A rise in the uptake of good quality solar power projects is expected in India. To this end, there is growing demand for quality balance-of-system equipment, with an increasing number of projects being installed across the country. In particular, cables and connectors form a crucial supporting network in the solar power generation set-up. Since such systems comprise a large number of electrical connections, they are also vulnerable to energy losses at contact points. To limit these losses, long-lasting and secure cable connections with low contact resistance are required. Meanwhile, connectors are needed to facilitate and ease the installation process.
Although these components account for a small share in the total capital cost, the cost of frequently replacing them can add up to a significant amount over the life of the solar plant. Thus, proper selection and sizing of cables and connectors is important for optimising costs and for ensuring a well-functioning system.
Overview of solar cables
Cables are used to transmit power. There are two types of cables used in solar power plants – direct current (DC) and alternating current (AC). DC cables directly connect solar panels to junction boxes or inverters. They can be of three types – earth wires, single-core wires and twin-core wires. Special extension cables are used to connect the positive and negative cables to the junction box (or directly to the solar power inverter). To avoid earth faults and short circuits, the positive and negative wires should not be laid together in the same cable. Single-wire cables with double insulation offer high reliability. DC cables that connect modules as well as the junction box and the solar power inverter are two-core cables comprising a current-carrying live wire and a negative wire, which are protected by an insulation layer.
AC cables connect inverters to the substation. In India, electricity is more commonly transmitted in AC form. Thus, inverters are used to convert DC power into AC. Solar systems with single-phase inverters require three-core AC cables, and those with three-phase inverters require five-core AC cables.
Companies specialising in solar cables adhere to certain standards for E-beam cross-linking, special purpose compounding solutions (for sheathing and insulation), conducting material, testing and certification. Since a solar plant, along with cables, has to function in an open environment over a long period, it should be able to withstand severities such as ultraviolet radiation, rain, dust, temperature variations, humidity and insects. Further, these plants have to withstand mechanical stress due to pressure, bending or stretching experienced during installation, as well as chemical stress caused by acids, alkaline solutions and salt water.
Frequent failure on part of solar cables decreases overall project efficiency. Therefore, it is crucial to ensure their successful functioning over the desired lifespan. For the optimal performance of solar systems, solar cable accessories, connectors and crimping tools are used to allow fast and error-free installation. As solar projects have a minimum life of 25 years, the components used for solar projects are also expected to last that long.
Material and design for cables
It is important to use correctly sized solar cables when connecting the various components of a solar photovoltaic (PV) system. This ensures that there is no overheating and limits the loss of energy. Undersized cables can be fire hazards. When choosing the size of the wire, the generation capacity of the solar panel and the distance between the panels and the load need to be taken into account. Cable sizes will increase with any increase in these two factors. The risk of loss is greater in the case of AC cables as compared to DC ones. DC main cables are designed to ensure that the generation loss is lower than 1 per cent of the peak power output from the solar project. This requires cables to have a low ohmic resistance.
Besides length and cross-section area, this resistance depends on the material used in making these cables. Typically, aluminium and copper are used to make solar cables. Copper has lower resistance than aluminium at a given temperature. Further, aluminium is a lighter and cheaper alternative for making cables than copper. The insulation and the sheath have to perform at a higher temperature range. They require high mechanical stability and flame retardation, and should be free of halogens. To meet these requirements, cross-linked polyolefin copolymers can be used.
Overview of solar connectors
Connectors used in solar power plants play an important role in facilitating connectivity throughout the system and preventing misconnection. This helps in avoiding loose cable ends, which can lead to energy losses and other performance issues. Thus, connectors provide secure and touch-proof connections between components. Many different versions of connectors or standard non-connector junction boxes are used in solar plants throughout the industry.
Similar to cables, connectors are exposed to harsh environmental conditions and mechanical stress. They should be able to withstand adverse conditions without getting disconnected. Hence, secure connections that can conduct current fault-free over a period of 25 years are required. These connectors should be able to meet the voltage and current requirements. They should have low contact resistance and firm locking mechanisms.
Every connector needs a cable coupler. Crimping the cable coupler is an important part of connecting modules in a solar PV system. If crimping is not done properly, resistance would be higher, which would significantly reduce efficiency. Thus, crimping has emerged as a safe solution for attaching connectors to cables, and is being used for on-field and pre-assembled connections. Connectors could either be pre-installed on solar panels, or installed on-site. Installing them on the field requires the end panels to be connected to an inverter or a combiner box. In microinverter projects, connections are made between solar panels and the microinverter. They usually have pre-installed cabling, and there are no field connections. Traditionally, screw terminals and spring clamp connectors have been used in solar applications. However, simple shock-proof plug connectors are rapidly taking their place. Plug connecters and sockets with welded cables and pre-assembled circular connection systems are also being used to save time and labour costs.
The restrictions imposed due to the pandemic disrupted the supply chain across all manufacturing industries. While the Covid-19 pandemic had an adverse impact on the cables and connectors market, it is not expected to dampen the sector’s long-term growth. Of late, inflation – particularly the rising cost of metals, electronics and fuel due to the Ukraine-Russia war – and supply chain restrictions on select cities in China have emerged as new challenges. Within the solar sector, a significant price rise has been witnessed for solar modules, which has impacted the financial viability of entire solar projects. It remains to be seen if the price of solar cables and connectors will also rise because of the geopolitical tensions at play currently.
The market for cables and connectors has been growing with the rapidly expanding solar segment. As per an industry report, the global market for solar cables reached a valuation of $613.3 million in 2019. It is expected that the market will grow at an average annual growth rate of about 7.7 per cent to reach nearly $823.7 million by 2025. The scaling up of the industry is expected to drive down costs, although this is subject to raw material availability. Innovations in technology are also expected to improve the quality of equipment. The emergence of floating solar projects, hybrids, energy storage and smarter digital technologies will demand more innovation in the cables and connectors space. Going forward, the demand for different kinds of solar cables and connectors is also expected to evolve with the emerging needs and applications in the solar power space.