best low light performance
Hi, Amorphous panels are clearly the best for low light performance--but are relatively speaking huge. Does any one know if Poly or Mono are better in low light?
Forum Discussion
Yet more fuel for the fire of these seeming discrepancies in low light performance different trustworthy people are seeing in the real world compared to presumed or predicted results:
Low light is not just full spectrum straight-on light at lower intensity. That's one form. That's the form in the standard tests.
Another form is light far from straight on, coming in at a high angle of incidence. This light hitting the cell is low due simply to geometry. Performance is similar across technologies if they are behind plate glass because it is responsible for the bulk of the light loss at these angles, but very different for other surfaces.
One form of low light is light with a skewed spectrum, either because of time of day, haze, fog or clouds. Not sure about Unisolar's spectrum specifically other than that it has 3 PVs in one, each for a different frequency range. But Amorphous silicon has a higher bandgap (1.7 eV) than crystalline silicon (c-Si) (1.1 eV), which means it absorbs the visible part of the solar spectrum more strongly than the infrared portion of the spectrum. So low light with lots of red will perform differently on the different technologies than low light with more blue. If you can feel warmth on your face from the sunlight there is IR, if not, much of it is filtered.
Also already mentioned, yet another form of low light is partial shade or dappled sunlight. Different technologies will respond differently to this form of low light than uniform light levels.
Honestly there are so many variables in low light performance, I don't think there are many here with enough information to legitimately discredit other's real-world results in most cases.
Jim
Low light is not just full spectrum straight-on light at lower intensity. That's one form. That's the form in the standard tests.
Another form is light far from straight on, coming in at a high angle of incidence. This light hitting the cell is low due simply to geometry. Performance is similar across technologies if they are behind plate glass because it is responsible for the bulk of the light loss at these angles, but very different for other surfaces.
One form of low light is light with a skewed spectrum, either because of time of day, haze, fog or clouds. Not sure about Unisolar's spectrum specifically other than that it has 3 PVs in one, each for a different frequency range. But Amorphous silicon has a higher bandgap (1.7 eV) than crystalline silicon (c-Si) (1.1 eV), which means it absorbs the visible part of the solar spectrum more strongly than the infrared portion of the spectrum. So low light with lots of red will perform differently on the different technologies than low light with more blue. If you can feel warmth on your face from the sunlight there is IR, if not, much of it is filtered.
Also already mentioned, yet another form of low light is partial shade or dappled sunlight. Different technologies will respond differently to this form of low light than uniform light levels.
Honestly there are so many variables in low light performance, I don't think there are many here with enough information to legitimately discredit other's real-world results in most cases.
Jim
