Photovoltaic power systems (PVPSs) - Roadmap for robust reliability

IEC TR 63292:2020 continues the effort started with the availability technical specification (IEC TS 63019). Availability is closely related to PVPS operational capability, health and condition and to produce energy and is a real-time or historical measure. The availability of a system or component is impacted by contractual and non-contractual reliability specifications, maintenance metrics and a corresponding maintenance and repair strategy, and also external factors such as site environmental and grid conditions. The intention of this document is to be a precursor examination of the reliability issues for further address in a task to produce an IEC Technical Specification on this topic.
While this document identifies reliability tools, topics and procedures, there are commercial products available to perform analyses and there is no assessment of those tools or to provide recommendations for one tool over another in this document.

General Information

Status
Published
Publication Date
25-Jun-2020
Current Stage
PPUB - Publication issued
Completion Date
26-Jun-2020
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IEC TR 63292
Edition 1.0 2020-06
TECHNICAL
REPORT
colour
inside
Photovoltaic power systems (PVPSs) – Roadmap for robust reliability
IEC TR 63292:2020-06 (en)
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IEC TR 63292
Edition 1.0 2020-06
TECHNICAL
REPORT
colour
inside
Photovoltaic power systems (PVPSs) – Roadmap for robust reliability
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.160 ISBN 978-2-8322-8472-8

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – IEC TR 63292:2020 © IEC 2020
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 8

2 Primary References ......................................................................................................... 9

3 Terms, definitions and abbreviated terms ...................................................................... 10

3.1 Terms and definitions ............................................................................................ 10

3.2 Abbreviated terms ................................................................................................. 12

4 Background ................................................................................................................... 12

5 Interrelationship of Reliability, Maintainability and Availability (RAM) ............................. 13

5.1 General ................................................................................................................. 13

5.2 Availability basics ................................................................................................. 14

5.3 Maintainability basics ............................................................................................ 15

5.4 Reliability basics ................................................................................................... 16

5.5 Link to IEC TS 63019 ............................................................................................ 17

6 Dependability ................................................................................................................ 18

6.1 Dependability uses reliability tools and topics ....................................................... 18

6.2 Stakeholders interests throughout the PVPS ......................................................... 21

7 Reliability tools and topics ............................................................................................. 22

7.1 General ................................................................................................................. 22

7.2 Reliability Block Diagram (RBD) / Monte Carlo simulations ................................... 23

7.3 Failure Modes and Effects Analysis (FMEA) .......................................................... 24

7.4 Fault Tree Analysis ............................................................................................... 25

7.5 Failure Reporting and Corrective Action System (FRACAS) .................................. 25

7.6 Maintainability and other RAM terms ..................................................................... 26

7.7 Critical items list ................................................................................................... 26

7.8 Data analysis ........................................................................................................ 27

7.9 Root Cause Analysis (RCA) .................................................................................. 28

7.10 Long term trend analysis ....................................................................................... 28

7.11 Pareto analysis ..................................................................................................... 29

7.12 Risk analysis......................................................................................................... 30

7.13 Life cycle costs of reliability .................................................................................. 31

7.14 Other reliability tools and topics ............................................................................ 31

8 Why reliability, why plan? .............................................................................................. 32

9 PVPS recommendations ............................................................................................... 33

9.1 General ................................................................................................................. 33

9.2 Recommendations ................................................................................................ 33

Annex A (informative) Reliability plan ................................................................................... 34

Annex B (informative) Reliability objectives, information sources and useful references ....... 35

B.1 Objectives ............................................................................................................. 35

B.2 Information sources .............................................................................................. 36

B.3 Other useful references not previously identified ................................................... 36

Bibliography .......................................................................................................................... 37

Figure 1 – Reliability tools information flow ........................................................................... 23

Figure 2 – Example of recommended metrics ........................................................................ 29

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IEC TR 63292:2020 © IEC 2020 – 3 –

Figure 3 – Frequency analysis of key weather terms in the PVROM database ....................... 30

Figure A.1 – Reliability plan example flowchart ..................................................................... 34

Table 1 – Information category overview for a PVPS (modified from

IEC TS 63019:2019) ............................................................................................................. 18

Table 2 – Primary reliability interest of stakeholders ............................................................. 21

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– 4 – IEC TR 63292:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
PHOTOVOLTAIC POWER SYSTEMS (PVPSs) –
ROADMAP FOR ROBUST RELIABILITY
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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The main task of IEC technical committees is to prepare International Standards. However, a

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data of a different kind from that which is normally published as an International Standard, for

example "state of the art".

