Photovoltaic panels can have 20 or 25 year underwritten warranties with a guaranteed remaining efficiency of 80 % of the new panel. That means, that photovoltaic panels seem to degrade somehow.


Why do they degrade? What exactly is reducing their efficiency?
How can this process of degrading be slowed down? E.g. if you don’t need your PV panels, is it possible to conserve them by covering them with a black, opaque coverage like tarp? If not, what else?



Question: What creates this strange flare and how to prevent it?
Answer: All cameras contain lenses which are actually comprised of several "lens elements." Lens flare is caused by non-image light which does not pass (refract) directly along its intended path, but instead reflects internally on lens elements any number of times (back and forth) before finally reaching the film or digital sensor



A good lens hood can nearly eliminate flare caused by stray light from outside the angle of view. Ensure that this hood has a completely non-reflective inner surface, such as felt, and that there are no regions which have rubbed off. Although using a lens hood may appear to be a simple solution, in reality most lens hoods do not extend far enough to block all stray light. This is particularly problematic when using 35 mm lenses on a digital SLR camera with a "crop factor," because these lens hoods were made for the greater angle of view. In addition, hoods for zoom lenses can only be designed to block all stray light at the widest focal length.

Petal lens hoods often protect better than non-petal (round) types. This is because petal-style hoods take into account the aspect ratio of the camera's film or digital sensor, and so the angle of view is greater in one direction than the other.Placing a hand or piece of paper exterior to the side of the lens which is nearest the flare-inducing light source can also mimic the effect of a proper lens hood. 

Lens flare also depends on the lens used - fixed focal length (or prime) lenses are less susceptible to lens flare than zoom lenses. Other than having an inadequate lens hood at all focal lengths, more complicated zoom lenses often have to contain more lens elements. Zoom lenses therefore have more internal surfaces from which light can reflect.

Source- http://www.cambridgeincolour.com/tutorials/lens-flare.htm