{"id":534,"date":"2026-03-18T09:46:39","date_gmt":"2026-03-18T09:46:39","guid":{"rendered":"https:\/\/solartester.nl\/index.php\/article-sampling-3\/"},"modified":"2026-03-18T09:46:47","modified_gmt":"2026-03-18T09:46:47","slug":"article-sampling-3","status":"publish","type":"page","link":"https:\/\/solartester.nl\/index.php\/article-sampling-3\/","title":{"rendered":"Article-Sampling"},"content":{"rendered":"\n \n
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Sampling Methodology for Testing Large Batches of Solar Modules
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Sampling Methodology for Testing Large Batches of Solar Modules <\/span>\n
When testing large batches of solar modules, Solar Tester applies a structured sampling approach. By agreeing on clear testing criteria upfront, we prevent discussions afterward. This article explains how the sample size is determined, what the escalation path looks like, and when a batch is accepted or rejected. 
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The determination of sample size and acceptance criteria is based on ISO 2859-1, an internationally recognized and widely used sampling standard. By applying this scientifically validated method, all stakeholders have clarity on how testing is performed and how results should be interpreted.
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Determining the Sample Size <\/span>\n
Two key factors determine the required sample size:
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Total population size<\/span><\/span>\n
This is the total number of modules used for a specific project.
  
Inspection level<\/span>\n
ISO 2859-1 defines three inspection levels:
  
Level I \u2013 Reduced Inspection <\/span>\n
Used when previous inspections at Level II have been successful, or when there is strong confidence in the supplier or production process. 
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Level II \u2013 Normal Inspection <\/span>\n
The standard inspection level used when no special circumstances apply. 
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Level III \u2013 Tightened Inspection <\/span>\n
Applied when previous issues have occurred with the supplier or product quality.\nThe inspection level is defined per test and can be adjusted during testing. For example, if excessive defects are found during a Level I inspection, the inspection level can be escalated to Level II or Level III. ISO 2859-1 clearly defines this escalation path in advance.
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Sample Size Tables <\/span>\n
By combining the population size with the inspection level, the required sample size is determined using the ISO sampling tables. First, the population range is identified. Next, the corresponding inspection level column is selected, resulting in a code letter. This code letter determines the final sample size in the sampling table.
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Sample Size Table<\/h2>\n

The lot numbers, letter code, and sample sizing based on ISO 2859-1<\/p>\n

\n \n \n \n \n \n \n <\/colgroup>\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n
LOT SIZE<\/th>\n LEVEL I<\/th>\n LEVEL II<\/th>\n LEVEL II<\/th>\n <\/tr>\n <\/thead>\n
2-8
\n <\/td>\n 		A<\/td>\n A<\/td>\n B <\/td>\n <\/tr>\n
9-15<\/td>\n A<\/td>\n B<\/td>\n C<\/td>\n <\/tr>\n
16-25<\/td>\n B<\/td>\n C<\/td>\n D<\/td>\n <\/tr>\n
26-50
\n <\/td>\n 		C<\/td>\n D<\/td>\n E<\/td>\n <\/tr>\n
51-90<\/td>\n C<\/td>\n E<\/td>\n F<\/td>\n <\/tr>\n
91-150<\/td>\n D<\/td>\n F<\/td>\n G<\/td>\n <\/tr>\n
151-280<\/td>\n E<\/td>\n G<\/td>\n H<\/td>\n <\/tr>\n
281-500<\/td>\n F<\/td>\n H<\/td>\n J<\/td>\n <\/tr>\n
501-1.200<\/td>\n G<\/td>\n J<\/td>\n K<\/td>\n <\/tr>\n
1.201-3.200<\/td>\n H<\/td>\n K<\/td>\n L<\/td>\n <\/tr>\n
3.201-10.000<\/td>\n J<\/td>\n L<\/td>\n M<\/td>\n <\/tr>\n
10.001-35.000<\/td>\n K<\/td>\n M<\/td>\n N<\/td>\n <\/tr>\n
35.001-150.000<\/td>\n L<\/td>\n N<\/td>\n P<\/td>\n <\/tr>\n <\/tbody>\n <\/table>\n <\/div>\n <\/div>\n <\/section>\n
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<\/span>Acceptance and Rejection Criteria 
<\/span>In addition to the sample size, acceptance and rejection criteria must be defined. Product defects are classified into three categories:
 
