Solar panel cleaning in Ontario: when is drone access worth assessing?

Soiling is real. A universal percentage is not

Sandia's PV Performance Modeling Collaborative explains that particles on module surfaces can absorb or scatter incoming light. The effect depends on the material and its accumulation. It also notes that nearby arrays can experience different soiling rates and that rain removes some kinds of soiling more effectively than others.[Sandia PVPMC]

For an Ontario owner, the implication is to investigate the actual installation rather than borrow an impressive loss percentage from a different site. A photograph can identify a reason to look more closely; it cannot establish the amount of recoverable energy on its own.

Our recommendation is to begin with the array's maintenance records and monitoring history. Ask the asset's operations team what evidence suggests a cleaning problem, what other causes of lower output have been considered, and what uncertainty remains. The cleaning proposal should fit that investigation rather than pre-empt it.

Does rain remove the need for cleaning?

There is no single answer for every array. Sandia identifies differences in local particulate sources and accumulation, including differences within the same system. Canadian Solar's customer guidance also recognises that rainfall can help clean suitably tilted modules, while maintenance needs increase in high-soiling conditions.[Sandia PVPMC][Canadian Solar]

Instead of choosing between never clean and clean on a rigid calendar, agree a review process. Record visible conditions, relevant events around the property and the observations of the operations team. Ask when those observations justify a closer inspection or a cleaning assessment.

This is especially useful for a portfolio. Two roofs in the same city do not need to be assigned an identical cleaning interval merely because they share an owner. Keep the decision at array level, even when purchasing and scheduling are coordinated.

The module instructions come before the access method

Canadian Solar's support guidance describes cleaning soiled modules with water and a non-abrasive implement in the cooler part of the day, warns against rubbing dry dirt, and discusses water mineral content. Those are examples of manufacturer-specific care considerations, not blanket approval of drone washing for all solar products.[Canadian Solar]

Provide the installed module model and the relevant current manual to the cleaning contractor. Ask how the proposed water quality, equipment and application will satisfy those instructions. Where the method is unclear or a warranty question remains, obtain clarification from the manufacturer or responsible solar service provider before authorising it.

The drone is only one part of the method. A proposal needs to explain how the process reaches the intended surface, handles the actual contamination and coordinates with the array's maintenance arrangements. If the required task needs direct contact that the proposed equipment cannot provide, access convenience does not resolve that mismatch.

Build an assessment brief the contractor can use

Use the following table to assemble the initial enquiry. These are questions for the project team, not instructions for an owner to carry out electrical work or access a roof.

Scroll the table sideways to compare all columns.

Compare value without inventing an energy promise

Ask for the cleaning cost as a defined scope: which modules, what method, what access arrangements and what exclusions. Separately, ask the asset team for its estimate of recoverable generation, including the assumptions behind it. Keeping these two documents distinct makes it harder for an equipment sales claim to become an untested forecast.

A simple worked example shows the distinction. If an owner's own analysis estimates 1,000 additional kWh over a chosen period and values each kWh at $0.15, the gross value in that hypothetical scenario is $150. It is not a statement of expected output, a tariff quote or a Wash With Drones price. Different evidence or electricity values would change the calculation.

Avoid treating a higher production reading on the next sunny day as proof of a cleaning gain. Agree with the operations team how a useful comparison will be made and which other conditions need to be accounted for. A documented cleaning visit and a measured performance assessment are related, but they are not the same deliverable.

Make access and the completion record explicit

For any proposed cleaning flight, the operator must establish the relevant aviation requirements. Transport Canada's categories depend on the operation and aircraft, not on the fact that the customer owns a solar installation.[Transport Canada]

For the cleaning handover, ask for the array areas completed, photographs, the method used and any unresolved observations. If something outside the cleaning scope is noticed, record the location for the asset's responsible service team rather than presenting washing as an electrical inspection.

This evidence-led sequence gives drone cleaning a fair assessment: investigate the need, check compatibility, compare a complete scope, then document the work. The outcome may be a drone-led clean, another method, further investigation or no cleaning at that time.