Fungal bio-soiling happens when biofilms, mainly black fungi, grow on the module glass, form dark masses and trap other dirt, which lowers how much light gets through the glass. Unlike ordinary dust, these deposits stay on after rain, so the loss is easy to mistake for dust, pollen or a weather-normalization error. Reported persistent losses in humid subtropical regions are 5-11%, and the average annual loss across that climate zone is 5%. To confirm it, look for a normalized production deficit that does not recover after rain but steps up repeatably after manual cleaning, and compare cleaning records with SCADA, irradiance and weather-normalized production. Confirm the biofilm itself with close visual inspection or a handheld microscope, and check several array areas because the deposits can be patchy. Clean manually or with targeted cleaning, add bio-soiling to the site cleaning schedule, and check how production responds after each cleaning. Update production forecasts from actual cleaning results instead of assuming rain resets the loss, especially at humid sites or sites near vegetation or water.
typical_power_lossc1 verified · fact 5–11 PERCENT
Conditions: Persistent production losses from fungal bio-soiling in humid subtropical regions; reported from 2024 field work at North Carolina solar farms
sec=front h=c791ea65d1dfsec=h2 h=201b23e0feffsec=h4 h=52ca8426fce1verified by: joshuahamsaverified on: 2026-10-16
c2 verified · fact nominal 5 PERCENT
Conditions: Average annual bio-soiling loss across the humid subtropical (Cfa) zone, extrapolated from more than 120 cleanings of operating solar farms
sec=h7 h=e287af93bef3verified by: joshuahamsaverified on: 2026-10-16
caused_byc3 drafted · lead Fungal biofilm growth
Sub-aerial biofilms, especially black fungi, grow on the glass, form dark masses and trap other particles
sec=h5 h=4e874b23e982sec=h4 h=52ca8426fce1c4 verified · fact Humid climate
Most reported in humid subtropical climates; humidity suggests the deposits will come back
sec=front h=c791ea65d1dfsec=h9 h=58157da0d37bsec=h4 h=52ca8426fce1verified by: joshuahamsaverified on: 2026-10-16review note: support check: partial - Humid climate is listed as a recurrence factor and humid subtropical regions are where it's reported, but nothing about humidity causing growth or deposits coming back specifically beyond 'suggest recurrence'.
c5 verified · fact Nearby vegetation
Listed as a factor suggesting bio-soiling will recur
sec=h9 h=58157da0d37bverified by: joshuahamsaverified on: 2026-10-16
c6 verified · fact Nearby water bodies
Listed as a factor suggesting bio-soiling will recur
sec=h9 h=58157da0d37bverified by: joshuahamsaverified on: 2026-10-16
affectsc7 verified · fact Module front glass
Deposits stick to the glass and lower its transmittance
sec=h5 h=4e874b23e982sec=h4 h=52ca8426fce1verified by: joshuahamsaverified on: 2026-10-16
presents_asc8 drafted · lead Dark surface deposits
Fungi form dark masses on the module surface; coverage can be patchy across the array
sec=h5 h=4e874b23e982sec=h8 h=d54a5f534d87c9 verified · fact Loss persists after rainfall
Normalized production deficit does not recover after rain
sec=front h=c791ea65d1dfsec=h2 h=201b23e0feffsec=h8 h=d54a5f534d87sec=h4 h=52ca8426fce1verified by: joshuahamsaverified on: 2026-10-16
c10 verified · fact Production step after cleaning
Output steps up repeatably after manual cleaning
sec=h8 h=d54a5f534d87verified by: joshuahamsaverified on: 2026-10-16
detected_byc11 drafted · lead Weather-normalized production comparison
Compare normalized production before and after cleanings against cleaning records, SCADA and irradiance
sec=front h=c791ea65d1dfsec=h2 h=201b23e0feffsec=h8 h=d54a5f534d87c12 drafted · lead Rainfall response review
Check whether output recovers after rain
sec=front h=c791ea65d1dfsec=h2 h=201b23e0feffsec=h8 h=d54a5f534d87c13 drafted · lead Visual inspection
Close inspection of several array areas, not just one representative module
sec=front h=c791ea65d1dfsec=h2 h=201b23e0feffsec=h8 h=d54a5f534d87c14 drafted · lead Handheld microscopy
Direct imaging of the module surface confirms biofilms; it has been used on more than 15 GW of assets
sec=front h=c791ea65d1dfsec=h2 h=201b23e0feffsec=h6 h=27c24638759csec=h8 h=d54a5f534d87mitigated_byc15 drafted · lead Cleaning schedule optimization
Add bio-soiling to site cleaning schedules and treat cleaning as required maintenance
sec=front h=c791ea65d1dfsec=h2 h=201b23e0feffsec=h9 h=58157da0d37bc16 verified · fact Manual cleaning
Targeted manual cleaning is needed to remove the deposits
sec=h5 h=4e874b23e982sec=h4 h=52ca8426fce1verified by: joshuahamsaverified on: 2026-10-16
c17 verified · fact Cleaning effectiveness validation
Check how production responds to cleaning
sec=front h=c791ea65d1dfsec=h2 h=201b23e0feffverified by: joshuahamsaverified on: 2026-10-16
c18 drafted · lead Production forecast update
Update revenue and loss forecasts from site cleaning results instead of assuming rain resets the loss
sec=front h=c791ea65d1dfsec=h2 h=201b23e0feffsec=h9 h=58157da0d37bdistinguished_fromc19 drafted · lead Granular Dust Soiling Losses — told apart by Rainfall response review
Ordinary dust partly washes off in rain. Fungal bio-soiling stays on after rain and recovers only after targeted or manual cleaning.
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