Solar panels degradation mechanisms induced by light and high temperatures

In a world where daily life requires more and more electrical energy, the seek of energy sources that are cleaner than oil and gas has become of great importance. Nowadays, different technologies are applied as renewable energies, offering the possibility to reduce the energy consumption coming from non-green sources. Among them, photovoltaic technologies hold an important place in the renewable energy market. In 2020, 3.1% of the global electricity generation came from photovoltaic devices, which placed it as the third-largest renewable electricity technology behind hydropower and onshore wind.

Silicon is, by far, the most common semiconductor material used in solar cells, representing approximately 90% of the modules sold today. But, in the quest of high-performance photovoltaic modules, the development of new materials that will convert more efficiently sunlight into electrical power is one of the priorities. Nevertheless, understanding of the reliability and lifetimes of already operational technologies is necessary. The comprehension of degradation mechanisms of photovoltaic systems is important because it directly leads to not efficient devices that present losses on the power output. Experimentally, the performance of solar cells is investigated by measuring the change of the output energy. Changes in the performance can be directly related to different degradation mechanisms coming from the exposure of solar cells into weather changes, ambient conditions or the aging of the components.

Among solar cells, silicon-based modules represent around 90% of the market. Their high efficiencies and low cost of the components makes them really demanded. One of the main degradation modes of silicon solar cells that remains to be understood is light and elevated temperature induced degradation (LeTID). Such degradation can decrease up to 15% the electricity production of the solar panel in one to two decades. In order to explore the insights of this phenomenon, the functioning of solar cells, the different types of solar cells and degradation processes are described along this article. The description of the working principle of photovoltaic module, from charge carries generation to their extraction and current production, is presented in this first part. The main types of PV modules along with the most common characterization techniques and degradation mechanisms are discussed along with the insights behind LeTID, the most important hypotheses and mitigation strategies.

At this end of the article, the reader will find a glossary, along with a table of notations and symbols used.