Soil reflectivity strongly influences the amount of light that reaches the underside of photovoltaic modules and therefore the energy yield of ground-mounted arrays. Albedo, the fraction of incoming solar radiation reflected by the ground, varies from low values for dark soils to very high values for fresh snow. Research by Matthew Lave National Renewable Energy Laboratory and by Wim van Sark Utrecht University identifies ground reflectance as a key variable for estimating energy from bifacial and some tilted monofacial systems, because reflected irradiance can augment rear-side or diffuse illumination and change module operating temperatures.
Mechanisms
When the ground is brighter, more sunlight is redirected upward and captured by the rear face of bifacial panels or by diffuse collection on monofacial arrays. This produces a bifacial gain that scales with albedo, panel height, tilt, and row spacing. Typical bare-soil albedos are around 0.1 to 0.25 while sand, light gravel, or crops have higher values; snow can reach 0.8 or above. Seasonal changes such as vegetation growth or snow cover therefore create measurable variability in monthly and annual output. Models and field measurements reported by Matthew Lave National Renewable Energy Laboratory and by Wim van Sark Utrecht University show that gains range from negligible on dark ground to tens of percent under high-reflectance conditions, with larger relative gains for taller racks and wider row spacing that expose more ground to view by the panels.
Implications for siting and sustainability
Understanding albedo is essential for accurate yield forecasting, project finance, and environmental assessment. Developers sometimes increase effective albedo with light-colored gravel or modular reflective fabrics to boost output, but those choices carry trade-offs: increased cost, potential habitat loss, impacts on soil moisture and local microclimate, and cultural or landscape objections in sensitive territories. Agrivoltaic systems illustrate a nuanced case: crops or managed vegetation reduce albedo compared with bare white ground but provide socio-economic and ecological co-benefits that may outweigh modest energy losses. Conversely, installing PV in snowy regions can produce unexpectedly high winter yields on bifacial modules but also alters surface energy balance and local melting patterns.
Accurate prediction requires site-specific surveys of ground reflectance across seasons and integration into performance models recommended by institutional sources such as the National Renewable Energy Laboratory. Incorporating albedo into design decisions improves energy estimates, informs mitigation of environmental consequences, and supports responsible land stewardship for utility-scale solar.