A low afternoon sun is shining on our office PV system just now – and the back row has a small amount of shading on it (was predicted in our modelling).
The photo below was taken 10min ago – it shows partial shading on 4 of the 10 modules in the string.
This part of the office system has two identical arrays – each feeding two identical inverters. One system is currently totally unshaded … and the other has the small amount of shade shown in the photo.
- Output of unshaded array – 805W
- Output of shaded array – 168W
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Andy O'Leary says:
February 3, 2012 at 11:58 am (UTC 0)
Always interesting to see impact of shading on modules. Coming from our experience in the cell/module manufacturing industry, it’s completely expected that horizontal shading on portrait-mounted modules will impact greatly on the overall string output. The reason being (as I’m sure you already know) that most modules are configured with sub-strings of cells in series, each protected by a bypass diode. Each sub-string tends to be vertical in layout (when looking at a module in portrait orientation) and most modules will have 3 or 4 sub-strings in their construction. Having a horizontal shade across a portrait module will therefore force all the bypass diodes into action removing the whole module (or string of modules) from the equation. Horizontal shadows are best countered by mounting modules in landscape orientation, in my opinion…….depends on sensitivity/range of the inverter’s MPPT capabilities though I guess…
Thanks, very informative and interesting blog, I will read more!
Andy