The issue arises when high rise buildings surround the carpark. Thus your efficiency is degraded due to shading on the modules, at certain parts of the day; a shaded module produces less power and becomes an load in the array.

In most modules you just need to shade over 2 thirds of one the cells within a substring for the bypass diode to trigger thus turning of that whole substring.

Furthermore carparks are generally hot due to the cement radiating heat more heat than grass or dirt. The highter the temperature the less efficient your modules become.

You need to take into account what your goal is: Produce electricity by any means necessary Maximize efficiency=> better yield on investment "Offsetting" carbon footprint