Methods for determining the soiling assessment of solar PV arrays

The large number of commercial solar power plants built and successfully operating in Ukraine is the reason that investors are paying more and more attention to the issue of maintenance and operation. One of the frequently asked questions is how often it is necessary to clean the surface of solar panels from dust and other contaminants. Determining a reasonable frequency of cleaning the surface of solar modules is not a trivial task, since the theoretical calculation is hampered by a large number of external factors. Avenston experts recommend planning such works based on a combination of theoretical calculations and practical measurements. It is such an integrated approach that will allow you to get the right recommendation for each solar power plant.

Due to the contamination of the surface of solar modules (dust, dirt, leaves, bird droppings), the penetration of light to solar cells will be significantly reduced, which leads to a decrease in the generation of electricity. Calculations show that at a uniform distribution of only 4 cubic centimeters of dust on one square meter of surface, the efficiency of solar cells drops by 40%. Very often, dustiness of solar panels is caused not only by natural causes, but also by heavy traffic, construction work or agricultural activities.

If we are talking about small private solar power plants, then the problem is solved relatively simply – it is enough to periodically water the surface of solar panels with a hose, thereby cleaning it. It is enough to repeat this procedure just a few times in order to temporarily eliminate the problem of dustiness on the surface of the solar modules.

The problem takes on a completely different scale when it comes to industrial solar power plants, which can cover a large area of several hectares and more. In this case, economic feasibility comes to the fore – will the future increase in electricity generation compensate for the costs of cleaning solar panels? That is why the main task is to determine the moment when the soiling of the surface of solar panels will become critical, leading to significant losses in electricity generation.

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Methods for determining the soiling of solar panels

Cleaning the surface of solar panels becomes economically feasible at a time when its cost becomes less than the cost of additional electricity generated after the completion of this work. Determining when solar panels need to be cleaned is a complex equation that has many factors to consider. Among them are the total surface area of ​​solar panels, the duration of cleaning procedure, the need to switch off the solar station during maintenance, and so on. For example, cleaning can be performed at night to minimize downtime losses. This decision looks quite good even in spite of the higher tariffs of cleaning companies for work in the second and third shifts.

Dust assessment for industrial solar PV power plants is a unique solution for each individual station; there is no single standard analysis method or mathematical model that can give a definite answer. That is why almost always the determination of the need for cleaning the PV panels is based on practical experience. Several basic methods for determining the contamination of the working surface of solar power plants are described below.

Voltage-current characteristics comparison method

This is a simple method that compares the actual volt-ampere characteristic with the data obtained when the solar power plant was put into operation. At the same time, it is categorically impossible to use the theoretical design data, because they were calculated under almost ideal conditions. When a solar power plant is commissioned, a number of basic tests and tests are required. They will be very important for further evaluating the efficiency of the solar power plant. Reliable and accurate measurements make it possible to accumulate a database on the efficiency and performance of a solar power plant in various environmental conditions. This base will be useful both for predicting the volume of energy production and for assessing the payback period of the project.

It should be understood that the most accurate data for comparison can be obtained only if they are obtained under the same weather conditions as the basic. Since this is difficult in practice, the data is usually recorded for several days in order to obtain averaged values, which are compared with the baseline values ​​recorded under similar weather conditions.

The main disadvantage of this method is that it does not take into account the natural degradation of solar modules or the failure of some of them. This error will only increase over time. Also, the method does not take into account losses during the DC/AC conversion of electricity, etc. In addition, it is worth keeping in mind the tolerance of the measuring instruments, so the data obtained will have an error of at least ± 2%.

Method of test cleaning

It is possible to compare the results of a solar power plant before and after cleaning procedure using the control group of panels. To do this, either a group of solar modules located in the middle of the PV array (assuming the distribution of pollution is approximately uniform), or several separate solar panels in different places of the solar farm are selected. They are measured, cleaned and re-measured under similar weather conditions. By comparing the result, it is possible to determine the increase in generation and assess how generally justified is the cleaning of the surface of PV panels for the entire solar power plant.

Method of the reference solar module

For one solar module (or several that are located in different parts of a large PV array), the generation of electricity is continuously or periodically measured. A decrease in generation below a certain level will require special attention and search for the reasons of the decrease in efficiency. One of them may be increased soiling.

Thermocouple pyranometers

Such devices have been used for a long time in meteorological observations and at climatic stations. They measure the total flow of solar energy that hits a surface. To maintain the accuracy of measurements, the pyranometer must be installed in the same direction and at the same angle as the solar panels are installed. Since thermocouple pyranometers have a wide spectral sensitivity, they can accurately measure the entire solar flux that hits the surface of a photovoltaic panel. The results obtained make it easy to predict how efficiently the solar modules can work and compare this data with its actual work.


The climatic conditions of Ukraine are quite favorable for the operation of solar power plants. The relatively large amount of precipitation largely compensates for the negative impact of soiling. However, if the results of the operation of your solar power plant began to deteriorate, the specialists of Avenston are ready to conduct a comprehensive analysis of its operation and calculate the need for periodic washing (cleaning) of solar panels.

Solar power plants are one of the key and many times approved competencies for companies belonging to the Avenston group. We provide all necessary services for solar energy projects, starting from the support of the development or pre engineering stages to maintenance of already built photovoltaic power plants or systems. All stages of the implementation of such projects are carried out by us independently or with the involvement of selected partners. In the second case, all key processes are managed and controlled by Avenston’s in-house project managers. List of our solar projects includes a large number of designed and built industrial solar PV power plants, commercial solar power plants as well as home solar power plants. If you have plans to build your own solar power plant of any type and size, please contact Avenston. We will be happy to help you implement your project in the most optimal way.