A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Opportunities and Challenges 

for Development of a Mature 

Concentrating Photovoltaic 

Power Industry 

S. Kurtz 

Technical Report 

NREL/TP-520-43208 

Revised September 2008 

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 
Opportunities and Challenges 

for Development of a Mature 

Concentrating Photovoltaic 

Power Industry 

S. Kurtz 

Prepared under Task No. PVA7.4401 

Technical Report 

NREL/TP-520-43208 

Revised September 2008 

National Renewable Energy Laboratory

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Opportunities and Challenges for Development of a Mature 

Concentrating Photovoltaic Power Industry 

Introductory Note 

The status of the solar industry is changing rapidly. If you would like this report to reflect the 

latest developments at your company, please send these to Sarah_Kurtz@nrel.gov. We will 

attempt to update this report periodically. 

This report attempts to identify problems that may be encountered as the concentrating 

photovoltaic (CPV) industry matures, with the ultimate goal of increasing the growth rate of the 

CPV industry. This report strives to guide industry investments as well as to help set research 

agendas for the National Renewable Energy Laboratory (NREL) and other R&D organizations. 

The first version of this report described the value of CPV based on multijunction concentrator 

cells. Representatives from a number of companies suggested including information about lowconcentration approaches using silicon or other inexpensive cells as well. This update contains 

two parts in response to this suggestion. 

The Promise of CPV 

Today’s photovoltaic (PV) industry is growing at a rapid rate, but the industry would grow even 

faster if costs could be reduced for both the final products and the capital investment required 

for scale-up. One strategy for reducing module cost is to reduce the amount of semiconductor 

material needed (the cost of the silicon solar cells typically comprises more than one-half of the 

module cost). Many companies are thinning the silicon wafers to reduce costs incrementally; 

others use thin-film coatings on low-cost substrates (such as amorphous/microcrystalline silicon, 

cadmium telluride, or copper indium gallium diselenide on glass or other substrates). CPV 

follows a complementary approach and uses concentrating optics to focus the light onto small 

cells. The optics may be designed for low or high concentration. Low-concentration concepts 

use silicon or other low-cost cells; high-concentration optics may use more expensive, higherefficiency cells. The higher-efficiency cells can reduce the cost per watt if the cost of the small 

cells is minimal. The high- and low-concentration approaches are described in Parts I and II of 

this report, respectively. 

Part I. High-Concentration CPV Using High-Efficiency, Multijunction 

Solar Cells 

 

Recently, concentrator cells have been reaching increasingly impressive efficiencies, inspiring 

new interest in the high-efficiency, high-concentration approach. The current record efficiency is 

40.8% for a three-junction GaInP/GaInAs (1.3 eV)/GaInAs(0.9 eV) cell. [1] A historical summary 

of champion cell efficiencies is shown in Fig. 1. Multijunction concentrator cells have achieved 

much higher efficiencies than any other approach. This is not surprising for two reasons: (1) the 

highest theoretical efficiencies may be achieved if multiple semiconductor materials (with a 

range of bandgaps) are chosen to match the spectral distribution of the sun, and (2) the 

compound semiconductors used in these cells are direct-gap materials and can be grown with 

 1
near-perfect quality. The multijunction approach has been described extensively in the 

literature.[2-11]

When compared with solar thermal approaches, CPV provides a qualitatively different 

approach, typically with lower water usage, greater flexibility in size of installation, and the ability 

to respond more quickly when the sun returns on a cloudy day. The tracking used for CPV also 

implies relatively higher electricity production per installed kilowatt, compared with fixed flat 

plate. 

Fig. 1. Historic summary of champion cell efficiencies for various photovoltaic technologies. 

The highest efficiencies have been achieved for multijunction solar cells, increasing at a rate of 

almost 1% per year in recent years. Multijunction cell efficiencies have the potential to 

approach 50% in the coming years. 

Ten years ago, there was little commercial interest in CPV for the following reasons: 

• The PV market was dominated by building-integrated or rooftop applications, whereas 

most CPV products are better suited to solar farms. 

• The champion concentrator cell was only ~30% efficient, compared with ~40% today. 

• The total size of the industry was about one-tenth of what it is today, making near-term, 

high-volume CPV deployment unlikely (i.e., CPV achieves low cost only when the 

volume of manufacturing is large). 

In the last 10 years, the solar industry has mushroomed, and the CPV industry is now growing 

rapidly. Cumulative investment in CPV is now on the order of $1 billion. Solar fields, which 

often use tracked systems, are becoming more common, providing a potentially huge market for 

CPV products. With the overall PV market growing in the gigawatt range, CPV has an 

opportunity to enter the market with production of tens or hundreds of megawatts per year. This 

 2
is significant because CPV is unlikely to achieve low costs when manufacturing at less than tens 

of megawatts per year. Ten years ago it would have been difficult for companies to have 

confidence that they could find markets for the needed volume. The growth of the market, and 

especially growth of the market segment that uses trackers, is an important contributor to the 

increased interest in CPV. The potential for CPV industry growth has been widely discussed in 

recent years.[4-6] The Bosi review includes almost 100 references. 

Some cost analyses have predicted that using high-efficiency concentrator cells can lead to very 

low costs for solar electricity.[5,6] These studies imply that there is a potential for cost-effective 

implementation of high-concentration systems even in locations such as Boston, 

Massachusetts, as shown in Fig. 2.[6] The cost assumptions used to calculate the data in Fig. 2 

are tabulated in Table 1. Other studies have also estimated the costs associated with CPV 

systems (see Table 2).[5] The energy payback of some CPV systems has also been studied.[12]

Demonstration that these cost structures can be achieved will require development of a reliable 

CPV product followed by large-scale deployment. Many are watching for the success of this 

demonstration. 

Figure A3 (from Ref.[6], color modified). For medium-sized plants in Boston, the GaAs dish surprisingly maintains its 

lead, despite the lower direct normal solar resources. (In other words, a dish based on 35% efficient cells is 

something of the ultimate technology.) The thin-film approach is a close second place. (R.M. Swanson, "The Promise 

of Concentrators," Prog. Photovolt. Res. Appl. 8, 93111, ©2000 John Wiley & Sons Limited. Reproduced with 

permission.) 

