Multistage PV Combiner Box Layout for Lower DC Cable Cost
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Solution Overview
Problem
The high cost of direct current cables in photovoltaic systems is a significant issue due to the large physical area occupied by combination groups and the extensive use of cables, which account for a substantial portion of the total system cost.
Innovation Solution
A photovoltaic system is designed with a multistage combiner box setup, dividing the photovoltaic array into multiple combination groups, where outputs of photovoltaic strings are combined through a single cable, reducing the total length and cross-section of cables, and arranging combiner boxes to minimize cable usage and improve failure resilience.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If each photovoltaic string is connected to the combiner box through separate direct current cables, then the connection is simple and reliable, but the total length and cost of cables increase significantly
Solution Approach 1:
The patent divides the combination group into multiple sub-combination groups, each with its own sub-combiner box. This segmentation allows cables to be bundled at the sub-combiner level rather than having separate cables from each photovoltaic string to the main combiner box, significantly reducing total cable quantity while maintaining connection reliability through modular architecture.
Solution Approach 2:
The patent merges multiple cable connections at the sub-combiner box level, where multiple photovoltaic strings within a sub-combination group are combined through a single cable to the sub-combiner box. This merging approach reduces the number of cables required compared to individual string connections, while the hierarchical structure ensures reliability is maintained.
2Productivity
If the combination group occupies a large physical area to accommodate multiple photovoltaic strings, then the system capacity increases, but the cable length and cost increase proportionally
Solution Approach 1:
By segmenting the large combination group into smaller sub-combination groups with distributed sub-combiner boxes, the patent reduces the average cable length from each photovoltaic string to its nearest sub-combiner box. This segmentation allows the system to maintain high capacity across large areas while minimizing total cable length through localized combining points.
Solution Approach 2:
The patent introduces a hierarchical spatial structure with multiple levels (photovoltaic strings → sub-combiner boxes → main combiner box). This dimensional organization allows efficient cable routing at each level, reducing the overall cable length required to connect a large number of photovoltaic strings across a large physical area.
3Quantity of substance
If a single cable combines multiple photovoltaic string outputs at the combiner box, then cable cost is reduced, but the cable cross-section must be larger increasing line loss
Solution Approach 1:
The patent segments the cable combining process into multiple stages: first at sub-combiner boxes where fewer strings are combined, then at the main combiner box where sub-combiner outputs are combined. This segmentation allows each cable to carry smaller currents, enabling the use of smaller cross-section cables that incur lower line losses, while still achieving overall cost reduction through reduced cable quantity.
4Device complexity
If the combiner box combines outputs from all photovoltaic strings directly, then the system structure is simple, but failure impact is magnified across the entire system
Solution Approach 1:
The patent segments the combining function into distributed sub-combiner boxes, creating a hierarchical structure where failures are contained within individual sub-combination groups. This segmentation maintains relatively simple system structure while significantly improving reliability by preventing single-point failures from affecting the entire system.
Solution Approach 2:
The patent implements local combining at sub-combiner boxes for each sub-combination group, where each local unit operates independently. This local quality approach ensures that failures in one local unit do not propagate to other units, improving overall system reliability while maintaining a structured and organized system architecture.
Data Source
AI summary
A photovoltaic system and a method for determining a combiner box set for the photovoltaic system are provided. The photovoltaic system includes a photovoltaic array divided into at least two combination groups, a photovoltaic converter, and a combiner box in at least one nonfinal stage and a combiner box in a final stage for each of the at least two combination groups. A direct current side of the photovoltaic converter is electrically connected to an output terminal of the combiner box in the final stage. The combiner box in the final stage and the combiner box in the at least one nonfinal stage are configured to combine outputs of photovoltaic strings in the combination group. Each combiner box combines multiple cables into a single cable.