June 2004 • NREL/CP-520-35346 

Concentrator Photovoltaic 

Qualification Standards for 

Systems Using Refractive 

and Reflective Optics 

Preprint 

R. McConnell 

National Renewable Energy Laboratory 

L. Ji 

Arizona State University

J. Lasich and R. Mansfield 

Solar Systems Pty Ltd. 

To be presented at the 19th European PV Solar Energy 

Conference and Exhibition 

Paris, France 

June 7–11, 2004

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CONCENTRATOR PHOTOVOLTAIC QUALIFICATION STANDARDS 

FOR SYSTEMS USING REFRACTIVE AND REFLECTIVE OPTICS 

Robert McConnell 

NREL, 1617 Cole Boulevard, Golden, CO 80401, USA 

Tel: 303-384-6419, Fax: 303-384-6481, e-mail: robert_mcconnell@nrel.gov

Liang Ji 

Photovoltaic Testing Laboratory, Arizona State University East, 7349 E. Unity Ave., Mesa, AZ 85212, USA 

Tel: 480-727-1219, Fax: 480-727-1223, e-mail: l.ji@asu.edu

John Lasich and Roger Mansfield 

Solar Systems Pty Ltd, 6 Luton Lane Hawthorn, Melbourne VIC 3122 Australia 

Tel: (03)9819 9544, Fax: (03)9819 9063, e-mail: jlasich@solarsystems.com.au

rmansfield@solarsystems.com.au

ABSTRACT: This paper describes a proposed international qualification standard for photovoltaic (PV) systems 

generating electricity from concentrated sunlight. The standard’s purpose is to provide stress tests and procedures to 

identify any component weaknesses in a system. If no weaknesses are identified during qualification, both the 

manufacturer and the customer can expect a more reliable product. In 2002, we began developing the standard, under 

the auspices of the International Electrotechnical Commission (IEC), that would describe testing procedures for 

concentrator PV systems using reflecting (mirrors) or refractive (lenses) optics for focusing sunlight onto solar cells. 

The initial draft of the IEC standard was based on the first concentrator PV qualification standard published by the 

Institute of Electrical and Electronics Engineers (IEEE) in the United States in 2001. Well-developed U.S. 

concentrator technologies use refractive optics, and the IEEE standard needed improvement for testing systems with 

reflective optics. Furthermore, with record III-V solar cell efficiencies above 37%, concentrator PV developers 

around the world would like to incorporate such cells into their next generation of technologies. The paper will 

highlight significant differences between the proposed IEC standard and the earlier IEEE standard. 

Keywords: Qualification and Testing – 1, Concentrators – 2, Reliability – 3 

BACKGROUND 

The United States Department of Energy (DOE), 

through its National Renewable Energy Laboratory 

(NREL), has supported the development of qualifications 

standards for testing concentrator PV systems since 1997 

[1]. Standards play an important role in the development 

of an emerging technology by reducing the risk for both 

the manufacturer and the customer through increased 

reliability of system components that have passed the 

tests in an approved qualification standard. For example, 

flat-plate PV qualification standards developed over the 

past two decades have contributed greatly to the present 

level of flat-plate module reliability such that some 

manufacturers can back their products with guarantees 

for as long as 20 years. Only recently, in May 2001, did 

the Institute of Electrical and Electronics Engineers 

publish the world’s first concentrator PV qualification 

standard [2]. The IEEE working group creating the 

standard consisted of representatives from U.S. 

manufacturers, organizations who had installed and 

tested concentrator PV systems, and engineers from 

government laboratories familiar with concentrator PV 

technologies. The group tried to develop a standard 

suitable for systems using reflecting surfaces (mirrors), 

as well as refracting optics (lenses), for concentrating and 

focusing sunlight onto solar cells. However, welldeveloped U.S. technologies used Fresnel lenses, 

whereas many concentrator PV systems in other 

countries use mirrors. 