Fig. 2. Cost of electricity calculated for a set of technologies as presented in Ref.[6] 

 3
Table 1. Cost Assumptions Used to Calculate the Cost of Electricity 

Presented in Figure 2 

Table A1 (in Ref. [6]). Detailed assumptions for medium-sized PV plants. (R.M. Swanson, "The Promise of 

Concentrators," Prog. Photovolt. Res. Appl. 8, 93111, ©2000 John Wiley & Sons Limited. Reproduced with 

permission.) 

MEDIUM PLANTALBUQUERQUE GaAs 

Dish 

GaAs 

 2-Axis 

Fresnel 

Si Dish 2-axis 

static

Si

 2-Axis 

Fresnel

Thin 

Film

Static 

Conc

Central 

Rec.

Albedo 

FFP 

2-axis 

FP 

Si 1-

Axis 

Fresnel

1-axis 

FP

FFP

Desert 

(Albuquerque) 

KWhr/ 

m2/day 

6.566 6.566 6.566 8.624 6.566 6.336 6.336 5.025 6.336 8.624 6.08 7.41 6.336

Diffuse (Boston) KWhr/ 

m2/day 

3.626 3.626 3.626 5.782 3.626 4.554 4.554 2.775 4.554 5.782 3.42 4.94 4.554

Albedo factor 1 1 1 1 1 1 1 1 1.3 1 1 1 1

BOS Area (low) $/m2 70 70 70 70 70 70 70 70 70 70 70 70 70

BOS Area (high) $/m2 140 140 140 140 140 140 140 140 140 140 140 140 140

BOS Power (low) $/W 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3

BOS Power (high) $/W 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6

Tracking (low) $/m2 35 35 35 35 35 0 0 35 0 35 20 20 0

Tracking (high) $/m2 67 67 67 67 67 0 0 67 0 67 40 40 0

Module (low) $/m2 90 115 90 115 115 75 85 30 85 75 90 75 75

Module (high) $/m2 160 230 160 230 230 150 160 60 165 150 160 150 150

Cell (low) $/m2 30000 30000 15000 300 15000 0 300 20000 200 200 5000 200 200

Cell (high) $/m2 10000

0 

100000 20000 1000 20000 30 1000 25000 400 400 15000 400 400

Cell Efficiency 

(high) 

0.3325 0.35 0.26 0.21 0.27 0.12 0.21 0.26 0.2 0.2 0.24 0.2 0.2

Cell Efficiency 

(low) 

0.285 0.3 0.23 0.17 0.24 0.08 0.17 0.23 0.15 0.15 0.2 0.15 0.15

Operating Temp. 65 65 65 60 65 55 60 65 60 55 65 55 55

deta/dteta 2.20E03 1.90E03 

2.20E033.30E

-03

2.20E032.00E

-03

3.30E

-03

2.20E033.30E03 3.30E

-03 

2.40E033.30E

-03

3.30E

-03

Concentration 1000 1000 400 4 400 1 4 400 1 1 50 1 1

Module 

Transmission 

0.85 0.85 0.85 0.9 0.85 0.95 0.9 0.85 0.95 0.95 0.9 0.95 0.95

BOS eff 0.85 0.85 0.85 0.9 0.85 0.9 0.9 0.85 0.9 0.9 0.85 0.9 0.9

Conc premium 0 0 0 0 0 0 0 0 0 0 0 0 0

O&M cost (low) ¢/KWhr 0.8 0.8 0.8 0.8 0.8 0.2 0.2 0.8 0.2 0.8 0.8 0.8 0.2

O&M cost (high) ¢/KWhr 2.0 2.0 2.0 2.0 2.0 0.8 0.8 2.0 0.8 2.0 2.0 2.0 0.8

Cost-diff low ¢/KWhr 12.8 13.2 15.8 13.7 16.6 13.2 13.4 17.1 15.4 16.5 19.9 18.6 18.5

Cost-diff high ¢/KWhr 30.0 31.8 32.4 37.5 35.4 41.1 37.7 34.9 39.6 42.7 52.2 48.0 48.2

Cost-Desert low ¢/KWhr 7.4 7.7 9.1 9.4 9.5 9.6 9.7 9.8 11.1 11.3 11.5 12.6 13.4

Cost-Desert high ¢/KWhr 17.5 18.4 18.8 25.8 20.4 29.7 27.3 20.2 28.7 29.3 30.3 32.7 34.9

Cost-low $/W 1.59 1.64 1.99 2.71 2.10 2.16 2.19 1.66 3.18 3.32 2.38 3.20 3.05

Cost-high $/W 3.70 3.94 4.02 7.49 4.42 6.69 6.14 3.33 8.18 8.58 6.27 8.30 7.89

 

 4
Table 2. Cost Assumptions and Cost of Electricity for CPV Estimated by Ref. [5]

Table 2 source: A. Luque, G. Sala, and I. Luque-Heredia, "Photovoltaic Concentration at the Onset of its Commercial 

Deployment," Prog. in Photovolt. 14, 413-428, ©2006 John Wiley & Sons Limited. Source: M. Yamaguchi and A. 

Luque, "High Efficiency and High Concentration in Photovoltaics," IEEE Transactions Electron Devices, 46: 2139, 

©1999 IEEE. Reproduced with permission. 

An additional potential advantage of the CPV approach is the reduced need for capital 

investment (scalability). The growth of the silicon PV industry has been challenged by the need 

for capital investment, especially in silicon purification facilities. By reducing the amount of 

semiconductor material, the capital investment need is also reduced. Although no company has 

ever demonstrated it, the relative ease of scale-up of CPV is logical, and could be a significant 

advantage in a rapidly growing market. 

Current Status of CPV Industry 

Table 3 provides a partial list of today’s CPV companies. This list has grown substantially in the 

last 5 years. Perhaps more important than the length of the list is the level of investment in the 

industry and the movement toward large-scale production. The industry has been projecting 

installations in the megawatt range for 10 years. In 2007, for the first time a CPV company 

delivered on such a projection: Guascor Foton installed 6 MW of high-concentration, siliconbased systems, using Amonix’s CPV technology.[13] A company that might have attracted a $1-

million investment 10 years ago may hope to attract $100 million today. Not surprisingly, the 

larger investment rates are enabling faster progress in the development, with multiple 

companies now reporting stable on-sun operation for months or years. At the Concentrated 

Photovoltaic Summit ’08, Solar Systems reported on-sun operation for 2 years with no 

measurable degradation. Similarly, Emcore showed stable operation of a 2.5-kW system for 

8 months, and ISFOC (Instituto de Sistemas Fotovoltaicos de Concentración) noted only “trivial” 

issues for systems at its CPV test site. ENTECH has been testing a 1+ kW triple-junction-cell 

concentrator array outdoors since July 2003 under a NASA-funded program, with no detectable 

performance degradation.[14] Reliable operation on-sun is the primary milestone that must be 

reached before CPV companies can begin the sort of rapid expansion that First Solar has 

 5
demonstrated to be possible for a new technology. These reports of stable on-sun operation 

are an indication that rapid expansion could occur within the coming years. 