IEC TR 63292 which is a technical report, has been prepared by IEC technical committee 82:

Solar photovoltaic energy systems.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
82/1671/DTR 82/1716/RVDTR
82/1716A/RVDTR

Full information on the voting for the approval of this technical report can be found in the report

on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

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IEC TR 63292:2020 © IEC 2020 – 5 –

Mandatory information categories defined in this document are written in capital letters; optional

information categories are written in bold letters.

The committee has decided that the contents of this document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

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– 6 – IEC TR 63292:2020 © IEC 2020
INTRODUCTION

Reliability of a PVPS or its components is perceived in many ways depending on the perspective

of the observer. This document addresses many of these perspectives ranging from component

failures to the human factors needed in operations and maintenance (O&M) of a PVPS.

Technically, reliability is the probability that a product or a system will perform its intended

functions satisfactorily without failure and within specified performance limits for a specified

length of time, operating under specified environmental and operational conditions. Stated as

such, reliability analysis is a physics problem in that it includes what, how, and why of failure.

Reliability is determined by a variety of factors (failure modes) and each failure mode is

generally characterized as an average or mean time to or between failure or by failure rates

(commonly failures per unit of time) or by failure distributions. Causes include failure

mechanisms such as overstress and below specification strength, natural and induced

environmental exposures, chemical aging, radiation, and other factors such as weak or

intermittent manufacturing quality or shipping and handling induced damage that lead to a

component failure. The failed items will need repair or replacement through a function of

maintenance actions. Reliability analysis and best practices should be applied throughout the

concept and design phases to identify, pre-empt, prevent, forestall, or mitigate such failures

during planned operation. Cognizance of reliability factors is important for owners, and others

performing project or program financial and technical risk asset management.

Acquiring data to find and understand failure trends, spares forecasting, manpower forecasting,

obsolescence planning and repeating component failures requires a management focus to

mitigate or eliminate recurring issues and document accurate failure tracking. The ability to

estimate the resulting loss of Photovoltaic Power System (PVPS) capability forms the basis for

how to allocate time, power, energy and even cost for reporting reliability metrics or, more

directly, unreliability due to failure events and/or trends, which in turn, necessitate corrective

actions.

Assuring reliability can generally be viewed as two specific and major interrelated efforts:

a) concept and design phase, and
b) the operational and maintenance (O&M) phase.

During concept and design evidence of prior product failures and system history and current

testing data are used to estimate the reliability of the system(s). The evidence comes in the

form of data from historical operation of existing plants that has sufficient breadth of information

to provide the basic reliability information as well as attributes such as the failure distribution

(e.g., normal, Weibull, exponential, etc.), failure mechanisms and failure modes, and required

corrective actions. With rapidly advancing technologies the concept and design phases also

require using engineering judgement, experience, design trade-off assessments, and

design/reliability testing of new components for developing failure models. For instance,

understanding the physics of failure applies to the design assessment.

During O&M, the owner/operators and the O&M contractor implement a failure detection and

data acquisition system that likewise provides data for analysis of the current failures including

root cause, failure modes, and failure rates by documenting and tracking the failures and then

using the data to develop corrective action plans and when feasible changing the design to

accommodate new stresses or to correct a flawed design.

