Partial shade and reduced power production affect different systems in different ways. In a stand-alone (off-grid) PV system, even minimal shading can have a big impact. Since shading reduces energy production, this may necessitate more careful load management (reducing energy consumed) or, if a generator is used, increased run-time (and the associated fuel consumption, pollution, and maintenance). If shade affects your PV system’s winter production, perhaps a hybrid PV-wind or PV-hydro system could be a solution.
For a grid-tied PV system, partial shading is not as critical—it will merely reduce the amount of utility power the system offsets. All of the mentioned site analysis tools can estimate energy loss due to shade. Because it is important to create realistic energy estimates, these losses should be factored into the amount of projected annual energy production for a grid-tied system. In some cases, you may be able increase the array size to offset the losses due to partial shading.
Given the knowledge and tools to perform a proper solar site analysis, PV system designers can ensure that their systems will not suffer needless energy reduction due to shade. PV systems are substantial financial investments and can only produce electricity if they have sunlight to work with, so it makes sense to make sure they are properly placed to maximize your green energy and your wallet power.
Justine Sanchez is a NABCEP-certified PV installer, Home Power Technical Editor, and Solar Energy International instructor. Justine lives, works, and teaches from an on-grid, PV-powered home in Paonia, Colorado.