Frequently asked questions

Dedicated section for you to find answers to the questions we are most often asked. If yours is not on the list, or if you would like to discuss it in depth, please feel free to contact us directly here, we will be happy to go into the details of your facilities & cleaning needs

“Generic” questions about soiling and cleaning

There is no single answer to that question, as it depends on the exact localization of the PV structure to be cleaned. Even in desertic areas without industrial or agricultural pollution, water-based cleaning may be necessary (occasionally), for instance to clean sand that has been cemented over the PV surface by dew overnight making dry cleaning ineffective or at least less relevant than in "normal" sandy conditions.

Again, no homogeneous answer can be given, as the combination of influencing factors on the cleaning frequency can be unlimited since one has to take into account:

  • climatic factors (rain, humidity, dew, wind direction and temperature)
  • the type and composition of the dirt (dust and sand, bird droppings, pollen, industrial and/or agricultural emissions, lichen growth, moss, etc.)
  • the architecture of the PV system itself: panel layout, tilt and module type (framed or unframed)

In any case, numerous studies and measurements have been undertaken to evaluate the frequency of soiling worldwide and to determine the optimal average frequency based on the soiling costs incurred. For example, Indian PV installations would require between 10 and 25 cleaning cycles per year, while the United States is between 2 and 5 times, followed by Mexico with 7 to 15 cycles per year. This is a case-by-case approach, in which one must also determine the objective of cleaning the solar panels: is it "only" to boost the energy yield of the installation, and/or to preserve the integrity of the modules over a period of operation of several decades?

Most often, the financials of a PV project are based on the LCOE (Levelized Cost Of Energy) which represents the total costs of production throughout its life cycle... As the today, cases where soiling (or non-cleaning) costs are integrated are rare, although awareness of these issues is changing the approach. So, in theory, one could instead decide to integrate the costs of non-cleaning and decide to make the financial decisions that follow. But that would involve a long list of prerequisites that are not so easy to integrate financially:

  • it would already require a long study over at least 1 year to calibrate the loss induced by the absence of cleaning and for a specific site;
  • it also supposes that no modification of the environment of the installation (road construction, agricultural activity, etc...) is undertaken during the duration of the project;
  • another requirement would be to take into account from day one the exceptional weather events (such as sandstorms, long periods without rain, etc.) that may occur more or less frequently;
  • finally, cleaning is not only a question of performance, but also of maintenance. Solar panel manufacturers do not guarantee the integrity of the modules during the whole lifetime of the PV project: therefore, more and more developers/operators dedicate, for example, a cleaning session after the summer period in order to avoid the formation of lichens and mosses that could penetrate between the glass and damage the PV cells.

In front of these uncertainties, one thing is certain: your modules will not produce at their full potential because of soiling. Only an on-site measurement will give you an idea of the percentage of losses percentages and the cleaning cycles required, and will therefore naturally guide your decision between cleaning and not cleaning...

Studies have demonstrated that flat PV modules are much more prone to the effects of soiling when compared directly to high angle structures. As mentioned above, other key dimensions such as the type of fouling material, wind direction, frequency of rain events, etc., must be taken into consideration when defining the cleaning procedure for a specific PV installation.

Let's take the example of your car windshield: in the absence of rain, without the mechanical contribution of water and the simultaneous action of the windshield wipers, it can quickly become clogged. More seriously, all studies done on the effects of clogging on PV production take into account "one-off" weather events such as rain, which have a positive (but limited) impact on cleaning, since it lacks the mechanical action of the brush.

Solar farms are built with an average lifetime of 20-30 years; not only will production losses be greater over time without a cleaning procedure in place, but the risk of hot spots will also be multiplied, rapidly damaging the panels, sometimes to the point of requiring complete panel replacement.

Questions " products " AX SOLAR ROBOT

Our WetSlider dedicated to the automatic cleaning of narrow-spaced tracker solar farms uses water both for its motion and for cleaning of the modules at the same time. To accomplish both tasks, only 0.5 L of water/m² is needed: unlimited movement and clean solar panels is no longer a utopia!

  1. Cleaning efficiency
  2. Specially developed hybrid brushes that eliminate the need to adapt the brush to the next site to be cleaned, and allow only one pass where other equipment requires two or more passes for the same result!
  3. Operational focus of cleaning
  4. Safety being the number one priority when it comes to roof cleaning sites, our Rider is equipped with anti-fall sensors, and can be assembled/disassembled in 5 minutes, without any tools.
  5. Product quality and technical support
  6. The cleaning of the photovoltaic installations will follow them throughout their operational life; so will the robots we develop, with a constant concern for durability and quality.

Solar parks using tracking systems are often equipped with several (tens of) thousands of solar panels, to be multiplied by an average of 1.5-2.5 m2 per module... the math is both simple and eloquent when calculating the total surfaces to be cleaned. Our hydraulic movement technology ensures that no battery limits will prevent the cleaning operations from running smoothly, while also offering the possibility of having several robots working in parallel, thus increasing the efficiency of the operations. The average roof area is more limited, and although we are seeing a rapid expansion in the average size of roofs, the Rider on its lithium batteries has enough range to clean them.

Our Rider, which is primarily designed for rooftop applications, can operate at maximum inclinations of 25°/47%, which is already a high-end operational feature. However, the same robot can be equipped with a lateral guidance system that will allow operation on ground-mounted solar panels at an inclination of more than 25°.

As for our WetSlider, dedicated to the cleaning of photovoltaic systems on tracker, its design allows operations at any angle of inclination, from -55 to +55°: a real advantage because it is not necessary to stop the tracking for cleaning operations, ensuring that the gains in cleaning production are not mitigated by stopping the tracking as is often the case!