Harnessing the potential of solar PV power safely and effectively



Solar photovoltaic (PV) systems are being installed in ever increasing numbers throughout the world and are expected to produce electricity safely and reliably for several decades. However, many systems are not satisfactorily evaluated prior to being put into service and many have little, if any, scheduled maintenance or testing over their lifetime which could lead to unsafe and under-performing systems.

To ensure the long-term safe operation of these systems, PV installation and service contractors should execute a thorough commissioning process followed by a regular periodic testing and maintenance programme. These practices can help to promote safety and optimise performance, and provide essential information to those who may need to effectively troubleshoot, diagnose and remedy any problems arising with the system. All PV systems require testing for performance and safety verification. The level of testing required will depend on local regulators, customer requirements and the quality commitments of the installation and maintenance contractors.

Fig. 1: There are concerns in a number of countries over the safety and quality of the installation of some PV systems.

A growing market

The almost exponential increase of solar PV installations in the last two decades has resulted in both rooftop systems and utility-scale PV farms to become an increasingly important mainstream source of electricity. As the sustainable energy benefits of solar PV attracts more support, and as the technology continues to evolve and reduce in cost, the global growth momentum behind photovoltaics is forecast to continue.

According to the Global Market Outlook for 2015-2018 [2], installed solar PV capacity has grown by a factor of 100 in only 14 years. A record 40 GW of solar PV systems were installed globally in 2014, up from 37  GW in 2013. Solar PV is now providing more than 7% of the electricity demand in Italy, Germany and Greece and it is anticipated that solar power capacity could grow in Europe by 80% by 2019. Overall, the latest report forecasts that global solar PV capacity could reach 540 GW in five years’ time.

The need for recognised installation standards

Because the solar PV industry has expanded so rapidly, electrical installation and safety standards have had to be revised in order to keep pace with the demands of the industry. However, in many cases it is recognised that the rate of growth of the industry has been at such a fast pace that standard-making organisations have found it difficult to keep up.

As a result, there have been concerns expressed in a number of countries over the safety and quality of the installation of some PV systems. In some circles the concerns are that incorrectly installed PV systems are not working efficiently and can also be linked to safety problems, including the creation of fire hazards with risks to property and human life.

According to the Australian consumer watchdog Choice [3], a quarter of owners had problems with their systems and a third had problems with their installer. There have been reports, for example, of a company which sold allegedly faulty circuit breakers, which were apparently responsible for 70 fires in rooftop solar panel arrays. At the time, it was claimed that faulty isolators were responsible for a number of incidents in Queensland and New South Wales, with fires causing wall and ceiling damage.

These findings mirror that of a similar survey a year earlier in France [5], when safety inspectors from the electrical safety certification agency found that 51% of all PV installations in the country posed a potential safety risk and did not conform to regulations. In the UK, as the number of solar PV installations has increased, separate newspaper stories have detailed a number of examples of fires in residential premises, supermarkets and schools, where the cause was attributed to faults in the rooftop solar PV installation.

Similar reports have emerged from the USA. All these cases highlight the fire risks that can be associated with PV systems and support the need for the maintenance of rigorous installation and inspection standards.

Safety and fitness for purpose

Given the political and financial support being given to solar PV around the world, the universal priority for governments, industry and regulators is to ensure that the integrity, safety and quality of solar PV installations is maintained at the highest standards.

The owners of solar panel installations need to have confidence that the system they have purchased will function correctly and will avoid any potential hazard throughout its usable lifetime. This is particularly important for installers working on “roof rental” schemes were the installation is provided free of charge in return for receipt of rebates or feed-in tariff payments. Similar financial performance considerations are also vital for the investors and operators of utility-scale solar farms.

Manufacturers of PV cells, inverters and components, should equally be concerned that their reputations can be held to account as, in the event of a system failure from poor installation practices, the supplier and their products might then be regarded as being inferior and contributing to the hazard.

The buildings insurance industry also has a vested interest in all of this by ensuring that installations are properly installed, and are not the basis of subsequent compensation claims. Last, though not least, the fire and rescue services that may need to deal with any incidents involving a rooftop PV installation need to be sure that they are not being exposed to a hazardous environment.

