Data and test results displayed in this article was obtained from a test and inspection of an actual installation that was inspected on the 17th June 2016 in Somerset west. Information that may cause a conflict will not be made available for reasons of anonymity.

Standards

PV systems can be tested against safety or performance criteria, this should be done both after the installation as a commissioning test and then periodically to ensure ongoing efficiency and safety of the system. Safety testing would be the type of testing that would have to be done in order for a certificate of compliance to be issued and generally involves the testing of polarity, insulation & continuity.

Naturally testing has to be guided by standards and since there has been significant progress with standards for solar PV installations the SABS has adopted a number of relevant IEC standards, of which SANS 61215 (IEC 61215), SANS 60364-7-712 (IEC 60364-7-712) & SANS 61730-1 (IEC 61730-1) are a few examples. IEC standards coupled with local standards supported by a solid testing regime creates a solid foundation & good baseline for a testing mechanism that is predictable, transparent and consistent.

Test equipment used

We arrived on site equipped with a full set of calibrated Metrel MI3109 PV testers which includes an IV curve tracer and software to print a full PV compliance report. The test started at around 11:00 and was concluded at around 15:00. This tester can do both safety and performance testing of the complete PV system. This report only covers certain aspects of the findings and does not include the comprehensive analysis of the complete system or the complete system test report.

The test overview

The photo in the header of the article shows the front view of 10 modules and the diagram indicates the same ten modules as if they were being viewed from behind. An individual IV curve test was done on module nr.9 to compare measured vs STC power generation. Module nr.9 was operating at about 60% capacity due to two cracked cells. Power generated by the 2 strings were measured to be about 2,2kWp at around 32’C cell temp with approximately 800W/m2 irradiation although collectively 4kWp was connected. Deviation in the calculated vs measured results were as a result of faulty modules and string configuration. Two strings were connected to a MLT 4000TL grid tied inverter although findings of only one of the strings are discussed in this report. The property in question had three different systems installed with only one system part tested. The available systems on site were:

1. Axpert backup system with 4 x 105Ah Trojan batteries – no modules (not tested)
2. Off-grid 600Wp system with 3 x 200W modules (not tested)
3. Grid tied PV system with mixed modules on two strings (tested)

Installer: Owner installed over a period of time as modules became cheaper.

Test reference number: AAB017/166/1

Supplier of solar equipment: MLT Drives

Module brand: Tenesol used in the string being assessed.

Inverter brand: Kyoto Grid tied 4kW 2 MPPT’s – Model 4000TL

Tester used: Metrel MI3109 + Metrel Remote tester (environmental conditions).

Supplier of testing equipment: African Instruments. Justin can be contacted at, justin@africaninstruments.co.za, or +27-84-500-0704

Summary of findings

1. No surge protection
   1. Although not required according to the SANS10142-1 standard, not installing surge protection leaves an installation exposed to potential damage by surges caused by the distribution network, or other types of fault conditions, lightning, induced voltages, etc.
   2. Insurance companies are unlikely to honor claims in the event of surges causing damages to solar equipment that have not been suitably protected.
   3. Inverter suppliers might also not honor claims in the event of damages caused by surges where no surge protection equipment was installed.
2. No DC disconnect
   1. SANS60364-7-712.536.2.1.1 to allow maintenance of the inverter means of isolation for both the AC & DC side shall be provided. See photo 3 of inverter.
3. Module mismatch
   1. Definitely not good practice to use modules of different sizes in the same string on this type of string inverter. This should be illegal.
4. Cracked PV cells
   1. A visual inspection showed snail trails caused by cracked cells, see photo 2.
5. Busbar corrosion
   1. Module nr.10 was severely corroded
6. No fuses
   1. SANS60364-7-712 Overload protection may be omitted to the main cable on the DC side of the installation for the PV modules if the continuous current carrying capacity is equal to or greater than 1,25 times the Isc of the PV generator.
7. Cross mating of Couplers
   1. The cross mating of couplers is not considered a failure of a solar PV module, but it can contribute to loss of power due to poor connections or increase the risk of fire due to improper contact.
   2. A statistical review of the source of fire in 75 PV systems, shows that the chance of the quick coupler causing the fire (29%) is nearly as high as for the rest of the module (34%) or other parts of the PV system (37%) [Schmidt 13]. There are no specific requirements in local standards.

This article was written and circulated on the 26th June 2016. Subscribe to our newsletters for updates on standards, more test results, information on training courses and more relevant info aimed at Solar PV conditions for the African and South African environment.

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