Minor defects: <\/span>Defects that most users would not notice or consider problematic
Major defects:<\/span> Defects that users would not accept
Critical defects:<\/span> Completely unacceptable defects
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Solar Tester applies the defect classification used by MBJ<\/span>, the supplier of our testing laboratory. Under these criteria, modules are classified as: 
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Class A<\/span>: No defects
Class B<\/span>: One or more minor defects
Class C<\/span>: Major defects
Class D<\/span>: Critical defects
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AQL \u2013 Acceptable Quality Limit 
<\/span>Acceptance decisions are based on the AQL (Acceptable Quality Limit) method. AQL defines the maximum allowable percentage of defects within the total population. 
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For example, an AQL of 4.0 for minor defects means that up to 4% of the entire batch may contain minor defects.\nSeparate AQL values must be defined for:
 
Minor defects
Major defects
Critical defects
  
Typical values used in the industry are: 
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Minor defects:<\/span> AQL 4.0
Major defects:<\/span> AQL 0.4
Critical defects<\/span>: AQL 0
  
Because a sample represents only part of the total population, the ISO tables allow a higher percentage of defects within the sample itself. The maximum number of allowed defects per AQL level is defined in the AQL tables.
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Letter code table - Sample lot<\/h2>\n

Letter codes and their corresponding sample size based on ISO 2859-1<\/p>\n

\n \n \n \n \n \n \n <\/colgroup>\n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n \n
Letter code<\/th>\n SIZE<\/th>\n AQL 0.4<\/th>\n AQL 4.0<\/th>\n <\/tr>\n <\/thead>\n
A <\/td>\n 2<\/td>\n 0<\/td>\n 0<\/td>\n <\/tr>\n
B<\/td>\n 3<\/td>\n 0<\/td>\n 0<\/td>\n <\/tr>\n
C<\/td>\n 5<\/td>\n 0<\/td>\n 0<\/td>\n <\/tr>\n
D
\n <\/td>\n 		8<\/td>\n 0<\/td>\n 0<\/td>\n <\/tr>\n
E<\/td>\n 13<\/td>\n 0<\/td>\n 1<\/td>\n <\/tr>\n
F<\/td>\n 20<\/td>\n 0<\/td>\n 2<\/td>\n <\/tr>\n
G<\/td>\n 32<\/td>\n 0<\/td>\n 3<\/td>\n <\/tr>\n
H<\/td>\n 50<\/td>\n 0<\/td>\n 5<\/td>\n <\/tr>\n
J<\/td>\n 80<\/td>\n 0<\/td>\n 7<\/td>\n <\/tr>\n
K<\/td>\n 125<\/td>\n 1<\/td>\n 10 <\/td>\n <\/tr>\n
L<\/td>\n 200<\/td>\n 2<\/td>\n 14<\/td>\n <\/tr>\n
M<\/td>\n 315<\/td>\n 3<\/td>\n 21<\/td>\n <\/tr>\n
N<\/td>\n 500<\/td>\n 5<\/td>\n 21<\/td>\n <\/tr>\n
P<\/td>\n 800<\/td>\n 7<\/td>\n 21<\/td>\n <\/tr>\n
Q<\/td>\n 1250<\/td>\n 10<\/td>\n 21<\/td>\n <\/tr>\n
R<\/td>\n 2000<\/td>\n 14<\/td>\n 21<\/td>\n <\/tr>\n <\/tbody>\n <\/table>\n <\/div>\n <\/div>\n <\/section>\n
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<\/span>Acceptance and Rejection Criteria 
<\/span>In addition to the sample size, acceptance and rejection criteria must be defined. Product defects are classified into three categories:
 
