The utilization of solar photovoltaic plants has grown significantly in recent years, and it is expected to increase even more in the future. As a result, the need for better maintenance and monitoring systems is becoming increasingly important. One of the biggest challenges faced by PV plants is soiling, which is the accumulation of contaminants on the surface of solar panels, including:
- Dust
- Sand
- Pollen
- Salt residues
- Bird droppings
- Industrial pollution and airborne particles
This accumulation can significantly decrease the efficiency of the PV panels, reducing the overall power output of the plant. To address this issue, SEVEN has developed a wide range of soiling sensor models.
How Is the Soiling Ratio Calculated by SEVEN?
SEVEN has developed different soiling sensor models for different measurement and monitoring needs in PV plants. The method SEVEN is following is by comparing the output of two irradiance sensors; one reference irradiance sensor which is cleaned periodically and the other one cleaned with the same cleaning schedule as the PV panels in the plant. According to IEC 61724-1 standard, the soiling ratio is calculated daily. The following Formula explains simply what the soiling ratio refers to.
Since the used irradiance sensors (reference cells) operate with a photovoltaic sensing principle similar to PV modules, the measured soiling ratio shows a behavior representative of the energy losses caused by soiling on the panels. Research indicate that the measured soiling ratio can be used as a reference for estimating the energy loss ratio caused by soiling in PV plants.
Models of Soiling Sensors by SEVEN
The requirements of clients differ but the purpose is the same; getting the soiling ratio of the PV Plant to avoid a significant power loss. Thus, SEVEN developed different models as per the market needs.
Automatic Soiling Sensor
The first question that comes to mind is how is the reference irradiance sensor cleaned. It is obvious that the user always prefers the easiest way to run a system, which is automatic cleaning in this case. On the other hand, sometimes manual cleaning can be time-consuming and can pose safety risks for the workers involved, especially for difficult-to-reach locations. For this reason, SEVEN offers a comprehensive system that can clean itself with an Automatic Soiling Sensor.
Cleaning Mechanism
The operator has only to fill the water tank with pure water, with antifreeze, when required, twice per year. In fact, the water tank included in the Automatic Soiling Sensor has a capacity of 18 L, which is enough to run the system for 6 months. The whole system can be installed in minutes with a single person and requires AC power (220V) to be powered. The cleaning is performed by a nozzle installed above the reference irradiance sensor and the cleaning time is defined in the firmware by following the standard IEC 61724-1.
Manual Soiling Sensor
Although automatic cleaning may be the best solution for all users, the limited budget in some projects makes the user unable to afford the cost of this model. Thus, the manual cleaning option is available.
In the Manual Soiling Sensor model, both irradiance sensors are combined in the same box with mounting facilities, which makes it easy for the operator to mount quickly on the Plane of Array (POA) of the panels. As for the cleaning, it is done manually by an operator on-site by using a glass cleaning wipe.
Portable Soiling Sensor
SEVEN also offers the SEVEN Portable Soiling Sensor for users who need direct on-site soiling measurements without installing a fixed soiling sensor system. Unlike automatic or manual fixed soiling sensors, the portable model is used directly on the PV panel surface to check the soiling ratio in the field.
The Portable Soiling Sensor calculates the soiling ratio by using the reflection and scattering properties of light. Before the measurement, the user selects parameters related to the panel and soiling characteristics, such as panel cell color, soil color, and soil tone. Then, the device applies stable light onto the panel surface, measures the reflected light, and calculates the soiling ratio through its internal software. The result is displayed directly on the integrated LCD screen.
This model is especially useful for cleaning companies, O&M teams, and users managing multiple PV plant sites. It allows quick field checks before and after panel cleaning and can help operators decide whether cleaning is required in a specific area. According to the measurement procedure, soiled and clean measurements should be taken on the same panel to avoid differences caused by panel-to-panel reflection characteristics.
For a practical demonstration of the field measurement method, you can also watch SEVEN Portable Soiling Sensor: Improved Field Measurement Technique
Monitoring Methods of the Soiling Ratio
The SEVEN Portable Soiling Sensor gives the soiling ratio directly in the field with on-site measurements. For fixed soiling sensor models, after deciding on the cleaning method, the next step is to decide how the soiling ratio will be monitored in the plant.
In general, the plant’s performance is controlled through a monitoring system by using a SCADA system or simply through the monitoring system of the datalogger itself. That is why the Modbus Output option is, usually, the most suitable way to monitor the soiling ratio. SEVEN provides the Modbus RTU Output, regardless the cleaning method, which is compatible with well-known brand dataloggers and all PLC & SCADA systems with RS485 Port. The distance between the Soiling Sensor and the datalogger or PLC can be up to 1200 m under suitable communication conditions.
