Albedo
In one line
The fraction of sunlight a surface reflects — the ground property that determines how much extra energy a bifacial array's rear side can collect.
What it means
Albedo runs from near zero for fresh asphalt to above 0.8 for fresh snow. For monofacial arrays it barely matters; for bifacial installations it is the single largest determinant of rear-side gain. Typical bifacial gains run 5–10% over vegetation and 10–20% over high-albedo surfaces such as light gravel, white membrane roofs or snow. Because rear-side irradiance also depends on mounting height, row spacing, tracker geometry and structural shading, albedo alone does not determine gain — but a project that specifies bifacial modules over dark ballast has spent money on a capability it cannot use. Albedo should be measured on site with an albedometer for bankable projects, not assumed from a land-cover table.
Worth knowing
- Only matters materially for bifacial arrays.
- Higher mounting and wider rows convert albedo into usable rear-side gain.
- Ground treatment is a design choice, not a fixed site property.
- Seasonal snow can double effective albedo for part of the year.
Field notes
- 1If you specify bifacial modules, budget for the ground treatment that makes them worth it — light gravel or a reflective membrane.
- 2Measure albedo on site across seasons; vegetation changes it substantially between wet and dry periods.
- 3Raising modules from 0.5 m to 1.5 m above ground typically adds several percentage points of bifacial gain.
Common mistakes
- Paying the bifacial premium for a flush rooftop install over dark membrane, where rear-side gain is near zero.
Frequently asked
What albedo do bifacial solar panels need?
Meaningful gain starts around 0.25 and rises steeply above 0.40. Over green vegetation expect roughly 5–10% bifacial gain; over light gravel, white membranes or snow, 10–20% is achievable with adequate mounting height.
Does painting the ground white increase solar output?
For bifacial arrays, yes — raising surface reflectance materially increases rear-side irradiance. The gain must be weighed against the cost and maintenance of the treatment, and it does nothing for monofacial modules.
Sources
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