includecost-shared, multiyear government-industry partnerships, national team-research efforts, and technologyinitiatives.

Research teams investigatea wide variety of promis-ing semiconductor materi-als and devices, and basicresearch at NREL includesinvestigations that explore the physics governing the behavior of solid-state photovoltaic materials.NREL’s scientists also support the PVProgram with device measurements,cell modeling and fabrication, and char-acterization of materials and devices using advanced measurement equip-ment and techniques.

NREL also conducts simulated and actual outdoor tests on cells, modules,and arrays for industry. Test data help toimprove PV devices and modules andto develop performance criteria andstandards for the PV industry. Solar radiation data are compiled to help cre-ate computer models, which are criticalto designers and manufacturers of solarsystems, and instrument calibrationsare provided in accordance with national and international standards.

■ Sandia NationalLaboratories

Sandia National Laboratories in Albuquerque, NM, is a multiprogramR&D laboratory of the U.S. Departmentof Energy. Sandia is responsible for addressing the technical aspects of national security issues, which includeenergy-supply security and weapons research and engineering. It has thebroadest range of energy-related R&Dactivities, gathered at one laboratory, in

the nation; Sandia’s researchers workon solar, wind, fossil, geothermal, andnuclear energy technologies.

Under the National Photovoltaic Pro-gram, Sandia is principally responsiblein assisting industry in developing crystalline silicon cells, concentratingcollectors, and systems and balance-of-systems technologies. Although theseactivities vary greatly in scope, the em-phasis in each is to work with industryand users to accelerate the developmentand acceptance of PV technologies.

These R&D activities are designed tohelp the industry develop cost-effectivecommercial products more rapidly thanit could alone. Cell research activitiessupport promising new concepts andprovide valuable services through thePhotovoltaic Device Fabrication Labora-tory. Indoor and outdoor measurementand evaluation facilities support indus-try in the measurement, evaluation, andanalysis of PV cells, modules, and systems.

Systems-level work at Sandia concen-trates on applications engineering, sys-tems engineering and performance, andtechnology assistance to overcome theremaining technical and institutionalbarriers to full market acceptance of PV technologies. Sandia’s Design Assis-tance Center distributed more than17,000 technical assistance publicationsin FY 1995.

The distribution of the National Photovoltaic Program budgetfor FY 1995.


NOTICE: This report was prepared as an account of work sponsored by an agency of the UnitedStates government. Neither the United States government nor any agency thereof, nor any of theiremployees, makes any warranty, express or implied, or assumes any legal liability or responsibilityfor the accuracy, completeness, or usefulness of any information, apparatus, product, or process dis-closed, or represents that its use would not infringe privately owned rights. Reference herein to anyspecific commercial product, process, or service by trade name, trademark, manufacturer, or other-wise does not necessarily constitute or imply its endorsement, recommendation, or favoring by theUnited States government or any agency thereof. The views and opinions of authors expressedherein do not necessarily state or reflect those of the United States government or any agency thereof.

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Documents

Photovoltaic Energy Program Overview, Fiscal Year 19951 Photovoltaic Energy Program Overview 1995 PV Program Accomplishments Research and Development Refined and continued to transfer