As a result of all these considerations, verifying the proper installation, checking system performance and confirming the sustained energy output from a solar PV system are fundamental requirements. In achieving these aims, it follows that the effective commissioning and periodic quality testing of the system is crucial – as well as being essential to comply with warranty and PV system guarantees.

Applying adequate test standards – IEC 62446

The installation of PV systems presents a unique combination of hazards linking the risk of electric shock with the implications of working at height.

PV arrays produce a DC voltage when exposed to sunlight. In the wiring system associated with PV panel installation‚ the DC current generated by the solar array is converted to AC by means of an inverter which then feeds into the AC mains supply of a building.

Most electrical installation standards focus on conventional AC installations and the advent of extensive DC systems in the form of photovoltaics installed outside an equipotential zone has required the introduction of revisions and amendments to existing national standards.

However, across the globe, the recognition of the need to implement specialist controls and guidance notes has varied. Indeed, until comparatively recently, only a handful of countries had documented a rigorous testing process to ensure that a PV installation had been properly tested, the results recorded to demonstrate that adequate precautions had been taken and that evidence was available to support periodic inspection.

What appears to have been overlooked in this situation is that an international standard already exists that, if properly incorporated in mandatory national documents, would significantly help to eliminate solar PV system safety and quality issues.

Fig. 2: Advanced multi-function test instrumentation is available to help solar PV installers to meet the requirements of IEC 62446.

IEC 62446 defines the minimum requirements for solar PV system documentation, commissioning tests and inspection. As such, this standard not only specifies minimum testing and inspection requirements on newly installed systems, but equally importantly, how those inspection and test results are documented and supplied to the consumer after installation.

The standard recognises that subsequent building or electrical works in the vicinity of the PV array may be likely and that the ownership of a system may also change. As a result‚ the standard recognises that only through the provision of adequate documentation at the outset can the long term performance and safety of the PV system be ensured.

IEC 62446 therefore sets out the testing, information and documentation that should be provided to the customer following the installation of a solar panel system and also the initial (and periodic) electrical inspection and testing required.

In short, the standard sets out measures to ensure that:

  • The PV panels and electrical supply connections have been wired up correctly
  • The electrical insulation is good
  • The protective earth connection is as it should be
  • There has been no damage to cables during installation

In addition, the standard sets out specific requirements for a range of electrical tests and functional testing of the system as part of its commissioning. In doing so, the system documentation required by IEC 62446 therefore not only provides evidence to the consumer that the work has been performed correctly, but it also acts as a best practice guide to the contractor to ensure that recommended procedures have been followed and that installed system performance is as it should be.

IEC 62446 was published in March 2009 and has been adopted as an EN standard in many of the European member states and is generally regarded as making a significant contribution to improving the quality and safety of PV systems.

In the USA, similar requirements for compliance with IEC 62446 are being listed in procurement contracts for new projects and many of the testing procedures listed in the standard correlate directly with NEC requirements for verification of electrical system safety.

In such countries, for all new solar systems, equivalent documentation and forms described in IEC 62446 are required in addition to any specialist information and paperwork required by each country’s domestic electrical installation standards.

Furthermore, it is effectively enforced because in most countries no feed-in-tariff or electricity rebate will be paid to a consumer unless the installation has been installed by a formally accredited installer with the proven capability of carrying out the quality of work required – and who follows the necessary procedures needed to comply with the regulations.

Following the core principles of IEC 62446 would therefore not only help safeguard the future integrity of solar PV installations – it would significantly help to allay the various quality concerns that have been raised over the proficiency of PV installers and the system components they are using.

Solar PV test instrumentation

After a PV system has been installed, simple electrical faults or wiring failures can cause a serious inefficiency in the ability of the panel to produce power and perhaps cause fire and other safety risks. In such circumstances, although proper metering will usually give an indication of system performance, visual inspections on their own will not be enough to determine what “invisible” system faults or problems may exist.

In response, advanced multi-function test instrumentation has been developed to ensure that solar PV installers can meet this requirement efficiently and cost-effectively – and that important tests and system checks are not overlooked. System data, collected by such testers, can be transferred to customer documentation packs and templates at the push of a button.

The absolute minimum testing that should be undertaken involves continuity measurements, open circuit voltage, short circuit current, insulation and irradiance. To meet the electrical test needs, some contractors have used multiple instruments that typically include an earth continuity and insulation resistance tester‚ a multimeter, and a DC clamp meter along with various associated connectors and leads.

