Researchers in Ireland investigated the effect of shunt resistance on the electrical performance of a PV cell. The team says its discovery could potentially lead to the development of models for the early detection of various forms of cellular degradation, allowing for interventions to repair or replace components before major power losses occur.
A team of researchers led by Ireland’s University College Cork further investigated the relationship between shunt resistance and other electrical properties of a solar cell, such as maximum power, duty cycle, open-circuit voltage and short-circuit current, with the aim of developing a model that detects cell degradation before it has progressed to the point where it causes major performance losses or safety issues.
Working with polycrystalline silicon solar cells, the team designed a system that allowed them to place a resistor between the p- and n-junctions of the cell, thereby controlling its shunt resistance. The experimental setup is fully described in the paper “Experimentally derived models for the detection of shunt resistance degradation in photovoltaic modules” published Energy reports.
After testing five cells with various combinations of shunt resistance, illumination, and other factors, the team found that maximum power, open-circuit voltage, and duty factor were all directly affected by changes in shunt resistance, while short-circuit current was unaffected. The work shows that when the shunt resistance has dropped to about 100 ohms per square centimeter, corrective measures must be taken.
Based on the numbers from their experiments, the group developed models to detect the decreasing shunt resistance. “These models can be easily applied to detect the onset of failure due to critical PV degradation or shunt resistance degradation and are suitable for use in online health monitoring systems,” the team said.
The team also suggests that future work could move towards classifying module degradation based on calculated shunt resistance loss.