Table 3. Summary of CPV Companies 

Company Type of System Location On Sun in 

2007 

Abengoa Solar Multiple designs Spain, USA 

American CPV Orange, CA, USA 

Amonix Lens, pedestal Torrance, CA, USA >100 kW (Sibased) 

Arima Ecoenergy Lens, pedestal Taiwan 

Boeing Mirror, Pedestal Seal Beach, CA, USA 

Concentracion Solar 

La Mancha 

Lens, pedestal Ciudad Real, Spain 

Concentrating 

Technologies 

Small mirror, 

pedestal 

Alabama >1 kW 

Concentrix Solar Lens, pedestal Freiburg, Germany ~100 kW 

Cool Earth Solar Inflated mirrors Livermore, CA, USA >1 kW 

Daido Steel Lens, pedestal Nagoya, Japan 

Emcore Lens, pedestal Albuquerque, NM, USA >10 kW 

Energy Innovations Lens, carousel Pasadena, CA, USA 

Enfocus Engineering Lens, flat pivot Sunnyvale, CA, USA 

ENTECH Lens, pedestal Keller, TX, USA >1 kW in 2003 

ESSYSTEM Lens, pedestal Gwangju-city, Korea 

EverPhoton Lens, pedestal Taipei, Taiwan 

Green and Gold Lens, pedestal South Australia 

GreenVolts Small mirrors, 

carousel 

San Francisco, CA, 

USA 

>1 kW 

Guascor Foton Lens, pedestal Ortuella, Spain ~10 MW (Sibased) 

IBM Lens Armonk, NY 

Isofoton Lens, pedestal Malaga, Spain 

Menova Modified trough Ottawa, Ontario, 

Canada 

OPEL International Lens, pedestal Shelton, CT, USA 

Pyron Lens, carousel San Diego, CA, USA >1 kW 

Sharp Lens, pedestal Japan 

Sol3g Lens, pedestal Cerdanyola, Spain >10 kW 

Solar Systems Dish, pedestal Victoria, Australia >100 kW 

SolarTech Lens, pedestal Phoenix, AZ, USA 

Solar*Tec AG Lens, pedestal Munich, Germany 

SolFocus Small mirror, 

pedestal 

Mountain View, CA, 

USA 

>10 kW 

Soliant Energy Lens, flat pivot Pasadena, CA, USA 

Xtreme Energetics Two designs for 

central station and 

rooftop 

Livermore, CA, USA 

 6
As documented in Table 3, multiple CPV companies have installed more than10 kW of 

prototypes in 2007. Many have plans to install hundreds of kilowatts or multiple megawatts in 

2008.* 

Most PV technologies have required years of development before showing success on a large 

scale. First Solar’s current expansion is based on years of development work. As noted above, 

the multijunction CPV industry may be preparing to emerge from the development phase. As 

the CPV companies transition from the prototyping phase of development to scaling up 

manufacturing, they will encounter the standard problems. The following discussion reflects the 

concerns that have been raised by industry participants during discussions related to this study. 

Prototype Development 

CPV companies are exploring a wide range of CPV approaches. Each has done its own 

assessment of which designs will give the best performance, lowest cost, and longest reliability. 

Considerations include: 

• Performance: Optical efficiency, cell cooling, and performance losses associated with 

manufacturing imperfections, soiling, tracking errors, flexing in the wind, thermal 

expansion/contraction, or wind stow. 

• Cost: Use of inexpensive components, ease/automation of assembly. 

• Reliability: Degradation of optics, poor performance of tracker or other loss of alignment, 

loss of adhesion or breakdown of bonds between cell and the optics and heat sink, etc. 

The companies reported that they have been successful in identifying solutions for the many 

technical problems, but that it can take some time to identify the suppliers needed to assemble 

all of the components. 

Prototype Testing 

Many of the companies currently have one or multiple prototypes on sun. Initial prototypes are 

usually on the order of 1 kW in size, with subsequent prototypes in the 2–30-kW range. 

After designing and assembling the prototypes, the most immediate need of many of the 

companies is testing. Most companies are testing prototypes and would like to accelerate the 

testing. Many of the stress tests are designed to run over several weeks. If these could be 

replaced by highly accelerated stress tests (HAST), testing cycles might be reduced to less than 

a week. For example, higher temperature and humidity could be applied in a slightly 

pressurized system. Unfortunately, the technical basis for this sort of acceleration has not been 

established. Some efforts to do this have concluded that the use of harsher conditions for a 

shorter time can expose failure modes that are not observed in the field, defeating the purpose 

of the tests. 

 

* Solar Systems and Amonix spent about 20 years developing Si-based concentrator systems. The 

advent of higher efficiencies for multijunction cells has motivated these two companies to reengineer their 

Si-based products. In the meantime, Amonix has worked with Guascor Foton to begin deployment of 

their Si-based CPV product at the multimegawatt scale. Table 3 shows these three companies with the 

largest installed systems in 2007, reflecting the many years of engineering invested in these systems. 

 7
There is concern that failures in the field for even a single company could discredit the entire 

CPV industry. Sharing observations of failures can facilitate early detection of failures, reducing 

the probability of premature deployment, but companies are often reluctant to do so. This year, 

the Accelerated Aging Workshop, which was sponsored and organized by the U.S. Department 

of Energy and the national laboratories, included a breakout session for the CPV industry. It 

was suggested that the national laboratories should place the highest priority on the cells, 

bonding, and packaging, although a myriad of other concerns were also expressed.[15]

Some testing standards are available, but the standards for CPV are behind those for flat-plate 

PV. Dozens of standards exist for silicon PV. Many of these were developed by the IEEE or 

ASTM for use in the United States, and then were placed in the international arena through the 

IEC. Table 4 summarizes a few of the key IEC standards for PV and tabulates those that have 

CPV versions. Clearly, the CPV industry and customers must work together to establish CPV 

versions of the standards to form the foundation for the emerging CPV industry. 

