CPV technology is quite different fromthe flat-plate PV modules soldaround the world. CPV units come in

larger module sizes (typically 20 to 35 kW),track the sun during the day, and are moresuitable for large installations. In 2004, lessthan 1 megawatt (MW) of concentrator PVsystems was installed, out of a total worldPV market of 1200 MW. Admittedly, 1MW does not constitute significant marketentry. However, the significant developmentis an increased number of projects with sizesof several hundred kilowatts (kW), creating

a market appropriate for CPV technology.And CPV technologies are ready today forthis market opportunity with high-efficien-cy solar cells and well-developed hardware.But it is the near-term prospects for evenbetter performance and lower installed sys-tem costs that are leading to real marketentry during 2005 and 2006.

Amonix, Inc., of Torrance, California,spent more than 15 years developing fivegenerations of CPV prototypes that led tothe products most recently installed inArizona by Arizona Public Service (Figure 1)

and in other southwestern U.S. locations[Amo 2005]. Recently, Amonix announceda joint venture with Spain's Guascor, whowill build a 10 MW per year assembly plantin Spain by the end of 2005. Amonix alsoplans to install 3 MW of CPV in the south-western United States, while Guascor plansto install 10 MW of CPV systems in Spainin 2006. This market is made possible bySpain's new feed-in tariffs and long-termcontracts that attract investors wanting tomaximize the kilowatt-hours generated fortheir invested project dollars. As we shalllearn below, this is an attribute of the newCPV technologies.

Similarly, Solar Systems Pty Ltd., ofHawthorn, Australia [Sol 2005], spent morethan 15 years developing several generationsof their CPV prototypes that led to recentinstallations on aboriginal lands in Australia,part of a market served by large diesel gen-erating plants with high transportation costsfor the diesel fuel (Figure 2). The companyplans to install more than 5 MW in 2006.Indeed, the growth from

1471 0846/05 © 2005 Elsevier Ltd. All rights reserved. July/August 2005 reFOCUS 35

After more than three decades of exploring a dizzying variety ofways to concentrate sunlight onto solar cells with mirrors orlenses, Concentrator photovoltaics (CPV) technologies are finallyentering the market - a market for 100 kW systems and larger.Robert McConnell, Sarah Kurtz, and Martha Symko-Davies fromthe U.S. National Renewable Energy Laboratory (NREL) report onrecent market prospects and new record CPV cell efficiencies thatportend the emergence of CPV systems in the next 2-5 years atinstalled system costs of $3 per watt.

CONCENTRATORPHOTOVOLTAICTECHNOLOGIES

Solar

Review and Market Prospects

Figure 1: Several 35-kW Amonix modules installed in an Arizona Public Service power plant. Thepickup truck underneath the module gives an idea of the scale.

Further informationContact: Robert McConnell, HighPerformance Photovoltaics Project,National Center for Photovoltaics,National Renewable EnergyLaboratory, 1617 Cole Blvd.,Golden, CO 80401-3393, USA. Tel:+1 303 384 6419; Fax: + 1 303384 6481; E-mail:robert_mcconnell@nrel.gov

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1 MW of CPV in 2004 to some 18 MW in2006 legitimately constitutes market entryfor this technology. In the words of VahanGarboushian, president of Amonix,"Concentrating solar electric power is on thecusp of delivering on its promise of low-cost, reliable, solar-generated electricity at acost that is competitive with mainstreamelectricity generation systems."

Latest developments Today's concentrator PV systems use siliconsolar cells having conversion efficienciesroutinely above 26% under concentration.In 1994, Amonix received the prestigious"R&D 100" award in the United States forthe world-record performance of a commer-cial silicon solar cell with an efficiencygreater than 26.5% under concentration.Unlike Amonix, Solar Systems Australiadoes not make its own silicon solar cells.Rather, it purchases its silicon concentratorcells from SunPower, of Sunnyvale,California [Sun 2005]. These commercialsolar cells also have efficiencies of about26% under concentrated sunlight. As a sub-sidiary of Cypress SemiconductorCorporation, SunPower recently entered theconventional flat-plate PV market with aback-contact product based on their exten-sive experience in concentrator solar cells.Without question, silicon solar cells are thebasis for today's market entry of well-devel-oped CPV systems. Looking forward, theultra-high-efficiency solar cells developedfor space satellites are causing new andincreasing excitement among investors andproject developers.

