10 Module Deployment and Energy Rating
267
10.4.3 The Timeline of Failure Modes
Before looking at some of the most relevant examples of the different failures modes,
we will consider the time when failures occur. In fact, it is common practice to divide
failure modes into three groups, depending on the time scale when they are likely to
occur during the life of a PV plant, as shown in the “Bathtub curve” of Fig. 10.10.
• “infant” failures occur on PV modules and components before the installation,
sometimes due to defects of production, to transport or installation;
• midlife failures occur during the expected lifetime of the plant;
• “wear-out” failures occur when the expected lifetime of the PV plant is over, and
typically cause modules or components to be replaced.
Let us now look in some more detail at these three different time scales.
Infant failures are unfortunately very frequent, as the Bathtub chart shows. They
may have originated in the production line (junction-box failures, defective interconnections, defective cells, early delamination). Other important cases of early, unrecoverable failures coming from transport and mounting are frame failures, glassbrakeage and cell cracks. Mechanical defects can also arise from natural or manmade hazards occurring during transport or installation (e.g. hail, lightning, module
mishandling, transportation and crashes) (Table 10.1).
The most dreaded failures for plant owners are midlife failures, as they always
occur unexpectedly and can cause power and investment losses for the owner. In
general, the failure rate (i.e. the number of failures detected per year) is smaller here
than for infant failures. However, all components (junction-boxes, cables, frames,
mounting structure, inverters, etc.) may deteriorate during the lifetime of the PV
plant, most often due to poor module quality. This is less and less frequent in the
last years, due to a generally broader recognition of the importance of quality, by
both PV module manufacturers and by engineering, procurement, and construction
companies. But the effect of poor-quality modules installed in the last two decades
is now gaining importance in the installations that are still in their midlife. Most of
these midlife failures are often difficult to detect, especially when they cannot be
visually observed (as is the case with PID and with microcracks). A similar problem
occurs in large power plants where visual inspection is often prohibitively expensive.
Fig. 10.10 The “Bathtub
curve”: infant failures,
midlife failures and wear-out
failures
267
10.4.3 The Timeline of Failure Modes
Before looking at some of the most relevant examples of the different failures modes,
we will consider the time when failures occur. In fact, it is common practice to divide
failure modes into three groups, depending on the time scale when they are likely to
occur during the life of a PV plant, as shown in the “Bathtub curve” of Fig. 10.10.
• “infant” failures occur on PV modules and components before the installation,
sometimes due to defects of production, to transport or installation;
• midlife failures occur during the expected lifetime of the plant;
• “wear-out” failures occur when the expected lifetime of the PV plant is over, and
typically cause modules or components to be replaced.
Let us now look in some more detail at these three different time scales.
Infant failures are unfortunately very frequent, as the Bathtub chart shows. They
may have originated in the production line (junction-box failures, defective interconnections, defective cells, early delamination). Other important cases of early, unrecoverable failures coming from transport and mounting are frame failures, glassbrakeage and cell cracks. Mechanical defects can also arise from natural or manmade hazards occurring during transport or installation (e.g. hail, lightning, module
mishandling, transportation and crashes) (Table 10.1).
The most dreaded failures for plant owners are midlife failures, as they always
occur unexpectedly and can cause power and investment losses for the owner. In
general, the failure rate (i.e. the number of failures detected per year) is smaller here
than for infant failures. However, all components (junction-boxes, cables, frames,
mounting structure, inverters, etc.) may deteriorate during the lifetime of the PV
plant, most often due to poor module quality. This is less and less frequent in the
last years, due to a generally broader recognition of the importance of quality, by
both PV module manufacturers and by engineering, procurement, and construction
companies. But the effect of poor-quality modules installed in the last two decades
is now gaining importance in the installations that are still in their midlife. Most of
these midlife failures are often difficult to detect, especially when they cannot be
visually observed (as is the case with PID and with microcracks). A similar problem
occurs in large power plants where visual inspection is often prohibitively expensive.
Fig. 10.10 The “Bathtub
curve”: infant failures,
midlife failures and wear-out
failures