1. Series and parallel connection of solar cell array components
(1) The purpose of series and parallel connection of solar cell modules The single solar cell cannot be used directly as a power source. In practical application, according to the requirements of electrical performance, dozens or hundreds of single solar cells are connected in series and parallel, and after packaging, they form a smallest unit that can be used as a power source alone, that is, a solar cell module. A solar cell array is an array of several solar cell modules connected in series and in parallel.
Generally speaking, the number of series and parallel of solar cell array components can be calculated according to user requirements and load power consumption and technical conditions. The output power of the square array is related to the number of components in series and parallel. The series is to obtain the required working voltage, and the parallel is to obtain the required working current. An appropriate number of components are connected in series and parallel to form the required solar cells. array.
The number of series connections is determined by the operating voltage of the solar cell array. In addition, the floating charge voltage of the battery, line loss and the influence of temperature changes on the solar cell should also be considered. After the number of solar cell modules in series is determined, the number of solar cell modules in parallel can be calculated and determined according to the total annual solar radiation or the 10-year average of the annual sunshine hours provided by the meteorological station.
(2) Determination of correction coefficients in series and parallel formulas of components
①DC correction coefficient In the practical application of solar power generation, the influence ability of the component to reduce the DC power emitted by itself due to various reasons can be expressed by a rough figure, which is the so-called correction coefficient of solar DC battery modules, referred to as DC correction coefficient . The DC correction factor is often composed of many influencing factors: the main influencing factors are the combination of different performance components, the performance of a single component itself, the dust on the surface of the solar cell, and the change of solar insolation intensity. These influencing factors will lead to the reduction of the output power of the solar module array, and the DC correction factor is generally about 0.8.
Some designers have determined the comprehensive loss coefficient (DC correction coefficient) of the solar cell module system as 1.05. Obviously 1/0.8=1.25>1.05. The possible reasons for this consideration are as follows: only one or two influencing factors of the DC correction factor are considered, such as only the degradation of component performance and the influence of dust.
Some designers take the value of 1.11 (its reciprocal is about 0.9), or all the influencing factors in the DC correction coefficient are considered, but the value obtained is also different due to different geographical locations (different air transparency, insolation intensity, etc.). different.
Some consider the DC correction factor and charging efficiency together, and the value is 0.6 to 0.7. This means that the actual power usage of the solar cell module (panel) is 60%~70%.
②Charging correction coefficient The solar cell module cannot charge the battery 100%, because the battery will heat up during the charging process, and the electrolyzed water will evaporate, so the charging correction coefficient is only 0.85 ~ 0.9, for this reason, the power of the solar cell module should be increased by 10%. ~15% to ensure the load at night or in rainy days.
③Inverter correction factor is generally 80%~93%.
(3) Calculation formula for determining the number of solar cell array components
①Determine the number of parallel solar cell array components
The number of solar cell array modules in parallel = the average daily power consumption of the load / (the average daily power generation of the module? the charging efficiency correction coefficient? the DC correction coefficient? the inverter efficiency correction coefficient)
②Number of solar cell array modules in series
The number of solar photovoltaic modules in series = system operating voltage / standard voltage of a single module
③The total number of solar cell array modules
The total number of solar cell array modules = the number of solar cell array modules in parallel? The number of solar cell array modules in series
2. Types of solar cell arrays
Solar cell arrays can be divided into two categories: flat panel type and concentrator type. Flat-plate square array: It is only necessary to connect a certain number of solar cell modules in series or parallel according to the requirements of electrical performance, without adding a device for concentrating sunlight. Concentrating square array: a collector that gathers sunlight is added, usually a plane reflector and a parabolic reflector are used to collect light to improve the incident spectral irradiance. Concentrating phalanx arrays can use fewer single solar cells than flat-panel phalanx arrays with the same power output, which reduces the cost, but usually requires the installation of sun-tracking devices.
