10 Module Deployment and Energy Rating
273
of the dopant boron with residual traces of oxygen in molten silicon during ingot
formation (it is therefore also referred to as boron-oxygen LID, or simply BO-LID).
The boron-oxygen molecules are able to capture the photogenerated electron-hole
couples and, thus, reduce short-circuit current and maximum power. The activation
energy needed for boron and oxygen to combine is provided by sunlight, hence
the name “light-induced degradation”, or simply LID. The reaction is relatively fast
and will start during the very first hours of light exposure at ambient temperature.
Since the best-known form of LID is a boron-oxygen effect, n-type
12 c-Si was initially
considered to be unaffected by LID. However, LID processes that are not related to the
presence of boron and oxygen have recently been detected and therefore light soaking
treatment of all c-Si PV modules has been inserted as a compulsory preliminary test
for the standard qualification and type approval of commercial modules according
to IEC 61215. It is also important to note that the nameplate power of all certified
commercial modules nowadays on the market would have usually already taken
into consideration LID and refers to stabilized conditions. Moreover, LID can be
artificially reverted by annealing the module at relatively high temperatures, such as
150 or 200 °C: as these temperatures cannot be reached naturally in the field, LID is
hardly considered a recoverable failure mode for modules within operation. But it is
basically partially recoverable.
Detection: power monitoring during the first weeks after installation.
Prevention: light-soaking (by the manufacturer).
10.4.5.2 Light and Elevated Temperature Induced Degradation
(LETID)
Another special form of light-provoked degradation has been observed at elevated
module operating temperatures (well over 50 °C for long periods, therefore affecting
modules mainly in hot climates); it takes place at a far slower degradation rate than the
originally observed LID. It is referred to as Light and Elevated Temperature Induced
Degradation (LETID) and represents the newcomer among the three recoverable
failure modes described in this section. It has been reported that:
1. LETID occurs if the module production process had included high-temperature
processing steps, followed by rapid cooling;
2. LETID does not manifest if the module operating temperature is kept below
50 °C or does not exceed that value for long periods;
3. the time span before LETID manifests itself is in the order of years of exposure
to sunlight at elevated temperatures;
4. LETID naturally reverses (although not necessarily up to full recovery) after
some time in the same high-temperature conditions that have generated it.
12 n-type c-Si uses phosphorous instead of boron as dopant and leads in general to cells with higher
efficiency; it is therefore expected to increase its market share in the future.
273
of the dopant boron with residual traces of oxygen in molten silicon during ingot
formation (it is therefore also referred to as boron-oxygen LID, or simply BO-LID).
The boron-oxygen molecules are able to capture the photogenerated electron-hole
couples and, thus, reduce short-circuit current and maximum power. The activation
energy needed for boron and oxygen to combine is provided by sunlight, hence
the name “light-induced degradation”, or simply LID. The reaction is relatively fast
and will start during the very first hours of light exposure at ambient temperature.
Since the best-known form of LID is a boron-oxygen effect, n-type
12 c-Si was initially
considered to be unaffected by LID. However, LID processes that are not related to the
presence of boron and oxygen have recently been detected and therefore light soaking
treatment of all c-Si PV modules has been inserted as a compulsory preliminary test
for the standard qualification and type approval of commercial modules according
to IEC 61215. It is also important to note that the nameplate power of all certified
commercial modules nowadays on the market would have usually already taken
into consideration LID and refers to stabilized conditions. Moreover, LID can be
artificially reverted by annealing the module at relatively high temperatures, such as
150 or 200 °C: as these temperatures cannot be reached naturally in the field, LID is
hardly considered a recoverable failure mode for modules within operation. But it is
basically partially recoverable.
Detection: power monitoring during the first weeks after installation.
Prevention: light-soaking (by the manufacturer).
10.4.5.2 Light and Elevated Temperature Induced Degradation
(LETID)
Another special form of light-provoked degradation has been observed at elevated
module operating temperatures (well over 50 °C for long periods, therefore affecting
modules mainly in hot climates); it takes place at a far slower degradation rate than the
originally observed LID. It is referred to as Light and Elevated Temperature Induced
Degradation (LETID) and represents the newcomer among the three recoverable
failure modes described in this section. It has been reported that:
1. LETID occurs if the module production process had included high-temperature
processing steps, followed by rapid cooling;
2. LETID does not manifest if the module operating temperature is kept below
50 °C or does not exceed that value for long periods;
3. the time span before LETID manifests itself is in the order of years of exposure
to sunlight at elevated temperatures;
4. LETID naturally reverses (although not necessarily up to full recovery) after
some time in the same high-temperature conditions that have generated it.
12 n-type c-Si uses phosphorous instead of boron as dopant and leads in general to cells with higher
efficiency; it is therefore expected to increase its market share in the future.