Table 4. Summary of Standards 

Silicon PV Standard Corresponding CPV Standard

IEC 60904-1 – Photovoltaic devices. Part 1: 

Measurement of photovoltaic current-voltage 

characteristics. 

IEC 60904-2 – Photovoltaic devices. Part 2: 

Requirements for reference solar devices. 

IEC 60904-3 – Photovoltaic devices. Part 3: 

Measurement principles for terrestrial photovoltaic 

(PV) solar devices with reference spectral 

irradiance data. 

IEC 60904-5 – Photovoltaic devices. Part 5: 

Determination of the equivalent cell temperature 

(ECT) of photovoltaic (PV) devices by the opencircuit voltage method. 

IEC 60904-7 – Photovoltaic devices. Part 7: 

Computation of spectral mismatch error introduced 

in the testing of a photovoltaic device. 

IEC 60904-8 – Photovoltaic devices. Part 8: 

Measurement of spectral response of a photovoltaic 

(PV) device. 

IEC 60904-9 – Photovoltaic devices. Part 9: Solar 

simulator performance requirements. 

IEC 60904-10 – Photovoltaic devices. Part 10: 

Methods of linearity measurement. 

IEC 61215 – Crystalline silicon terrestrial PV 

modules. Design qualification and type approval. 

IEC 62108 – CPV modules and 

assemblies. Design qualification and type 

approval. 

IEC 61853 – Photovoltaic (PV) module 

performance testing and energy rating. Part 1: 

Irradiance and temperature performance 

measurements and power rating (out for vote). 

Initial draft being discussed. 

 8
Manufacturing Scale-Up and Retesting 

After reliable prototypes have been demonstrated, companies must automate the manufacturing 

of these and then retest the reliability to ensure that subtle changes in the design do not 

negatively impact reliability. Some of the companies have planned for high-volume 

manufacturing from the start, but all companies must include this step in their development 

plans at some stage. 

The details of high-volume manufacturing will be key toward cost reduction. Automated 

manufacturing of complete systems under a single roof will take substantial effort to set up, but 

may show significant advantages in the long run. 

Performance (Power) Rating 

A power rating is traditionally used as a nameplate rating and is useful for sizing of inverters and 

other system parts as well as for verification of system delivery under some contracts. The IEC 

Technical Committee 82 Working Group 7 has prioritized the power rating as the highest need. 

However, a technical basis for the performance rating is not well established. Some questions 

that need to be addressed include: 

• How should the variable spectrum be treated? 

• If spectral effects are to be addressed, what is the best approach (reference cells, 

spectral radiometer, etc.)? 

• Should ambient temperature or cell temperature be used for the rating? 

• What methodology should be established for indoor performance rating? Specifically, if 

flash lamps are used, how is the normal operating condition temperature determined and 

adjusted? 

• Should issues related to acceptance angle, tracker alignment, etc., be considered? 

Energy rating is most important for power purchase agreements and utility applications. The 

methods for these ratings are still being debated; methods that give precise and accurate 

ratings require technical studies. The methods used for predicting energy production for flatplate systems are well enough documented to convince most investors, but investors have 

much less confidence in similar predictions for CPV systems. This puts CPV companies at a 

disadvantage for some applications. 

A useful tool would be a model that could take readily available data and create a set of hourly 

data for direct spectrum, temperature, and wind speed. If the model were created, such data 

could be generated to represent an average day for each month of the year for any site in the 

United States. Tools for estimating energy production (e.g., PV Watts) are available for flatplate systems and might be extended for CPV systems. 

Some companies are interested in solar resource data for Spain and other locations outside the 

United States. Such data exist, but this information is not widely available. The direct solar 

resource is strong in southern Spain, but is significantly reduced toward the northern part of the 

country. 

The National Solar Radiation Data Base and other solar resource data that include the direct 

resource usually include the circumsolar resource, which most CPV systems are unable to 

utilize. The importance of this effect has not been quantified, although anecdotal information 

 9
implies that it can be significant in locations with pollution or other sources of haze that can 

cause small-angle scattering. 

Cell Supply 

A key concern of all of the CPV companies has been the availability of concentrator cells. 

Spectrolab and Emcore are currently shipping concentrator cells to multiple CPV companies, 

and all CPV companies reported adequate cell availability as of this writing. In the last few 

months, a significant number of new companies have demonstrated the capability for epitaxial 

(single-crystal) growth of multijunction cells. These are summarized in Table 5. Multiple startup companies are developing recipes and are supplying samples in small volumes. 

Table 5. Summary of Companies with Capability for Epitaxial Growth 

of Multijunction Cells**

Company Name/Web Link Comment

Spectrolab Datasheet describes minimum average 36% cells and 

cell assemblies at 50 W/cm2

Emcore Datasheet describes typical 36% cells and receivers at 

470 suns 

Spire (Bandwidth) Datasheet describes typical 35% cells at 500 suns 

Cyrium North America 

Microlink Devices North America 

Azur Space (RWE) Europe 

CESI Europe 

Energies Nouvelles et 

Environnement (ENE) 

Europe 

IQE Europe 

Arima Asia 

Epistar Asia 

Sharp Asia 

VPEC Asia 

 ** List does not include a number of other companies in R&D or stealth modes. 

A quick review of the companies in Table 5 implies that the supply of cells could quickly 

mushroom. The efficiencies from the new companies are expected to be inferior to those from 

Emcore and Spectrolab, but may be acceptable to some CPV companies (see below). A 

number of companies are fabricating cells with efficiencies greater than 30%; some have 

demonstrated efficiencies in the range of 35%. As part of this study, cells were measured for 

both Arima and VPEC, confirming that these companies have cells approaching or exceeding 

35%. We expect that these companies will be marketing multijunction solar cells in the near 

future. Although all of the companies on this list have some capability for growing multijunction 

cells, not all of them have demonstrated a capability for high-yield manufacturing. 

The most immediate concern about the concentrator cells expressed by CPV representatives is 

whether the reliability testing is adequate. Both Spectrolab and Emcore report that they have 

tested the cells and are confident of their stability and performance, but most CPV 

representatives were not satisfied with the detail of the test data. Emcore bases its 20-year cell 

(and receiver) warranty on (1) years of experience with space cells manufactured for operation 

at up to 250°C; (2) a firm understanding of both the physical-degradation mechanisms and the 

 10
design/manufacturing methodologies needed to ensure long-term reliability of its CPV products; 

and (3) a year (and counting) of stable on-sun terrestrial operation at 500 suns. Spectrolab has 

a similar space heritage and has tested its CPV cells using the thermal-cycling, humidity, and 

humidity-freeze tests described in IEEE 1513-2001. 

