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Capacity design of solar cell module

2021-09-24 18:36:17

Solar cell module is not only the core part of solar power generation system, but also the most valuable part of solar power generation system. It can convert the radiant energy of the sun into electric energy, or send it to the battery for storage, or drive the load to work; In addition, as the light control element of the system, the solar cell can detect the outdoor brightness according to the voltage at both ends of the solar cell, that is, judge the darkness and dawn according to the voltage of the solar cell. At present, solar cells are mainly crystalline silicon cells, and thin-film solar cells will be included in the future. A standard module of crystalline silicon cell includes 36 monomers, so that a solar cell module can produce a voltage of about 17V. When the application system needs higher voltage and current components, multiple components can be formed into a solar cell array to obtain the required voltage and current.

 

Calculation method of solar cell module output

The output of solar cell module refers to the situation under the standard state, but in actual use, sunshine and other environmental conditions cannot be exactly the same as the standard state. Then, how to use the rated output of solar cell module and meteorological data to estimate the daily output of solar cell module under the actual situation? The output of solar cell modules is usually estimated using the peak hours method. The solar radiation on the actual inclined plane can be converted into equivalent standard solar radiation. 1000W/m² is the standard radiation used to calibrate the power of the solar cell module. Then the average radiation of a place is 6.0kW · H/m², which is basically equivalent to the solar cell module irradiating for 6h under the standard radiation. For example, the monthly average daily radiation on an inclined plane with an inclination of 40 in an area is 6.0kW · H/m², which can be written as 6.0h × 1000W/m². For a solar cell module, if Imp  (optimal working current) is 5A, the ampere hours of power generation per day is 6 × 5A = 30A · H / day.

 

The above is the peak hour calculation method, which has some deviation for the following reasons.

 

① The temperature effect of solar module cell output is ignored in this method. The temperature effect has a greater impact on the output of solar cell modules with fewer cells in series than on the output of solar cell modules with more cells in series. It is more accurate for 36 solar cell modules in series, but it is poor for 33 solar cell modules in series, especially in high temperature environment. For all solar cell modules, the prediction in cold climate will be more accurate.

② In the peak hour method, the total solar radiation measured in the meteorological data is used. In fact, in the early morning and evening of each day, the voltage generated by the solar cell module is too small to supply the load or charge the battery because the radiation is very low, which will lead to excessive estimation. However, in general, the above errors do not affect normal use.

 

The above is only the basic estimation method of capacity. In practice, many performance parameters will have a great impact on capacity (Design). During the design of photovoltaic system, professional software can be used to assist the design. If used properly, it can greatly reduce the amount of calculation, save time, and improve efficiency and accuracy.

 

Operating voltage of independent photovoltaic system

The selection of the operating voltage of the independent photovoltaic system depends on the voltage and current required by the load. If the system voltage is set equal to the maximum load voltage, these loads can be directly connected to the output of the system. However, for any part of the system with a limited current of 100A, the current in any power circuit shall be less than 20A to ensure safe use; If the current is lower than the recommended value, standard and ordinary electrical equipment and wires can be used. When the load needs AC power supply, the DC system voltage shall be determined according to the characteristics of the inverter. Some basic rules are as follows

 

① DC load voltage is usually 12V or multiple of 12V, such as 24V, 36V, 48V, etc. for DC system, the system voltage shall be the voltage required by the maximum load. Most DC photovoltaic systems are less than 1kW at 12V.

② If the load requires different DC voltages, select the voltage with the maximum current as the system voltage. When the voltage required by the load is inconsistent with the system voltage, the DC-DC converter can be used to provide the required voltage.

③ Most AC loads of independent photovoltaic systems work at 120V.

 

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