Selection of the number of collector box circuits in photovoltaic power plants.

Selection of the number of collector box circuits in photovoltaic power plants.

The commonly used method for photovoltaic power stations is to use a two-stage combiner: the photovoltaic string is first converged through the combiner box, and then converged to the DC distribution cabinet (or the DC side inside the inverter).

The selection of the number of circuits in the combiner box varies for different projects, and the design plan for large-scale photovoltaic power station arrays mainly selects 16 circuit combiner boxes. The above plan is now widely applied to photovoltaic power stations in various terrains, landforms, and climatic conditions in China. Comparative analysis of the number of circuits for shortage. This article will analyze and compare the following models in theoretical state (natural terrain at zero degrees) and field state (with relevant design values based on practical engineering values of a mountainous photovoltaic power station):

Unit MWp photovoltaic array. Latitude of the photovoltaic array: 23 °; The photovoltaic module consists of 60 pieces of polycrystalline silicon 250W modules, with Vmppt=30.7V and Impt=8.15A; 22 sets of strings are selected, and 182 sets of strings are connected in parallel; Select 1 × 4mm22 cable from the component to the combiner box; 8 and 16 circuit combiner boxes are selected for the combiner box, with corresponding quantities of 24 and 12 units. The cable cross-sections for the outlet of the combiner box are 1 × 35mm22 and 1 × 70mm22, respectively.
To simplify the model in the analysis, this article takes photovoltaic modules as the desired current source, where the voltage is constant and the current varies with environmental parameters.
After consulting the corresponding parameters and using classical theoretical formulas for calculation, the conclusion is as follows:
1) In theoretical state, when the calculation diameter is consistent, the theoretical loss of the selected combiner box is not significantly different from the selection of the combiner box. Considering the differences between cable parameters and practice, it can be considered that the theoretical loss is consistent in various states.
2) In the actual state, the connection length of the cable increases significantly under chaotic terrain conditions, therefore, compared to the theoretical state, the cable loss increases significantly. Due to the large installation range of multi circuit combiner boxes, the cable loss of multi circuit combiner boxes is significantly greater than that of circuits.