| Work Detail |
New research carried out in Belgium shows the importance of evaluating the reliability of inverters by including the degradation rates of photovoltaic panels depending on the climate. Scientists found that, especially in hot and arid climates, PV inverters should be designed with parameters higher than the standard value.
Scientists at the Belgian University of Hasselt have discovered that weather-dependent degradation rates of solar modules could have a significant impact on the power electronics of photovoltaic systems.
In the study “ Assessing the impact of PV panel climate-based degradation rates on inverter reliability in grid-connected solar energy systems ” of grid-tied solar energy), recently published in Heliyon , the academics warned that using similar climate-based degradation rates for PV systems in all climate zones of the world represents an “unrealistic approximation” that can lead to misleading results . “This can lead to an overestimation or underestimation of the useful life of photovoltaic systems, with the consequent impact on the reliability estimates of the power electronics,” they add.
The research group evaluated panel degradation rates based on climate stresses in three different geographic locations: Genk (Belgium), Accra (Ghana) and Kabd (Kuwait). These places represent moderate, hot and humid, and hot and dry climates, respectively.
A physics-based approach was used that took into account meteorological data such as ambient temperature, irradiance, wind speed and direction, as well as material properties such as optical, thermal and electrical constants, and the thicknesses of each module layer. Panel parameters such as temperature coefficients, external quantum efficiency and interconnection layout were also taken into account.
The researchers explained that insulated gate bipolar transistors (IGBT), which are the switching devices of the photovoltaic inverter, are extremely sensitive to high temperatures and, without proper management, can cause failure or reduce their useful life.
“Every time an IGBT is turned on, power losses are generated inside the layers of material, and these power losses can generate heat inside the IGBT,” they explained. “Consequently, each activation induces a thermal cycle attributed to these power losses.”
The team analyzed the possible degradation rates in a standard 4 kW PV system that included a DC-DC boost converter and a single-phase inverter using four IGBTs with a nominal voltage of 700 V and a nominal current of 40 A. They considered a scenario without intrinsic degradation rate of the solar module and a scenario that took into account the intrinsic degradation rate of the photovoltaic system.
Through a series of simulations, the researchers discovered that the inverter of the PV system located in Kabd has a much shorter lifespan than the inverters located in Genk and Accra.
“The Kabd PV inverter experiences significant thermal stresses without the effects of PV degradation, and the IGBT can fail in just 5 years, resulting in PV inverter failure in just 3.8 years,” they stressed. “With the introduction of linear PV degradation, the useful life of the PV inverter at Kabd will increase to 5.8 years, but it is still lower than that of the other two sites. “The physics-based photovoltaic degradation model will increase the useful life of Kabd to about 6.5 years.”
The group concluded that the deployment of photovoltaic systems in hot and arid climates could require different parameters for inverter design. “These results demonstrate the importance of incorporating various factors and parameters when evaluating the reliability of a photovoltaic inverter and its switching device,” he said. |
