The QE in our name stands for “Quantum Efficiency.” Quantum Efficiency (QE) is the ratio of the number of charge carriers collected by a solar cell to the number of photons of a given energy shining on the solar cell. Simply put, Quantum Efficiency relates to the response of a solar cell to the various spectrums of light shining on the cell, for instance, sunlight.
Benefits of IV Curve Tracing
If using a digital multimeter is like measuring a patient’s blood pressure and heart rhythm, using an I-V curve tracer is like administering an MRI. Rather than being EMTs responding to an emergency, we should be physicians helping to keep our patients healthy through preventative maintenance and regular screening.
While it is possible for technicians in the field to get a basic snapshot of system performance and diagnose many field failures using affordable and widely available tools like digital multimeters and clamp meters, [Issac] Opalinsky [of SunPower] notes that I-V curve tracers have two unique advantages. First, I-V curve tracers make it easier and safer to take Isc measurements. Second, curve tracers can reveal what happens to an array under load. “The four key measurements that can be performed with a digital multimeter (Voc, Vmp, Imp, Isc) are inadequate if we want to get a picture of how the PV system responds to a varying load,” states Opalinsky. “Without disassembling an array, it can be difficult to determine if a perceived problem is just a function of varying environmental conditions, a single bypass diode that has failed or high resistance in a corroded connector.”
The stakeholders in newly built systems want to verify that all the PV modules are of a consistent quality, that they were not damaged during shipment or assembly, and that the array is producing at the contracted capacity. These stakeholders would also like a permanent record of the as-built system performance, a benchmark for comparison as arrays age and degrade—particularly in cases where warranty negotiations are required.
–“Field Applications for IV Curve Tracers,” SolarPro Magazine, August/September 2011, Paul Hernday.