Solar Power Output Drops 4–7% Globally Due to Soiling, PVPS Warns

Soiling commonly caused by dust, pollution, and even biological debris remains one of the leading reasons behind the solar underperformance globally. A news factsheet shared by PVPS found that soiling to be responsible for 4% to 7% average global energy loss and causes a multi-billion-euro loss every year worldwide. 

The factsheet categorizes into two styles of soiling first is the aerosol deposits, such as: Natural: mineral dust, sea salt, pollen Anthropogenic: industrial emissions, vehicle exhaust, agricultural particles. Second is the Macroscopic deposits and growths, such as, Bird droppings Leaves and organic debris Lichen, moss, and other biological growths. 

Impact of Soiling on PV Systems Performance

Soiling doesn't just reduce the energy yield, it also raises O&M costs, accelerates degradation, and increases the uncertainty in PV production forecasts. The PVPS report reccomends that soiling data should be included in the yield assessment and project planning to allow operator to select adequate mitigation measures.

Soiling monitoring, measurements and forecasting are also crutial during the acceptance and operation phases of a PV plant. In fact, they are required for Class A monitoring systems according to Photovoltaic System Performance–Part 1: (IEC 61724-1).

Using Forecasting to For Stating Ahead

Soiling forecasts can play a decisive role in improving, solar production, forecasts and to optimize the cleaning scheduling to avoid unnessicary cleaning just before strong rainfall or dust event. The impact of soiling losses can highly vary depending particularly on aerosols particulate matter, (PM) and precipitation, and with the season and from year to year. 

The impact of soiling is highly variable, however, reliable site-specific soiling data is often scarce, and when available, it usually covers only short periods. While soiling models based on meteorological data can fill some gaps, their accuracy depends heavily on data quality and local conditions. Rainfall assumptions, in particular, remain a major source of uncertainty. PVPS suggests that calibrating models with on-site soiling measurements significantly improves accuracy.

The model assumptions related to the cleaning effect of rain are also a major source of uncertainty. A calibration of the models with site specific soiling measurements can help to enhance accuracy. When using modelled soiling data, the uncertainty involved must be considered, and further research is required. The report also cautions that as extreme weather events intensify, PV technologies evolve, and market dynamics shift, managing soiling losses will become increasingly complex and critical for project economics. 

One often overlooked issue is clipping—when production exceeds inverter capacity, masking the true extent of soiling losses.

PVPS’s Work on Soiling

PVPS has been addressing soiling through Task 13 (Reliability and Performance of Photovoltaic Systems) and Task 16 (Solar Resource for High Penetration and Large-Scale Applications).

Their work includes:

• Assessing the current magnitude of soiling losses and predicting future trends worldwide, for specific regions and sites.
• Analysing the influence of technological advancements (e.g., bifacial modules) on soiling losses; evaluating the effect of shifting environmental conditions on soiling.
• Reviewing and enhancing soiling monitoring and modelling options (incl. uncertainties, intercomparison studies or round-robin tests)
• Assessing current and perspective mitigation strategies considering the impact of factors external to PV production, such as inverter size and grid constraints.