Safety through module electronics? Less is more · test DC connectors from different manufacturers...

1 SMA Solar Technology

Safety through module electronics?

Less is more !

Presented by Angelika Löning & Christopher Merz

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2

SAFETY OF PV PLANTS: STATUS QUO

More than 400GW installed PV systems world wide are already safe

Angelika Löning & Christopher Merz 3

WHAT DOES SAFETY MEAN?

Safety of PV plants consists of 3 major parts:

> Protection of life and health

> Prevention of harmful situations to reduce risk (especially fire prevention)

>Managing the PV plant in abnormal situations, i.e. an emergency


TABLE OF CONTENTS

1) Status Quo

2) Fire prevention – Facing the root causes

3) Role of Module Level Power Electronics (MLPE) regarding safety

4) Requirements for further safety enhancement

5) Recommendation

6) Summary


SAFETY OF PV PLANTS: STATUS QUO

Two German institutes (TÜV Rheinland and Fraunhofer ISE) analyzed the status quo of the safety of PV plants:

> A Fraunhofer ISE study1 provided statistics relating to PV-related fires and the number of fatalities in Germany over the last 20 years:

> Only 0.006 % of all PV plants have caused a fire resulting in serious damage

> To date, no firefighter has been injured by PV power while putting out a fire

> Note: In Germany not even a string level rapid shutdown is common practice

> The consequent use of best practice while extinguishing a fire allows safe work of first responders

> Minimum distance between fire hose and a 1500 Vdc electrical system2:

> Spray water jet: 1 m

> Full water jet: 5 m

1 Recent Facts about Photovoltaics in Germany, Fraunhofer ISE, 2015 2 Assessment of the Fire Risk in Photovoltaic Systems and Elaboration of Safety Concepts for Minimization of Risks TÜV Rheinland, Fraunhofer ISE, 2015

Experience shows, that conventional PV systems with string technology are safe and can be managed in an emergency


SAFETY OF PV PLANTS: SAFETY MEASURES

> Throughout the history of rooftop PV systems a variety of safety measures have been established with a focus on plant and personal safety

> These measures led to a high safety level

What is the next step?

Can Module Level Power Electronics (MLPE) increase the safety of future PV plants?

Angelika Löning & Christopher Merz

? Rapid Shutdown (Module Level)

double electrical insulation

Residual current monitoring

DC disconnector

Arc fault detection

Rapid Shutdown (String Level)

time

safe

ty le

vel

safety measures Measurement of insulation resistance Riso

1990 2000 2020 2010

7

FIRE PREVENTION – FACING THE ROOT CAUSES

1.Bewertung des Brandrisikos in Photovoltaik-Anlagen und Erstellung von Sicherheitskonzepten zur Risikominimierung, TÜV Rheinland, Fraunhofer ISE , 2015

Analysis of the TÜV Rheinland about the root cause of fires in PV plants 1


35%

17%

38%

10%

Root cause

Product failure

Planing failure

Installationmistake

externalinfluence

FIRE PREVENTION – FACING THE ROOT CAUSES

1.Bewertung des Brandrisikos in Photovoltaik-Anlagen und Erstellung von Sicherheitskonzepten zur Risikominimierung, TÜV Rheinland, Fraunhofer ISE , 2015

The root causes are mainly contact failures and product failures

To improve safety, these two items need to be addressed

> Root causes:

1. Installation mistake: bad connection of DC connectors, insufficiently crimped connectors, missing strain relief etc.

2. Product failure: relate to failures of the modules and inverters

3. External influence: animal bite, lightnings etc.

4. Planing failure: wrong mechanical and electrical installation


Analysis of the TÜV Rheinland about the root cause of fires in PV plants 1

35%

17%

38%

10%

Root cause

Product failure

Planing failure

Installationmistake

externalinfluence

> Contacts are proven to be very robust when connectors from exactly the same manufacturer are used. This is the case for direct contacts from module to module. They are very robust and have a life long safety as field tests have proven.