Effective reliability practices will reduce overall system costs through reduction of failures and

their consequences. There are initial costs associated with design analyses and reviews,

component selection, and analysis of reliability testing. In this context, reliability should be

viewed as an investment in the plant or company future. Failure to perform reliability practices

results in a low reliability product and its ramification of extended costs for field repairs and

replacements, impact to energy generation, problems during warranty, or worse, the loss of

business.
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IEC TR 63292:2020 © IEC 2020 – 7 –

This document continues the effort started with the availability technical specification (IEC

TS 63019). Availability is closely related to PVPS operational capability, health and condition

and to produce energy and is a real-time or historical measure. The availability of a system or

component is impacted by contractual and non-contractual reliability specifications,

maintenance metrics and a corresponding maintenance and repair strategy, and also external

factors such as site environmental and grid conditions. Reliability has a focus more closely

aligned on the capability of the components, their health and condition, systems to sustain

production, and what manner of operations, maintenance, analysis and actions are effective for

economic asset management of the PVPS.

The PV industry has had a recent period of rapid growth of installations. Existing PV plants are

starting to age. Concurrently, new and evolving products are being introduced and a lack of

reliability data is a general issue of concern as often there is insufficient testing or test data to

properly assign the reliability attributes to these new technologies. This goes to the intended

function of the systems, which is a topic for addressing through reliability analyses to determine

the impact of known and unknown (postulated) failures and/or the effects of underestimated

declining performance. There has been expressed levels of dissatisfaction for many plants not

meeting power/energy expectations and, in some cases, this has led to plant shutdowns or

expensive upgrades or down rating (derating) of the plant. In some instances, the loss of or the

renegotiations of power purchase agreements has also occurred.

Clarity is needed to specifically address issues of the intended function not meeting appropriate

specifications, and to numerically assess reliability performance and economic impacts.

Throughout, there is competition in the market with cost pressures and without the expectations

of continuous process improvement, those pressures will continue to exist.

The motivation for addressing reliability in the implementation and operation of a PVPS is

founded in the desire for long lasting energy performance, energy production, secure production

and revenue, and safe function. Management of a PVPS may come in many forms, but for

reliability to be properly addressed, it is derived from a commitment to establish practices from

the beginning development of concept and plans to take necessary actions and financial

investment to ensure results and avoid the costs of unreliability. The commitment for reliability

must begin at the highest levels of the organization and for those who have financial risks in

the project, the course of action must be defined and implemented in a manner similar as that

of environmental safety, health and quality. This document is supportive of that approach and

defines methodology for accomplishment.

An intention of this document is to be a precursor examination of the reliability issues for further

address in a task to produce an IEC Technical Specification on this topic.

While this document identifies reliability tools, topics and procedures, there are commercial

products available to perform analyses and there is no assessment of those tools or to provide

recommendations for one tool over another in this document.
---------------------- Page: 9 ----------------------
– 8 – IEC TR 63292:2020 © IEC 2020
PHOTOVOLTAIC POWER SYSTEMS (PVPSs) –
ROADMAP FOR ROBUST RELIABILITY
1 Scope

PVPS component and system reliability engineering works to define the PVPS probability of

making the indicated value such as energy or revenue, also at a given statistical confidence

level for an estimate. This needs to be assessed properly as an accurate levelized cost of

energy (LCOE) results from identifying and acting on a set of quantifiable metrics based upon

real measured data of actual plants under the widest variety of real site conditions. In many

instances, the use of P numbers (which stands for "percentile") may not be clearly understood

and as a result, inappropriate conclusions drawn which have a financial result. P values are

used to establish the confidence that one can require to provide the assurance that the item

will meet specification. A P50 value, for example, provides that there is a 50 % confidence in

the value used in reliability predictions. This value of confidence translates to the median of the

population or in other words, it is equivalent to a coin toss on whether the value is valid. It is

better to have a higher confidence that the system will work to specification. For reliability

metrics, this is typically defined as being a P90 or P95 values. This level of confidence

significantly characterizes financial and technical risk plant availability.

The failure rates and mode become important for predicting future failures. In a worst case,

significant wear out failures may be indicative of serial failures and attention is warranted. A

needed caution is the components may have multiple failure modes and root cause analyses

may be useful discerning the failure modes.

The LCOE calculations may not adequately include all the relevant costs, i.e. all-in costs, and

risks which create further uncertainty. That uncertainty has a high probability of coming to

inaccurate conclusions and choices.