3. Azimuth of solar cell array
The influence of the azimuth angle of the solar cell array on the power generation capacity of the solar cell module must not be underestimated. In general, when the orientation of the solar cell array is due south (that is, the angle between the vertical plane of the array and due south is 0°), the solar cell power generation is the largest. When it deviates from due south (northern hemisphere) by 30°, the power generation of the phalanx will decrease by 10%~15%; when it deviates from due south (northern hemisphere) by 60°, the power generation of the phalanx will decrease by 20%~30%. However, on a clear summer day, the maximum solar radiation energy is after 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 phalanx is slightly east or west, and there is a time when the maximum power generation is obtained. The location of the square array is related to many factors: such as the azimuth of the land when it is set on the ground, the azimuth of the roof when it is set on the roof, or the azimuth when it is to avoid the shadow of the sun, as well as layout planning, power generation efficiency, design planning , construction purpose, etc.
Determination of the azimuth angle of the solar cell array:
Azimuth = [peak time of load in a day (24h)-12]×15+(longitude-116)
4. The tilt angle of the solar cell array
The angle of inclination is the angle between the plane of the solar cell array and the horizontal ground, and it is hoped that this angle is the best angle of inclination when the array produces the most power in a year. The best tilt angle of the year is related to the local geographic latitude. When the latitude is higher, the corresponding tilt angle is also larger. In the design, it should be noted that the inclination angle of the roof and the inclination angle of the snow fall should also be considered.
How to actually determine the optimum tilt angle of a solar cell module? When the direction of the solar cell module is due south (the azimuth angle is 0°), and then the inclination angle of the solar cell module is gradually increased from the horizontal (0°), it will be found that there is an optimal inclination angle. The largest amount, the largest power generation. Then increase the inclination angle, the insolation decreases continuously, especially after the inclination angle is greater than 60°, the insolation drops sharply, until the final vertical placement, the power generation drops to the minimum value. As for the square array from vertical placement to 10° to 20° inclined placement, there are practical examples.
Generally speaking, the inclination angle of the solar cell array is roughly determined according to the local latitude plus 5° to 20°, although this determination is not very strict (because the latitude of some areas is not much different, and the solar irradiance on the horizontal plane is often different. It is very large), but it is still a simple and feasible method to approximately determine the inclination angle of the battery square. Of course, it is best to calculate the optimal inclination angle of the square array by comparing the battery array and battery capacity required for different inclination angles under the condition of satisfying the load power consumption. The ideal inclination angle of solar cells in the lower reaches of the Yangtze River is about 40°, and the direction is due south.
In general, when calculating the power generation, it is obtained on the premise that the square array has no shadows at all. Therefore, if the solar cell cannot be directly illuminated by sunlight, only the scattered light is used to generate electricity, and the electricity generation at this time is 10%~20% less than when there is no shadow. In this case, the theoretical calculation value should be corrected. Usually, when there are objects such as buildings and mountains around the phalanx, after the sun comes out, there will be shadows around the buildings and mountains. Therefore, when choosing to lay the phalanx, try to avoid shadows. If it is really unavoidable, the position of the solar cell array should be adjusted as much as possible to minimize the impact of the shadow generated by the building on the power generation of the solar cell array.
When the latitude is higher, the distance between the square arrays will increase, and the area of the setting place will also increase accordingly. In order to facilitate the automatic sliding of snow from the phalanx, the inclination angle of the phalanx should be increased, thus increasing the height of the phalanx. In order to avoid the influence of shadows, the distance between the squares is also increased accordingly. Usually, when arranging a square array, the construction size of each square should be selected separately, and its height should be adjusted to an appropriate value, so as to use its height difference to adjust the distance between the squares to a minimum.
6. Other issues to consider
For the specific solar cell array design, while reasonably determining the azimuth angle and the inclination angle, comprehensive consideration should also be carried out, so that the square array can achieve the best state. Guardrails or walls should be added around the solar cell array and its supporting equipment. For solar cell arrays without tracking devices, the solar inclination angle and azimuth angle of the square array brackets should be adjusted according to seasonal changes.
The power generation of the solar cell array is proportional to the solar radiation it receives. In order for the phalanx to receive solar radiation more effectively, the installation orientation and inclination of the phalanx are very important. A good phalanx installation is to track the sun so that the surface of the phalanx is always perpendicular to the sun, and the angle of incidence is 0°. For fixed installation, the radiant energy on the horizontal plane obtained from the meteorological station should be converted to the phalanx slope in the design.
The lighting surface of the solar cell array should always be kept clean; the output connection should pay attention to the positive and negative polarities; regular detection, timely troubleshooting, and anti-aging of the battery.