Soiling on bifacial PV modules installed near roadsides has a significant, often accelerated, negative effect on energy production due to the accumulation of airborne dust, vehicular exhaust particles, and debris

 Soiling on bifacial PV modules installed near roadsides has a significant, often accelerated, negative effect on energy production due to the accumulation of airborne dust, vehicular exhaust particles, and debris. While bifacial modules are generally more efficient, soiling—particularly on the front side—can lead to power losses ranging from 5% up to over 50% in arid environments. 

Soiling Effects on Roadside Bifacial PV:

Reduced Light Transmittance: Dust blocks solar rays, causing a significant drop in power output. Roadside environments are particularly harsh due to high-density, often oily, pollutant particles from traffic, which adhere more strongly than dry desert dust.

Asymmetric Soiling (Front vs. Rear): The front side typically experiences much higher soiling rates than the rear side. Studies show the rear side soiling rate can be over 8 times smaller than the front side rate. However, if the rear side is mounted low to the ground, it can still accumulate significant dirt from the ground-up, reducing the "bifacial gain".

Hotspot Formation: Uneven dust distribution, common in roadside environments, leads to partial shading. This causes some cells to underperform, resulting in hotspots, reduced voltage, and accelerated panel degradation.

Impact on Bifacial Gain: Soiling reduces the light reflected from the ground (albedo) that hits the rear side, directly lowering the additional energy production that makes bifacial technology advantageous. 

Impact on Solar Production:

Immediate Power Drop: In uncleaned conditions, power losses can exceed 20% to 50% depending on dust density.

Long-term Degradation: Roadside pollutants (e.g., iron dust, oily emissions) create semi-permanent, sticky layers that are not fully removed by rain, requiring frequent, sometimes manual, cleaning.

Lower Yield for Vertical Mounts: While vertical bifacial panels can reduce dust accumulation due to gravity, they can still collect contaminants from traffic-induced wind vortexes, potentially reducing their efficiency. 

Mitigation Strategies:

Optimized Cleaning: Because the rear side soils less than the front, an "asymmetric" cleaning strategy—cleaning the front more frequently than the rear—is highly effective.

Increased Mounting Height: Increasing the tilt angle and height of the module from the ground reduces dust accumulation by allowing wind to pass underneath and reducing the buildup of ground debris.

Water-free/Robotic Cleaning: In high-pollution areas, automated dry-cleaning solutions are necessary to maintain performance without excessive water usage.