Dependency of the bifacial gain to the bifacial and front irradiance. The roof on which the devices were installed has an albedo of ∼10%. The irradiance at the rear of the tandem devices is never less than 5% of the irradiance at the front of the devices. The high values of bifacial irradiance ratio and irradiance can be explained by local effects of the apparent yearly solar movement. Note that the photovoltaic data is not temperature corrected, and data with an incidence less than 5 times is omitted.