National foreword

This Published Document is the UK implementation of IEC TS 61724‑2:2025. It supersedes PD IEC TS 61724‑2:2016, which is withdrawn.

The UK participation in its preparation was entrusted to Technical Committee GEL/82, Photovoltaic Energy Systems.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

This publication is not to be regarded as a British Standard.

Compliance with a Published Document cannot confer immunity from legal obligations.

This Published Document was published under the authority of the Standards Policy and Strategy Committee on 30 September 2025.

FOREWORD

The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC Publication(s)"). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees.
IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user.
In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services carried out by independent certification bodies.
All users should ensure that they have the latest edition of this publication.
No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.
Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication.
IEC draws attention to the possibility that the implementation of this document may involve the use of (a) patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which may be required to implement this document. However, implementers are cautioned that this may not represent the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC shall not be held responsible for identifying any or all such patent rights.

IEC TS 61724‑2 has been prepared by IEC technical committee 82: Solar photovoltaic energy systems. It is a Technical Specification.

This second edition cancels and replaces the first edition published in 2016. This edition constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous edition:

Adapting the document for bifacial PV systems, in accordance with the latest edition of IEC 61724‑1 and current industry practices.
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).
Adapting the test procedure to achieve a test that can be performed in a short time of three to five days during favorable conditions.
Focusing the document more heavily on the use of modern PV system modeling software to obtain the expected performance of the system under test.
Simplifying the mathematical procedure for calculating the test results.
Clearly identifying test elections (optional choices to be made in conducting the test) and providing a template for documenting these elections.
Clarifying the discussion of the test boundary that separates tested variables from untested variables.
Expanding and clarifying the discussion of data filtering.

The text of this Technical Specification is based on the following documents:

Full information on the voting for its approval can be found in the report on voting indicated in the above table.

The language used for the development of this Technical Specification is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are described in greater detail at www.iec.ch/publications.

A list of all parts in the IEC 61724 series, published under the general title Photovoltaic system performance, can be found on the IEC website.

The committee has decided that the contents of this document will remain unchanged until the stability date indicated on the IEC website under webstore.iec.ch in the data related to the specific document. At this date, the document will be

reconfirmed,
withdrawn, or
revised.

INTRODUCTION

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.

NOTE This type of test is sometimes referred to as a capacity test, whose result is a capacity test ratio, which is equivalent to PPI.

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.

1 Scope

The test 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. Accordingly:

Data used for the test is limited to times when inverters are maximum-power-point tracking, so that PV system output power is unconstrained by inverter limitations (clipping) or interconnection limits (curtailment).
The maximum operational capacity of the system can ultimately be determined by maximum inverter output.

Results of a performance test can be affected by various choices made in the procedure. Therefore, this document clarifies how test choices ("test elections") affect the boundary between external variables and the part of the system being tested.

For a procedure that evaluates system performance over an extended period, including during constrained operation, refer to IEC TS 61724‑3, Photovoltaic system performance – Part 3: Energy performance evaluation method.

2 Normative references

3 Terms and definitions

4 Purpose of the test

5 Test boundary and test elections

6 Schedule

7 Measurement equipment

7.1 General

7.2 Irradiance measurement

7.3 PV cell temperature

7.4 Electrical power

8 Soiling

9 Trackers

10 Performance model

10.1 Overview

10.2 Performance model option 1

10.3 Performance model option 2

10.4 Performance model option 3

11 Partial shading

12 Plant design modifications

13 Multiple plant sections

14 Filtering data

14.1 Purpose

14.2 General requirements

14.3 Test limits

14.4 Invalid readings

14.5 Operational issues

14.6 Unstable irradiance

14.7 Non-linear or non-uniform conditions

15 Procedure

15.1 Determine and document test elections

15.2 Acquire measured data

15.3 Filter the data

15.4 Determine coefficients of the performance equation, if used

15.5 Calculate expected power

15.6 Calculate power performance index (PPI)

16 Test report

Bibliography

PD IEC TS 61724-2:2025

Photovoltaic system performance - Power performance index and capacity evaluation method

Current

Published:

30 Sep 2025