A bulk silicon photovoltaic module is composed of multiple independent solar cells, which are almost always connected in series to improve the power and voltage, exceeding a single solar cell. The voltage of photovoltaic solar panels is usually selected to be compatible with 12V batteries. Under 25 ℃ and AM1.5 lighting conditions, the maximum power point voltage of a single ordinary silicon (single crystal or polycrystalline) solar cell is about 0.5V, and the maximum power point voltage of a single high-efficiency silicon (Sunpower) solar cell is about 0.55V. Considering the expected drop in PV module voltage due to temperature, and the fact that the battery may require 15V or higher voltage to charge, most solar panels contain 36 solar cells in series. Thus, under standard test conditions, the open circuit voltage is about 21V, while the operating voltage under maximum power and operating temperature is about 17 or 18V. The remaining excess voltage is included to take into account the voltage drop caused by other elements of the photovoltaic system, including the operation away from the maximum power point and the reduction of light intensity.
The voltage of photovoltaic modules is determined by the number of solar cells, and the current of solar panels mainly depends on the size of solar cells. Under AM1.5 and optimum tilt conditions, the current density of commercial solar cells is about 30 mA/cm2 to 36 mA/cm2. Single crystal solar cells are usually 15.6 × 15.6 cm2, the total current of a solar panel is almost 9 – 10A.
The output of solar charging panel under STC has been tested before. Imp and Isc have little change, but Vmp and Voc increase with the increase of the number of solar cells in the solar photovoltaic system.
If all the solar cells in a solar panel have the same electrical characteristics, and they all experience the same sunshine and temperature, then all the cells will work at the same current and voltage. In this case, the IV curve of the PV module is the same as that of a single cell, but the voltage and current increase.
For a group of solar cells with the same connection, the total current is just the current of a single cell multiplied by the number of cells in parallel. thus. The total voltage is the voltage of a single cell multiplied by the number of cells in series.
If the solar cells are the same, the filling factor will not change when the cells are connected in parallel or in series. However, there is usually a mismatch in the cells, so when the cells are combined, the fill factor will decrease. The mismatch of the battery chip may come from the manufacturing, or from the light difference on the battery chip, that is, one battery chip has more light than the other.
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