System configuration and calculation of photovoltaic power generation system

System configuration and calculation of photovoltaic power generation system

(1) The number of photovoltaic cell modules connected in series NN

The required working voltage can be obtained by connecting the photovoltaic cell components in series according to a certain number. In addition, when the solar photovoltaic cell array charges the battery, the number of photovoltaic cell components in series must be appropriate. If the number of series connection is too small, the series voltage is lower than the floating charging voltage of the battery, and the square array cannot charge the battery. When the output voltage of the series components is much higher than the float voltage, the charging current will not increase significantly. Therefore, the optimal state of charge can only be achieved when the series voltage of the PV modules is equal to the appropriate float voltage. The calculation method is as follows:

Ns=Ur+Uoc=(Uf+Ud+Uc)/Uoc   (1-1)

In the formula, Ur is the minimum output voltage of the photovoltaic array; Uoc is the optimal working voltage of the photovoltaic cell module; Uf is the floating charge voltage of the battery; Ud is the diode voltage drop, generally 0.7V; Uc is the voltage drop caused by other factors .

The floating charging voltage of the battery is related to the selected battery parameters, and should be equal to the maximum working voltage of the selected battery cell at the lowest temperature multiplied by the number of batteries connected in series.

(2) The number of parallel connection of photovoltaic cell modules Np

Before determining this problem, first determine the calculation method of its related quantity.

① Convert the solar solar radiation Hi at the installation site of the photovoltaic cell array into the average solar radiation hours H under standard light intensity

H=Hi ×2.778/1 000  (1-2)

In the formula, Hi is the daily radiation amount; 2.778/1000 is the coefficient of converting the daily radiation amount to the average daily radiation hours under standard light intensity (1000W/m2).

H=Hi ×2.778/10 000  (1-3)

②Daily power generation of photovoltaic cell modules

  Qp=Ioc×H×Kop×Cz   (1-4)

In the formula, Ioc is the optimal working current of the photovoltaic cell module; Kop is the slope correction coefficient; Cz is the correction coefficient, which is mainly the loss of combination, attenuation, dust, charging efficiency, etc., and is generally taken as 0.8.

③ The shortest interval days Nw between the longest continuous cloudy and rainy days between the two groups, the main consideration is to supplement the lost battery power during this period. The battery capacity to be supplemented is:

Bob=A×Q1×N1     (1-5)

④Calculation method of parallel number Np of photovoltaic cell modules

Np=(Bob+Nw×Q1)/(Qp×Nw)     (1-6)

Equation (1-6) shows that: the number of photovoltaic cell modules used in parallel, the power generated in the shortest interval between the two groups of consecutive rainy days is not only used by the load, but also needs to make up for the battery’s loss in the longest continuous rainy days. .

⑤Power calculation of photovoltaic cell array

According to the series and parallel number of photovoltaic cell modules, the power of the required photovoltaic cell array can be obtained:

    P=Po×Ns×Np          (1-7)

In the formula, Po is the rated power of the photovoltaic cell module.

⑥Calculation result

Since the photovoltaic panel not only needs to charge the battery, but also provide the required power to the load, so the photovoltaic cell array with the power P is selected, and the Ns photovoltaic panels with the rated power Wp are required to be connected in series, and the Np blocks must be connected in parallel.