The existing qualification standards may or may not identify all of the degradation modes. High 

solar fluxes may be more harmful to encapsulant materials than to the semiconductor material. 

Si modules are known to exhibit corrosion associated with moisture ingress near the Ag 

gridlines. Thus, CPV cells with Ag grid lines could experience similar corrosion. Nevertheless, 

if CPV cells are operated in hot, dry climates, moisture ingress may be less of a problem. A 

technical basis has not yet linked the standard damp heat (85°C/85% relative humidity) with 

field performance for CPV systems. Until the correlation between accelerated testing and fieldtesting is established, most CPV companies are applying the standard damp heat test to identify 

potential failures. 

Emcore’s current production capacity is ~300 MW/yr at 1000 suns, with expansion in progress 

to boost that capacity to 350 MW/yr by mid-2008. Spectrolab has plans for capacity in a similar 

range. Both Emcore and Spectrolab report that their primary barrier to expansion is confidence 

in future sales. As is standard in the business world, they are hesitant to invest in new capital 

equipment before expanded orders are in hand. Incremental additions to capacity can be 

implemented in less than 6 months once firm orders have been received. Additions requiring 

expansion into new facilities may require about a year depending on how long it takes to build a 

new building or acquire access to appropriate facilities. In the event of a rapid growth in 

demand for multijunction cells, the situation could quickly evolve into that which is currently 

observed for the silicon PV industry: companies must plan on negotiating firm multiyear 

contracts so that the semiconductor suppliers can appropriately plan and finance their 

expansion. 

Just as some silicon PV companies are moving toward vertical integration, many of the CPV 

companies are considering vertical integration with cell companies to ensure adequate cell 

supply. In contrast, the cell companies are trying to avoid vertical integration in order to retain 

their ability to supply many CPV companies. The situation may become very complex as 

companies attempt to define whether to merge or separate these efforts. Examples: Emcore 

(cell and system supplier) has announced a spin-off of its CPV systems company; Spectrolab 

(cell supplier) is owned by Boeing (system supplier); Arima Ecoenergy is developing CPV 

systems alongside of Arima’s development of multijunction cells. Many discussions of mergers 

appear to be ongoing. 

Expansion of the manufacturing volumes should allow reduction in cost because of economies 

of scale. This consideration would tend to associate lower cell costs with a small number of cell 

companies. In 2007, cell supply was a primary concern among CPV representatives. With the 

growing number of companies with cell capability, this concern is substantially reduced. 

Cell Efficiencies 

Cell efficiencies have been increasing at a rate of about 1% per year in recent years. 

Efficiencies are expected to continue to increase toward 45%–50%. Spectrolab has reported a 

record efficiency of 40.7%.[2] Emcore claims an efficiency of 39%. NREL has described a new, 

inverted structure at 40.8%.[1] Although a 50% solar cell should be achievable, the addition of 

 11
multiple junctions may add cost and may have marginal benefit in terms of additional energy 

production in the field. 

The trade-off between cell cost and cell efficiency is highly dependent on the relative costs of 

the cells and the systems. A simplistic analysis is shown in Fig. 3. The cell cost in $/W is 

strongly dependent on concentration. Emcore reported a sale to Green and Gold at $24 million 

for 105 MW. This translates to $0.23/W for a concentration ratio of 1100. The cell costs of 

$0.50/W and $0.10/W represent the high end of what Emcore is currently delivering and lower 

costs that might be achieved, respectively. The $1,000/m2

 area cost potentially includes not 

only the module costs, but also installation and land-use costs, and may approximate an entrylevel system today. Lower costs will need to be achieved to be competitive in the marketplace; 

the $100/m2

 target is aggressive, but demonstrates how the role of cell efficiency changes when 

the system cost becomes dominated by the cell cost. Clearly, for $1,000/m2

 systems, efficiency 

is a strong cost driver. But, if the balance-of-system cost can be reduced to $100/m2

 without 

change in cell cost, then efficiency becomes less important. The evaluation of the importance of 

cell efficiency and cost is fairly straightforward once the system design (especially the 

concentration) is fixed and the relative costs are known. An example equation is included in the 

Fig. 3 caption. This analysis assumes that cell cost is fixed. In practice, more efficient cells 

tend to cost more, implying that the curves in Fig. 3 would be flatter in a specific scenario. 

5

6

7

8

9

1

2

3

4

5

6

Cost ($/W)

26 28 30 32 34 36 38 40

Cell efficiency (%)

Area cost $0.10/W $0.50/W Cell cost

$1000/sq m 

$300/sq m 

$100/sq m 

Fig. 3. System cost as a function of cell cost and non-cell costs. The power was decreased 

from 850 to 690 W/m2

 to account for optical and thermal losses. The equation used to calculate 

these data was Cost ($/W) = Area cost ($/m2

)/Efficiency X 690 (W/m2)) + Cell cost ($/W). The 

definition of cell cost in $/W has 20%–35% uncertainty because it may or may not account for 

optical and/or thermal losses. 

 12
Substrate Supply 

The manufacture of multijunction space cells in the last decade has been based primarily on 

germanium wafers supplied by a single company: Umicore (Brussels, Belgium). Now, multiple 

companies are developing a germanium wafer capability, including AXT (Fremont, California); 

Sylarus (St. George, Utah); and PBT (Zurich, Switzerland). Umicore has announced plans to 

build a second plant in Quapaw, Oklahoma, to help service this growing market. In addition, if 

the inverted method[11] of fabricating the multijunction cells becomes popular, the substrates 

may be reused or the material recycled. Although it is possible that the industry could be so 

successful as to create a shortage of wafers, this is not currently on the horizon. 

