Snow Sensor – 3S-SS-MB

Technical Specifications of Snow Sensor

What is The Effect of Snow on Solar Power Plants?

Snow creates not just one problem, but two separate problems simultaneously at a solar power plant.

The first is production loss. Snow covering the panel surface prevents sunlight from reaching the cells. Even a thin layer of snow significantly reduces production, and the panels cannot function properly until the snow melts.

Secondly, there is the mechanical load. Accumulated snow places a heavy load on the panels and supporting structure. This load is particularly stressful for mobile solar tracking systems and floating PV sites and can lead to damage over time.

The first step in managing these two problems is measuring the snow cover. Without knowing how much snow there is, it’s impossible to make the right decision about when to intervene. Snow sensors make this decision data-driven.

Working Principle of the SEVEN Snow Sensor

At the heart of the snow sensor there are two reference cells. Because these cells operate on the same principle as the panels in the field, they react to snow and light in the same way as the panels. This is what it means for the sensor to be ‘PV-based’. It measures how snow cover affects production not through an indirect guess, but through the same physical behavior as the panel itself.

The two cells perform different functions:

• The snowy cell is left exposed, much like panels, and snow falls on it. This represents how much the snow reduces production.
• The snow-free cell is heated by a heater inside the box. Snow doesn’t accumulate on it, and it always remains clean. It serves as a reference point for the question, ‘What would production be like without snow?’

The measurement process proceeds in the following steps:

1. Both cells measure the solar irradiance in W/m².
2. The cell covered in snow will have a lower reading due to the snow on its surface. A cell without snow, however, will receive the actual irradiance.
3. The system compares the irradiance values of the two cells.
4. This comparison is converted into the snow ratio on the panels.
5. The result is transmitted via Modbus RTU as a value between 0% and 100%.

In short, the snow ratio is calculated as below.

The less light the snow-covered cell receives, the higher the rate. As the rate approaches 100%, it means the panels are covered with many cm of snow.

How are SEVEN Snow Sensors Integrated with Tracker Systems?

In solar tracking systems, snow presents a twofold problem. It reduces production by covering the panels and also puts extra strain on the system by adding load to the mounting structure. This is where 3S-SS-MB comes in, working in conjunction with the tracker control center.

The process works as follows:

1. The system continuously monitors the snow ratio measured by the sensor.
2. When the snow ratio reaches the threshold defined by the user, the control center sends a command to move the PV panels to a suitable angle, such as 90 degrees, so that the accumulated snow can slide off.
3. As the panels rotate to this angle, the snow is removed from the panel surface. Since the sensor is mounted on the same moving structure, this movement also helps clear the snow-covered cell of the sensor.
4. Once the snow has fallen off, the system is free from snow accumulation. The operator can then rotate the panels back to the desired operating position to achieve maximum energy production.

The most important benefit of this cycle is the prevention of unnecessary movement. Rotating the panel towards the sun while there is snow cover both wastes energy and provides no benefit. Thanks to the sensor, the tracker only moves when necessary and for the right purpose. This saves energy and relieves the structure of snow load.

Snow Sensor Installation in Fixed and Tracker Systems

The basic rule for installation is simple: the snow sensor must be positioned in the same direction and at the same angle as the panels. The sensor will only provide accurate results if it observes the same conditions as the panels.

In tracker systems, the sensor is mounted directly onto the tracker and rotates at the same angles as the system. Thus, the sensor is covered by as much snow as the panels. In fixed systems, the sensor is placed at a fixed point in the same direction and at the same angle as the panels.

In both cases, the following points should be considered:

• Position the sensor at least 10 times the height of any obstacles. Shadows and obstacles will interfere with the measurement.
• Avoid heat sources such as chimneys and vents. These sources can melt the snow and confuse the measurement.
• Avoid dark, reflective, or heat-trapping surfaces.

The materials required for assembly are supplied by SEVEN.

What are the Advantages of SEVEN Snow Sensor?

• It is the world’s first and only PV-based snow sensor.
• It takes measurements with real PV cells, giving an exact replica of the response from the panels.
• It easily connects to monitoring systems via Modbus RTU output over RS485 and SunSpec compatibility.
• With its UV-resistant junction box and IP65 protection rating, it is ready for the field.
• Installation materials are included with SEVEN customer support available.