Physics-based model to predict soiling losses in bifacial solar modules

Scientists in India have developed a novel way to predict soiling accumulation on bifacial modules. Their approach considers dust deposition, rebound, and resuspension phenomena.

Dust particles on a PV module

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Martin Abegglen, Flickr

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Researchers from the Indian Institute of Engineering Science and Technology, Shibpur’s (IIEST Shibpur) have developed a novel physics-based model to estimate dust accumulation on the front and rear surfaces of bifacial modules.

“This model is equally applicable for both rooftop plant and commercial ones,” researcher Saheli Sengupta told pv magazine. “In India, a larger plant with bifacial modules is not yet available and hence we could not validate the model for the larger set-up. But this is in our research program to carry out the same for larger plants from India and abroad.”

The proposed model considers a few input parameters such as particulate matter (PM) concentration, panel tilt, the sun’s angle of incident, solar radiation, albedo, and PV module specifications. It also considers weather parameters such as wind direction, speed, and ambient temperature.

“The considerations made in this analysis are that the shape of the particles is assumed to be spherical; the dust deposition over the module is considered to be uniform; and the effect of different composition of dust is not considered separately,” said the academics.

The model calculates dust accumulation on the front surface of the PV module by considering deposition, rebound, and resuspension phenomena. Deposition involves dust landing on the surface, rebound occurs when particles bounce back into the air, and resuspension involves settled particles lifted by mechanisms like wind and air turbulence.

The model then calculates dust accumulation on the rear surface, taking into account deposition, rebound, and resuspension phenomena. Different types of particle deposition on the back are considered, including particles moving along with airflow and particles lifted from the ground surface.

Following this, the model calculates transmittance, assessing the material's ability to allow light passage, based on previous results. By summing beam radiation, diffuse radiation, and ground-reflected radiation, the model determines the energy yield of the PV plant.

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Testing their physical model, the researchers have compared its projected results to real observation on a 10 kW PV system. The array was stationed on the rooftop of a university building located in the Indian city of Howrah, West Bengal.

“It is observed that surface density of dust on back surface for 34 days is 0.08 g/m2, for 79 days 0.6 g/m2 and for 126 days 1.8 g/m2, which are deviated from model based calculated ones by 10%, 33.33% and 4.4% respectively,” the researchers said. “The surface density of dust accumulated on the glass based rear surface is about 1/6th of the front glass surface, which is validated by the model also.”

In addition, the scientists found that the error between the observed DC power generation and the calculated one was 5.6% on the back surface and 9.6% on the front.

“It is necessary to validate this model for large capacity bifacial plant at different locations,” the academics concluded.

They introduced their findings in “Physics based modeling of dust accumulation on a bifacial solar PV module for generation loss estimation due to soiling,” which was recently published in Solar Energy Advances.

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