> Fire due to contact failures happens when connectors of different manufacturers are used or connectors are crimped:

> Thermal measurements in the panel level electronic to shut down the system in case of emergency don‘t work reliably e.g. when connectors are crimped. The thinner crimped part of the connection increases the thermal resistance:

CONTACT FAILURES


10

35%

17%

38%

10%

Root cause

Product failure

Planing failure

Installationmistake

externalinfluence

USE OF INAPPROPRIATE COMPONENTS

> Australia: Requirements for shutdown of DC power lines led to the market entry of a large number of DC disconnectors from a variety of vendors without considering environmental conditions

3 http://www.recalls.gov.au (Australian Competition and Consumer Commission)

Adding components to the PV system without appropriate safety standards increases the risk of fire!


Pict

ure:

Ma

tthew

Sm

ithw

ick

> Some of these DC disconnectors were causing a fire instead of making the PV array safer

> Three types of DC isolators were recalled in Australia in February, March and May 2014 3

11

35%

17%

38%

10%

Root cause

Product failure

Planing failure

Installationmistake

externalinfluence

ROLE OF MLPE REGARDING SAFETY

12

Example: 10 kWp plant (40 modules à 250 Wp)

> MLPE significantly increases the overall number of electrical components higher risk of a failure in the whole PV system

> The number of DC connectors is doubled when using MLPE


Facing the main root causes for failures in PV Plants (contact failures, product failures) is contrary to the use of MLPE

String technology MLPE

Additional number of electrical components 0 40

Number of DC connectors n 2*n

OPERATING CONDITIONS & SYSTEM FAILURES


Operating Conditions

•extended environmental conditions

•reverse and bypass currents due to shading

•capacitive switching currents

•asynchronous switching

•ageing

System Failures

•ground faults within the PV generator

•short circuits within the PV generator

•Installation faults (i.e. reverse connection)

•Lightning discharge

Both „Operating Conditions“ and „System Failures“ were specified in the public funded project „PV-Firebreaker“ under the guidance of TÜV Rheinland with collaboration of SMA et al.

An accurate analysis of the operating conditions and system failures is mandatory to assess the possible risk of Module Level Power Electronics concerning the PV plant

13

INTERIM SUMMARY

> Experience shows, that conventional PV systems with string technology are safe and can be managed in an emergency

> To further enhance the safety level, the focus should be on the most significant root causes for failures in PV plants:

> Contact failures

> Product failures

> In contrast, MLPE increases the number of DC connectors and the overall number of components in the PV system

> Requirements on appropriate test standards for MLPE are necessary


SAFETY OF PV PLANTS

Requirements to further enhance safety


35%

17%

38%

10%

Root cause

Product failure

Planing failure

Installationmistake

externalinfluence

SAFETY OF PV PLANTS: REQUIREMENTS FOR FIRE PREVENTION

Safety remains a concern of the PV industry

1. Measure to reduce installation mistakes (38%)

Define installation standards for DC connectors:

> IEC 62548 Photovoltaic (PV) arrays - Design requirements

> IEC 60364-7-712 Low voltage electrical installations

> IEC 62852 Connectors for DC-application in photovoltaic systems – Safety requirements and tests

1.Neue Erkenntnisse in Brandprävention und Brandbekämpfung von Photovoltaik Anlage; Prof. Urs Muntwyler; Berner Fachhochschule für technik und Informatik Angelika Löning & Christopher Merz

Finalise IEC DTR 63225: Incompatibility of connectors for DC-application in photovoltaic systems

Define a common interface standard for DC connectors and develop a testing document to test DC connectors from different manufacturers for long-term reliability

However all these explicitely exclude applications with connectors from different manufactures which are used in ~50% *1of the PV plants and don‘t cover reliability aspects

16

35%

17%

38%

10%

Root cause

Product failure

Planing failure

Installationmistake

externalinfluence

SAFETY OF PV PLANTS: REQUIREMENTS FOR FIRE PREVENTION


2. Measures to reduce product failures in the field (35%)

> IEC 62093 Balance of System Components for Photovoltaik Systems – Design and qualification

> Update required and on the way

> Covers environmental conditions of inverters


What are the exact conditions on the roof under the PV Module?

