A solar balance of system (BoS) encompasses several elements that play a significant role in ensuring smooth and efficient transmission and delivery of power by a solar module. Cables, connectors and junction boxes are key elements of the BoS. The photovoltaic (PV) junction box is an enclosure on the module where the PV strings are electrically connected. The presence of diodes in junction boxes ensures that the flow of power remains unidirectional, preventing power from feeding back into the panels. Diodes also prevent damage and corrosion of the module and counteract low efficiency outcomes. While there are several types of junction boxes in the market, next generation technologies are rapidly being adopted in the form of smart junction boxes and auto cut-off junction boxes. These technologies are in the research and development stage and can be expected to be developed over the coming few years. Renewable Watch looks at the upcoming trends, challenges and recommendations for the market of junction boxes, cables and connectors in India…
Upcoming changes in the segment
The solar market is expected to witness the onset of higher efficiency PV modules with 600 W plus capacity soon. With such advancements in the wattage of modules, the type and quality of junction boxes required in the market would need significant improvements. Junction boxes would also be required to support the increasing capacity of string inverters and central inverters. Further, bigger installations due to increased module Pmax are also expected in the coming months. This can potentially improve return on investment and levellised cost of energy. Better quality junction boxes and connectors would also lead to lower overall operations and maintenance activities and project execution time.
Split junction boxes are slowly replacing traditional/conventional four-rail junction boxes in higher wattage modules with double glass or twin type assemblies. When the wattage increases, more rated current is required from split junction boxes and their diodes to meet the module current requirement. Split junction boxes also save cable lengths, thereby reducing product cost, lowering module losses and increasing performance efficiency. Over the coming years, junction boxes are expected to entail enhanced carrying capacity for PV connectors.
Increased insulation thickness for solar cables may also make them relatively longer lasting. Compact and robust designing of BoS elements would also lead to increased efficiency and optimised costs. Compact structures can reduce the shading effect on the rear side of bifacial modules and allow usage of an optimal volume of silicone glue inside the junction box, enabling an overall reduction of PV model cost. Usage of integrated module type dual chip diodes, which have superior heat dissipation abilities and excellent switching responses over conventional diode packages, can be expected. Cables and connectors that meet lower contact resistance requirements can reduce module losses. Proven and advanced grade engineering plastics may be widely used for better performance under harsh environmental conditions.
Potential modes of failure
There exist several scenarios in which junction boxes, cables and connectors may fail or underperform. Bypass diodes and junction boxes can burn due to lightning strikes and other secondary surge impacts. PV connectors may get burnt due to poor crimping out of unauthorised and manual rework. Partial or incomplete mating of counterparts during commissioning can also lead to failure of PV connectors due to burns. Another potential risk is the cross-mating of PV connectors, which may lead to high contact resistance. Improper connections caused by tightening issues during rework is also a cause for concern. While over-tightening leads to stress on the module, under-tightening may create IP issues. Solar cables may also get damaged due to sharp edges.
Technical specifications and recommendations
There are several technical specifications that can be taken into consideration to improve the output of solar modules. Ensuring the availability of connectors in a pre-assembled state would greatly ease the assembly at site in case of any rework activities. Certain parameters such as the use of material grade equipment with advanced grade engineering plastics are also recommended. Double insulation and EBM cross-linked cables and wires may be utilised for better product life and performance in harsh conditions. Finally, upgrading the product licences of junction boxes, connectors and cables to the latest available versions is important. Fine-tuning test specifications according to the respective IEC standards can ensure better product reliability and life cycle. All components must be tested and certified as per established international standards. n
Based on remarks by Manjunath Reddy, Managing Director, DhaSH PV Technologies Private Limited, at the “BoS for Solar Power Plants” virtual conference organised by Renewable Watch