Page 206 - A Comprehensive Guide to Solar Energy Systems

208 A COmPrehenSIVe GUIDe TO SOlAr enerGy SySTemS

FIGURE 9.29 SmartWire contacting technology.

into modules. The degradation rate of modules depends also on the specific characteris-
tics of the module being used and the local climatic conditions.
For crystalline modules prepared from P-type silicon, the degradation rate is typically
higher in the first year upon initial exposure to light (light-induced degradation as dis-
cussed in Section 9.4.2) and then stabilizes. Additional degradation for c-Si modules may
be caused by

• environment effects on the surface of the module (e.g., pollution),
• discoloration or haze of the encapsulant or glass cover,
• lamination defects,
• mechanical stress and humidity on the contacts,
• cell contact breakdown, and
• wiring degradation.
The long-term reliability of a PV module is highly affected by the degradation behav-
ior of the polymeric components within the module, such as the encapsulant and back-
sheet [44]. For example, corrosion, a major field failure mode leading to loss of power, is
strongly accelerated by acetic acid, a product from the degradation of encapsulant eVA.
The cracking and delamination of backsheet due to degradation can lead to the dielectric
breakdown of PV systems and safety concerns as well as lower reliability of PV modules.
Different types of failures are described in ref. [45].
Because of these problems standardized methods (Performance standard IeC 61215)
are used for quality testing of PV modules. These tests can be divided into the following
sections:
• Diagnostic: Visual inspection, hot spot.
• Electrical: Insulation resistance, wet leakage current.
• Performance: P max at STC, temperature coefficients, nOCT, P max at low irradiance.
• Thermal: Bypass diode test, hot spot.
• Irradiance: Outdoor exposure, UV exposure, light soaking.
• Environmental: Temperature cycles, humidity freeze, damp heat.
• Mechanical: mechanical load, robustness of terminations, hail impact.