“No Two Modules Alike” – Nor Are All PV Panel Tests Consistent
Wednesday, February 29th, 2012
ReVision has installed several manufacturers' PV modules over the years, and CSI is our favorite for its rugged construction and excellent field-installed efficiency.
After a couple of us found a chance to read a recent review of photovoltaic modules by Photon magazine(based in Aachen, Germany), we had to write a response to an unfair analysis of Canadian Solar modules (ReVision’s current choice for a standard grade solar panel based on ruggedness, efficiency and affordability).
While the Photon article does show interesting data on field installed performance (i.e. kWh/kW yields), it arranges data in a confusing way. Specifically, the authors show performance ratios from modules of different ages, as if they were all comparable. The “top-performer”– a 230-watt REC module from Norway–installed in 2010, was matched up against Canadian Solar’s 170-watt module, which has been installed and working since 2007!
The rating neglects the fact that photovoltaic cells degrade over time, and that a cell that has been installed for one year will show a higher efficiency. The older cells will be trailing by around 0.5 – 0.7% per year, simply because their circuits’ performance has degraded a bit. In fact, the ranking largely reads chronologically–so the modules that have been sitting in the field at Aachen for 4-5 years are shown as poorer-performing cells. In the specific case of the Canadian Solar 170-watt module, the California Energy Commission’s test result shows 87.4% module performance ratio at PTC (photovoltaic test conditions; this is right around the industry average.)

In a recent test, a 4-year-old Canadian Solar module placed - not surprisingly - behind newly installed solar panels by competing manufacturers.
ReVision currently installs a much younger product generation: the 240-watt Canadians, which we see as a highly evolved component, and one comparable to the Norwegian RECs shown at the top of the rankings. We’d love to see Photon come out with a field-test study with a synchronous start date for all the different manufacturers; putting apples next to apples.
For the full article, read on: “No two modules alike” (PDF) Photon Magazine, February 2012