However, the danger with such “homemade kits” is that not all of the tests required by IEC 62446 will be covered and, with different PV system electrical tests potentially requiring the use of different testers, using such an array of instruments can be cumbersome and time consuming.

This sort of consideration has led to the introduction of a new generation of dedicated multi-function solar PV electrical testers, such as the Seaward Solar PV150, that are capable of carrying out all electrical tests required by IEC 62446 on grid connected PV systems.

With the push of a single button, the combination tester automatically carries out the required sequence of electrical tests in a safe and controlled manner. Testing can be conducted quickly and easily with the PV150 being pre-programmed to run a test sequence of required tests and using specially designed PV test leads which quickly connect and disconnect from the installation circuit. This also avoids the risk of contact with exposed live DC conductors.

For a comprehensive approach, alongside electrical testing, an irradiance meter is also required to measure how much solar power is available at any particular location.

The most accurate solar readings are produced from irradiance meters which use sensors similar to the technology utilised in the panels themselves. The ideal solution is an irradiance meter which uses a photovoltaic cell as its sensor rather than a pin diode which will not necessarily have the same response to sunlight as the PV cell itself.

In addition, some irradiance meters are themselves ‘multi-function’ and incorporate other useful features such as a digital compass, a digital tilt meter and a dual channel precision thermometer. In this respect, and intended for maximum operational efficiencies, special solar PV test kits have been introduced to help installers to work faster and more effectively without reducing the integrity of testing.

As an example of this approach, the Solarlink Test Kit includes all the necessary test equipment and datalogging capabilities needed to perform pre-installation site surveys and measure the electrical safety and performance of PV systems in line with IEC 62446. The kit combines the comprehensive electrical commissioning test capabilities of the PV150 hand-held solar installation tester with the advanced Solar Survey 200R multi-function PV survey meter.

Special wireless Solarlink connectivity between the two instruments enables real-time irradiance to be displayed and measured at the same time as electrical testing is being undertaken. This means that irradiance, module and ambient temperature can be recorded in real time, within the PV150, as the electrical tests are conducted.

Once testing is completed, the USB download of time and date stamped test results, irradiance and temperature measurements provides full traceability and speeds up the completion of PV system documentation and customer handover packs. This equipment can also be used for conducting site surveys of potential installations, by quickly providing the information needed to calculate estimated annual solar irradiation and system yields of PV and solar thermal systems.

In terms of working more efficiently, multi-function PV testers and dedicated test kits can also record and provide results in a format that can easily be accommodated in comprehensive system information folders for use in customer test certificates and system commissioning packs.

Editor’s comment

The latest issue of the South African National Standard (SANS) 10142 “The wiring of premises” , Part 1 “Low voltage installations” was published in March 2017. Until such time as SANS 10142-Parts 3 (The wiring of premises – embedded generators) and 4 (The wiring of premises –direct current and photovoltaic) are published and until such time as an SABS mark is issued for inverters, all embedded generation systems installed on an electric utility’s grid must be signed off after commissioning by a registered professional engineer or technologist.

References

[1] Global Market Outlook for Photovoltaics 2014-2018, EPIA, 2014

[2] Global Market Outlook for Solar Power 2015-2018, www.solarpowereurope.org/

[3] Solar power survey results Choice, 2015, https://www.choice.com.au/home improvement/energy-saving/solar/articles/solar-power-survey-results

[4] Solar Panel Installations Audit: Results of Taskforce Eclipse, NSW Government, 2011,  http://www.fairtrading.nsw.gov.au/biz_res/ftweb/pdfs/Tenants_and_home_owners/Taskforce_ eclipse_results.pdf3

[5] Shock risk from solar panels, Connexion edition: June 2010. Available at http://www.connexionfrance.com/solar-panels-electric-shock-risk-safety-report-news-article.html

[6] Fire Fighter Safety and Emergency Response for Solar Power Systems, The Fire Protection

[7] Research Foundation, May 2010. Available at http://www.nfpa.org/research/fire-protection-research-foundation/reports-and-proceedings/for-emergency-responders/fireground-operations/fire- fighter-safety-and-response-for-solar-power-systems last accessed 16/06/2015.

Contact Jacques Franken, Action Instruments SA, Tel 011 403-2247, sales@aisa.co.za

 

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