The Bifacial Year

During the wet season, rainwater puddles caused reflections on the surface, with an unusual effect on bifacial modules: higher rear irradiation due to short-lived albedo increasement. However, such effect did not result in significant power generation gains. In fact, albedo decreased during the following days due to the dark color of wet soil.

Ground surface conditions were subject to continuous changes impacting their albedo. As an example, the experience at BiTEC supports the hypothesis that albedo, and in turn irradiation reflected on the rear side of modules, decreases in humid environments [5].

Measurements for the different types of surfaces analyzed at BiTEC confirm that soil changes in time have a direct impact on the albedo value. The figure 10 shows measurement variability compared to the range of typical values established by NREL for each type of surface.

It is important to mention that bifacial gain estimates for long-term analyses requires the use of representative albedo values throughout the period being analyzed.

Figure 11 shows full-year results for different albedo combinations.

As seen in the table:

• For high albedo (55.6%), that is, white sand or snow-covered ground, the bifacial gain of a 2P SF7 bifacial tracker is 15.7%
• For a medium albedo (29.5%), such as sand, the bifacial gain is around 9.6%.
• For cultivation areas with an albedo of 19.9%, the bifacial gain of a 2P SF7 bifacial tracker is 7.3%.

BiTEC analyses revealed a linear dependency between bifacial gain and albedo. Besides, the influence of the remaining parameters under analysis, such as height, GCR and temperature, is always affected by the albedo. However, its influence can be assessed separately.