Clir’s detectors: Solar panel soiling losses

Solar panel soiling refers to the accumulation of dirt, dust or debris on the face of PV modules. Soiling on the face of the modules will reflect or absorb radiation, reducing the irradiance available for modules to convert to power.

Clir’s soiling loss detector quantifies lost production caused by the reduced irradiance on the PV modules due to soiling.

Clir's solar panel soiling detector

The soiling detector enables reporting on soiling losses, allowing owners to understand the impact of dirt and debris on modules and if preventative measures need to be taken in order to reduce underperformance associated with soiling. ​​If there is a soiling sensor installed on site, Clir is able to quantify soiling losses at the farm.

Soiling can significantly reduce PV plant production and is a major loss factor in deserts, industrial areas and coastal regions. Benchmarking these losses against farms in similar regions can help owners decide if they need to spend more time ensuring soiling levels are acceptable.

Identifying soiling on solar panels

As soiling generally occurs relatively evenly across PV plants, it’s not possible to assess losses using a peer-to-peer comparison of modules, as is typically done to identify other types of underperformance. Instead, solar panel soiling rates and losses can be assessed by:

• Installing a soiling detector
• Maintaining a clean control string (or set of strings) at the site.

Leveraging the soiling detectors, owners can quantify the cost of losses associated with dirty panels and compare this to the cost of cleaning and maintenance to optimize clean schedules.

According to our data, production losses associated with soiling are usually between 3-5% annually.

Soiling use cases: Clean scheduling

Soiling can significantly reduce PV plant production. Production can be increased by cleaning the modules at suitable intervals. The ideal cleaning timing and frequency will depend on a few factors:

• How quickly soiling builds up on the modules at the site (may vary seasonally).
• How frequently it typically rains at the PV plant.
• The cost of cleaning.

PV soiling losses at the plant should be assessed, considering factors such as the time of year and the time since the last significant rainfall. This can be used to decide the optimal frequency for cleaning at the site through the year in order to avoid exceeding the budget soiling losses.

For example, the graph shows that the solar farm experiences heaviest soiling in the driest months, with soiling losses decreasing with rainfall. The least amount of soiling losses are seen during the rainiest months. 

All three soiling sensors show similar soiling rates and soiling ratios, with slight variations.

Operational data from the soiling sensors suggest the soiling loss percentage to be around 1% during the wet season and about 2% during dry season.

Once the soiling analysis has been carried out, and the optimal cleaning schedule is established, the impact of the new panel cleaning schedule can be monitored and validated using the Clir platform.

To optimize cleaning, we recommend the following:

• As modules can crack from sudden temperature changes, cleaning should take place in the early morning or late evening to ensure the modules are cool.
• For similar reasons, lukewarm water should be used.
• Only clean, demineralized water should be used.
• To avoid damage to modules, high-pressure washing systems should not be used.
• Particular care should be taken if bird soiling is prevalent.

Identifying solar panel soiling with detectors