SEVEN Monitoring Platform
For projects that do not have an existing SCADA system, PLC, or datalogger on site, the SEVEN Monitoring Platform can be provided through the SEVEN Gateway device. In this setup, the soiling sensor data is collected via the gateway and displayed on the SEVEN Monitoring Platform.
For soiling sensor applications, the platform allows the user to monitor parameters such as soiling ratio, clean and soiled cell irradiance values, clean and soiled cell temperature values, wash tank status, and data stability status. These values can be followed through dashboard indicators, trend graphs, and data tables. The user can also review the data for a selected time interval and export the recorded values in various formats, such as Excel-compatible files, when required.
The SEVEN Monitoring Platform is not limited to soiling sensors. It can also provide monitoring for other SEVEN Sensor products according to their Modbus maps and available measurement parameters. This allows users to monitor irradiance sensors, pyranometers, weather stations, module temperature sensors, ambient temperature sensors, wind sensors, humidity sensors, precipitation sensors, and other compatible field sensors through the same platform.
HMI-PLC Option for On-Site Monitoring
In some projects, SEVEN also offers an HMI-PLC option for users who prefer to monitor the soiling ratio directly on-site. The HMI-PLC allows the user to check the daily calculated soiling ratio on-site by simply checking the displayed value on the screen.
The other feature that can be added to this model, upon request, is the alarm system. So, if the user wants to receive a warning when the soiling ratio reaches a certain level, this can be added while programming the PLC.
What Are the Benefits of Using SEVEN Soiling Sensors?
In general, the benefit of soiling sensors is that they help plant operators optimize their cleaning schedules. By providing real-time data on the soiling ratio, these systems enable operators to determine the frequency of cleaning that is necessary to maintain optimal energy production. This not only improves overall plant performance but also helps maintain long-term PV plant performance.
In addition, by helping to improve energy production and reduce maintenance costs, soiling monitoring systems can help solar PV plant operators achieve a faster return on investment. They are an important tool for any plant operator looking to maximize the efficiency and profitability of their solar PV plant
As for SEVEN Soiling Sensor, it is preferred by the clients thanks to its flexibility, easy operation and the diversity of available options, as well as the high quality of both products and after-sales service. SEVEN also supports its clients with technical assistance and after-sales support for different project requirements.
Frequently Asked Questions (FAQ)
What is a soiling sensor in PV plants?
A soiling sensor is used to monitor the impact of dirt accumulation on PV panels by comparing irradiance measurements from a clean reference sensor and a soiled sensor. This helps operators estimate energy losses caused by soiling and optimize panel cleaning schedules.
How is the soiling ratio calculated?
The soiling ratio is calculated according to the formulation defined in IEC 61724-1 by comparing the irradiance measured from a clean reference sensor with the irradiance measured from a sensor exposed to the same soiling conditions as the PV panels. This comparison allows the estimation of performance losses caused by soiling in PV plants.
Why is soiling monitoring important in utility-scale PV plants?
Even a small amount of soiling can reduce PV plant performance and energy yield over time. Continuous soiling monitoring helps operators optimize cleaning schedules, reduce unnecessary maintenance, and improve long-term plant performance.
What is the difference between automatic and manual soiling sensors?
Automatic soiling sensors clean the reference sensor automatically using a water-based cleaning mechanism, reducing manual maintenance and improving operational convenience, especially in large-scale PV plants. Manual soiling sensors, on the other hand, provide a more cost-effective solution for projects where periodic on-site cleaning can be performed by the operator. The selection between these solutions is further explained in Seven Soiling Sensors: Which One Should You Choose?.
Where should a soiling sensor be installed in a PV plant?
Soiling sensors should be installed on the Plane of Array (POA) with the same tilt and azimuth angle as the PV modules to ensure representative soiling measurements under actual operating conditions. More information about the installation process can be found in Seven Automatic Soiling Sensor: Unboxing, Setup & Installation Tutorial.
Can soiling monitoring help reduce O&M costs?
Yes. By monitoring the actual soiling ratio, operators can optimize cleaning schedules and avoid unnecessary cleaning operations, helping reduce operational and maintenance costs.
What is the difference between a portable soiling sensor and a fixed soiling sensor?
A fixed soiling sensor is installed permanently in the PV plant and monitors the soiling ratio daily. A portable soiling sensor is used for direct field measurements on the PV panel surface and does not require permanent installation. It is useful for O&M teams, cleaning companies, and users who want to check soiling levels at different points or multiple PV plant sites. Fixed sensors are generally preferred for continuous monitoring, while portable sensors are more suitable for on-site checks before and after panel cleaning.
