IEC TS 61724-2:2025
(Main)Photovoltaic system performance - Part 2: Power performance index and capacity evaluation method
Photovoltaic system performance - Part 2: Power performance index and capacity evaluation method
IEC TS 61724-2:2025 applies to grid-connected PV systems comprising at least one inverter.
The test evaluates the PV system only in conditions where output is unconstrained by limitations in AC power output from the inverters. This document defines a test of a PV system's power performance index (PPI). PPI, defined in IEC 61724‑1, is the ratio of a system's measured power output under test conditions to its expected output at those conditions based on the system's design.
The test is intended to be performed over a short period of typically three to five days and is typically used to satisfy a contractual performance guarantee as part of the final completion of a PV power plant. This second edition cancels and replaces the first edition published in 2016. This edition includes the following significant technical changes with respect to the previous edition:
a) Adapting the document for bifacial PV systems, in accordance with the latest edition of IEC 61724‑1 and current industry practices.
b) Adapting the test procedure to account for the limited times of unconstrained system operation which are now common because of high DC-to-AC ratios (clipping) and interconnection limits (curtailment).
c) Adapting the test procedure to achieve a test that can be performed in a short time of three to five days during favourable conditions.
d) Focusing the document more heavily on the use of modern PV system modelling software to obtain the expected performance of the system under test.
e) Simplifying the mathematical procedure for calculating the test results.
f) Clearly identifying test elections (optional choices to be made in conducting the test) and providing a template for documenting these elections.
g) Clarifying the discussion of the test boundary that separates tested variables from untested variables.
h) Expanding and clarifying the discussion of data filtering.
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Standards Content (Sample)
IEC TS 61724-2 ®
Edition 2.0 2025-09
TECHNICAL
SPECIFICATION
Photovoltaic system performance -
Part 2: Power performance index and capacity evaluation method
ICS 27.160 ISBN 978-2-8327-0656-5
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CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Purpose of the test . 8
5 Test boundary and test elections . 8
6 Schedule . 9
7 Measurement equipment . 9
7.1 General . 9
7.2 Irradiance measurement . 10
7.3 PV cell temperature . 11
7.4 Electrical power . 12
8 Soiling . 12
9 Trackers . 13
10 Performance model . 13
10.1 Overview. 13
10.2 Performance model option 1 . 14
10.3 Performance model option 2 . 15
10.4 Performance model option 3 . 16
11 Partial shading . 17
12 Plant design modifications . 17
13 Multiple plant sections . 18
14 Filtering data . 19
14.1 Purpose . 19
14.2 General requirements . 19
14.2.1 Documentation . 19
14.2.2 Synchronization . 19
14.2.3 Manner of excluding data . 19
14.2.4 Consistency . 19
14.2.5 Multiple sensors . 19
14.3 Test limits . 19
14.3.1 POA irradiance . 19
14.3.2 Inverter utilization . 20
14.3.3 Partial shading. 20
14.3.4 Angle of incidence . 20
14.4 Invalid readings . 20
14.4.1 Data out of range of reasonable physical limits . 20
14.4.2 Stuck values . 20
14.4.3 Missing data . 21
14.5 Operational issues . 21
14.5.1 Equipment not functioning . 21
14.5.2 Trackers not tracking . 21
14.6 Unstable irradiance . 21
14.7 Non-linear or non-uniform conditions . 21
15 Procedure . 22
15.1 Determine and document test elections . 22
15.2 Acquire measured data . 22
15.3 Filter the data . 22
15.4 Determine coefficients of the performance equation, if used . 22
15.5 Calculate expected power . 22
15.6 Calculate power performance index (PPI) . 22
16 Test report . 23
Annex A (informative) Template for documenting test elections . 24
Bibliography . 26
Figure 1 – Illustration of test boundary and test elections . 9
Table 1 – Problems that are either detected or potentially not detected by the test . 8
Table 2 – Solar resource test elections . 10
Table 3 – POA irradiance sensor type test elections . 11
Table 4 – PV cell temperature test elections . 12
Table 5 – Soiling test elections . 13
Table 6 – Tracker system test elections . 13
Table 7 – Performance model test elections . 14
Table 8 – Partial shading test elections . 17
Table 9 – Plant design modifications test elections . 18
Table 10 – Multiple plant sections test elections . 18
INTERNATIONAL ELECTROTECHNICAL COMMISSION
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Photovoltaic system performance -
Part 2: Power performance index and capacity evaluation method
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