# Solar photovoltaic power generation system design

The design of solar photovoltaic power generation system is mainly divided into two parts: one is the design of photovoltaic power generation system capacity, which mainly designs and calculates the capacity and quantity of solar cell arrays and storage batteries to meet electricity demand and work reliably; the second is the configuration and design of the system, the selection, configuration and design calculation of other main components and auxiliary equipment in the system. The purpose is to select and configure appropriate facilities, equipment and materials according to the actual situation to match the previous capacity design.

The design content of solar photovoltaic power generation system are:

(1) Power demand analysis and calculation

(2) Determine the form of photovoltaic power generation system

(3) Data collection and calculation of local solar energy resources and climatic and geographic conditions, such as local longitude and latitude; annual maximum and minimum temperature; average peak sunshine hours; annual solar radiation; annual maximum continuous cloudy and rainy days, etc.

(4) System capacity design: ①Design and calculation of solar cell module power and square matrix composition; ②Design and calculation of capacity and combination of storage battery (group).

(5) System configuration and design: ①Selection and configuration of controller; ②Selection and configuration of AC inverter; ③Component bracket and fixing method and design; ④Design of AC power distribution system; ⑤Configuration and design of lightning protection and grounding system; ⑥Configuration of supervisors and measurement system

The solar cell array is formed by combining multiple battery modules in series and parallel according to the demand of the load. The required operating voltage is obtained in series, and the required operating current is obtained in parallel. The number of series and parallel determines the output power. Generally, the voltage of the independent photovoltaic power generation system is consistent with the voltage level of the electrical appliance, corresponding to the nominal voltage of the battery or designed to be an integer multiple, such as 12, 24, 36, 48, 110, 220V, etc. The grid-connected photovoltaic power generation system’s square array voltage level is mostly 110V or 220V. Photovoltaic power generation systems with higher voltage levels use multiple square arrays in series and parallel to form the same voltage level as the grid, such as 10kV, and then connect to the grid through an inverter.

The number of series components required by the square array is mainly determined by the system operating voltage or the inverter rated voltage, and factors such as the floating voltage of the battery, temperature changes, and line loss must also be considered. Generally, the output voltage of the system square array with battery is 1.43 times of the nominal voltage of the battery pack. For photovoltaic power generation systems without batteries, the output voltage of the square array should generally be increased by 10% on the basis of the rated voltage, and then determine the number of modules connected in series.

For example, the maximum output power of a certain photovoltaic cell module is 108W, and the maximum working voltage is 36.2V. Assuming that the user needs a power of 3kW, select a DC110V/AC220V single-phase grid-connected inverter to calculate the battery module design plan.

First of all, according to the voltage demand calculation, considering the voltage surplus, the output voltage of the solar cell square array should be increased to: 1.1×110=121V, then the number of modules in series is 121÷36.2=4. Then calculate the total number of battery modules according to the power required by the user as 3000÷108=28, thus calculating the number of modules in parallel as 28÷4=7. Therefore, the system should choose this type of power module with 4 series and 7 parallel, with a total of 28 modules, and the maximum output power of the system is 28×108=3.024kW.