“No Two Modules Alike” – Nor Are All PV Panel Tests Consistent
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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.)
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