The power output delivered from a photovoltaic module highly depends on the amount of solar irradiance, which reaches the solar cells. There are many parameters that determine the ideal output or optimum yield in a photovoltaic module. One of the most important factors especially in big installations of solar PV arrays is dust. Accumulated over a time period, dust will cause a considerable reduction in the total solar irradiance reaching the panels. More new studies have actually quantified the solar cell energy output loss occurring due to the air pollution and dust showing that in some parts of the world, solar panels energy output of a PV solar plant may have a 25% due to the airborne particles such as air pollution and dust.
Our company was requested by a client working in Gulf Arab countries for designing a solar panel cleaner. The design was aimed at an automatic system that could clean big areas of solar PV arrays without the need for any human work.
The design was requested to meet the following requirements.
- Safety of solar panels during the operation of the device
- Durability and robustness of the system in terms of withstanding different environmental condition such as:
- High temperature
- High wind speed
- Rainy weather
- Efficiency regarding the following issues
- Energy consumption
- Speed of cleaning
- Quality of cleaning
- Stability of the system
- Low manufacturing cost
- Low maintenance cost
- Ease of installation
- Easy to mount
- Easy to replace
Challenges and design considerations
The customer requested us to solve the problem of dust and air-borne contamination on PV panels which had a negative effect on the panel’s performance (loss of output power). The most important challenge was the different regional environmental conditions over a seasonal change that should be dealt with, like dust, rain, harsh rain, etc.
There are currently many methods like mechanical methods, Nano-film method, super-hydrophilic method, super-hydrophobic method and static electric method.
The most reliable, cost-efficient methods are mechanical methods. In this method, a brush is attached to a mechanism and this mechanism is capable of scanning the whole surface of the panel. To find which mechanism worked best with the client, four concept designs were prepared, discussed and compared from multiple points of views and offered to the client. They included the followings:
Design 1: Brush with water sprayer– In this concept, a clamp was mounted on the four corners. Clamps would allow the client to use this machine on any size of PV. A bracket was attached to this clamps, 2 shafts one with power screw and the other without screw were mounted inside the brackets. A water sprayer was attached to the movable cross member. This sprayer was to help the brush to ensure surface cleaning. The motor speed and direction reverse was controlled according to the size of the PV panel.
Design 2: Brush with air sprayer – It was like the previous one but instead of using motor and power screw, the cross member had its own motor and it moved via rack and pinion concept. Also, instead of a water jet, an air sprayer was attached to the cross movable member. This air sprayer helped to ensure surface cleaning with brushes. The cross member, brush, and the motor movement were to scan and clean the PV panel.
Design 3: Brush with both air and water sprayer – This is the same design of concept one but instead of a static brush, a rotating brush with its own motor will be used. The brush now moves in a linear direction and rotates about its axis at the same time. A sprayer (with both air and water) will be attached before and after the rotating brush. In this method, complete cleaning using two sprayers is guaranteed.
Design 4: Water and air sprayer without Brush – As is evident from its name, in this concept, there is no brush and cleaning is done by both water and air jet sprays. This concept was aimed at deleting brush that could harm PV panel surfaces over a long period of time.
Comparison of the concept designs
Having offered the above concept designs, a comparative study was made to find the pros and cons of each concept, and the following table was prepared. In the below table, each figure was the grading of each parameter according to a well-defined table with the higher figure referring to the higher grade.
The parameters that were important for the choice of the best design included:
- Energy Efficiency
- Speed Efficiency
- Cleaning Efficiency
- Low product cost
- Low maintenance cost
- Low Manufacturing cost
- Easy to mount
Based on the definition for each of the above factors, a comparison table containing these parameters and their weighting factor was prepared which showed that the 3rd design concept had the highest ranking.
The other issue to be considered was the electrical part. The electrical part of the project consisted of a BLDC or stepper motor to drive the set of brush, air blower and fluid injector on the shafts and fluid and air pumps for blowing off the sands and washing up the PV modules. These parts were controlled by a processing unit with an STM32 or ESP8266 in its core programmed to control the sequences of procedure of PV washing device. The device was connected to a central control unit operated manually or automatically based on predefined interval times. The communication between devices mounted on the PV modules and the central control unit was done through LAN or Wi-Fi.
The final choice of the design
Based on previous concept designs and analysis, concept 3 with water jet was suggested as the most appropriate design for this case and received the first rank. The concepts received the following ranking
- 1st rank: Concept 3 (brush with a water jet and air spray)
- 2nd rank: Concept 1 (brush with a water jet)
- 3rd rand: Concept 4 (no brush and a water jet and air spray)
- 4th rank: Concept 2 (brush with an air spray)
Design and analysis work
Having determined the proper choice of design, the design team initiated the actual design and took all steps for finalizing the design. The design consisted of the following steps
- Mechanical design and choice of components
- Electronic design and choice of components
- Software simulation for both the electronic and mechanical design (FEA analysis, …)
After 4 months of work by a team of engineers, the final design was completed and submitted to the client. It covered all the design requirements requested by the client and received his good feedback.