What are the electrical performance of photovoltaic modules?
Early photovoltaic power generation mainly adopted the off-grid power generation mode, and only the DC power supply demand needs to be considered. Generally speaking, 36 crystalline silicon cells connected in series can output an operating voltage of 18V and can charge a 12V battery, and 72 crystalline silicon cells connected in series can charge a 24V battery. Modern large-scale photovoltaic power generation mainly adopts the grid-connected mode, and the mainstream products are mostly modules composed of 60 and 72 cells in series.
The output current of a crystalline silicon cells changes linearly with the light intensity, and its voltage is slightly affected by the light intensity. A piece of 125mm×125mm crystalline silicon cells can reach a working current of more than 5A, while a piece of 156mm×156mm battery can reach more than 8A. Usually, the cells in the crystalline silicon module are connected in series. It should be noted that the consistency of the electrical performance of crystalline silicon cells is very important to the performance of the module. Only crystalline silicon cells with the same electrical properties can be connected in series or parallel. Here, two cells are taken as an example to introduce the electrical performance of photovoltaic modules.
(1) The performance of the two batteries is exactly the same, that is, V1=V2, I1=I2, then after the two batteries are connected in series, the total voltage V=V1+V2, the total current I=I1=I2, it can be seen that the voltage is simply superimposed, and the current is The current of a monolithic battery.
(2) The performance of the two batteries is different, that is, V1=V2+Δ1, I1=I2+Δ2, then after the two batteries are connected in series, V=V1+V2, and the total current I is equal to the minimum current, which can be approximated as I= I1; (assuming I1, the smallest). In this case, the circuit loss of the component is relatively large.
Therefore, in a module with batteries in series, the module voltage is the sum of all battery voltages, and the battery with the smallest output current limits the total output current of the module. Since there are more or less differences in electrical performance between each cell, and the performance of the cell will also change during use, it is necessary to select solar cell components with consistent performance parameters to reduce current mismatch. Loss.
In addition, in the module production process, the increase in power consumption of interconnection bar resistance, solder, etc. caused by high current is also a problem that cannot be ignored, so the advantages of using small-area batteries in series to form modules are obvious. In recent years, some manufacturers have introduced half-slice battery modules, which can reduce current consumption and increase module power. However, the half-slice battery will cause the connection points in the module to increase exponentially, and if it is not handled well, it will cause reliability problems. Therefore, comprehensive consideration is needed to optimize the selection during component production.
