Among the many elements affecting the power generation of a PV power system, shadow shading is one of the most common. Common shading factors include natural shading objects, man-made shading objects, etc. These shading objects lightly affect the light transmittance, reducing the amount of light radiation on the surface of the module, and heavily in the local formation of hot spot effect in the module, affecting the power generation efficiency and service life of photovoltaic modules, and even leading to localized burning of the module to form a dark spot and other permanent damage, which will bring about potential safety hazards.
What are the common photovoltaic shadows?
I. Natural Shade
Photovoltaic power stations are often built on the ground, mountain tops, roofs, water and other outdoor scenes, so the surface of the component is easy to attach dust, sand, snow, ice and other natural accumulations of debris settlement, will weaken the penetration of the sun, resulting in component surface temperature increases and affects the power generation efficiency. The environment around the power station varies, with dense vegetation around the water surface power station and the forest-optical complementary power station, and the mountains, vegetation, weeds, and fallen leaves will form a shade. Birds stay on the surface of the module, leaving excreta, feathers and other fallout.
II. Man-made shading objects
Some residents use PV modules as the surface of buildings, while drying clothes, grains, fruits, vegetables and other objects on them, which seriously affects the power generation effect of PV modules. Due to the power station construction environment is not the same, power station construction before or after the completion of the construction of the surrounding new buildings, pylons, utility poles, guardrails and other facilities, will be on the photovoltaic power station to produce shade.
Photovoltaic shadow shading will cause what consequences?
I. Reduce power generation efficiency
Being blocked by foreign objects, part of the battery cell electronic jump activity decreases, corresponding to the resistance increases, the blocking area will become energy-consuming load, resulting in the blocking part of the temperature rises, PV module temperature is not uniform, will be localized in the "hot spot effect", the component's light absorption and conductivity decreases, the component output power decreases, power generation efficiency decreases. If you do not clean the surface dirt area for a long time, the difference in power generation can be up to 10% or more.
II. Shorten the life of the component
If the shade exists for a long time, the overheating area can cause EVA to accelerate the aging and yellowing, so that the light transmittance of the region decreases, thus further deteriorating the hot spot. In serious cases, it may lead to localized burning of components, forming dark spots, melting of solder joints, destruction of grid lines, aging of encapsulation materials and other permanent damage, thus reducing the service life of components, and even the formation of safety hazards.
How to solve the problem of PV module shading?
I. Optimize component protection
In order to avoid the hot spot effect of the series branch circuit, need to install bypass diodes on the PV module, the purpose is to let the high reactance of the solar cell unit or PV module in the flow of current shunt, in order to enhance the reliability; in order to prevent the hot spot of the series circuit, it is necessary to install a DC insurance on each PV string to protect the PV module to maintain the normal operation of photovoltaic power generation device.
II. Pre-construction survey and planning
In the pre-construction of photovoltaic power plant, the need to survey the surrounding environment, select the appropriate geographic location for installation, try to avoid mountains, utility poles, railings, vegetation, buildings, water heaters and other obstruction, and combined with the topography of the direction, the components of the array between the obstruction, floor intervals, etc., to design the appropriate component placement to reduce the impact of the shadow obstruction. If the vegetation is scattered, you can discuss whether it can be removed or cut down according to the requirements of the local forestry department; if it is a large area of woods, it can be avoided in the pre-siting stage. In addition to considering the existing shading factors, but also need to combine with the future planning to eliminate hidden dangers, considerations include the power station near the building in the planning, vegetation production rate, geographic environment brought about by weather changes.
III. Regular Inspection and Operation and Maintenance
In order to improve the efficiency of photovoltaic module power generation, the need for photovoltaic modules for scientific operation and maintenance, regular inspection of photovoltaic arrays, timely cleaning of photovoltaic arrays have blocking weeds, ash, bird droppings, and other foreign matter, to prevent the blocking and hot spot effect to do to prevent the problem before it occurs. In the process of cleaning PV modules, attention should be paid to the season, morning and evening, water temperature, prohibit the use of corrosive alkaline reagents and other chemicals, and seek the help of professional PV cleaners when necessary. Pay close attention to the weather conditions, such as heavy snow, hail, typhoons, sandstorms and other inclement weather, we should check in time, remove the component surface of the snow, ice, tree limbs and other obstructions, and make preparations before the arrival of extreme weather, and repair or replace the PV modules as soon as power generation failures are found.
IV. Do a good job of scientific guidance
Strengthen the PV module operation and maintenance knowledge popularization to the power station users and the surrounding people, and reduce man-made shading from the source. Correct people's wrong behaviors such as drying clothes, vegetables, grains, etc., and prohibit standing, sitting, lying and other actions on the components to prevent internal damage to the components. At the same time, it is necessary to strengthen the daily maintenance of the components, and stop the unreasonable addition of fences, rack bird repellent devices and other behaviors in a timely manner.
