SolarSoiled · Tools
Compare what one cleaning can recover from regular dry-season buildup and from Persistent Soiling that survives rain. The calculator shows both recoveries, one service cost, and the resulting net benefit. Persistent Soiling remains a conditional scenario until site evidence supports its loss percentage.
Your system
Soiling conditions
Cleaning method
~$90 · water-fed pole, no roof access · takes off ~70% of the dirt
Persistent Soiling scenario
Annual scenario: use a field-confirmed Persistent Soiling loss to value the next 12 months of generation.
Pollen films, cemented dust, and biological growth can survive winter rain. Persistent loss is unknown until site evidence supports a percentage, so this slider starts at zero. A field inspection confirms residue; production history or a calibrated assessment estimates its energy effect. Use the same confirmed percentage for either horizon: at 3%, the two-year energy value is twice the annual value.
A light-rinse scenario assumes 70% of a confirmed Persistent Soiling loss is recoverable. Use a lower fraction if residue needs deeper treatment.
Where are you now?
Breakeven curve
Seasonal recovery
—
early-July Regular Soiling value
Persistent recovery
—
requires a confirmed loss
Combined recovery
—
seasonal value while Persistent Soiling is unknown
Cleaning cost
—
one service visit
Net benefit
—
enter a confirmed Persistent Soiling loss to complete this comparison
Each layer has its own timing, evidence, and cleaning value.
Regular Soiling
An early-July wash gets back 34.6%
Builds up through the dry months and washes off with the winter rain. Each extra day adds more dust on top of what is already there, so the losses grow faster the longer you wait. That is why the line curves upward instead of running straight.
The model schedules the clean in early July, when it removes the accumulated layer before the final three dry-season months. The percentage above follows the cleaning method you picked and includes its expected cleaning efficacy.
Persistent Soiling
A confirmed loss can protect a full year of value
Pollen films, cemented dust, mineral edge bands, and biological growth can stay on the glass after winter rain. This layer can carry from one season to the next, so it lifts the whole curve and moves the cleaning decision earlier.
A confirmed loss is valued across a full year. The selected cleaning method then applies its stated removal fraction to that value. A confirmed 3% loss stays at that rate until it is removed, so two years of loss carries twice the undiscounted energy value. That is why persistent material can change the cleaning decision.
Persistent Soiling starts with an inspection, then prices confirmed loss
National soiling measurements describe the loss observed between perfect cleanings. Persistent material that carries across rain events needs a separate measurement. The calculator therefore starts at zero because the loss is unknown and excluded, not because the roof is assumed clean. A visual inspection confirms residue; production history or a calibrated assessment supplies a site-specific loss estimate.
The Persistent Soiling screen makes that inspection practical. Low racking angle contributes 70% of the current score, nearby canopy contributes 30%, and the map highlights the highest-scoring tenth of panel groups. A confirmed 3% persistent-loss scenario is priced over a full year instead of being averaged into the seasonal dust estimate.
Low-angle panels can develop a bottom-edge band because rainfall transports particles toward the downhill frame. Panel-level electronics keep the electrical impact localized to the affected module, while the visible band, tilt, panel layout, nearby canopy, and production history guide the field inspection. Ground-truth inspections will let us calibrate the screen over time.
The flagging rule: combine the early-July Regular Soiling recovery with a field-confirmed Persistent Soiling scenario across the selected interval.
The two layers retain separate evidence and time horizons. Regular Soiling uses remaining dry-season production after an early-July clean; Persistent Soiling uses the selected full-year interval after site evidence supports its loss percentage. Their recoveries can then be combined against one visit cost.
Regular Soiling (the early-July cleaning curve)
On day N of the April-September dry season, the panel is N × soiling_rate dirtier than at the start. Cleaning on that day removes the accumulated layer and prevents that same layer from reducing the remaining (180 − N) dry-season days:
The curve rises toward early July, when both accumulated dust and remaining production are substantial, then falls as the rainy season approaches. The calculator uses clear-sky seasonal production weights for Santa Cruz, so summer output receives its proper value.
Persistent Soiling (the field-confirmed scenario)
Persistent loss is modeled as a sustained, site-supported percentage of annual output, so its value remains steady across dry days. The calculator uses the same electricity rate, peak sun-hours, and 0.84 system derate as the seasonal term, then applies the selected service's stated removal fraction:
The annual setting prices a confirmed 3% loss across 12 months. The two-year setting prices the same confirmed 3% loss across 24 months, doubling the undiscounted value. The Persistent Soiling map supplies inspection priority; a field check confirms residue and production history or a calibrated assessment supplies the percentage.
Combined breakeven
Cleaning pays once the two channels together beat the cleaning cost. The seasonal term peaks around an early-July clean. A confirmed persistent layer is recovered across the selected interval, while the service cost is counted once:
The map keeps Persistent Soiling and Regular Soiling in separate tracks. This calculator lets a field-confirmed rate show how the longer-lived layer changes the decision.
Seasonal timing
Winter rainfall is represented as a reset for Regular Soiling. The model uses one effective early-July cleaning point to reflect that seasonal pattern. The 70–90% figures in the cleaning-method selector describe how much of the material present on the glass is removed; they are applied to the remaining three-month seasonal value.
Why we wait for two months in a row
Production data would check a system at the end of May, June, and July. Two consecutive positive checks provide a stronger signal than one cloudy or anomalous month. Until site-level production data is available, the map uses its Regular Soiling baseline and the separate Persistent Soiling inspection screen.
Regular Soiling uses Kimber (2007) linear accumulation over an April-September dry season, then values an early-July reset across the remaining dry-season production. Heavy soiling rate: average 0.05%/day; the California study by Mejia and Kleissl (2013) found an important upper tail near 0.10%/day. Persistent Soiling stays separate: its local rate is unmeasured, so the calculator starts it at zero and the map shows it as a conditional 3% annual inspection scenario. Persistent recovery applies the selected service's stated 70% basic-rinse or 90% professional-scrub removal fraction. Cleaning prices use a one-truck-roll floor of $90 basic and $150 professional, plus a declining per-panel schedule at larger systems. Assumes 5.5 peak sun hours per day and a 0.84 system derate, giving about 1,686 kWh/kWp/year. The dashboard substitutes each roof's lidar-derived sun hours. The electricity-rate slider opens at $0.4284/kWh, the vintage-weighted Santa Cruz blend; a post-April-2023 home can move it toward $0.16/kWh.