Considerations on Series Design of Photovoltaic Modules (Part 2) - Changes to Traditional Designs
Introduction: In the "Thoughts on the Series Design of Photovoltaic Modules (1)", the author shared the traditional way of designing photovoltaic string strings. However, some calculation errors tend to occur in traditional designs. Today, the author will analyze these errors and propose relevant improvement ideas.
In traditional designs, calculation errors occur.
1, the error caused by the temperature value
Since extreme cold temperatures are the lowest values ​​of ambient temperature throughout the day, the component temperatures during operation should be higher than this value. Therefore, the N1 result above will be low.
Assuming that the minimum ambient temperature is -30°C throughout the day, it certainly appears during non-operating nights; if the extreme low temperature during daytime operation is above -18°C, N1≤23 is calculated and 23 strings can be used for each string. The program.
Therefore, if you use the extreme cold temperatures for the daytime, the number of strings in each string may increase.
2, the value of open circuit voltage
In the calculation of "Example 1", Voc is taken as the open circuit voltage at the nominal power, that is, the open circuit voltage at 260 W. At this time, the irradiance is 1000 W/m2.
However, when the irradiance = 1000W/m2, it must be around noon, and certainly no extreme low temperature. From the IU curve in Fig. 2, it can be seen that when the irradiance decreases, the open circuit voltage changes slightly but still decreases slightly.
Figure 2 IU curve of photovoltaic modules
The component parameters in Table 1 are divided into STC conditions and NOCT conditions. Under the condition of NOCT, if the irradiance is 800W/m2, although extreme low temperature will certainly not occur at this time, relative to the irradiance=1000W/m2, the parameter values ​​are relatively more accurate. According to Table 1, when using the post-correction method to perform the string design of "Example 1", the values ​​of each quantity are as follows:
Table 3 Corrected Voltage Values
The results are shown in the table below.
It can be seen that when the other conditions are exactly the same, the correction method is used to calculate. The calculation result of "Example 1" is: open circuit voltage: N1 ≤ 24; MPPT voltage: 17 ≤ N2 ≤ 25, and the final series number is taken as 24.
Of course, if the irradiance is 800W/m2, the possibility of extreme low temperatures is also relatively small. If the irradiance = 200W/m2 component parameters, the calculation results should be more accurate; but after correction, the 260W components In the case of extremely low temperature ≥ -30°C, it is feasible to use 24 components per string.
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