Some manufacturers deal with the problem of shading better than others. The ability of PV modules to perform well in low-light conditions and in shadows becomes one of the selling points. For example, Canadian Solar
panels barely lose any efficiency on cloudy days. Uni-solar cells have good shading resistance. Some Panasonic
PV modules have four bypass diodes which allows them to retain higher efficiency in shade.
If you know in advance that your panels will most likely be overshadowed – for example, there are lots of tall buildings and trees around – consider thin-film or amorphous panels, because they are less affected by shading.
A lot can happen around you during the standard 25-year lifespan of a solar panel. Trees may grow, high buildings may appear nearby. If initially your panels were free from shade, and now something is always blocking the sun, there are countermeasures to be taken.