At a May 2005 international concentratorPV conference in Scottsdale, Arizona,NREL scientists announced that their mul-tijunction solar cell group had confirmed anew solar cell record efficiency of 37.9% at10 suns [Wan 2005]. And one month later,Spectrolab Inc., a Boeing company inSylmar, California, announced at theEuropean PV Solar Energy Conference andExhibition in Barcelona, Spain, that theyhad surpassed the NREL record with a cellshowing 39.0% efficiency at 236 suns [Mc2005, King 2005] (Figure 3). This ultra-high-efficiency technology was initiallydeveloped at NREL, funded in part byNREL and the U.S. Department of Energy,and successfully implemented by Spectrolab

in the 1990s for space satellites [Spe 2005].At the conference in Arizona, Dr. NasserKaram, vice president of AdvancedTechnology Products at Spectrolab, summa-rized the progress [NREL 2005], "Today, weare capitalizing on the major investmentsmade by the space satellite industry andreducing the cost of the semiconductor solarcell by 2-3 orders of magnitude by operatingthe cells under high sun concentrations, typ-ically 300 to 1000 times. Boeing-Spectrolaband NREL have demonstrated over 37%efficient concentrator solar cells, and fieldtesting of Spectrolab's cells for over one yearwith no degradation promises a brightfuture. We expect concentrator solar cellperformance to reach or exceed 40% by2006 and anticipate continued enhance-ment in performance and reliability."

Dr. Raed Sherif, director of PVConcentrator Products at Spectrolab, added[NREL 2005], "We are working closely withPV concentrator manufacturers to ensuretheir success and expedient deployment ofthe multijunction PV concentrator cells."Concentrator PV companies and their cus-tomers are beginning to comprehend thesignificance of these achievements. DaveHolland, CEO of Solar Systems Australia,emphasized [NREL 2005] that his compa-ny, with "…experience gained frominstalling and operating reliable PV concen-trator systems over the last decade, com-bined with its strong relationship withSpectrolab Inc., a leading manufacturer ofmultijunction solar cells, is poised to make amajor step towards being a mainstreampower producer." He added, "The new solarcell technology from Spectrolab will enableus to upgrade our systems from 24 kW to 35kW - a 46% increase in output." ArizonaPublic Service (APS) has been a pioneeringutility in deploying and evaluating a varietyof solar electric technologies. It has installedmore than 3 MW of flat-plate PV since1997 in a variety of applications employinghorizontal and tilted modules, as well asfixed and tracking systems. Since 1995, APSand Amonix have installed and operatedAmonix CPV systems, with more than 600kW presently operating on a daily basis.They have reported total installed systemcosts for the present Amonix systems at $6per watt [Joh 2005], which is comparable toinstalled system costs of large flat-plate PV

systems - a surprising result since flat-platePV systems are so well-developed. As theAmonix technology matures or when the sil-icon cells are replaced by high-efficiencycells, APS expects that the cost of theAmonix system will drop below the flat-plate cost [FAQ 2005].

Before the announcement of the newrecords Herb Hayden, Solar Program coor-dinator at APS, described their optimism[NREL 2005], "We have seen steadyprogress in photovoltaic concentrator tech-nology. We are working with advanced mul-tijunction PV cells that are approaching38% efficiency, and even higher is possibleover time. Our goal is to install PV concen-trator systems at $3 per watt, which canhappen soon at production rates of 10megawatts per year. Once that happens,higher volumes are readily achieved."Further emphasizing the significance ofthese new records, Amonix' Garboushian, inconsidering the next 2-5 years, said [NREL2005], "With the advent of the multijunc-tion solar cells, PV concentrator power gen-eration at $3 per watt is imminent in thecoming few years."

Future growthWith market entry comes the question ofsustained market growth. Carlos Algora,from the Instituto de Energia Solar,Universidad Politecnica de Madrid, pub-lished a useful cost analysis in 2004 for con-centrator PV technologies [Alg 2004].Many of the costs came from installed sys-tem costs for the 480 kW CPV project inTenerife, but included technology improve-ments for production of 10 MW and incor-porated learning curve reductions for cumu-lative production greater than 10 MW. Theanalysis included a wide range of

Figure 2: Several 25-kW Solar Systems mod-ules. Again, note the people in the foregroundfor an idea of module scale.

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parameters. Concentrations ranged from 400to 1000 suns, with cell efficiencies rangingfrom 32% to 40%. The present-day CPVinstalled system cost was estimated at 2.34euros per watt (US$3.0 per watt with thepresent exchange rate) using 32%-efficientmultijunction solar cells in today's CPVtechnology with only 10 MW of product.This part of Algora's analysis did not incor-porate the impact of a learning curve. The $3per watt result substantiates the industry andcustomer forecasts for the next 2-5 years,presented in the previous section.

