Soiling

Summary

The soiling model accounts for irradiance losses due to dust, dirt, pollen, and other particulate matter accumulated on module surfaces. PlantPredict implements three soiling approaches: None (no soiling loss), Monthly (user-specified monthly loss values), and Weather (time-series loss values from weather data). The soiling factor is applied uniformly to all POA irradiance components after shading losses and before IAM corrections.

Inputs

Name	Symbol	Units	Description
Soiling Loss	$S_{loss}$	%	Soiling loss percentage for the current timestep

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Outputs

Name	Symbol	Units	Description
Soiling Factor	$U_{soil}$	—	Fraction of irradiance transmitted (0-1)

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Detailed Description

The soiling factor is calculated from the soiling loss percentage:

$$U_{soil} = 1 - \frac{S_{loss}}{100}$$

The source of $S_{loss}$ depends on the selected model:

• None: $S_{loss} = 0$ (modules assumed perfectly clean, $U_{soil} = 1$)
• Monthly: $S_{loss}$ is retrieved from user-specified monthly values (12 values, one per month)
• Weather: $S_{loss}$ is read from the weather file for each timestep (e.g., from PVRADAR soiling data)

Application to Irradiance

The soiling factor is applied uniformly to all plane-of-array irradiance components (beam, sky diffuse, and ground-reflected irradiance):

$$G_{beam,soiled} = G_{beam,shaded} \times U_{soil}$$ $$G_{sky,soiled} = G_{sky,shaded} \times U_{soil}$$ $$G_{ground,soiled} = G_{ground,shaded} \times U_{soil}$$

Soiling is applied after near-field shading and horizon shading, and before incidence angle modifier (IAM) corrections.