Annual Degradation Rate Analysis of Mono-Si Photovoltaics Systems in Thailand Using the Mixed Effects Method

The annual degradation rate (DR) of photovoltaics (PV) system is a critical factor to evaluate the energy performance and the levelized cost of electricity (LCOE) during its operation lifetime. However, the DR of a particular system strongly depends on the technical configuration such as PV module and array, inverter configuration, and also the climatic conditions. Therefore, a real operation dataset of DR is necessary to PV engineer in order to estimate energy performance and the LCOE for a particular system. This article presents the annual DR for a group of PV systems in Bangkok, Thailand which share the same monocrystalline silicon (Mono-Si) solar cell and inverter brand, over a four-year period. Instead of using simple linear regression, we apply the linear mixed effects method to estimate the DR value, which is suitable to formula a time-series data. The annual DR was found about 2.7% per year, with the 95% confidence interval from 0.7% to 4.6% per year. Hence, the operation lifetime of PV system until it reaches 80% of their initial energy conversion performance is about 7 years, with the 95% confidence interval from 4 years to 28 years. The resulting DR is informative and useful for further study on PV system performance and cost of investment in tropical region. Furthermore, we are the first group in Thailand to estimate the DR of PV station at system scale based on the mixed effects method. Finally, our study has enriched the knowledge about the operation of Mono-Si PV station in real operation condition.