The fast growth of PV installed capacity in Spain has led to an increase in the demand for analysis of installed PV modules. One of the topics that manufacturers, promoters, and owners of the plants are more interested in is the possible degradation of PV modules. This paper presents some findings of PV plant evaluations carried out during last years. This evaluation usually consists of visual inspections, I-Vcurve field measurements (the whole plant or selected areas), thermal evaluations by IR imaging and, in some cases, measurements of the I-V characteristics and thermal behaviours of selected modules in the plant, chosen by the laboratory. Electroluminescence technique is also used as a method for detecting defects in PV modules. It must be noted that new defects that arise when the module is in operation may appear in modules initially defect-free (called hidden manufacturing defects). Some of these hidden defects that only appear in normal operation are rarely detected in reliability tests (IEC61215 or IEC61646) due to the different operational conditions of the module in the standard tests and in the field (serial-parallel connection of many PV modules, power inverter influence, overvoltage on wires, etc.).
In stand-alone photovoltaic (PV) systems, charge controllers prevent excessive battery overcharge by interrupting or limiting the current flow from the PV array to the battery when the battery becomes fully charged. Charge regulation is most often accomplished by limiting the battery voltage to a predetermined value or cut-off voltage, higher than the gassing voltage. These regulation voltages are dependent on the temperature and battery charge current. An adequate selection of overcharge cut-off voltage for each battery type and operating conditions would maintain the highest battery state of charge without causing significant overcharge thus improving battery performance and reliability. To perform this work, a sample of nine different lead-acid batteries, typically used in stand-alone PV systems including vented and sealed batteries with 2 V cells and monoblock configurations have been selected. This paper presents simple mathematical expressions fitting two charge characteristic voltages: the gassing voltage (V g ) and the end-of charge voltage (V fc ) as function of charge current and temperature for the tested batteries. With these expressions, we have calculated V g and V fc at different current rates. An analysis of the different values obtained is presented here focusing in the implication in control strategies of batteries in standalone PV systems.
Three types of reference sensors for outdoor measurements and PV installation monitoring purposes have been analyzed: pyranometers, reference solar cells and equivalent technology solar cells (ETSC) with the same type and encapsulation system as -PV modules. A l l of the set points measured withan automatic adquisition system along a sunny and completed day on tilted and fixed platform andanaluzed by statistical linear regression passing to the ( 0 , O ) point allow the determination of the calibration values of reference sensors. The obtained calibration deviation value for ETSC using a pyranometer as reference sensor was + 2% and a value of +0.5% when the reference sensor was other k:TSC. Witc this method the spectral mismatch and kmperature corrections and special ground preparation are not necessary for the Madrid condi--Lions. The same analysis is helpful to reject non I ineari ty and badly encapsulated sensors. Finally wc conclude that a single solar cell with the same technology, encapsulation system, frame andbox connection as the PV modules, with a precision resistor, as the best reference sensor for outdoor PV measurements.
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