An albedo irradiance model usable for bifacial PV modules based on LiDAR data and ray casting

Abstract

Despite the fact that the price per watt-peak for photovoltaic modules are decreasing rapidly, there is a large population of people which have still not implemented photovoltaic technology in their everyday lives. An important reason why PV is still not the main source of electrical energy for these people is the uncertainty that comes with installing a PV system on the roof of a house. Consumers are afraid that an investment in a PV system will cost them too much money, while it will take a long time before their investment is paid back for. Therefore, it is important to accurately estimate the energy yield of PV systems before installation. By doing so, consumers will be more likely to see the benefits of a PV system, thus implementing the technology on their houses.

This thesis aims to improve the accuracy of the annual energy yield estimation using LiDAR data and a new model for the albedo component of irradiance. LiDAR has been used to determine the irradiance on a surface previously, however, this thesis uses LiDAR data in the Unity 3D game engine, which enables the user to apply changes and build on the environment rapidly. This eliminates the disadvan- tage of LiDAR data, which is often outdated, thus missing crucial objects surrounding the location of the potential PV system.

Ray-casting is used extensively to determine the sky view factor, view factor, shading factor and to determine the surfaces visible to the PV module. Being able to determine the sky view factor without doing any field work greatly reduces the time required to design a PV system.
The albedo component is often neglected entirely when estimating the irradiation on a surface, while it may significantly contribute to the energy yield, reaching up to 10% of the total. The albedo com- ponent is mainly important for highly tilted PV modules or BIPV. The albedo component is also crucial for bifacial PV modules. Measurements have shown that the albedo of a material is not determined easily using a sample of the material along with two inversely installed pyranometers making up an albedometer. It has been found that the albedometer is only able to determine the specific albedo of a location for the weather condition and the time in which the measurement has been done. Extensive research has been done in order to determine the factors which have an influence on the albedo of a location. The spectral reflectivity of materials is expected to play an important role in finding a final model which describes the albedo factor accurately.

In order to estimate the irradiance due to reflectance, first the irradiance on the surfaces that are visible to the PV module are estimated one by one along with the view factor of each of the visible surfaces to the PV module in question. Finally using the reflectivity of the material of each surface, the contribution of each surface to the irradiance on the PV module as a result of reflectance is summed up resulting in the albedo component of the irradiance. The same method is used for the back side of the PV module to determine the irradiance on the back side of a bifacial PV module.

This research aims to play an important part in the automation of PV system design, striving to com- pletely eliminate necessary field work, while improving the accuracy of the predicted annual energy yield.