Germanium (Ge) metal is obtained principally as a by-product of zinc refining or coal-burning 

(recovered from the fly ash). In 2007, Ge suppliers produced about 100 metric tons, most of it in 

the form of germanium tetrachloride (GeCl4) and germanium dioxide (GeO2).[16] Canada and 

China are the world's largest Ge sources, each supplying more than one-third of the world's Ge 

production. Mining companies indicate there is a 50-year known reserve at today's consumption 

rate, and that this reserve does not include vast new reserves available in Africa (especially the 

Democratic Republic of Congo), where political stability (and therefore access) appears to be 

improving. The major Ge consumers in 2007 were fiber optics (35%), infrared optics (30%), PET 

catalysts (15%), and electronics and solar applications (15%).[16]

Wafer industry experts tell us there is sufficient Ge to support a CPV installation rate of 

~4 GW/yr. Industry experts also point out that a significant Ge consumer, PET plastics, is 

moving aggressively to replace Ge with lower-cost catalysts, and at least two Chinese PET 

manufacturers have reported using a titanium-based solution.[17] It is significant that the PET 

catalyst percentage of the Ge market has declined from 31% in 2005 to 15% in 2007.[18] As 

worldwide Ge production increases and PET demand diminishes, the experts contend that there 

will be ample Ge available to support even the most optimistic terrestrial III-V CPV market 

scenarios through 2030 and beyond. 

Optics 

The primary concerns expressed about the optics are related to the reliability. Yellowing or 

pitting of plastic lenses, the need for washing, etc., are all concerns. Some companies are 

using glass lenses to avoid the abrasion expected for plastic lenses. The availability of optics 

was not raised as a concern. 

Trackers 

Although industry representatives did not describe trackers as a serious problem, trackers are 

known to require periodic maintenance, and glitches in performance or outright mechanical 

failure can decrease performance and increase maintenance costs substantially. 

Lead-Free Solders for Tracker Controllers 

As the world has moved away from using lead in solder, the long-term (~30-year) reliability of 

the newer solders is not widely understood. The controllers for CPV trackers include soldered 

components that need to be reliable for many years. Whereas it is clear that lead-containing 

 13
paints are a hazard to public health, the hazard of using leaded solder for cell interconnections 

or printed circuit boards for controllers is less clear. It would be useful for the national 

laboratories to quantify the risks associated with these uses of lead. Some possibilities for 

responding to the need for reliable printed-circuit boards include: identifying a lead-free solder or 

method for applying that solder to provide the needed reliability, and/or identifying companies 

that supply low-cost leaded solders and the associated electronics boards. 

Cell Bonding and Encapsulation 

The bonds between the cell and heat sink and between the cell and the optics (or air) can be 

problematic. Many of the companies report degradation of these bonds during stress testing 

and have had to study multiple designs. One study reported subjecting five encapsulant 

materials to the equivalent of 20 years of UV exposure, and found only one that did not 

degrade.[19] Optical coatings may, for example, darken over time or trap moisture and accelerate 

degradation. A wormlike bubble has been found at the interface between the cell and the 

secondary optics. The cell suppliers and the system integrators need to work together to 

understand potential issues here, but concerns over competition and protecting proprietary 

processes inhibit the necessary disclosure and cooperation. 

Weathering from sunlight is well known; when the sunlight is concentrated 1000 times, or even 

higher locally, the associated weathering problems can be severe. Accelerated testing of the 

effect of concentrated light is especially challenging and has not been well defined. 

Cell Assembly/Receiver Fabrication 

The solar cells must be attached to a heat sink and electrical connections completed. In most 

cases, the resulting piece is called a receiver or cell assembly. Spectrolab and Emcore have 

currently developed a couple of standard concentrator cell assembly/receiver designs. Ideally, 

cell assemblies can be tailored to match each CPV optical design. For each design, the 

assembly equipment must be automated and the final product carefully tested. Although more 

than a dozen companies are developing a cell capability and more than 30 companies are 

developing CPV systems, we identified only one company (in addition to the cell companies) 

that is marketing multijunction CPV cell assemblies: Delta Electronics of Taiwan. The expertise 

needed to create these cell assemblies is fairly well established in the LED industry, so this 

represents a business opportunity for such companies. In the long run, it is probable that 

entities with cell assembly capabilities will be targeted for acquisition, as the industry later 

moves toward vertical integration. 

Skilled Labor 

The availability of appropriately skilled labor is a challenge for all of the CPV companies. 

Nevertheless, individuals with experience working with LEDs, optical design, reliability testing, 

etc., are making important contributions to developing CPV prototypes. This difficulty is shared 

across the board among renewable energy firms today. 

 14
Utility Interactions 

Electricity bills use a variety of algorithms for defining charges. An understanding of these is 

necessary to calculate payback times for installations in different billing areas. Some of the 

companies expressed a desire to have this information compiled for easy access. 

Underwriters Laboratories (UL) certification is required for building-integrated applications. UL 

is developing the capability to complete a UL certification on CPV systems. 

Material Availability Limits 

Projections of materials availability are always complicated by the potential development of new 

mining techniques driven by increased demand. Nevertheless, raw material costs have been 

rising lately. Here, we reference a study by Feltrin and Freundlich (Fig. 4).[20] Their use of 200X 

as the concentrating factor is conservative compared with what most companies are currently 

pursuing (500X–1000X). The first bar implies a fairly severe limitation regarding the availability 

of Ge, based on U.S. supplies. The dotted box includes the supplies they estimated would be 

available worldwide. Compared with the first bar, the second bar implies 60 times higher 

availability, this time limited by Ga availability. The third bar in Fig. 4, labeled “EPI Lift-off,” is 

potentially relevant to the inverted, metamorphic approach,[11] with availability of indium as the 

limiting factor, allowing four times higher production than indicated by the second bar. More 

studies of this sort are needed to gain confidence in the conclusions, but these data imply that 

material availability will not prevent the success of CPV. 

Fig. 4. Material availability study from Ref.[20] (A. Feltrin and A. Freundlich, "Material Challenges for 

Terawatt Level Deployment of Photovoltaics," Conference Record of the 2006 IEEE 4th World Conference on 

Photovoltaic Energy Conversion, ©2006 IEEE, Reproduced with permission.)

 15
Summary 

The use of concentrated sunlight on very small, but highly efficient (~40%) solar cells has the 

potential to provide cost-effective, large-scale, solar-electricity generation, especially in sunny 

locations. More than a dozen companies have learned to fabricate multijunction concentrator 

cells, positioning themselves to respond to the growing demand for these cells. About 30 

companies are developing concentrator photovoltaic systems, and many have already deployed 

1–100 kW in the field. This industry is showing signs of being poised for substantial growth in 

the next years as the world enthusiastically embraces solar energy. 

