Real-Time Anticipation and Prevention of Hot Spots by Monitoring the
Dynamic Conductance of Photovoltaic Panels
Hot spotting in photovoltaic (PV) panels causes physical damage, power
loss, reduced lifetime reliability, and increased manufacturing costs.
The problem arises routinely in defect-free standard panels; any string
of cells that receives uneven illumination can develop hot spots, and
the temperature rise often exceeds 100°C in conventional silicon panels
despite on-panel bypass diodes, the standard mitigation technique.
Bypass diodes limit the power dissipated in a cell subjected to reverse
bias, but they do not prevent hot spots from forming. An alternative
control method has been suggested by Kernahan  that senses in
real time the dynamic conductance |dI/dV| of a string
of cells and adjusts its operating current so that a partially shaded
cell is never forced into reverse bias. We start by exploring the
behavior of individual illuminated PV cells when externally forced into
reverse bias. We observe that cells can suffer significant heating and
structural damage, with desoldering of cell-tabbing and discolorations
on the front cell surface. Then we test PV panels and confirm Kernahan’s
proposed panel-level solution that anticipates and prevents hot spots in
real time. Simulations of cells and panels confirm our experimental
observations and provide insights into both the operation of Kernahan’s
method and panel performance.