The Value of Testing with a PV Laboratory

PV Lab, Australian Solar Testing Facility

Earlier this month Blair and the engineering team took a visit to PV Lab, a testing laboratory that specialises in solar modules evaluation. The independent PV laboratory based in Canberra is well equipped to provide a series of solar assessment services and is undergoing accreditation.

Michelle McCann, a director of PV Lab, was generous in providing a detailed tour of the facilities and equipment that enabled the testing capabilities at the IEC Standard. The educational experience helped identify the correct methods for testing solar panels and factors that can significantly affect the results of improper testing. The Standard Testing Conditions (STC) for testing are:

  • 25 Degrees Cell Temperature
  • 1.5 Air Mass (AM) Spectrum
  • 1000 W/m^2 Solar Irradiance

The 25 Degrees Cell Temperature is an incredibly difficult factor to replicate outside of a PV Laboratory. PV Lab uses a heat soak machine which ensures a uniform temperature across the cells with exposure of between 3 hours to an overnight session. Equipment that is capable of completing this test is seldom used when testing outside of a certified laboratory. Furthermore, irradiation onto a module will immediately raise the temperature of the cells, altering the output power and invalidating the results. The process to flash a module without changing the internal temperature can only be done by well trained and experienced technical operators.

The Air Mass is another factor that is impossible to replicate outside of a dedicated laboratory. The factor refers to a specific type of solar irradiation and different AM measurements will significantly alter the power output of solar modules. Using an Air Mass Indication of 1.5 enures that the type of light used in a test is almost identical to the suns radiation. Air Mass sensors and equipment that can calibrate for this setting are quite rare and are only found in genuine PV testing facilities.

Finally, ensuring a uniform level of Solar Irradiation is difficult but not impossible to replicate. The sun is a single light source that generates immense volumes of light energy across the surface of the earth from an incredible distance away.  Replicating the uniformity of the sun with artificial light sources is close to impossible due to artificial invariability. To ensure the identical level of irradiation across a module, PV Lab utilises a mini reference cell to confirm the 1000 W/m^2 is achieved at all areas. The accuracy of this procedure is within 1% of the target radiation and is an example of another factor that is theoretically difficult to properly replicate outside of a dedicated solar testing laboratory.

PV Laboratory
Blair and Lawrence discussing with PV Lab
Michelle McCann Explaining the EL Imaging Set-Up
Michelle McCann Explaining the EL Imaging Set-Up
Reference Cell from www.eets.co.uk
Reference Cell from www.eets.co.uk

What sets a PV Laboratory Apart?

The IEC 61215 Standard is the basic testing certification for solar modules to be available for installation in Australia. The standard reflects the portfolio of testing procedures that set a foundation to analyse and compare solar modules from all manufacturers around the globe.

It is critical to apply the same level of quality control, accuracy and technology when testing modules for their electrical performance. This echelon of evaluation quality can only be achieved by laboratories that genuinely tests in relation to the IEC Standard. Considering the equipment required and technical experience that was previously identified in the STC conditions, only dedicated PV testing facilities should complete this evaluation.

By ensuring the same quality of solar assessment for certification and module testing ensures a genuine comparison for performance. We would like to demonstrate the difference in assessing solar panels by a dedicated laboratory and an ill-suited facility.

Xenon light source used for STC power measurements
Xenon light source used for STC power measurements

Certified Vs Non-Certified PV Testing Facilities

To demonstrate the significance of a genuine PV laboratory we will compare the reports for WINAICO's panels that were submitted for assessment at two testing facilities. The first is PV Lab which applied the techniques and procedures outlined above. The second was to a non-specialised lab which did not have access to most of the equipment that is necessary to achieve genuine STC. Here are some of the results.

Mismatched Results for a WSP-260P6

Non-Dedicated Laboratory

The following image is an extract from a report generated by a testing facility that does not specialise in PV panel testing. This particular module is claimed to perform at 216 Watts which reflects a 16.71% drop in total power compared to STC measurement. The power measurement would fall outside of the 25-year performance guarantee provided by WINAICO.

If correct, this module has failed its minimum requirement and will trigger the appropriate warranty procedure to remedy the lost potential generation of the solar array.

Extract from Non-Accredited Lab
Extract from Non-Accredited Lab
PV Lab, Dedicated Solar Testing Facility

The exact same module was then submitted to PV Lab with the results illustrated on the right. The testing using an appropriate laboratory has demonstrated that the module in real STC conditions is producing 242 Watts of power or a 6.9% drop in power after 7 years in the field.

Extract from PV Lab Report
Extract from PV Lab Report

Electroluminescence (EL) Imagery Verification

Identifying Faults with Electroluminescence Imagery

Another key element of using a correct PV Testing facility is the additional contribution of electroluminescent imagery (EL). This technique is incredibly difficult to recreate outside of a PV laboratory and is crucial for determining certain faults that are not identifiable with the naked eye.

The testing report developed by PV Lab includes EL Images for each module, which can provide insight into the cause of any faults. The WSP-260P6 that was used to demonstrate the loss of power at an inappropriate testing facility produced this following EL Image.

The module presents ideal solar cell performance with no discernible discolouration, cracks or other elements that could lead to performance issues. This is a representation of how a module is expected to look after installation on a roof for several years. Cell damage and cracking leads to dark areas appearing, which show that less power is being produced in these areas.

The image illustrates no critical issues of performance which can lead to degradation in a PV module. The information from the performance measurement correlates with the electroluminescent images of a healthy and ready-to-perform solar module.

WSP260P6 EL Image by PV Lab 2020
WSP260P6 EL Image by PV Lab 2020

Where Can I Find a Genuine PV Testing Laboratory?

PV Lab in Canberra is an example of a high-quality testing facility however there are several others that can generate similar evaluations for solar modules. Another example is the CSIRO Energy Centre which has been completing detailed solar panel testing for several years and worked with Choice Magazine. Both facilities have several commonalities that can act as a guideline for identifying a proper PV testing laboratory. When completing solar module testing, check to see if the following equipment is being applied:

  • An A+ or Triple-A High-End Solar Simulator
  • Heat Soak equipment
  • The testing calibration set for STC (Reference Cell, Air Mass Sensor, Temperature monitoring)
  • Dedicated Electroluminescence imagery.

Without this minimum set of equipment, facilities are inadequately prepared to test the performance of solar modules. We highly advise you use this checklist as a gauge when searching for the best testing laboratory for your performance analysis.

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