10 Module Deployment and Energy Rating
275
Electroluminescence is probably the best-known method nowadays to detect both
LETID and PID modules in the field at any phase of their lifetime. However, in
the production phase neither LETID, nor PID are at the time of writing part of the
international module qualification standard IEC 61215: it is therefore more difficult
with PID and LETID, than with LID, to get assurance by the manufacturer that
their modules will not be affected by such degradation mechanisms. While PID has
already a dedicated technical specification (IEC TS 62804), which will most likely
be included in the near future into IEC 61215 (with additional pass-fail criteria), a
similar protocol for LETID test is still not available. Moreover, it is important for
the plant owner to ask the module manufacturer for evidence that his products are
LETID-free products.
10.4.6 “Recoverable” Failure Modes
Let us conclude this section on failure modes with two examples where the original
functionality of the modules can be fully recovered. In what we have called “recoverable failure modes”, detection can be done easily by visual inspection; prevention can
be done by accurately eliminating the cause of failures when they occur (Fig. 10.14).
10.4.6.1 Partial Shading
Partial shading is the most trivial case of a fully recoverable failure mode that can be
solved, by removing the shade, if more dangerous hot spot failures have not occurred
in the meanwhile.
10.4.6.2 Soiling
The second and last example of failure modes that is naturally recoverable is soiling,
which can be due to a number of causes: deposition of sand (particularly severe in
desert installations), snow and hail (in the continental climatic zones), leaves and bird
drops (everywhere). In continental climates and at high latitudes where modules are
oriented with an optimal tilt of 20 degrees or more, rain can be sufficient to remove
most of the soiling and active cleaning is usually not needed. At lower tilts and
in desert climates, where soiling is a major failure mode, it can be mitigated with
periodic cleaning of the system and the full functionality of the power plant can be
easily restored, provided the soiling has not yet generated severe hot spots or corrosion
failures, as described in the previous section. Self-cleaning tools (Fig. 10.15) are
under investigation for large installations in locations particularly prone to soiling.
275
Electroluminescence is probably the best-known method nowadays to detect both
LETID and PID modules in the field at any phase of their lifetime. However, in
the production phase neither LETID, nor PID are at the time of writing part of the
international module qualification standard IEC 61215: it is therefore more difficult
with PID and LETID, than with LID, to get assurance by the manufacturer that
their modules will not be affected by such degradation mechanisms. While PID has
already a dedicated technical specification (IEC TS 62804), which will most likely
be included in the near future into IEC 61215 (with additional pass-fail criteria), a
similar protocol for LETID test is still not available. Moreover, it is important for
the plant owner to ask the module manufacturer for evidence that his products are
LETID-free products.
10.4.6 “Recoverable” Failure Modes
Let us conclude this section on failure modes with two examples where the original
functionality of the modules can be fully recovered. In what we have called “recoverable failure modes”, detection can be done easily by visual inspection; prevention can
be done by accurately eliminating the cause of failures when they occur (Fig. 10.14).
10.4.6.1 Partial Shading
Partial shading is the most trivial case of a fully recoverable failure mode that can be
solved, by removing the shade, if more dangerous hot spot failures have not occurred
in the meanwhile.
10.4.6.2 Soiling
The second and last example of failure modes that is naturally recoverable is soiling,
which can be due to a number of causes: deposition of sand (particularly severe in
desert installations), snow and hail (in the continental climatic zones), leaves and bird
drops (everywhere). In continental climates and at high latitudes where modules are
oriented with an optimal tilt of 20 degrees or more, rain can be sufficient to remove
most of the soiling and active cleaning is usually not needed. At lower tilts and
in desert climates, where soiling is a major failure mode, it can be mitigated with
periodic cleaning of the system and the full functionality of the power plant can be
easily restored, provided the soiling has not yet generated severe hot spots or corrosion
failures, as described in the previous section. Self-cleaning tools (Fig. 10.15) are
under investigation for large installations in locations particularly prone to soiling.