Definitely orientation makes a difference, but there is a lot of factors to take into consideration here. I am a mechanical design engineer for a solar company so I really know about how the industry works. The trending design in solar at the moment, especially in utility projects are the “solar trackers”. Solar trackers, which can track the sun positioning at different times of the day can improve the power density of a solar field by more than 40%. Now, the efficiency in the solar plants can be affected by other issues such as shading and backtracking. As it was mentioned before if there is soil particles in the panels, this can also affect efficiency. However, real efficiency problems come with microcracking of the PV cells and Potential Induced Degradation or PID. Microcracking can happen if the installation process is not efficient, therefore is the responsibility of us the engineers to make the design simple and practical enough for installation. PID is caused usually for wrong installation on the PV cells in the solar panel or excess of humidity in the field, but it can also be triggered by high-powered systems connected in series. As you can see, there are many factors that can affect the power output of a solar field over time, so therefore capable companies have to take all these conditions into account in PV and racking design.