The service life or life cycle modeling of photovoltaic modules is based on a series of premises. These premises are combined with laboratory measurement data, and in some cases, are associated with information obtained through field practice and products returned on site. However, the photovoltaic industry is a relatively new and rapidly changing industry that focuses on improving efficiency (ie, more efficient batteries, new materials, new designs, etc.). In contrast, the life expectancy of PV can reach 20 to 30 years. These factors severely limit the availability and value of data currently available for predicting the expected service life of PV.
In order to answer major questions related to the service life of PV modules, accelerated aging test schemes are usually adopted. Through these tests, the Arrhenius method can be used to determine the activation energy (Ea). Under normal circumstances, the Ea measured values for temperature, humidity and ultraviolet (UV) will be used for the first service life prediction calculation after they are determined. *1, *2, *3, *4 Ea combined with local weather data can provide a basis for calculating the expected service life.
However, the basic problem with this method is that it only depends on the triggering of a single failure mechanism. In fact, the exposure of photovoltaic arrays to the atmosphere is accompanied by almost unpredictable random and highly regional weather events (wind, squally, storm, snow, icing and hail), which will produce different concurrent degradation mechanisms.
Photovoltaic modules are usually constructed from an aluminum frame that can be mechanically fixed, and the cells are covered with glass. The most common form of construction is to encapsulate photovoltaic cells with ethylene-vinyl acetate copolymer (EVA), laminate them with glass and one or more backside protective layers.
If moisture penetrates, the circuit connection between the batteries will have corrosion problems. The other conditions that photovoltaic modules must be able to withstand are as follows:
(1) Thermal cycling, which occurs when the photovoltaic module is exposed to changes in temperature between day and night.
(2) Humidity and freezing.
(3) Cyclic pressure load, caused by strong wind.
(4) The installation surface is distorted, caused by the photovoltaic module being installed on a non-planar surface.
(5) The hail test, the hail falls on the surface of the photovoltaic module at a high speed.
Before installing the photovoltaic module, you should check the characteristics of the photovoltaic module provided by the manufacturer (or check it as close as possible, because the actual conditions are different from the conditions of the laboratory photovoltaic module test). The simple method is to connect a multimeter to the terminal of the photovoltaic module to record the short-circuit current and open circuit voltage of the photovoltaic module. This inspection can simply test whether the photovoltaic modules are defective, but once the array is integrated, it will become very difficult to inspect the defective photovoltaic modules.
After installing the array, it is important to confirm that the output of the photovoltaic array under the test light conditions is consistent with the expected total current.
For example, if the weather is partly cloudy or at dusk, the output current of the array will not reach the rated current.