# Photovoltaic system – the location of the solar cell array The placement form and placement angle of the solar cell array in the photovoltaic system have a great influence on the solar radiation received by the photovoltaic system, thereby affecting the power generation capacity of the photovoltaic power supply system. The following two angle parameters are related to the placement of the solar cell array: the inclination of the solar cell array, and the azimuth of the solar cell array. The inclination angle of the solar cell array is the angle between the plane of the solar cell array and the horizontal ground. The azimuth angle of the solar cell array is the angle between the vertical plane of the array and the positive south direction (the eastward deviation is set as a negative angle, and the westward deviation is set as a positive angle). Generally, in the northern hemisphere, when the solar cell array faces due south (that is, the angle between the vertical plane of the array and due south is 0°), the solar cell array will generate the largest amount of electricity.

1. Calculation of the optimal inclination angle

For an independent photovoltaic power generation system, the plane of the solar cell array should face the equator and have a certain inclination relative to the ground plane. With different inclination angles, the amount of solar radiation received by the phalanx varies greatly from month to month. Therefore, determining the optimal inclination angle of the square array is an indispensable and important link in the design of photovoltaic power generation systems. There are many calculation methods and theories. The following is a method of iterating on the amount of deficit.
According to the determined power consumption of the load, the working voltage V of the battery is selected, and the average daily power consumption QL (A·h/d) of the load is calculated. If the load is commonly used in the light control system, the daily working time of the load is calculated according to the following method:

In the formula: the sun’s declination angle. Considering that under normal circumstances, there is still light in the sky within half an hour before sunrise and after sunset, so there is no need to turn on the lights, so the actual working time t=T-1.
According to the data from the Bureau of Meteorology, the annual average solar irradiance on a certain horizontal plane can be obtained, and the monthly average daily solar irradiance in a certain area on a fixed inclined plane can be calculated. The more commonly used method adopts the method proposed by Klien and Theilacker to calculate the monthly average solar irradiance on the inclined plane. For a fixed inclination angle (such as inclination angle β = latitude angle Ф), if the inclined plane is inclined towards the equator, the calculation method can be simplified. The ratio of the average total irradiance in the last month is:

In the formula, the latitude angle of the region; the inclination angle of the square array; the monthly average scattered radiation on the horizontal surface; the monthly average total radiation on the horizontal surface; ρ is the ground reflectivity. The coefficients a, b and d are calculated as follows:

ωs is the sunset angle on the horizontal plane. After obtaining the radiation amount at a certain inclination angle of the solar cell square array, the minimum current output by the square array can be calculated as:

In the formula, η1 is the input efficiency from the square array to the battery circuit, including the dust shielding loss on the square array, performance mismatch, anti-reverse charging diode and line loss, battery charging efficiency, etc.; η2 is the discharge from the battery to the load. Loop efficiency, including battery discharge efficiency, controller and inverter efficiency, and line losses. Similarly, the maximum current required to output the square array can be obtained from the minimum value Ht·min of the monthly solar irradiance on the square array surface:

The actual working current of the square array should be between Imin and Imax, and an intermediate value I can be arbitrarily selected first, then the monthly power generation of the square array is:

In the formula, N is the number of days in the month; Ht is the amount of solar radiation in the month.
The monthly load power consumption is Qc=NQL; thus, the monthly power generation profit and loss ΔQ=Qg-Qc is obtained; if ΔQ<0, it is a deficit, indicating that the monthly power generation is insufficient, and the battery needs to provide part of the stored power. Determine the cumulative deficit Σ|-ΔQi| in units of years, and list the power generation profit and loss in each month. If there is only one continuous deficit period with ΔQ<0, the accumulated deficit is the sum of the monthly deficits in the deficit period. If there are two or more discontinuous periods of ΔQ<0, then the accumulated deficit Σ|-ΔQi| should deduct the positive surplus of ΔQi between two consecutive deficit periods, and finally obtain the accumulated deficit Σ|- ΔQi |. The square matrix output current can be determined according to the accumulated deficit, and the accumulated deficit Σ|-ΔQi| is substituted into the following formula:

Compare n1 with the specified self-sufficiency days n of the system design, if n1>n, increase the current I and recalculate, and vice versa. Through repeated iterations until n1≈n, the square matrix output current Im is obtained. Change the numerical value of the inclination angle in the calculation, repeat the above calculation, and compare the obtained results to obtain the minimum square matrix output current Im value, and the corresponding inclination angle is the optimal square matrix inclination angle βopt.

1. Azimuth of the solar cell array

The azimuth angle of the solar cell phalanx is the angle between the vertical plane of the phalanx and the positive south direction (the eastward deviation is set as a negative angle, and the westward deviation is set as a positive angle). In general, when the square array faces due south (that is, the angle between the vertical plane of the square array and due south is 0°), the solar cell generates the maximum power. When it deviates from due south (northern hemisphere) by 30°, the power generation of the phalanx will decrease by about 10%~15%; when it deviates from due south (northern hemisphere) by 60°, the power generation of the phalanx will decrease by about 20%~30%. However, on a clear summer day, the maximum radiant energy of the sun is late at noon, so when the orientation of the phalanx is slightly westward, the maximum power generation can be obtained at noon. In different seasons, the orientation of the solar cell array is slightly east or west, and there are times when the maximum power generation is obtained. The place where the square array is installed is subject to many conditions, such as the azimuth angle of the land when it is installed on the ground, the azimuth angle of the roof when it is installed on the roof, or the azimuth angle when it is to avoid the shadow of the sun, as well as layout planning, power generation efficiency , design planning, construction purposes and many other factors are related. If you want to adjust the azimuth angle to be consistent with the peak load moment of the day and the peak power generation moment, please refer to the following formula

Azimuth = [peak time of load in a day (24-hour clock) – 12] x 15 + (longitude – 116)

In different seasons, the peak insolation time of each azimuth is different, so there will be different azimuth requirements. In my country, the azimuth angle of solar cells is generally selected in the south direction, so as to maximize the power generation per unit capacity of solar cells. If it is limited by the location of solar cells such as roofs, soil slopes, mountains, building structures and shadows, etc., the azimuth angle should be considered consistent with them, so as to make full use of the existing terrain and effective area, and try to avoid Shadows from surrounding buildings, structures, or trees.

As long as it is within ±20° of due south, it will not have much impact on the power generation. If conditions permit, it should be within 20° of the southwest as far as possible, so that the peak of solar power generation occurs sometime after noon. It is beneficial to generate more electricity in winter. In the design of some solar photovoltaic building-integrated power generation systems, when the laying area of ​​solar cells in the due south direction is not large enough, the solar cells can also be laid in the due east and due west directions.