Part II – Low-Concentration Approaches Using Silicon or Other Cells 

The silicon PV industry has grown dramatically in recent years. The industry is working hard to 

cut costs for every step of the manufacturing and installation processes. Significant effort has 

focused on thinning the silicon wafers in order to reduce the usage of silicon material. A 

complementary approach is to reduce the area of silicon needed by using optics to redirect the 

light toward smaller cells. This approach can also be applied to thin-film PV such as copper 

indium gallium diselenide (CIGS) or cadmium telluride (CdTe). The primary cost advantage is 

achieved with even a small concentration of light. A concentration ratio of 2–4 reduces the 

amount of semiconductor material to one-half or one-quarter of the original cost. 

This advantage must be balanced with the loss of solar resource that comes from a reduced 

use of diffuse light. The maximum acceptance angle is a function of the concentration and the 

index of refraction of the medium.[21] Specifically, for a linear concentration ratio, C, and index of 

refraction, n, the theoretical maximum acceptance angle, θ, can be found from 

C=n/(sin θ). 

For fixed systems, a small acceptance angle can dramatically reduce the available resource. 

For two-axis tracked systems, and low concentration ratios, the reduction in the available 

resource may be less than 10%. A few years ago, most systems were deployed on rooftops in 

a fixed configuration, but, recently, the number of systems deployed on trackers has increased. 

If a tracker is cost effective for flat-plate modules, chances are that it can also be cost effective 

for concentrator modules. Thus, the increased use of trackers for flat-plate applications could 

be viewed as paving the way for concentrator systems when PV system costs are reduced. 

A contradictory viewpoint is that trackers will not be used in the future because PV cost must be 

significantly reduced in order to compete with fossil fuels. As the PV cost is reduced, if the 

tracker cost is not reduced by a similar amount, it may no longer be cost effective to use a 

tracker. Thus, we may conclude that low-cost trackers may be key to the success of lowconcentration systems. 

Currently, the development of low-concentration systems is lagging that of high-concentration 

systems. However, the approach is not new: ENTECH developed a linear, ~20X concentrator 

system using silicon cells in the 1980s. In the 1990s, the company deployed hundreds of 

kilowatts of this low-concentration technology.[22] The performance of these was well 

documented through the PVUSA project, demonstrating the highest efficiency of the systems 

studied. However, it appears that this was a technology before its time: the market for tracked 

systems was very small in the 1990s, and ENTECH needed high volume to achieve competitive 

costs. After several years of developing concentrators for space applications, ENTECH, in 

 16
partnership with WorldWater, is now marketing these systems afresh. Although, ENTECH's 

early efforts were not a commercial success, today’s companies can learn much from 

ENTECH's early field experience. 

BP Solar also developed a linear-focus, low-concentration system using Si cells. Working with 

the Instituto de Energia Solar within the EUCLIDES project, BP Solar used a reflective trough, 

first demonstrating a single unit, then scaling up to 480 kW with multiple troughs.[23] Today’s 

companies may also learn from the EUCLIDES experience, which suffered from inadequate 

design testing before scale-up. 

The number of companies working on low-concentration designs has increased significantly in 

recent years, as shown in Table 6. The range of approaches extends from the types of systems 

just described to designs that can function much like flat plate, including holographic and 

luminescent concentrators. Although in the early developmental stages, many of these 

companies are making good progress and are receiving substantial public recognition. 

JX Crystals has deployed more than 100 kW. WS Energia was selected from 3500 candidates 

for recognition in the LIVE EDGE competition. Solaria was selected for funding by the U.S. 

Department of Energy through its Incubator program. 

Table 6. Summary of Companies Developing Low-Concentration PV Products 

Company Type of System Location On Sun in 2007

Covalent Solar Luminescent, 

multiple types of 

cells 

Boston, MA, USA 

CPower Reflective, 25X–30X 

(point focus), Si cells

Ferrara, Italy 

ENTECH Linear Fresnel lens; 

Si cells 

Fort Worth, TX, USA > 100 kW in the 

1990s 

JX Crystals Reflective, linear, Si 

cells 

Issaquah, WA, USA > 100 kW 

Maxxun Luminescent Eindhoven, Netherlands 

Morgan Solar Non-tracking, 

building integrated 

Toronto, ON, Canada 

Netcrystal Non-tracking; Si 

cells 

San Francisco, CA, 

USA 

Pacific Solar Tech Dome-shaped lens; 

Si cells 

Fremont, CA, USA 

Prism Solar 

Technologies 

Holographic; Si cells Lake Katrine, NY, USA 

Pythagoras Solar Static Hakfar Hayarok, Israel 

Silicon CPV Fresnel (point focus) 

Si cells 

Essex, UK 

Skyline Solar CA, USA 

Solaria 2X–3X; Si cells Fremont, CA, USA 

Solbeam Tracking optics in 

flat configuration 

Laguna Niguel, CA, 

USA 

Stellaris Static North Billerica, MA, 

USA 

Silicon Valley Solar Flat-plate 

dimensions 

Sunnyvale, CA, USA 

 17
Company Type of System Location On Sun in 2007

Sunengy Liquid; Si cells Australia 

Thales Research Static, reflective Severna Park, MD, USA 

Whitfield Solar Linear Fresnel lens, 

~40X; Si cells 

Reading, UK 

WS Energia Reflective, linear, Si 

modules 

Oeriias, Portugal >10 kW 

Zytech Solar Reflective, linear, Si 

modules 

Zaragoza, Spain 

Cell Supply 

Historically, a key challenge of the low-concentration approach has been obtaining a consistent 

supply of solar cells that function well under the desired concentration. The primary difference 

between standard, one-sun solar cells and the concentrator cells is the need for a reduced 

series resistance. In addition, the cells may need to be fabricated in different geometries and 

may benefit from improved thermal contact with a heat sink. Typically, as with the highconcentration approach, there is benefit to purchasing higher-efficiency cells. The buriedgroove-contact cells and back-point-contact cells have been of special interest for lowconcentration applications in the past. With the current shortage of silicon feedstock, most 

companies can easily sell silicon cells as fast as they can make them, providing little motivation 

for companies to develop both one-sun and concentrator product lines. However, any of the 

silicon cell companies could diversify in preparation for the possibility that low-concentration 

approaches could become important. Companies that may be involved include Q-cells AG, 

SunPower, NaRec, and BP Solar. There is also interest in the use of CIGS or CdTe. The 

concentrator version of the CIGS cell must be moved from a glass substrate to a metal or other 

thermally conducting substrate. Daystar originally planned to develop a low-concentration 

system using CIGS cells, but has now dropped the concentrator approach. 

