Light soaking losses or Light Induced Degradation (LID), is the loss of performance at the first light exposure of crystalline cells. As a result, the first year performance will not match the performance rated by the final factory flash test. The LID loss is related to the quality of the wafer manufacture, and may be between 1% to 3%. This phenomenon is due to traces of oxygen included in the molten silicon during the crystallization process.
The LID performance loss is usually included in the manufacturer’s aging warranty. For example, if the warranty stipulates 20% de-rating over 25 years, it will also warranty 3% the first year and .7% per year in each of the following years (i.e. years 2 to 25).