Almost all types of modules have degradation through the exposure of sunlight and the output of modules recuces every year and so does the generation. System price, capital interest rates, energy yeild, and module life are the four major factors which affect the profitability of a solar plant. Module power putput is generally specified at standard test conditions, and this is generally at a temperature of 25 oC. Most manufacturers claim their panels will produce 90% of the maximum power after a period of 10 years, and 80% of the maximum power after 25 years. Hence, most power plants are also designed for a life of 25 years.
To estimate the lifetime from degradation, standard tests called ‘Type Approval Tests’ have been introduced by the International Electrotechnical Commission (IEC). These are essentially accelerated test procedures based on accelerated climatic testing.