In spring 2002, we began a series of meetings and email exchanges under the auspices of the International 

Electrotechnical Commission (IEC) to develop an 

international standard with clearer and better 

specifications for tests for concentrator PV systems with 

mirrors while still providing an opportunity to review and 

update the IEEE standard’s tests for concentrators using 

lenses. The IEC working group, consisting of 

international representatives from companies, utilities, 

and research organizations around the world, began with 

a draft based on the IEEE standard. Since then, the U.S. 

manufacturer, Amonix, Inc., has submitted components 

of its Fresnel-lens-based concentrator to the Photovoltaic 

Testing Laboratory at Arizona State University to 

become the first company with its product qualified 

according to the IEEE standard. In Japan, Daido Steel 

and Sharp are using tests in the IEEE standard to develop 

components of a Fresnel lens concentrator system 

incorporating III-V multijunction solar cells with 

production efficiencies above 30% and record 

efficiencies above 37%. Although the IEEE standard 

was developed with high-efficiency crystalline silicon 

solar cells in mind, concentrator PV companies around 

the world are very interested in incorporating III-V solar 

cells into their next generation of systems because their 

product’s power output can increase by as much as 50% 

with a relatively small increase in system cost. These 

developments provide additional insight and impetus for 

a new IEC standard. The IEC working group plans to 

complete the balloting and publishing of the IEC 

standard in 2006. 

In considering changes to the IEEE standard, the 

group found it very important to hold the IEC meetings 

in parts of the world where companies have welldeveloped technologies. The last IEC meeting was held 

in Melbourne, Australia, in November 2003, just prior to 

the International Solar Concentrator Conference held in 

1 

1 
Figure 1: Solar System concentrator PV unit with one 

receiver on each unit. 

Alice Springs [3]. IEC working group members had the 

opportunity to gather important first-hand information 

about the concentrator PV technology developed by 

Solar Systems Pty Ltd over a period of 15 years. Their 

system uses a dish-shaped solar concentrator with 

reflecting surfaces focusing sunlight onto high-efficiency 

crystalline silicon solar cells manufactured in the United 

States by SunPower Inc. (Fig. 1). 

Concentrator PV systems with both reflective and 

refractive optics systems are now entering distributedgeneration utility markets. For example, Solar Systems 

installed a 200-kW system in an Australian distributedgeneration utility grid in 2003 and is presently installing 

another 720 kW in 2004. In the United States, Amonix 

has developed several generations of its technology, also 

over a period of 15 years. Amonix installed 600 kW over 

the past 2 years in the service territory of Arizona Public 

Service (Fig. 2), and both companies have indications 

that megawatts of their systems will be installed in 2005 

[4]. These sales are small in comparison with the 740 

MW of flat-plate PV systems produced throughout the 

world in 2003. But if the time for solar electric 

concentrators is finally here, international concentrator 

PV qualification standards will soon be available to 

support their penetration of the world’s electricity 

generation markets. 

2 OVERVIEW OF QUALIFICATION TEST 

PROGRAM 

2.1 Definitions 

A fundamental difference between flat-plate and 

concentrator PV standards is the need to differentiate 

between receivers and modules [1]. The IEEE standard 

has definitions for each that had to be substantially 

revised to provide a rigorous yet flexible set of 

definitions that apply to all types of generators as defined 

in the present draft of the IEC standard. The present 

definitions are aimed at providing clarity for 

simultaneously specifying tests for concentrator PV 

systems using mirrors or lenses. In decreasing size, the 

proposed standard defines a concentrator PV system, 

solar concentrator unit on a tracker with assemblies, 

assembly of receivers, receiver, and module. Figures 1 

and 2 show concentrator PV systems composed of solar 

concentrator units with receiver assemblies using 

reflecting optics (Fig. 1) or refractive optics (Fig. 2). A 

receiver is defined as the smallest, complete assembly of 

one or more concentrator PV modules and secondary 

optics (and related components such as interconnects and 

mounting) that accepts concentrated sunlight. A 

concentrator PV module is defined as a subassembly of 

one or more PV cells that accepts concentrated sunlight 

and incorporates the means for thermal and electric 

energy removal. In the present draft, a manufacturer 

needs to provide the test laboratory with seven module 

sections, five receivers, one receiver assembly, and one 

specially constructed module if required for the intrusive 

bypass diode sequence. 

