1 Scope
This part of IEC 63202
describes procedures for measuring the light and elevated temperature induced degradation
(LETID) of crystalline silicon
photovoltaic (PV) cells in simulated sunlight.
The requirements for measuring initial light induced degradation (LID) of crystalline
silicon PV cells are covered by IEC 63202‑1, where LID degradation risk of PV cells under moderate temperature and initial durations
within termination criteria of
20 kWh·m−2 are evaluated.
Energy yield of PV modules is significantly affected by the inherent LETID performance
of the PV cells, which are used in it.
This LETID performance includes LID and other degradation mechanisms. The procedures
described in this document are to evaluate the
degradation behaviour of PV cells under elevated temperature and longer duration of
light irradiation. The degradation rate, maximum
degradation ratio and possible regeneration are determined by comparing the cell maximum
power, Pmax, at Standard Test Conditions (STC) during the light irradiation process with respect
to the initial Pmax. A Pmax degradation profile with respect to cumulative irradiation is presented, which helps
cell manufacturer to judge whether the
cells are prone to LETID before being assembled into modules.
Different from some other standards which separate boron-oxygen induced LID from LETID
or are limited to charge carrier
injection induced degradation [1]1, the overall degradation under light irradiation at elevated temperature is included
in the procedures described in this document. The overall degradation, determined
using this procedure, is more relevant to various
degradation mechanisms under field condition and gives a better evaluation of LETID
risk. For cells with strong initial degradation within
around 20 kWh·m−2, the procedures to measure initial light induced degradation (LID) in IEC 63202‑1 can be applied. Compared with module LETID detection method described in IEC TS 63342, higher injection level under open-circuit condition is used to shorten the test
duration, while the temperature is identical.
The procedures described in this document can be used to detect the LETID risks of
PV cells [2],[3] and to judge the effectiveness of LETID mitigation measures, e.g. quick test
for production monitoring, thus helping improve the energy yield of PV modules.