Photovoltaic module (square array)

The smallest indivisible solar cell assembly device with packaging and internal connections that can independently provide direct current output, also known as photovoltaic modules. A DC power generation unit composed of a number of solar cell modules or solar panels mechanically and electrically assembled together in a certain way and with a fixed support structure is also called a photovoltaic square array. The foundation, sun tracker, temperature controller and similar components are not included in the square array. The following still takes a 30kWp grid-connected photovoltaic power station as an example for description. The system can use high-power monocrystalline silicon solar cell modules, each with a power of 180Wp and a working voltage of 35.4V. A total of 168 units are configured, and the actual total power is 30.24kWp. The entire power generation system uses 8 components in series to form a unit, a total of 21 branches are connected in parallel, and 4 combiner boxes are input, of which 3 combiner boxes are connected to 5 inputs, and the other combiner box is connected to 6 inputs. The so-called combiner box refers to a device in which a certain number of photovoltaic modules with the same specifications are connected in series in a solar photovoltaic power generation system to form a photovoltaic series, and then several photovoltaic series are connected in parallel after converging. After confluence, the cable enters the AC/DC power distribution cabinet of the main control room through the cable trench, connects to the grid-connected inverter through the DC unit of the AC/DC power distribution cabinet, and finally is inverted and output by the grid-connected inverter, and then connected to the 380V three-phase low-voltage power grid through the AC unit of the AC/DC power distribution cabinet.

If several cells in the photovoltaic array are shaded, they will not generate current and will become reverse bias. The cells consume power and generate heat, which will cause malfunctions over time. But some accidental shielding is inevitable, so bypass diodes are needed for protection. If all the components are connected in parallel, bypass diodes are not needed, that is, if the output voltage of the array is required to be 12V, and the output of each component is exactly 12V, there is no need to add bypass diodes to each component. If a 24V array (or higher) is required, then 2 (or more) components must be connected in series, and then bypass diodes need to be added, as shown in Figure 1. Any independent photovoltaic system must have a method to prevent the reverse current flowing from the battery to the array or a method to protect or fail the unit. If the controller does not have this function, a blocking diode must be used. The blocking diode as shown in Figure 2 can be in each parallel branch as well as in the main circuit between the array and the controller. However, when multiple branches are connected in parallel to form a large system, blocking diodes should be used on each branch to prevent the current from flowing from the strong current branch to the weak current branch due to branch failure or shadowing. In a small system, it is enough to use a blocking diode on the main road. Do not use both, because each diode will drop 0.4~0.7V, which is 6% of a 12V system, which is not a small proportion.

Photovoltaic module (square array)
Figure 1 – Series battery with bypass diode
Photovoltaic module (square array)
Figure 2 – Connection method for 24V array blocking diode

In the design of photovoltaic power generation system, the placement form and placement angle of the photovoltaic module square array have a great impact on the solar radiation received by the photovoltaic system, thereby affecting the power generation capacity of the photovoltaic power generation system. The parameters related to the placement of the photovoltaic module array are the inclination angle of the solar cell module and the azimuth angle of the solar cell module.

The inclination angle of the solar cell module is the angle between the plane of the solar cell module and the horizontal plane. The azimuth angle of the photovoltaic module square array is the angle between the vertical plane of the square array and the positive south face (the eastward deviation is set as a negative angle, and the westward deviation is set as a positive angle). As for how to choose the best inclination angle, the continuity, uniformity and maximumness of the inclination angle selection need to be comprehensively considered.

In the horizon coordinate system, the horizon meridian circle passing through the south point and the north point is called the meridian circle. The meridian circle is divided into two 180° semicircles by the zenith and the bottom. The half arc with the north point as the midpoint is called a sub-circle, and the half arc with the south point as the midpoint is called the meridian circle. In the horizon coordinate system, the role of the meridian circle is equivalent to the role of the prime meridian in the geographic coordinate system, and it is the starting surface of the horizon longitude (azimuth) measurement.

The azimuth is the horizon longitude, which is a dihedral angle, that is, the angle between the plane of the meridian circle and the plane of the horizon meridian circle where the celestial body is located. The plane of the meridian circle is the starting plane and measured in a clockwise direction. The measurement of the azimuth can also be carried out on the horizon circle, with the south point as the starting point, and the measurement is clockwise from the south point, and the azimuth varies from 0° to 360°.

For convenience, generally choose a more approximate method to determine the inclination angle. Generally speaking, in southern China, the inclination of the phalanx can be 10°~15° higher than the local latitude, and the inclination of the northern area is 5°~10° higher than the local latitude. For example, the latitude and longitude of Anyang, Henan are: between 113°37’~114°58′ east longitude and 35°12’~36°22′ north latitude. Choose a latitude of 36°, and the inclination angle of the solar cell array Q=36°+10°=46°.

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