Minor defects: <\/span>Defects that most users would not notice or consider problematic
Major defects:<\/span> Defects that users would not accept
Critical defects:<\/span> Completely unacceptable defects
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Solar Tester applies the defect classification used by MBJ<\/span>, the supplier of our testing laboratory. Under these criteria, modules are classified as: 
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Class A<\/span>: No defects
Class B<\/span>: One or more minor defects
Class C<\/span>: Major defects
Class D<\/span>: Critical defects
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AQL \u2013 Acceptable Quality Limit 
<\/span>Acceptance decisions are based on the AQL (Acceptable Quality Limit) method. AQL defines the maximum allowable percentage of defects within the total population. 
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For example, an AQL of 4.0 for minor defects means that up to 4% of the entire batch may contain minor defects.\nSeparate AQL values must be defined for:
 
Minor defects
Major defects
Critical defects
  
Typical values used in the industry are: 
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Minor defects:<\/span> AQL 4.0
Major defects:<\/span> AQL 0.4
Critical defects<\/span>: AQL 0
  
Because a sample represents only part of the total population, the ISO tables allow a higher percentage of defects within the sample itself. The maximum number of allowed defects per AQL level is defined in the AQL tables.
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Example: Determining a Sample <\/span>\n
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To illustrate the methodology, consider a project with 3,000<\/span> solar modules.
 
Inspection level: Level II<\/span> (limited experience with supplier)
  
AQL values<\/span>\n
Minor defects: AQL 4.0
Major defects: AQL 0.4
Critical defects: AQL 0
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From the ISO sampling table:\nPopulation of 3,000 modules at Level II corresponds to code letter K<\/span>\n
  
Code letter K results in a sample size of 125 modules<\/span>\n
  
From the AQL table: 
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AQL 4.0 \u2192 up to 10 modules with minor defects allowed
AQL 0.4 \u2192 up to 1 module with major defects allowed
AQL 0 \u2192 no critical defects allowed
  
Translated to MBJ classifications<\/span>: 
Maximum 10 Class B modules  
Maximum 1 Class C module
0 Class D modules
   
Escalation During Testing <\/span>\n
If the number of detected defects exceeds the allowed AQL limits, the inspection level can be escalated. In this example, escalation from Level II to Level III moves the code letter from K to L, increasing the sample size from 125 to 200 modules. 
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Under Level III: 
AQL 4.0 \u2192 up to 14 minor defects
AQL 0.4 \u2192 up to 2 major defects
  
This escalation mechanism ensures transparency, consistency, and statistically valid decision-making throughout the testing process.
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Sampling Methodology for Testing Large Batches of Solar Modules Sampling Methodology for Testing Large Batches of Solar Modules  When testing large batches of solar modules, Solar Tester applies a structured sampling approach. By agreeing on clear testing criteria upfront, we prevent discussions afterward. This article explains how the sample size is determined, what the escalation … Continue reading “Article-Sampling”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":8,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-534","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/solartester.nl\/index.php\/wp-json\/wp\/v2\/pages\/534","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/solartester.nl\/index.php\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/solartester.nl\/index.php\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/solartester.nl\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/solartester.nl\/index.php\/wp-json\/wp\/v2\/comments?post=534"}],"version-history":[{"count":1,"href":"https:\/\/solartester.nl\/index.php\/wp-json\/wp\/v2\/pages\/534\/revisions"}],"predecessor-version":[{"id":553,"href":"https:\/\/solartester.nl\/index.php\/wp-json\/wp\/v2\/pages\/534\/revisions\/553"}],"wp:attachment":[{"href":"https:\/\/solartester.nl\/index.php\/wp-json\/wp\/v2\/media?parent=534"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}