The lowest projected costs in Algora'sanalysis was 0.69 euros per watt (US$0.85per watt) for 40%-efficient solar cells, 1000-sun concentration, and cumulative produc-tion of 1000 MW, using a conservative learn-ing curve of 17.5% that started with 10 MWof product. Although 1000 MW may seem adistant cumulative production target forCPV, it is informative to realize that a totalof about 1 MW of multijunction productioncapacity already exists at Spectrolab andother space satellite solar power providers.This 1 MW production capacity of high-effi-ciency multijunction solar cells correspondsto ~ 1000 MW of CPV plants at 1000-sunconcentration. The Algora cost projection at1000 MW is exciting. But Dov Raviv inIsrael has developed an innovative financingmodel that extends cumulative CPV produc-tion from gigawatts to more than 2 terawatts(TW). Raviv's very large-scale CPV plantanalyses have unearthed some hitherto unap-preciated attributes of financing sustainabili-ty that caught the attention of attendees atthe recent PV Solar Energy Conference and

Exhibition in Barcelona, where his presentation received an award as the bestposter in its category [Fai 2005]. The financ-ing sustainability occurs because of electrici-ty revenues accumulating to the point thatplant expansions can occur without the needfor continued external funding beyond thatneeded to initiate the project.

These recent installation forecasts and costanalyses might suggest that CPV systems cando everything, right now. Alas, they cannot.Raviv's bold vision is to power all of Israel orCalifornia, Arizona, or the United States-with TWs of CPV power plants. CPV sys-tems will surely become a major energy play-er, but they have a long way to go to catch upto flat-plate PV, let alone with conventionalenergy technologies. However, Raviv's analy-sis clearly shows that if proper investmentsare made now and sustained by industry andgovernments, the impact, in TWs, of CPVon the world's energy picture can be has-tened.

Energy paybackHaving made this caveat, some characteristicsof concentrator PV technologies certainly dosupport these visionary projections. CPV sys-tem costs are much more sensitive to the priceof steel than to the price of silicon. In thisregard, CPV systems share similar concernswith the wind industry [Mc 2002]. Othertechnological similarities with wind systemsinclude the low cost of production plants,suitability for distributed and large-scale util-ity generation, modularity, moving parts, andthe need for a good resource, be it wind orsolar. Such observations suggest that CPV

systems could follow in the footsteps of windsystems. It seems plausible that CPV systemcosts can approach wind system costs (typi-cally US$0.80 per watt today or about thesame as projected CPV costs) if only becausecommon materials (e.g., steel, glass, plastic)are dominant and because production plantcosts are relatively low. Also consistent withthese observations are recent estimates ofenergy payback for CPV technologies that arevery close to values published for wind tur-bines at good wind sites. Specifically, theenergy payback has been estimated as 8months for a CPV system in a site having agood solar resource [Bett 2005].

The cost of production plants can be a crit-ical element in how rapidly a technology canexpand to meet market demands (Figure 4).For manufacturing flat-plate modules of crys-talline silicon, amorphous silicon, or poly-crystalline thin films, published costs rangebetween $150 and $300 million for a pro-duction capacity of 100 MW per year. A 100MW per year production facility for windsystems may cost between $10 and $15 mil-lion. Manufacturing of wind turbines or CPVsystems resembles the assembly-line produc-tion of automobiles, including the depend-ence on suppliers and the sensitivity to steelprices [Mc 2002]. It is much easier for anindustry with low production-plant costs tosustain high growth rates because consider-ably less capital is needed to expand produc-tion facilities. However, uncertainty exists inthe cost of a 100 MW per year CPV plantbecause one has yet to be built. Publishedestimates range between $15 and $50 million[Mc 2002]. Production-plant costs in thisrange are an asset for sustainable and aug-mented market growth of CPV technologies.

Qualification standardsThe 2005 International Conference on SolarElectric Concentrators had almost threetimes as many attendees as the previous con-ference [Mc 2004] held only 18 months ear-lier. Among the new attendees were investors,policy analysts, and quite a few new small andlarge companies developing new CPV prod-ucts. And the PV Solar Energy Conferenceand Exhibition in Barcelona saw a recordnumber of CPV presentations [Oss 2005],along with new companies displaying newconcepts for rooftop concentrators [FAQ2005].Figure 3: World-record conversion efficiencies for various PV technologies.

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Although this excitement is heartening,the history of concentrator PV is replete withprototypes and projects that did not get veryfar. Today, with solar cells available havingefficiencies of 35% and higher, many peopleare in a rush to develop a product and enterthe market. But history also reminds us thatearly flat-plate deployment was characterizedby large-scale failures in the field. A primaryreason was an absence of qualification stan-dards. The development of standards in theearly 1980s has led to a complete reversal ofthe old perception that terrestrial PV mod-ules are unreliable. A similar story can betold for wind systems deployed in the 1980s.The creation of wind system standards in thelate 1980s and their use in certifying windsystems in the 1990s contributed to theirsuccess. Currently, almost 50 GW of windsystems are operating reliably around theworld.

