Solar Power Generation Root Cause Analysis
IEA has completed solar array installation at one of its facilities. This installation had been in service for over a year, and enough data was collected to confidently assess its performance.
One peculiarity noticed was that one of the modules appeared to consistently generate less electricity than the other 11 modules in the array. Upon further review of the data, we determined that the under-generation occurred in the morning hours. By 10:30 AM or so, that particular module had “caught up” with the other modules in its production. What could be going on?
Even small amounts of shading of a solar module can “short out” the cells within the module and cause dramatic reductions in output power. During a site visit, we looked suspiciously at nearby high-voltage utility lines as a culprit. We propped a ladder on the roof and upon further review, we noticed the installer had installed a small electrical disconnect switch, required by the local Utility, for safety reasons. The button was located about one foot east of the end of the array and was mounted on a strut, sticking up about two feet into the air.
In the accompanying photograph, you can see a shadow from the switch on an end solar module. As the sun rises in the morning, the shadow begins to fall across the module from east to west. At around 9:00 AM, the shadow cuts across about one-third of the width of the module, while the module’s output is only about 1/3 of its neighbors.
By around 10:15 AM, the sun has risen sufficiently that the shadow only cuts across 10% of the module’s width. Output is reduced by only about 25% when compared to the others. By 10:30-11:00 AM, the sun has risen high enough that the shadow is no longer touching the module and the output is similar to the other modules in the array.
A valuable lesson in solar array placement has been learned. Even a small shadow from a nearby object can have a dramatic negative impact on the productivity of your solar power generation project.