The low- and high-concentration approaches share many of the same challenges of prototype 

and tracker development and testing, as well as the need for development of appropriate 

standards. These are discussed in detail in Part I and are not repeated here. 

Summary 

The use of optical concentration to reduce the amount of silicon needed per watt in solar 

systems has the potential to provide cost-effective, large-scale, solar-electricity generation. 

Although only a couple of companies have completed large low-concentration systems, almost 

20 companies are publicly developing products. The reduced need for silicon could allow these 

companies to grow at a rate that significantly exceeds that of the rest of the industry. 

Acknowledgments 

We extend our sincere gratitude to the many individuals who contributed to this report. Special 

thanks go to David Danzilio, Geoff Kinsey, Greg Peisert, Jerry Olson, Bob Cart, Brad Hines, Jeff 

Gordon, Craig Cornelius, Lori Greene, and Susan Moon. This work was funded by the U.S. 

Department of Energy under Contract No. DE-AC36-99-GO10337. 

 18
 19

References 

[1] Geisz JF, Kurtz SR, Wanlass MW, Ward JS, Duda A, Friedman DJ, Olson JM, McMahon WE, Moriarty 

TE, Kiehl JT, Romero MJ, Norman AG, and Jones KM, "Inverted GaInP/(In)GaAs/InGaAs triplejunction solar cells with low-stress metamorphic bottom junctions," Proceedings of the 33rd IEEE 

Photovoltaic Specialists Conference, San Diego, CA, 2008 (IEEE). [2] King RR, Law DC, Edmondson KM, Fetzer CM, Kinsey GS, Yoon H, Sherif RA, and Karam NH, "40% 

efficient metamorphic GaInP/GaInAs/Ge multijunction solar cells," Appl Phys Lett 90, 183516 

(2007). [3] Olson JM, Friedman DJ, and Kurtz S, in Handbook of Photovoltaic Science and Engineering, edited by 

A. Luque and S. Hegedus (John Wiley and Sons, West Sussex, England, 2003), p. 359-412. [4] Bosi M and Pelosi C, "The Potential of III-V Semiconductors as Terrestrial Photovoltaic Devices," 

Progress in Photovoltaics 15, 51-68 (2007). [5] Luque A, Sala G, and Luque-Heredia I, "Photovoltaic Concentration at the Onset of its Commercial 

Deployment," Progress in Photovoltaics 14, 413-428 (2006). [6] Swanson RM, "The Promise of Concentrators," Prog. Photovolt. Res. Appl. 8, 93-111 (2000). [7] Hering G, "X marks the spot," PHOTON International April, 123 (2007). [8] Baur C, AW B, and F D, "Triple-junction III-V based concentrator solar cells: Perspectives and 

challenges," Journal of Solar Energy Engineering 129, 258-265 (2007). [9] Hering G, "Vertically integrated at 520 suns," PHOTON International March, 86-87 (2008). [10] in Concentrator Photovoltaics, edited by A. Luque and V. Andreev (Springer Series, 2007). [11] Geisz JF, Kurtz SR, Wanlass MW, Ward JS, Duda A, Friedman DJ, Olson JM, McMahon WE, Moriarty 

T, and Kiehl J, "High-efficiency GaInP/GaAs/InGaAs triple-junction solar cells grown inverted with 

a metamorphic bottom junction," Appl Phys Lett 91, 023502 (2007). [12] Peharz G and Dimroth F, "Energy Payback Time of the High-concentration PV System FLATCON," 

Prog. Photovolt. 13, 627-734 (2005). [13] Presented at the Concentrated Photovoltaic Summit '08, http://www.cpvtoday.com/eu08/. [14] Mehdi IS, George PJ, O'Neill MJ, Matson R, and Brockschmidt A, "High voltage solar concentrator 

experiment with implications for future space missions," Solar Power from Space and 5th 

Wireless Power Transmission Conference, Granada, Spain, 2004. [15] Accelerated Aging Testing and Reliability in Photovoltaics Workshop II Summary Report, April 1 and 2, 

2008, http://www.eere.energy.gov/solar/solar_america/pdfs/accelerated_aging_report_2008.pdf [16] http://minerals.usgs.gov/minerals/pubs/commodity/germanium/mcs-2008-germa.pdf, USGS Mineral 

Commodities Summary, January (2008). [17] http://www.foodproductiondaily.com/news/ng.asp?id=72474-wellman-pet-carbonated, "Titanium PET 

bottles take the pressure," (2006). [18] http://minerals.usgs.gov/minerals/pubs/commodity/germanium/germamcs06.pdf, (2006). [19] Araki K, Uozumi H, Kondo M, Takamoto T, Agui T, Kaneiwa M, Egami T, Hiramatsu M, Miyazaki Y, 

Kemmoku Y, Akisawa A, Lee HS, EkinsDaukes NJ, and Yamaguchi M, "Development of a new 

550X concentrator module with 3J cells - performance and reliability," Proceedings of the 31st 

IEEE Photovoltaic Specialists Conference, Orlando, Florida, 2005 (IEEE), p. 631-634. [20] Feltrin A and Freundlich A, "Material Challenges for Terawatt Level Deployment of Photovoltaics," 

(2006). [21] Welford WT and Winston R, "The Optics of Nonimaging Concentrators: Light and Solar Energy," 

Academic Press (1978). [22] O'Neill M and McDanal AJ, "The 25 kilowatt SolarRow: a building bock for utility-scale concentrator 

systems," 25th IEEE Photovoltaic Specialists Conference, Washington D.C., 1996 (IEEE, New 

York), p. 1529-1532. [23] Arboiro JC, Sala G, Molina JI, Hernando L, and Camblor E, "The EUCLIDES concentrator: a 

lightweight 84 m long structure for sub-degree tracking," 2nd World Conf. on Photovoltaic Energy 

Conversion, Vienna, 1998 (IEEE), p. 2229-2232. 
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This report assesses the current status of the rapidly growing concentrating photovoltaic (CPV) industry, 

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published in July 2008 focused on the value of using multijunction solar cells and high-concentration 

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15. SUBJECT TERMS

concentrating photovoltaics; CPV; concentrator cells; industry; vertical integration; prototype development; 

qualification standards; material availability 

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