The solar market is actively moving to embrace bifacial solar panel technology.  But to realize maximum gain of the second side or the back side of solar panels, many external variables need to be in place, including the 1) reflectivity of smooth freshly fallen snow, 2) best time of day, 3) best geographic location, 4) module mounting height, 5) most effective tilting of the solar array and a few others.

This reflectivity AND smoothness (of freshly fallen snow) is measured with an albedometer and prior studies have indicated that the ground must have an albedo of .8 or higher to assist in maximum gain. 

From our conversations with numerous bifacial panel users, it appears that many do not clearly understand the foregoing.  Developers are investing in bifacial technology without the assurance that gains (often stated by bifacial panel manufacturers on their product technical data sheets with specific percentages) are possible.  Albedo is the fraction of light reflected from the surface.  So, because a manufacturer states that the second side of a bifacial panel is capable of xx% gain increase, that gain cannot be guaranteed without the five external variables mentioned above.

To approximate freshly fallen snow, we have spoken to many developers who have considered and tested these materials:

1. White Gravel or Rock:  Because some white rock is inconsistently colored, the albedo might be less consistent.  When maintenance vehicles drive over white gravel, their tires will tend to disburse the rocks which may “fly” and other rocks will be pushed further into the soil.  So, at some point, additional white gravel or rock may have to be delivered.  White gravel or rock can cost $17-$20/sqm 

2. White Agricultural Fabric:  While white fabric agricultural ground cover is an option, it will not last for 30 years.  White specialty fabric can cost $5 per sqm.  Costs do not factor in installation and maintenance cost.

In 2019, Burns McDonnel shared the following in their white paper “Bifacial Modules” authored by Will Porter:
“Albedo — Annual energy production increases of 5% to 10% are typical with bifacial modules. In most areas, imported groundcover is often needed to push the increase much over 10%. The question is, does it pay to bring in light-colored gravel or roofing to control albedo? The answer to this question is both location- and project-specific, and a cost evaluation is needed to make the final determination. The estimated albedo for various surfaces is outlined in Figure 2.”

Green field / grass                        23

Concrete                                         16

White painted concrete            60-80

White gravel                                    27

White roofing material                   56

Light gray roofing foil                    62

White roofing foil for solar          >80