The solar panel spend its life in rains, hot sun, etc. It works outdoor and exposed to harsh environment in summer and winter. These changes in weather will of course affect the solar internal components and material bonded to each other, there will be chemical changes which will affect not only the solar panel performance, but it will affect its life time, its efficiency and reliability, because these chemical reactions will create new chemical material. Moreover, the elasticity of these internal materials will change with the time pass and affect the tension and stress forces taken place between different parts.
So, the cheap low quality solar panel which uses cheap and low quality materials, and which its manufacturer has not taken into consideration the parameters aforementioned will not withstands/survives much, provides low performance and low service life.
If your building/house is heavily shaded. As the shadow will dramatically reduce the solar system generated output electricity. In your vision you have to take care and consider about the impact of the current shadow and the anticipated shadow comes from trees grow or known renovations and extensions in surrounding buildings, that what we called shadow analysis study. It is an important study assisting us deciding whether the solar system will be a good beneficial investment project that worth to proceed or not. One more thing to note, is that in case of locations subjected to such shadow, its recommended to use micro solar inverter, so you can distribute your solar panels freely and avoid areas with heavy shadow.
What will be the expected annual generated electricity (kwh) form your solar system as a whole? And will your solar system installation company be ready to provide written statement about that. That is the strict performance indication, and if the solar company provide such statement, then be rest assured your system will be of high performance and efficiency.
The solar installation company has to agree with you before installation who will be responsible of repair and replacements costs if needed. This point should be clear and documented.