Albedo

Albedo is the share of sunlight that the ground reflects. Some of that reflected light can reach the PV array. For monofacial modules, ground-reflected irradiance is usually a small contribution. It matters much more for bifacial modules, because reflected light on the back side is the main source of bifacial gain. A common estimate gives ground-reflected irradiance as albedo times horizontal irradiance times (1 minus the cosine of tilt), divided by two. This means the contribution grows with tilt and is quite low at moderate tilt angles. White surfaces such as snow can push albedo close to one. Fresh snow often beats other white surfaces because new snowfall covers any soiling. In performance models such as PowerTrack, an albedo factor sets how much of the diffuse light the array cannot see is added back to the total irradiance. A separate ground reflectivity constant has a default value of 0.1. To measure albedo, mount a pyranometer level, facing down, 1.5 to 2 m above ground that matches the ground under the array. Keep it at least 10 times the height of nearby objects away from those objects. Backside irradiance on bifacial arrays is measured or calculated in a separate step. Measuring it requires backside plane-of-array sensors.

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• sentence 1: support check: partial - GroundReflectivity is described as the amount of sunlight reflected from the ground and some reflected radiation hits the array, but albedo is not explicitly defined as a share. -->