Capacity design of solar cell module

The solar cell module is the core part of the solar power generation system and the most valuable part of the solar power generation system. It can convert the sun’s radiant energy into electric energy, or send it to the storage 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 across 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 also be included in the future. A standard module of a crystalline silicon cell includes 36 cells, which enables a solar cell module to generate a voltage of approximately 17V. When the application system requires higher voltage and current components, multiple components can be formed into a solar cell square array to obtain the required voltage and current.

Calculation method of solar cell module output

The output of the solar cell module refers to the situation under the standard state, but in actual use, the environmental conditions such as sunshine cannot be exactly the same as the standard Zhuangjie. Then, how to use the rated output of solar cell modules and meteorological data to estimate the daily output of solar cell modules under actual conditions? Usually, the method of peak hours is used to estimate the output of solar cell modules. The actual solar radiation on the inclined surface can be converted into the equivalent standard solar radiation. 1000W/m2 is the standard radiation used to calibrate the power of solar cell modules, so an average radiation of 6.0kw·h/m2 in a certain place is basically equivalent to solar cell modules irradiated with standard radiation for 6 hours. For example, the monthly average daily radiation dose on a slope with an inclination of 40 in a certain area is 60kw·h/m2, which can be written as 6.0hx1000W/m2. For a solar cell module, Imp (optimal working current) is 5A, so the ampere-hours of power generation per day is 6×5A=30A·h/day.

The above method uses the peak hour calculation method. This method has certain deviations due to the following reasons.

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

②In the peak hour method, the total solar radiation measured in the meteorological data is used. In fact, in the early morning and dusk of every day, there is a period of time because the radiation is very low, and the voltage generated by the solar cell module is too small to supply the load or charge the battery, which will cause the estimate to be too large. However, in general, the above-mentioned error does not affect normal use.

What is given above is only the basic estimation method of capacity, there are many performance parameters in actual situation that will have a great influence on capacity (design). When designing a 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.

Working voltage of independent photovoltaic system

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

①The DC load voltage is usually a multiple of 12V or 12V, such as 24V, 36V, 48V, etc. For a DC system, the system voltage should 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 largest current as the system voltage. When the voltage required by the load is inconsistent with the system voltage, a DC-DC converter can be used to provide the required voltage.

③The vast majority of AC loads of independent photovoltaic systems work at 120V.

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