17

Results of an analysis during SMAs Micro Inverter development:

REQUIREMENTS FOR ELECTRONIC UNDER A PV MODULE


The requirements concerning reliability can be harsher than automotive environment

Comparism of operating hours at high temperatures at different locations (calculated from data of Meteonorm*)

18

Comparism of operating hours at high temperatures at different locations (calculated from data of Meteonorm*)

Geo

da

ta

Passenger Car

Truck

Negev Desert

Mission Profile

Un

de

r

the

P

V

mo

du

le

35%

17%

38%

10%

Root cause

Product failure

Planing failure

Installationmistake

externalinfluence

SAFETY OF PV SYSTEMS: REQUIREMENTS FOR FIRE PREVENTION


2. Measures to reduce product failures in the field (35%)

> IEC 62093 Balance of System Components for Photovoltaik Systems – Design and qualification

> Update required and on the way

> Covers environmental conditions of inverters


Test criteria for Panel Level Electronics are needed and have to be fixed in test standards

What are the exact conditions on the roof under the PV Module?

19

RECOMMENDATION

> Conventional PV systems are safe and can be managed in an emergency

> MLPE doesn’t prevent fire and potentially can increase risk of fire

> To make MLPE a sustainable success:

> Harsh environment of MLPE must be reflected in quality standards which must be applied

> Common interface standard for DC connectors need to be defined

> Standardised tests for DC connectors from different manufacturers for long-term reliability to be developed


Until these measures are in place:

Use MLPE only where needed - Less is more safe 20

1990 2010 2020

TÜV STUDY CONFIRMS RECOMMENDATION

> To prevent fires TÜV recommends to check if measures like fuses or switches are really needed or if the goal can be reached with alternative measures e.g. cable conduits *1

> Operational maintenance and regular checks e.g. parallel arc faults against ground can be detected by residual current measurements or measuring the isolation against ground via Riso

> For the case of fire fighting TÜV revokes the requirement for shut-down reasoning that any shut-down equipment can potentially fail *1

1.Bewertung des Brandrisikos in Photovoltaik-Anlagen und Erstellung von Sicherheitskonzepten zur Risikominimierung, TÜV Rheinland, Fraunhofer ISE , 2015 Angelika Löning & Christopher Merz 21

PV SAFETY – HOW TO LIMIT THE AMOUNT OF MLPE

22

Partially Shaded Roofs

Situation:

> Shaded modules through trees, chimneys etc.

Solution:

> Equip only affected modules with Optimizers

Complex Roofs

Situation:

> Roofs with several arrays and orientations.

Solution:

> Equip only partial-array with Optimizers

Requirement for Module-level Monitoring

Situation:

> Desire for module-level monitoring

Solution:

> Equip all other modules with Monitoring-Modules

Until Standard Tests are defined, follow recommendation of TÜV and check where MLPE is needed:

SUMMARY


> Test standards need to be revised and added when new technologies are introduced

> There are existing technologies that minimize the amount of components without compromising on functions

> SMA continuously drives new standards to improve reliability and safety

SAFETY OF PV PLANTS


Zero risk as a stated goal

Focus on fire prevention before fire fighting

24

25 SMA Solar Technology

Sonnenallee 1

34266 Niestetal, Germany

Tel. +49 561 9522 0

Fax +49 561 9522 100

www.SMA.de

[email protected]

SMA Solar Technology AG

Thank you

Safety through module electronics? Less is more · test DC connectors from different manufacturers...

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