Does Cleaning Rooftop Solar Panels Really Improve Performance? Results from Our Cornwall Trial
Dirty solar panels can reduce electricity generation, but how much difference does cleaning actually make?
At Horizon Agri Ltd, we wanted to measure the results rather than rely on assumptions.
In April 2026, we carried out a controlled rooftop solar panel cleaning trial at Treveale Farm in Cornwall. Using our DJI Agras T50 heavy-lift drone, we cleaned a 50 kW rooftop installation and monitored its electricity generation against other, uncleaned solar arrays on the same farm.
The results were particularly interesting.
An initial 12% improvement in relative generation performance, reducing towards 6% over the following month.
How We Measured the Results
One of the biggest challenges when measuring solar panel cleaning is separating the effect of cleaning from changes in the weather.
A sunny day after cleaning doesn't necessarily mean the cleaning made a difference.
To address this, we analysed electricity generation data from January to April 2026, before any cleaning took place.
We then cleaned the 50 kW rooftop installation on 25 April, leaving other solar arrays on the farm untreated for comparison.
The pre-clean data showed a strong relationship between the installations' daily performance, allowing us to compare how each responded to changing conditions.
By comparing the cleaned installation against its own baseline and the uncleaned control, we could measure the additional performance advantage after cleaning.
What Did the Solar Cleaning Trial Show?
Immediately after cleaning, the treated installation showed approximately 12% higher relative electricity generation compared with the untreated installation.
That initial advantage gradually declined, reaching around 6% over the first 30 days.
Over the following 98 days, the performance advantage averaged approximately 6%, demonstrating a measurable and sustained improvement in electricity generation.
Why Did the Initial Improvement Reduce?
Treveale is a working dairy farm.
Dust from farm machinery, feeding operations, bedding materials and general yard activity can all contribute to contamination building up on rooftop solar panels.
During dry weather, airborne dust may be particularly noticeable.
Renewed contamination is one possible explanation for the reduction in the initial performance advantage, although the monitoring cannot establish the exact cause.
This highlights something important: solar panel cleaning isn't necessarily a one-off decision. The surrounding environment and rate of soiling are relevant when determining how frequently cleaning is worthwhile.
How We Cleaned the Rooftop Solar Panels
We used our DJI Agras T50 agricultural drone to apply a specialist cleaning solution across the rooftop solar installation.
Our non-contact cleaning method allows us to work on large or difficult-to-access roofs without using brushes or putting cleaning personnel directly onto the panels.
For agricultural and commercial properties, this can help reduce disruption and avoid some of the access requirements associated with conventional cleaning methods.
What Could a 6% Solar Generation Loss Cost?
Consider a 50 kW rooftop solar installation producing 50,000 kWh of electricity annually.
If contamination were responsible for a sustained 6% reduction in output, that could represent approximately 3,000 kWh of electricity per year.
At an illustrative electricity value of 25p per kWh, that would be equivalent to £750 annually.
This is an example rather than a measured financial saving at Treveale. The actual value depends on generation, electricity tariffs and how much power is used on-site.
For larger commercial installations, even relatively small percentage losses can represent significant amounts of electricity.
Want to see what reduced solar generation could be costing your business?
Use our Solar Loss Calculator to explore the potential financial impact on your installation.
Read the Full Treveale Farm Case Study
The full study includes our monitoring methodology, generation comparisons and charts showing how the relative performance changed after cleaning.
Rooftop Solar Panel Cleaning in Cornwall and the South West
At Horizon Agri Ltd, we provide non-contact drone cleaning for agricultural, commercial and ground-mounted solar installations.
Our approach is straightforward: understand the problem, identify whether cleaning is worthwhile and use the right equipment to complete the work efficiently.
If you manage a rooftop solar installation and would like to discuss its performance, get in touch with Horizon Agri.
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