Ideally, the owners, maintainers and operators should look for reliability issues early in the

concept, system, and hardware and software design engineering efforts. Otherwise, the defects

in software code and poor design or weak components will manifest themselves in a multitude

of unexpected failures resulting in unwanted and unexpected risks and costs.

In addition, there is another issue that is a by-product of unexpected costs. Organizational angst

is the result of not addressing issues at specification prior to design that in turn results in

organizational effort, time, and expense in the solving of problems (often originally simple) that

become quite complicated after the plant has been built. Because this effort may not be

adequately budgeted, and places additional stress on the organization, it tends to have a

negative impact on the human performance of scope and adds risk to the PVPS performance.

Without analysis of accurate field data and metrics, there are a series of negative results that

include unidentified or unexpected levels of plant failures and degradation. Lack of ongoing

(from concept to end-of-life project phases) reliability analyses, the results of inaction raise

unaddressed costs, risks, reduced plant capacity and capability, and potential for plant derating.

All these issues could potentially result in substantial negative financial impacts to the owners,

insurers, users and/or operators.

Reliability of a PVPS requires a comprehensive approach to identify, maintain, correct, and

understand costs. Some critically necessary specific gaps for the PV industry need

advancement:

a) A standard way to define failure statistics for PV, for PV components and specifically PV

modules where failure can be either catastrophic- or degradation-driven. This can be

accomplished by a bottoms-up fault tree nodal model with further guidance on how each of

the nodal distributions can be derived qualitatively.
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IEC TR 63292:2020 © IEC 2020 – 9 –

b) Defining a common nomenclature of describing failures in the field so that failure statistics

can be gathered and analysed (i.e., failure coded or word search capability). Further there

needs to be coordination between the various stakeholders to standardize data capture in

a format that allows for meta-analysis. Different levels of data can be used for different or

enhanced understanding of reliability issues depending on available technology and

installed capability. Improvement in monitoring is assumed but there is a need to create

standardization criteria, and details on data capture.

c) Defining a standard for how operational failure data is classified, root cause identified, and

reported to aid objective b) with guidance or criteria established or cited.

Reliable systems, processes, and procedures produce energy more safely at a consistently

lower cost while reducing waste, unnecessary labour, unplanned O&M, and unnecessary

organizational angst while providing additional actionable information to continually build and

operate better, higher producing and safer plants.

An obvious concern is that the system appears imposing at first sight. It is not the intention that

the effort be a greater cost than its benefits. The resultant specifications and design shall fit the

business /financial needs of the project. The cost of ensuring reliability needs to be weighed

against the costs of not ensuring reliability at achievable levels. The types of data and

commitment to data collection, however, should be tempered while addressing the initial and

future data requirements. The Pareto techniques allow insights to be gained on the vital few as

per the 80/20 % rule (see 7.11). However, much data needs to be collected and this provides

references to other documents that address data.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies.

For undated references, the latest edition of the referenced document (including any

amendments) applies.

IEC 60050-192, International Electrotechnical Vocabulary (IEV) – Part 192: Dependability

IEC 60300-1:2014, Dependability management – Part 1: Guidance for management and
application

IEC 60300-3-3:2017, Dependability management – Part 3-3: Application guide – Life cycle

costing
IEC 60812:2018, Failure modes and effects analysis (FMEA and FMECA)
IEC 61078:2016, Reliability block diagrams

IEC 61215 (all parts), Terrestrial photovoltaic (PV) modules - Design qualification and type

approval
IEC 61649:2008, Weibull analysis

IEC 61703:2016, Mathematical expressions for reliability, availability, maintainability and

maintenance support terms
IEC 62740:2015, Root cause analysis (RCA)

IEC TS 63019:2019, Photovoltaic power systems (PVPS) – Information model for availability

ISO 9001: 2015, Quality management systems – Requirements
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– 10 – IEC TR 63292:2020 © IEC 2020
ISO 55000:2014, Asset management – Overview, principles and terminology
IEEE 493, DoD Failure Modes and Distributions, Gold Book
3 Terms, definitions and abbreviated terms
For the purposes of this document, the following terms and definitions apply.

The International Organization for Standardization (ISO) and IEC maintain terminological

databases for use in standardization at the following ad
...

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