**The number of solar cell modules in series N**_{s}

_{s}

The required working voltage can be obtained by connecting the solar cell modules in series according to a certain number, but the series number of the solar cell modules 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 solar cell array cannot charge the battery. If the number of series connection is too large, the output voltage is much higher than the floating charging voltage of the battery, and the charging current of the battery will not increase significantly. Therefore, the best state of charge can only be achieved when the terminal voltage of the solar cell module is equal to the appropriate battery float voltage.

N_{s}=V_{R}/V_{oc}=(V_{F}+V_{D} +V_{C})/V_{oc } (1-1)

In the formula: V_{R} is the minimum output voltage of the solar cell array; V_{oc} is the optimal working voltage of the solar cell module; V_{F} is the floating charging voltage of the battery. 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; V_{D} is the diode voltage drop, generally 0.7V; V_{C} is the voltage drop caused by other factors.

**The number of solar cell modules in parallel ****N**_{p}

_{p}

Before determining N_{p}, determine the calculation method of its correlation quantity.

(1) Convert the solar solar radiation H_{t} at the installation site of the solar cell array into the average daily radiation hours H under standard light intensity

H=H_{t}×2.778/10 000h (1-2)

In the formula: 2.778/10 000 (hm^{2}/kJ) is the coefficient of converting the daily radiation amount to the average daily radiation hours under standard light intensity (1000w/m^{2}).

(2) Daily power generation Qp of solar cell modules

Q_{p}=I_{oc}×h×K_{op}×C_{z} (1-3)

In the formula: I_{oc }is the optimal working current of the solar cell module; K_{op} is the slope correction coefficient, and the correction coefficient K_{op} is 1.09~1.14 according to the solar cell module installation latitude and different slope daily radiation; C_{z} is the correction coefficient, mainly for combination, attenuation , dust, charging efficiency and other losses, generally take 0.8.

(3) The shortest interval days NW between the two longest consecutive rainy days, this data mainly considers the capacity B_{cb} to be supplemented by the battery during this period

B_{cb} =A×Q_{1}×N_{1} (1-4)

In the formula: A is the safety factor, which is 1.1~1.4; Q_{1} is the daily power consumption, which is equal to the working current multiplied by the daily working hours; N_{1} is the longest continuous rainy days.

(4) Number of parallel connections of solar cell modules N_{p}

N_{p}=(B_{cb}+N_{W}×Q_{1})/(Q_{p}×N_{W}) (1-5)

The expression of the above formula means the number of parallel solar battery groups, and the power generated in the shortest interval between two consecutive rainy days is not only used by the load, but also needs to make up for the loss of power in the longest continuous rainy days.

(5) Power calculation of the solar cell array. According to the number of series and parallel of solar cell modules, the required power P of the solar cell array can be obtained.

P=P_{0}×N_{s}×N_{p} (1-6)

In the formula: P_{0} is the rated power of the solar cell module.

The basic idea of solar cell module design is to meet the electricity demand of the annual average daily load. The basic way to calculate a solar module is to divide the energy (Ah) required by the load on an average day by the amount of energy (Ah) that a single solar module can produce in a day. In this way, the number of solar cell modules that the system needs to be connected in parallel can be calculated, and the current required by the system load can be generated by using these modules in parallel. By dividing the nominal voltage of the system by the nominal voltage of the solar cell module, the number of solar cells required in series for the solar cell module can be obtained, and the solar cell module can generate the voltage required by the system load. The output of the solar cell module will be reduced by some external factors. The solar cell module calculated according to the above basic formula usually cannot meet the electricity demand of the solar LED lighting system in practice. In order to get more correct results, it is necessary to revise the above basic formula, which will be introduced in the next article.