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Myths Part 13: Soiling Loss is a Fixed Percentage (Usually 5%)

The Myth

“Assume 5% soiling loss. That’s standard.”

This single number is frequently used in proposals, simulations, and performance discussions across Pakistan.

Why This Sounds Reasonable

The assumption appears sensible for several reasons:
⚡ A single percentage simplifies calculations.
⚡ Many software tools require a default input.
⚡ Cleaning schedules are often informal or irregular.
Over time, a placeholder value becomes a belief.

What’s Actually True

Soiling loss is not a constant. It is a time-dependent process influenced by:
▪ location and surrounding activity
▪ dust type and particle size
▪ wind patterns
▪ rainfall frequency
▪ cleaning intervals
In Pakistan, these factors vary widely — even within the same city.

Pakistan-Specific Reality

Typical soiling behaviour can look very different:
⚡ coastal areas: salt film and fine dust
⚡ urban zones: construction dust and pollution
⚡ industrial areas: heavy particulate build-up
⚡ dry seasons: rapid accumulation with no natural cleaning
As a result, soiling loss can range from very low to very high, depending on conditions and maintenance.

How to Explain This Clearly to Clients

Client Explanation: “Soiling is not a fixed loss — it builds up over time and resets when panels are cleaned.”
Or:
Alternative Explanation: “Cleaning frequency has a direct impact on energy yield.”

A Simple Way to Think About It

Soiling is like dust on a car windshield. The first layer may not matter much, but over time visibility — and performance — drops significantly.

Why This Myth Matters

Treating soiling as a constant:
▪ hides poor maintenance
▪ masks gradual underperformance
▪ makes yield guarantees unreliable
Understanding soiling as a process allows:
⚡ better O&M planning
⚡ more realistic performance expectations
⚡ clearer accountability
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