SOILING
LOSS
CALCULATION
- Prepare by
Harshal Bapu Kuwar
(Sr. Engineer – O&M)
https://www.linkedin.com/in/harshal-kuwar-1946a015a/
Soiling losses in solar PV systems occur when dust, dirt, pollen, bird droppings, or other
contaminants accumulate on the surface of solar panels, reducing the amount of sunlight
reaching the cells. These losses can be calculated using different methods:
1. Energy-Based Calculation
This method compares actual energy generation with expected generation in clean
conditions.
Where:
Eclean = Expected energy generation under clean conditions (from simulation or
historical data).
Esoiled = Actual energy generation under soiled conditions.
2. Performance Ratio (PR) Method
Performance ratio (PR) is used to assess system efficiency. A drop in PR can indicate soiling
losses.
Where:
PRclean = Performance ratio when the panels are clean.
PRsoiled = Performance ratio under soiled conditions.
PR is calculated as:
where:
Eactual = Measured energy output (kWh).
G = Irradiance on the module plane (kW/m²).
A = Module area (m²).
ηSTC = Module efficiency at standard test conditions.
3. Short-Circuit Current (Isc) Method
Since soiling affects irradiance reaching the solar cells, monitoring the short-circuit current
(Isc) can indicate soiling losses.
Where:
Isc,clean = Short-circuit current when the panel is clean.
Isc,soiled = Short-circuit current under soiled conditions.
4. Transmittance Measurement
If a soiling sensor is available, it can measure the reduction in light transmittance due to dirt
accumulation.
Where:
Gsoiled = Irradiance reaching the soiled panel.
Gclean = Irradiance reaching the clean panel.
Key Considerations:
The rate of soiling varies based on location, weather, and environmental conditions.
Regular monitoring and cleaning schedules should be optimized based on soiling
impact.
Automated cleaning robots can reduce soiling-related losses efficiently.
🔹 Step-by-Step Guide for Energy Based Calculation
Soiling loss in a solar power plant refers to the reduction in energy generation due to the
accumulation of dust, dirt, and other particles on the surface of solar panels. To optimize
energy production and maintain efficiency, it is crucial to monitor and quantify soiling losses.
This document provides a detailed methodology for calculating soiling losses using SCADA-
based energy analysis.
Step 1: Collect Data from SCADA/RMS
To perform soiling loss calculations, the following key parameters must be extracted from
the SCADA/RMS system:
Parameter Unit Source in SCADA
Energy Before Cleaning (Soiled Energy) kWh Inverter generation log before
Esoiled cleaning
Energy After Cleaning (Clean Energy) kWh Inverter generation log after
Eclean cleaning
Irradiation Before Cleaning Gsoiled kWh/m² Pyranometer or SCADA weather
station
Irradiation After Cleaning Gclean kWh/m² Pyranometer or SCADA weather
station
Step 2: Normalize the Energy Data for Irradiation Differences
Irradiation varies daily, so energy must be adjusted to a common reference to ensure a fair
comparison.
Use the formula:
Where:
Eclean, adjusted = Theoretical clean energy at the same irradiation as before
cleaning.
Gsoiled = Irradiation before cleaning.
Gclean = Irradiation after cleaning.
Step 3: Calculate Soiling Loss
Now, calculate the soiling loss percentage using the adjusted clean energy:
Where:
Esoiled = Energy before cleaning.
Eclean, adjusted = Energy after cleaning, normalized for irradiation
🔹 Example Calculation for 1MWp Plant
Assume your collected SCADA/RMS logs show:
Parameter Before Cleaning After Cleaning
Energy (kWh) 4,500 kWh 5,000 kWh
Irradiation (kWh/m²) 5.8 kWh/m² 6.2 kWh/m²
Normalize Clean Energy
Calculate Soiling Loss
Result: Your plant had 3.79% energy loss due to soiling before cleaning.
