Solar cell grading – is A grade the best?


How are solar cells graded?

Just like chicken eggs, solar cells are created by a process where no two cells are exactly identical. Consequently, just like eggs, a solar cell manufacturer has to grade solar cells and place them into a range of bins, primarily based on power output and appearance.  
There is also a range of bins into which cells with a variety of imperfections or defects can be placed.  The cell manufacturer then puts a selling price on each bin, with a high price on the best and going down from there.

Unlike eggs which are graded in accordance with national standards by graders having accredited competency, solar cells are graded by manufacturers who set their own parameters for each bin, and this can vary from batch to batch or other production needs.

Usually generic cell grades are defined as A, B, C and D with A being the highest, B and C having various defects and D being rubbish.


Premium lightweight flexible solar panel


A grade cells! 

A simple reference to “Grade A” masks the fact that there is a range of “sub-grades” beneath this.  Grade A is assumed to be free of defects, but there is always a range of power (voltage * amps) and appearance (mostly colour) that determine the bin into which a cell will be placed.  

Just from the power output and appearance parameters there could be 9 or more bins, e.g. 3 power bins each having 3 appearance levels just for cells that are bandied together and called “Grade A”.  

For cells that are not good enough to be classified as Class A the imperfections may be due to low power and appearance, or other defects such as chips, fractures, scratches, blotches, etc, etc.  It’s easy to see the number of bins lower grade cells could be placed in will multiply greatly.  


Lower grade cells

The lower grades are generally referred to as Grade B, C and D with D generally being almost rubbish.  But unlike the egg industry it’s not really feasible to define the parameters in standards for the lower grade bins because of the number and combinations of the imperfections and defects over time and from batch to batch.  Consequently, solar panel manufacturers making “cheap panels” will buy lower cost and grades of cell.  The imperfections or defects in the cells may vary; one batch may have all functional cells, while another batch may have a proportion of cells that are not entirely functional. 


Confusion regarding the grading of SunPower cells

Now, specifically to the grading of Sunpower Cells.  A LinkSolar article on their website states that SunPower has grades ranging from L (highest) to A (lowest) and this has caused significant confusion as these SunPower numbers are entirely different to the large number of publications that refer to generic grading where A Grade is the highest quality and D is rubbish.  

The SunPower letters refer to bin classifications e.g. Le1, Ke1 and Je1.  This is different to the generic grading (A-D).  SunPower also reference an M bin with a higher power for solar car race teams. SunPower are free to add/change/remove their bin grades as they own the information.  It should not be confused with generic grading where A grade is the highest quality.


Quality of cells for grid-connect approved panels

Within a cell manufacturing plant using the same raw materials the quality of the grade A cells should be quite consistent.  These Grade A cells are required by the panel manufacturers who supply “grid approved” panels; i.e. panels that pass wide ranging and stringent tests defined by international standards that demonstrate they satisfy requirements for safety (e.g fire test), and longevity (e.g. at least 80% output after 25 years).   

This testing is a pre-requisite before manufacturers/importers can apply to get their solar panels added to the Clean Energy Council accredited module database – only these panels can be installed into grid connected systems in Australia and satisfy the relevant Australian standard, principally AUS/NZS 5033 “Installation and safety requirements for photovoltaic (PV) arrays”.    Certified panels on the database cannot be modified from what was tested and received accreditation.


Quality of cells for off-grid flexible solar panels

The flexible solar panel market has a reputation as being the dumping ground for cells that are not Grade A.  There can be huge variation in the price for whaCheap inferior quality flexible solar panelt appears to be “the same panel”.  The higher priced panel should have higher grade cells as they costl more but that is not always the case – if the appearance is ok it can be impossible to visually tell a higher grade cell vs a lower grade cell and you are dependent on the honesty of the seller.  Sometimes outragious quality claims are made but this my only be evident to the professional or experienced buyer.

Even though the quality of solar cells is not usually apparent by its appearance you can get a good indication by looking at the quality of the overall flexible solar panel.  The quality of the overall solar panel can provide a strong indication of the quality of solar cells used.  Indicators can be:

  • overlapping cells;
  • damaged cells;
  • dull cells with various colourations throughout the panel; 
  • sharp edges.

Testing of solar cells that indicates quality

  • Electrical testing, i.e. voltage (V) and current (I); plus
  • Electroluminescence (EL) testing.
Special test equipment is needed to see ‘inside’ the cell.  
The electrical test confirms the current and voltage are within production limits while the EL test confirms that the cells are free of defects and are well matched.  If present these result in a lower panel output and possibly a shortened lifespan.
During the EL test a current is passed through the panel which turns part of the current into short-wave infra-red (SWIR) light at a wavelength of around 1150nm, i.e. the panel will “glow” with invisible infra-red light.   A photo of the “glowing” panel taken by a special camera will show up micro-cracks or other defects in the cells and any significant mismatch between cells.  
These issues are only visible with this EL test:
Electrical Testing of flexible solar panels shows quality of cells
  1. The first of the above three images show a very poor quality panel with many defective cells. 
  2. The second image shows up visible mismatches between cells, i.e. the intensity of the glow is related to the efficiency with which the cell will convert sunlight into electricity. 
  3. The third image shows a panel free of cell defects and with only small variations in cell efficiency. 


Highest grade cells are considerably more expensive than B and lower grades.  So a cheap panel will have cheap cells. 

The Solbian SP range with SunPower cells are tested during production - they are all subjected to I and V and EL testing prior to shipment to our warehouse.  In our warehouse we also selectively carry out this testing as an added quality control initiative – we have a dark room and a specially modified camera to do this.

Variations in appearance of cells

With appearance of cells, no two cells are identical but generally differences in appearance are not visible within a single panel, however, variations between solar panels can happen.  The array on a BP service station has a good example of variations in appearance between different panels. The panels here were installed at the same time but probably from different batches of solar panels.


variations in appearance of different solar panels


In Conclusion

A cheap panel can only be cheap because there is cost cutting on cells and materials as well as manufacturing processes.  Usually this means inferior quality materials with little or no quality control. 

It is recommended that higher priced panels are purchased from experienced businesses that have good technical expertise.  You may like to read our buyer guide on How to compare good and bad flexible solar panels

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