The surface albedo of a PV site can be measured by albedometers for a longer time period of 1 year prior to installation to monitor the seasonal changes of a site's albedo and get reliable parameters for energy yield predictions. Such a device consists of 2 individual, but optically identical, pyranometers. Thereby, one pyranometer is installed facing up to the sky to measure the global horizontal irradiance (GHI), while the second one is placed facing the ground to determine the global reflected irradiance (GRI). The actual surface albedo is the ratio of the ground-reflected to the global-horizontal irradiance.
Alternatively, the irradiance of the back and front side of modules can be determined using reference cells. There by, it is essential that the cells 'match' the PV panels. Meaning that reference cells and envisaged modules should utilize the same bill of materials (cell, glass, encapsulant, backsheet, ribbons, etc.) and are produced using the same manufacturing processes, especially the same antireflective (AR) coating layers. In order to consider the mismatch due to light not hitting the back of the tilted modules uniformly, several reference cells are needed, which are placed in different positions behind the panel (see Complexities Of Bifacial PV Systems).
Measuring albedo on-site: 2 pyranometers – one looking up and one down – are used to measure the albedo on-site. (Source: TaiyangNews)
These cells have the same spectral response as the modules and measure only the reflected part of irradiance usable for the solar modules. In cases where it is difficult to get cells that perfectly 'match' the PV panels, a combination of albedometers and reference cells are used.
The text is an excerpt from the TaiyangNews Bifacial Solar Systems 2024 Report, which can be downloaded for free here.