1、 The necessity of cleaning photovoltaic modules
Photovoltaic modules are the core part of photovoltaic systems and also the most valuable part of photovoltaic systems. The quality or cost of photovoltaic modules will directly determine the quality and cost of the entire system. The theoretical power generation efficiency of photovoltaic modules is 25%, but the actual efficiency is 23%; After pollution, the power generation efficiency decreased to 17-18%. Therefore, the cleanliness of photovoltaic modules has a significant impact on power generation efficiency and benefits. Photovoltaic modules are installed outdoors, and the small dust particles and snow attached to their surfaces can affect the transmittance of light, thereby affecting the amount of radiation received by the module surface and affecting power generation efficiency; Surface soil, bird droppings, and other local obstructions can cause hot spot effects on photovoltaic modules, reducing power generation efficiency and even burning the modules. In order to improve the power generation efficiency of photovoltaic modules, it is necessary to regularly clean them.
The service life of photovoltaic modules is over 20 years. In order to maintain normal power generation efficiency during the service life, the photovoltaic power station needs to arrange dedicated personnel to regularly clean the surface dust and pollutants of the photovoltaic modules. The cleaning plan includes three methods: general dust removal, local cleaning, and overall cleaning.
General dust removal: In general, a duster or dry mop is used to clean the dust on the surface of photovoltaic modules to reduce the impact of dust on power generation.
Local cleaning: When there are difficult to remove pollutants such as bird droppings in a certain part of the photovoltaic array, the photovoltaic array will be locally cleaned with clean water.
Overall cleaning: When the dust accumulation on the surface of photovoltaic modules is thick due to long cleaning intervals or harsh weather conditions, the photovoltaic array needs to be cleaned as a whole. The first consideration for cleaning photovoltaic modules is natural rainwater cleaning, while manual cleaning is considered in seasons with less rainfall.
The general dust removal plan is conducted every two weeks, and the overall cleaning plan is conducted every three months or after a particularly severe weather week.
The cleaning of photovoltaic modules should be carried out in the early morning, evening, night, or rainy days (when the irradiance is less than 200W/m2), and it is strictly prohibited to choose the period around noon or when the sunlight is strong for cleaning work. When cleaning in the morning and evening, it is also necessary to choose a time period with weak sunlight.
2、 Methods for cleaning photovoltaic modules
The common cleaning methods for photovoltaic modules are as follows:
1) Manual cleaning
Artificial photovoltaic module cleaning is a primitive method of module cleaning that relies entirely on human labor. This cleaning method has low work efficiency, long cleaning cycle, high labor cost, and poses personal hazards. Mainly divided into manual washing and manual dry cleaning.
a. Artificial water washing
Artificial water washing is achieved by spraying water onto the surface of photovoltaic modules using a nozzle attached to a water truck (or water pipe) to achieve the desired effect
The purpose of cleaning is that this cleaning method is superior to manual dry cleaning, with higher cleaning efficiency, but requires a larger amount of water. Special electric brushes, roller brushes, and disc brushes for cleaning photovoltaic modules can be used. The water pipe should be tied to the brush rod, and some electric brushes are also equipped with water pipe nozzles to achieve the effect of simultaneous brushing and rinsing.
b. Manual dry cleaning
The operator uses a long handled velvet mop combined with a specialized dust cleaning agent for cleaning.
Main principle: Utilizing the principle of electrostatic adsorption, it has the function of adsorbing dust and sand particles, enhancing the dust pushing and cleaning ability, and effectively preventing dust and sand particles from flying during cleaning. As long as you gently tap the dust pusher, you can shake off the sand particles. It is commonly used for cleaning curtain walls, hotels, guesthouses, and other places.
2) Automatic cleaning
The automatic cleaning method is to install the cleaning device on the photovoltaic module array and control the rotation of the motor through a program to achieve automatic cleaning of the photovoltaic modules by the device. Alternatively, a photovoltaic cleaning vehicle can be used, which adds a free arm cleaning brush on top of the tractor and is equipped with a water delivery nozzle to rinse with water while brushing. The automatic cleaning machine can be operated in two ways: "with water" and "without water" according to the on-site environment. The cost of automatic cleaning equipment is high.
a. Clean the car
At present, the cleaning equipment modified with engineering vehicles as carriers has high power and efficiency. The cleaning work has good consistency in the pressure of photovoltaic modules, and will not produce uneven pressure on photovoltaic modules, causing hidden cracks. Moreover, cleaning can be carried out in two modes: cleaning and washing. Operations companies can purchase or lease. 10MWp was cleaned with 30 cubic meters of water, which is equivalent to a 0.23mm light rain falling on the surface of a 22Km × 3.5m photovoltaic array.
The following picture shows the photovoltaic cleaning machine GEKKO developed and produced by Swiss company Serbot. It supports water washing and consists of a small car and a water pipe about 100m long. It requires remote control operation and has a cleaning efficiency of 400 ㎡/h.
The following picture shows a photovoltaic module cleaning car developed and designed by Miraikikai, a Japanese company. The company's photovoltaic module cleaning robot has the characteristics of autonomous walking and cleaning, and can clean the panel without using water. The sand and dust accumulated on the photovoltaic module are swept by a rotating brush and blown out from the panel by a fan.
The following picture shows a photovoltaic cleaning vehicle designed by an Australian company, which is equipped with a free arm cleaning brush on top of the tractor and a water delivery nozzle for rinsing with water while brushing. The designer stated that 'a person can clean about 1000 photovoltaic modules per day, and this type of car can clean 1500 to 2000 modules per hour.' The expected price of the car is between $130000 and $145000 (plus consumption tax). The price of competitive products designed and manufactured overseas is approximately $165000 (+consumption tax).
b. Cleaning robot
To effectively improve the efficiency of cleaning dust on the surface of distributed solar panels, intelligent cleaning robots are used for regular cleaning, thoroughly removing dust and dirt from the surface of photovoltaic modules to enhance power generation efficiency. The method is to install a photovoltaic module cleaning robot in each row of the power station (or install a line breaking trolley, with multiple rows sharing one robot) to automatically clean the photovoltaic modules on a regular basis without human supervision. It can come with its own photovoltaic modules and power storage devices, without the need for an external power source.
At present, the large-scale photovoltaic cleaning robot commonly used in outdoor photovoltaic power plants is the one shown in the figure below. This robot is a waterless rail robot with a horizontal cleaning brush.