Qualification standards help developersdesign their new products by identifyingweaknesses before production and projectinstallation. They give customers the confi-dence that their project investments will payoff. In short, they can contribute immenselyto a technology's successful market entry.Fortunately, the CPV industry thoughtabout this situation in the 1990s. Standardstake years to develop because the process isbased on consensus. Companies do not wantstandards that are unnecessarily strict orrequire expensive test procedures. Customerswant standards that ensure good productperformance. So, input from both groups -companies and customers - as well as fromrelatively objective research organizationsleads to an accepted set of test proceduresvital for successful entry of CPV into the

market. The first CPV standard [IEE 2001]was published in 2001. This standard, how-ever, was most suitable for U.S. concentratorPV technologies using Fresnel lenses. TheInternational Electrotechnical Commission(IEC), with input from engineers from morethan 10 countries, has been developing astandard suitable for concentrators usingmirrors or lenses with solar concentrationratios ranging from a couple of suns to 1000sof suns. The IEC group working on thisstandard hopes to complete their work andpublish the standard in 2006 [McC 2005].They are also working on new standards forsolar trackers and safety.

Significant playerPhotovoltaics, has become a successfulmultibillion dollar business today because ofmarket opportunities and because of steadytechnology improvements leading to betterperformance, lower cost, and excellent relia-bility. As new market opportunities through-out the world have opened up for concentra-tor photovoltaics, this technology nowappears to have the necessary performance,cost, and reliability to be a significant playerin the world's energy markets.

References[Alg 2004] The Importance of the Very High

Concentration in the Third-Generation Solar Cells,

C. Algora, Chapter 6 of Next Generation

Photovoltaics, Edited by A. Marti and A. Luque,

Institute of Physics Publishing, Bristol and

Philadelphia, 2004

[Amo 2005] www.amonix.com

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Technology Ready for the Market, A.W. Bett, G.

Siefer, C. B. Baur, S.v. Riesen, G. Peharz, H.

Lerchenmuller, and F. Dimroth, Presentation at the

20th European PV Solar Energy Conference and

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[Fai 2005] The Triple Sustainability of CPV with

the Framework of the Raviv Model, D. Faiman, D.

Raviv, and R. Rosenstreich, Presentation at the 20th

European PV Solar Energy Conference and

Exhibition, Barcelona, Spain, June 2005

[FAQ 2005] PV FAQs: What's New in

Concentrating PV? NREL Report No. FS-520-

36542; DOE/GO-102005-2027, February 2005

[IEE 2001] IEEE Recommended Practice for

Qualification of Concentrator Photovoltaic Receiver

Sections and Modules, IEEE std. 1523-2001

[Joh 2005] The Role of CSP in Filling APS' Future

Solar Energy Needs, P. Johnston, Proceedings of the

International Conference on Solar Concentrators for

the Generation of Electricity or Hydrogen, Scottsdale,

Arizona, USA (CD-ROM). NREL Report No. CD-

520-38172 (in preparation) 2005

[King 2005] Pathways to 40% Efficient

Concentrator Photovoltaics, R.R. King, C.M. Fetzer,

R.A. Sherif, D.C. Law, K.M. Edmondson, G.S.

Kinsey, H.L. Cotal, D.D. Krut, J.G. Ermer, and N.G.

Karam, Presentation at the 20th European PV Solar

Energy Conference and Exhibition, Barcelona, Spain,

June 2005

[Mc 2002] Large-Scale Deployment of

Concentrating PV: Important Manufacturing and

Reliability Issues, R. McConnell, Proceedings of the

First International Conference on Solar Electric

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590-32461, May 2002

[Mc 2004] R. McConnell, International Solar

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Electricity or Hydrogen, Alice Springs, Australia (CD-

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[Mc 2005] High Performance PV Future: III-V

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M. Symko-Davies, Plenary presentation at the 20th

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Testing, R. McConnell, L. Ji, and G. Tamizhmani,

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[NREL 2005] Cost Competitive Electricity from

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[Sol 2005] www.solarsystems.com.au

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[Sun 2005] www.sunpowercorp.com

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Tandem Cells for High-Performance Solar

Concentrators, M. W. Wanlass, S.P. Ahrenkiel, D.S.

Albin, J.J. Carapella, A. Duda, K. Emery, J.F. Geisz,

K. Jones, S. Kurtz, T. Moriarty, and M.J. Romero,

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2005

Figure 4: An Amonix production facility in LosAngeles is strikingly different from a flat-platePV manufacturing facility. This differenceresults in much lower capital costs for the facility.