With the advancement of technology and the popularization of photovoltaic power stations, the design of photovoltaic power station systems has matured. Among the system designs that we have widely adopted today, there are 24 modules in the southern region, 24 in the southern region, 22 in the north, 72 in the south, 20 in the south, and 18 in the northern region. However, our country is vast and diverse. The regional climate temperature is quite different. This author discusses its influence on the number of PV modules in series from the temperature factor.
We all know that the number of photovoltaic modules in series should be guaranteed to meet the inverter's DC MPPT voltage and maximum DC allowable voltage requirements. At present, the more commonly used centralized inverter model is 500kW, its MPPT voltage tracking range is 500~850V, and the maximum open circuit voltage is 1000V.
In the following, we will calculate the serial number of PV modules according to the calculation formula of GB 50797-2012 “Design Specifications for Photovoltaic Power Plants†with 60 pieces of 260W, 280W and 72 pieces of 305W and 325W photovoltaic modules from a certain manufacturer. The formula is as follows:
The author has selected 10 representative regions with large differences in temperature from south to north in China, and calculated the following results based on the above formula.
Table: Number of strings in 10 different regions
From the above table, the conclusions are as follows:
60 pieces of 260W modules can be connected in 22 series with extreme minimum temperature below -40°C, 23 series can be connected from -40°C to -7.5°C, and 24 can be connected in series at -7.5°C or above.
The minimum minimum temperature of 60 280W modules can be 21 in series below -27.5°C, 22 in series from -27.5°C to -12°C, 23 in series at -12°C to 2.7°C, and 24 in series at 2.7°C or above.
72 pieces of 305W components can be connected in series of 18 under the low temperature of -22°C, 19 in the range of -22°C to -4.5°C, and 20 in the -4.5°C range.
72 pieces of 325W modules have extremely low temperatures of 17 series below -32.5°C, 18 series of -32.5°C to -13°C, and 19 series of more than -13°C.
Under the premise of satisfying the MPPT tracking voltage and maximum open circuit voltage, the greater the number of series connections is, of course, the more economical.
However, the above calculations actually have certain problems. The temperature parameters usually obtain the years of observation data of the regional weather station where the power station is located. On the one hand, weather stations are generally located in urban areas, and large-scale photovoltaic power stations are mostly located in the wild, even in mountainous areas. The heat island effect is higher than 3~4°C in the wild. If the power station is located in the mountainous area, the temperature rises by 6.5°C for each elevation of 1000m. That is, the extreme air temperature at the site is lower than the weather station observation data;
On the other hand, the temperature in the calculation formula is the “limit temperature under the working conditions of photovoltaic modulesâ€, and the minimum temperature within one day appears at 4 o'clock to 8 o'clock before sunrise, and varies with the season, and during this time, the photovoltaic components It does not work. If the difference between the weather station and the photovoltaic site is not taken into consideration, the minimum temperature at the working conditions of the PV modules is slightly higher than the all-day minimum temperature at the weather station.
Therefore, the calculation of this paper can provide reference for everyone's theoretical data, but may vary slightly depending on the specific project conditions.
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