Figure 2: Amonix concentrator PV unit with seven 

receivers. 

2.2 Baseline tests 

As in the IEEE standard, the IEC draft standard 

includes baseline tests for electrical performance, ground 

continuity, electrical isolation, and wet insulation 

resistance, along with visual inspections, to determine the 

initial status of all receiver and module sections. See Fig. 

3 for the entire qualification test sequence. 

2.3 Bypass diode and thermal cycle sequence 

In this sequence, the draft standard specifies thermal 

tests for bypass diodes and test conditions for 250 or 500 

thermal cycles between minimum rated temperature and 

1100

C or 900C, depending on the design of module 

sections. There is a separate intrusive bypass diode 

thermal sequence if access to the bypass diode is not 

possible without compromising the integrity of the 

receiver. 

2.4 Humidity-freeze and thermal cycle sequences 

In this sequence, the draft standard specifies a 

different set of thermal cycle tests for modules in parallel 

with a similar set of tests for receivers, followed by 20 

humidity-freeze cycles for both receivers and modules. 

This is another case where differences in the concentrator 

optics affect the sequence options because concentrator 

units with reflecting optics typically use active cooling of 

their receivers, whereas units with refractive optics are 

2 
Figure 3: IEC draft concentrator photovoltaic qualification test program. 

3
usually passively cooled. The tests are followed by 

electrical isolation tests. 

2.5 Damp-heat sequence 

In this sequence, the draft standard specifies tests for 

receivers in 85% relative humidity and temperatures of 

850

C for 1000 hours, followed by electrical isolation 

tests. 

2.6 Environmental stress sequence 

This is the longest sequence of tests in the standard. 

It specifies receiver tests for relatively short periods of 

outdoor exposure to identify problems that might not be 

seen in laboratory tests, water spray, off-axis solar beam 

damage, hail impact, and hot-spot endurance. Additional 

final tests and inspections in this sequence include visual 

inspection and electrical performance of receivers and 

modules, followed by final electrical isolation, wet 

insulation resistance, ground continuity, and final visual 

inspection and electrical performance tests. 

2.7 Significant differences 

We have already mentioned some significant 

differences between the earlier IEEE standard and the 

present IEC draft standard, such as new definitions for 

receivers and modules. The IEC draft includes test 

options for systems with active or passive cooling of 

receivers. Another significant difference arises in the 

specification for electrical isolation tests to determine 

whether or not the module or receiver is sufficiently well 

insulated between current-carrying parts and the frame or 

the outside world. The requirements in the IEEE test had 

a history traceable to the electrical isolation tests for flatplate PV modules. However, as can be seen from Figs. 1 

and 2, concentrator PV systems may have receivers and 

modules with areas significantly different than those of 

flat-plate systems. Concentrator PV receivers and 

modules may also be less accessible to personnel. The 

isolation resistance requirements for modules and 

receivers now depend on their areas. Finally, there are 

some differences in the specifications for electrical 

performance tests. 

