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PV Bonding Information
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Photovoltaic (PV) Bonding
For many PV modules, special earthing arrangements are required. As an example, Thin-Film modules may suffer from TCO (transparent conductive oxide) corrosion, which can destroy the entire PV plant. PV modules with backside contact cells may see a reduction in efficiency of approx. 30% due to polarisation effects. To prevent these issues, manufacturers specify the earthing of the negative/positive side of the DC string.

TCO corrosion is an inherent problem for all thin film technologies, but can be effectively blocked by the implementation of adequate inverter earthing and tightening of the module edges. Both measures are recommended.

Note: It is especially important that PV frame earthing is provided when using non-isolated (transformer-less) inverters.
Types of earthing in a PV Array
Protective earthing: earthing of exposed parts
Functional earthing: system earthing (+ve or -ve of PV array)
System Earthing
- why do it?
Performance (i.e. PV modules)
Warranty (i.e. TCO layer corrosion in some thin film modules types)
System design choice (i.e. earthed battery bank on stand-alone power system)

Earthing +ve conductor
Modules that utilise back contact conductors may require +ve conductor
bonded to earth to achieve maximum performance

Source:SunPower Corp.

Thin film module degradation

Damp-heat-test with negative Bias Voltage (NREL)

Above: "Bar Graph Corrosion" of an a-Si-module after 200 hours at 85C, 85% RH and a negative bias voltage (-600V) from cells to frame.
Source: Osterwald et al NREL2003

TCO on superstrate construction
Source: Dr. Herbert Schmidt, Franhofer Institute
TCO on Superstrate Construction
Capacitive Coupling

Example of Earthing a GC System

Summary of TCO Corrosion

Still incomplete understanding of TCO corrosion
Migration of Na+ ions from glass probable cause
Superstrate technology (a-Si & CdTe) has higher risk
Substrate technology (CIS, partially a-Si) less affected
Accelerated damage through humidity and high

Construction and material of edge seals are of key

A metal frame increases rate of degradation
Negative voltage potential to ground has a strong
  acceleration effect (earthing of solar negative

Protective Earthing

Earthing of PV array frame to protect against electric
  shock hazard from indirect contact through capacitive
  coupling with the PV array by touching modules or the
  module/array frame
Not just a theory - incident has already occurred in
Now a requirement iin the CEC GC Installation Guidelines
  for all LV PV arrays

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