| Work Detail |
A Finnish-Norwegian research group has investigated model chains for horizontal to vertical solar irradiance conversion in east-west oriented vertical photovoltaic systems located at high latitudes. They have found that the precision and bias of the model chains are different for the eastern and western sides of the solar field.
An international research team led by the Norwegian University of Science and Technology (NTNU) has developed a new methodology to identify the most effective model chains for estimating solar irradiance in east-west oriented vertical bifacial photovoltaic installations at high latitudes.
The scientists explained that previous studies focused on validating a specific step of a given chain of models, and said that their work, on the contrary, considered the entire chain of models and the impact of combining different models on the precision of the final results.
“The objective of this study is to contribute to filling the gap in the literature on modeling solar irradiation taking into account high latitudes and irradiation on photovoltaic surfaces oriented vertically towards the east and west,” they explained. “Reviewing the state of the art of decomposition and transposition models, 29 decomposition and 25 transposition models are chosen for detailed evaluation using model chains.”
The group tested their approach on an east-west oriented vertical bifacial photovoltaic system located in Turku, Finland. Modeling was carried out in six steps: data acquisition, review of existing solar decay and transposition models, implementation of the model library, initialization of model chains, experimental validation, and comparison between model chains.
The academics considered 725 possible combinations of the decomposition and transposition models for both sides of the photovoltaic installation.
They then compared the performance of these models with that of reference models used to estimate solar irradiance on inclined surfaces. They also created a data set with the necessary data to initialize the model chains considering the solar zenith and azimuthal angles, the air mass and the angle of incidence of light, as well as to validate their results.
Through their analysis, the research team concluded that identifying a single chain of models that can perform best, regardless of system orientation, is a difficult task at high latitudes. “Model chains that work optimally for the east side of the panel achieve a different level of accuracy when they model the solar irradiance incident on the west side,” he added.
The researchers recommended using two different model chains for the front and rear faces of the vertical PV system.
“The models of the Yang and Pérez families should be preferred for the solar decay stage when evaluating the Western side of the system,” they said, referring to the models adopted in previous literature. “The Erbs and Pérez family models should be preferred for the solar decay stage when evaluating the eastern side of the system.”
They also added that the so-called Hay and Steven transposition models should be preferred for the western and eastern sides of the system, respectively.
They presented the new methodology in the study “ Validation of model chains for global tilted irradiance on east-west vertical bifacial photovoltaics at high latitudes ”, published in Renewable Energy . The research group includes scientists from the University of Turku and the Turku University of Applied Sciences (TUAS) in Finland.
“To improve the accuracy of solar analysis results, a metamodel-based approach is needed that can apply different model chains based on a parameter, such as the angle of incidence or the geometry of the investigated surface,” they conclude.
Other scientists at the University of Turku (Finland) have recently created a new method to calculate the yield loss rate (PLR) in vertical bifacial photovoltaic systems. This metric is commonly used by project developers to evaluate the expected power of a photovoltaic system over its installed useful life.
The same research group presented in July a methodological workflow to increase the electrical performance of bifacial vertical photovoltaic systems that connect to low voltage (LV) networks located at high latitudes and have different locations, orientations and panel technologies. |