ELECTRICAL PERFORMANCE TESTS 

A critical issue after a test or sequence of tests is the 

evaluation of electrical performance of the module or 

receiver to determine survival of the test. In the case of 

flat-plate PV modules, a solar simulator and reference 

cell provides a means to verify performance after a test 

sequence. This is not possible for the large systems 

shown in Figs. 1 and 2. The IEEE standard specified 

three possible tests to verify the degradation in the 

performance of receivers and modules. The most 

complex test involved outdoor baseline testing under 

various temperature and solar irradiance conditions to 

obtain an analytical expression for module and receiver 

performance. This option is not available in the present 

IEC draft due to the complexity and cost of determining 

the many parameters in the analytical expression for 

electrical performance under different outdoor 

conditions. The IEEE standard specified a second 

measurement technique to identify power degradation of 

a test receiver before and after stress tests by comparing 

its relative power with respect to a control receiver never 

subjected to stress tests. This method is based on the 

assumption that the changes in the control or reference 

receiver’s electrical performance are negligible 

throughout the qualification testing period. By using this 

method, test condition variables are self-correcting, and 

the complex analytic translation procedures are 

eliminated. The third test in the IEEE standard is the use 

of dark current-voltage (I-V) measurements before and 

after some of the intermediate stress tests. Experience 

gained with the use of a control receiver has been 

sufficiently positive that it is the principal method in the 

present IEC draft standard for determining performance 

degradation in receivers and modules. 

4 CONCLUSION 

For the past couple of years, we have been developing a 

set of test procedures to qualify concentrator PV systems 

as reliable products in international markets. We are 

building international consensus for the new standard 

through a series of meetings to review successive drafts 

of the standard. Even though the first concentrator PV 

qualification standard was completed only 3 years ago, 

there are significant differences between it and the 

present proposed draft IEC standard. This appears to be 

in the nature of standards development activities, as new 

technologies appear and experience with previous 

standards is acquired. While the details of the tests and 

procedures are under consideration and modification by 

the IEC working group, we plan to complete the IEC 

balloting and publication process in 2006. A new IEC 

standard, suitable for international technologies and 

markets, will be useful as concentrator PV systems begin 

to emerge in the world’s energy markets. 

ACKNOWLEDGMENT 

We wish to acknowledge the work of the IEEE Standards 

Association and its concentrator PV qualification 

working group for their efforts in developing the world’s 

first concentrator PV qualification standard. We also 

acknowledge the support of the International 

Electrotechnical Commission and its Technical 

Committee No. 82 (TC 82) for Solar Photovoltaic Energy 

Systems. NREL’s coordination of the standard’s 

development through the IEC TC 82 Working Group 7 

for concentrator PV systems is supported by DOE under 

Contract No. DE-AC399GO10337 and through DOE’s 

Solar Energy Technology Program within its Office of 

Energy Efficiency and Renewable Energy. Finally, we 

acknowledge Mani TamizhMani at Arizona State 

University for his guidance and encouragement. 

REFERENCES 

[1] R. McConnell, S. Kurtz, W. Bottenberg, R. 

Hammond, S. Jochums, A. McDanal, D. Roubideaux, 

C. Whitaker, and J. Wohlgemuth, Proceedings 16th 

European Photovoltaic Solar Energy Conference, 

(2000) 2237. 

[2] IEEE Concentrator Photovoltaic Module 

Qualification Working Group, IEEE std. 1513-2001, 

(2001). 

[3] Proceedings of the International Solar Concentrator 

Conference for the Generation of Electricity or 

Hydrogen, NREL/CD-520-35349, (2004). 

[4] R. McConnell, Photon International, 4/2004 (2004) 

64. 

4 

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This paper describes a proposed international qualification standard for photovoltaic (PV) systems generating 

electricity from concentrated sunlight. The standard’s purpose is to provide stress tests and procedures to identify 

any component weaknesses in a system. If no weaknesses are identified during qualification, both the manufacturer 

and the customer can expect a more reliable product. In 2002, we began developing the standard, under the 

auspices of the International Electrotechnical Commission (IEC), that would describe testing procedures for 

concentrator PV systems using reflecting (mirrors) or refractive (lenses) optics for focusing sunlight onto solar cells. 

The initial draft of the IEC standard was based on the first concentrator PV qualification standard published by the 

Institute of Electrical and Electronics Engineers (IEEE) in the United States in 2001. Well-developed U.S. 

concentrator technologies use refractive optics, and the IEEE standard needed improvement for testing systems with 

reflective optics. Furthermore, with record III-V solar cell efficiencies above 37%, concentrator PV developers around 

the world would like to incorporate such cells into their next generation of technologies. The paper will highlight 

significant differences between the proposed IEC standard and the earlier IEEE standard. 

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PV; qualification and testing; concentrators; reliability; 

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