**2.10. Defective bypass diode**

Bypass diodes reduce the effects of intermittent cloud cover and partial shading on power generation by limiting reverse voltage potentials [5]. Power output is decreased significantly without bypass diodes and partial shading may cause local overheating, hot spots, and damage [25]. The complete PV power plant should first be introduced into the GIS software (ESRI ArcGIS) through aerial orto-photography before geometrical parameters are projected. The geograph-

Degradation Monitoring of Photovoltaic Plants: Advanced GIS Applications

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Furthermore, it is necessary to identify the exact position within the panel of any possible faults that may appear. For this reason, split installation of photovoltaic panels and the thirds of cells within each panel are taken into account. The maps have been geo-referenced by

PV modules are identified by their rack number and by a code that includes the serial string

A systematic procedure needs to be set up to identify the geographical position of a defect within a panel. A photovoltaic module is made up of 180 thirds of cells so the following nomenclature is suggested. Each cell in the panel can be split into 6 columns (A–F) and 10 rows (0–9). Each cell is, in turn, split into three thirds (X, Y, or Z). In this way, the position of a defect can be indicated in the third of the cell where it is located by an alphanumerical code

With the graphical part of the GIS tool delimited and the identification procedure for each PV cell established, a geo-referenced database or geo-database can be implemented. The geodatabase consists of a set of various kinds of geographical datasets in a common file system folder. From this a comprehensive information model can be created to represent and manage all the geographical information related to the power plant. This information model is real-

The model can be divided into three sorts of information: measurements of electrical variables, graphic information (pictures and thermographs), and defects and their description. **Figure 6** shows the schematic diagram of the relational database that has been created. According to

ical position of the PV serial strings and limitation of plots can thus be set.

(e.g., 4EY). **Figure 5** shows such an identifying code applied to a panel.

ized as a series of tables storing entity classes, raster datasets, and attributes.

assigning them projected coordinates ETRS89 UTM 30 N.

and the relative position of the string within the series.

**Figure 5.** Adopted nomenclature for PV defect identification.

A new bypass system has been designed [26] allowing significant hot spot temperature reduction in both partial and full shading conditions. It relies on a series-connected power metal oxide semiconductor field effect transistor (MOSFET) that subtracts part of the reverse voltage from the shaded solar cell, thus acting as a voltage divider. The authors claim that it would be possible to cool up to 24°C with respect to the case in which standard bypass diodes are adopted.
