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Circuit composition of grid connected system

2021-11-05 16:09:17

Photovoltaic module

The smallest and indivisible solar cell combination device with packaging and internal connection, which can independently provide DC output, is also called photovoltaic module. The DC power generation unit composed of several solar cell modules or solar panels mechanically and electrically assembled together in a certain way and with fixed support structure is also called photovoltaic array. Similar components such as foundation, solar tracker and temperature controller are not included in the array. Positive energy battery modules, each module has a power of 180wp and a working voltage of 35.4v. A total of 168 modules are configured, and the actual total power is 30.24kwp. The whole power generation system adopts 8 components in series as a unit, with a total of 21 branches connected in parallel and input to 4 combiner boxes, of which 3 combiner boxes are connected to 5-way input and the other combiner box is connected to 6-way input

Loser. The so-called combiner box refers to a device that connects a certain number of photovoltaic modules with the same specifications in series to form a photovoltaic series, and then connects several photovoltaic Series in parallel. After confluence, the cable enters the AC / DC distribution cabinet in the main control room through the cable trench, and is connected to the grid connected inverter through the DC unit of the AC / DC distribution cabinet. Finally, it is output by the grid connected inverter and connected to the 380V three-phase low-voltage power grid through the AC unit of the AC / DC distribution cabinet.

If several photovoltaic cells are shaded, they will not generate current and will become reverse bias. The cells consume power and generate heat. Over time, they will form faults. However, some accidental shielding is inevitable, so bypass diodes need to be used for protection. If all components are connected in parallel, bypass diodes are not required, that is, if the array output voltage is required to be 12V and the output of each component is exactly 12V, bypass diodes are not required for each component. If 24V array (or higher) is required, two (or more) components must be connected in series, and bypass diodes need to be added at this time, Any independent photovoltaic system must have a method to prevent the reverse current from the battery to the array or a method to protect or fail the unit. If the controller does not have this function, the blocking diode will be used. However, when multiple branches are connected together into a large system, Blocking diodes shall be used on each branch to prevent the current from flowing from strong current branch to weak current branch due to branch fault or shielding. In a small system, it is enough to use a blocking diode on the main road, not both, because each diode will reduce the voltage by 0.4 ~ 0.7V, which is 6% of a 12V system, which is also a large proportion.

 

solar photovoltaic support

 

In the design of photovoltaic power generation system, the placement form and placement angle of photovoltaic module array have a great impact on the solar radiation received by the photovoltaic system, thus affecting the power generation capacity of the photovoltaic power generation system. The parameters related to the placement of photovoltaic module array are the inclination of solar cell module and the azimuth of solar cell module. The inclination of solar cell module is the angle between the plane and horizontal plane of solar cell module. The azimuth of the photovoltaic module array is the included angle between the vertical plane of the array and the positive South plane (the East deviation is set as a negative angle and the West deviation is set as a positive angle). As for how to select the best dip angle, it is necessary to comprehensively consider the continuity, uniformity and maximum of the dip angle.

In the horizontal coordinate system, the horizontal meridians passing through the South and North points are called meridional circles. The meridian circle is divided into two 180 ° semicircles by the zenith and the zenith. The half arc with the north point as the midpoint is called the sub circle, and the half arc with the south point as the midpoint is called the meridional circle. In the horizon coordinate system, the function of the meridian circle is equivalent to the function of the primary meridian in the geographic coordinate system, and it is the starting surface of the horizon longitude (azimuth) measurement.

Azimuth is the horizon longitude, which is a kind of two-sided angle, that is, the included angle between the plane where the meridian circle is located and the plane passing through the horizon meridian circle where the celestial body is located. It is measured clockwise with the plane where the meridian circle is located as the starting plane. The measurement of azimuth can also be carried out on the horizon, starting from the South Point and measured clockwise from the south point. The variation range of azimuth is 0 ~ 360 °.

For convenience, a more approximate method is generally selected to determine the inclination. Generally speaking, the dip angle of the square array in the south of China can be 10 ° ~ 15 ° higher than the local latitude, and the dip angle in the north can be 5 ° ~ 10 ° higher than the local latitude. For example, the longitude and latitude of Anyang, Henan Province are between 113 ° 37 '~ 114 ° 58' e and 35 ° 12 '~ 36 ° 22' n. The latitude is 36 °, and the inclination of the solar cell array is q = 36 ° + 10 ° = 46 °.

Solar cell module bracket

(1) Function and classification of supports

The power generation efficiency of solar cell modules is directly related to time, sunshine intensity, placement position and inclination angle of battery modules. The design of its support system also plays an indispensable role in the process of construction and daylighting power generation. Low cost, easy maintenance and reliable installation, such as being able to withstand the impact of various loads such as rain corrosion, atmospheric corrosion, wind pressure load and snow load, which is a necessary condition for solar photovoltaic power generation.

According to the requirements of different forms of solar photovoltaic power generation, the solar photovoltaic support system can be divided into different specifications and models, such as tracking system series support, matrix solar support, single column solar support, double column solar support, wall solar support, roof solar support, or roof installation system according to different installation methods Ground installation system and installation system of building energy-saving integrated support.

 

At present, the commonly used solar photovoltaic support system can be divided into three types: steel support, aluminum alloy support and concrete support. Aluminum alloy support is usually used in the roof solar energy of civil buildings, which has the characteristics of beauty, durability, corrosion resistance and light weight. However, due to its low bearing capacity, it can not be used in the project of solar power station. Concrete support is mainly used in large-scale photovoltaic power stations. Because of its great, it can only be placed in the field, and it is an area with good foundation. Because of its strong stability, it can support large-scale battery panels. The steel support has stable performance, mature manufacturing process, high bearing capacity, excellent anti-corrosion performance, beautiful and unique connection design, simple and fast installation, and the steel and stainless steel parts made of structural anti-corrosion materials have a service life of more than 20 years.

 

photovoltaic module

 

(2) Design of support strength

In support design, in order to achieve the load borne by the support, it is necessary to determine what kind of material and how much to use, and then calculate the strength accordingly. The strength of the support is mainly determined by the fixed load, and the component mass g includes the frame mass GM, the frame self weight GK1 + and other mass GK2, that is, the fixed load G=GM+GK1+GK2

At present, there are two common ways to install the base of photovoltaic support, one is concrete foundation and the other is ground pile foundation. Considering the construction cost and local geographical environment, at present, most large-scale photovoltaic power stations in China adopt concrete foundation. The ground pile foundation is widely used in foreign countries, such as Italy, Germany, Australia and other countries. Due to the consideration of land reuse, the economic cost is appropriately relaxed.

In terms of ground matrix technology, two aspects should be paid attention to: one is the wind resistance requirements of supports, and the other is the distance between support matrices. Under the condition of ensuring wind resistance, the support shall be mixed with steel structure and aluminum alloy, which can not only ensure the wind resistance of the support, but also ensure the overall appearance of the support.

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