Solar cables are one of the most critical parts of a solar power plant as they connect the various equipment of solar power plants. For instance, they connect solar modules to inverters and inverters to batteries and other important components. A solar panel generates solar energy, but without solar cables to transport this power, it cannot reach its intended location. Therefore, it is essential to have solar cables for a solar power plant to function properly.
Since solar power plants are built to last 20 years or longer, it is crucial that all equipment, including cables and connectors used in these projects, is of top quality. Poor quality cables can cause frequent glitches in solar power plants and lead to an increase in equipment downtime, energy losses and overheating, impact durability and cause fires. Since solar power projects are exposed to natural elements such as rain, sun and wind, the cables used should be sturdy and capable of withstanding harsh weather conditions. Further, they need to be built of material that is flame retardant and ultra violet (UV) resistant.
As the safety of manpower and costly equipment deployed at solar power plants is of utmost importance, solar cables should be sized properly and designed with materials that can ensure reliable use in extreme weather conditions. Against this backdrop, this article discusses the key considerations for ensuring solar cable quality and the technology trends in the solar cable space…
Materials and design
A typical solar cable is made of three layers – conductor, insulation and sheath or outer jacket. The conductor is the innermost layer and is responsible for carrying electricity from solar panels to the inverter. It is made of conductive materials such as copper or aluminium. The insulation layer, made of cross-linked polyethylene or ethylene propylene rubber, surrounds the conductor layer and provides protection to the conductor to prevent energy loss. Finally, the sheath is made of polyvinyl chloride or halogen-free flame retardant and it forms the outermost protection layer for the cable.
There are different types of cables used in solar projects based on applications. Solar direct current (DC) cables are modules or string cables that are placed inside solar panels and come pre-installed in a solar panel. These single-core cables connect individual solar panels in strings, and have small diameters to cater to low voltages. Meanwhile, solar DC main cables connect junction boxes, which house multiple panel strings, to inverters. They are different from solar DC cables due to their larger diameters and higher voltage as they carry output from not one but multiple strings. They can be single-core with double insulation or twin-core cables. Finally, alternating current (AC) cables then connect solar inverters to the grid. They are similar to normal AC cables with five cores and are designed to handle the AC voltage of the power plant.
While copper and aluminium are largely used for making conductors for solar cables, they both have different advantages. Copper has greater conductivity and can carry more current than an aluminium one. However, copper wires are more expensive than aluminium wires.
There have been various innovations in the solar cable space to improve efficiency and reduce faults in cables. Thus, there has been a significant focus on improving cable insulation and conductivity. While neoprene-insulated cables were commonly used in solar power plants earlier; cable insulation is now made from electron beam, cross-linked polymers. These newer cables are more durable and are not susceptible to high levels of mechanical or thermal stress, unlike the earlier cables that would get damaged in harsh conditions.
Cable conductivity can also be improved by making them stranded. When compared to solid cables, stranded cables consist of many small wires and have a higher surface area. This increases the conductivity as current tends to flow on the outside of the wire.
Another popular trend, especially in large ground-mounted projects, is trenching and airborne cables. This protects cables from abrasion and other possible stresses and has also proven to be safer for the manpower working in solar projects. However, digging trenches for laying cables can lead to additional costs.
Solar cable characteristics
Solar cables are different from normal cables as they need to meet the challenging conditions at solar power project sites. The challenges are particularly significant in the case of utility-scale projects that are located in remote locations as compared to rooftop projects. Further, cabling can become more complicated in the case of floating solar projects, where cables would have to be installed underwater.
In India, the majority of solar projects are located in hot regions such as Rajasthan and Gujarat, where solar cables are exposed to extreme heat and high temperatures. Thus, it is necessary for these cables to withstand these hot conditions. In other sites, they should be able to withstand high moisture content or extreme cold temperatures. Another challenge can be in the form of chemical stresses such as acids, salt water or alkaline solutions, as well as mechanical stresses such as stretching, bending and compression. Thus, solar cables need to be sturdy to withstand not just weather-related phenomena but also other kinds of stress.
An ideal solar cable should have the following characteristics:
- Ability to withstand extreme temperatures and humidity
- Resistance to acids, alkalis and other chemicals
- High dielectric strength
- Flame retardant
- Halogen-free
- Ability to withstand mechanical stress
- Resistance to termites and rodents
- UV and ozone resistance
Cable selection and sizing
Voltage and current carrying capacity are of critical importance when selecting cables for a solar power project. Thus, cables should be capable of handling the voltage rating of solar projects to prevent overloads and should be designed to carry the maximum current output of these projects. They must be carefully selected to ensure there is no overheating or voltage drop due to technical reasons. While cables come in different sizes, cable sizing must account for the distance between equipment, apart from current and voltage ratings.
Other considerations when selecting cables and determining their sizing include the location of a project and the environment, as well as the geological conditions. Thus, factors such as temperature differences, humidity and chemical stresses need to be considered, to ensure appropriate insulation and sheathing.
Along with cables, connectors are also required to provide proper connections and prevent faults, and therefore, need to be carefully selected. Like cables, these connectors must be able to meet the voltage and current requirements and provide firm locking mechanisms. Connectors can be installed on-site or they can even be pre-installed on panels to save installation time.
After the proper selection of cables and connectors, it is equally important to install them properly to prevent accidents or faults and ensure overall project safety. Thus, both cables and connectors must be secured properly and monitored regularly for any possible leakage or failure. Although cables are designed with quality materials and should last for long periods of time, they can be damaged by extreme temperature differences, moisture and mechanical stresses. Thus, they need to be checked routinely and replaced in case of wear and tear.
Conclusion
As India’s solar power market continues to grow, so does the demand for quality cables and connectors. While cable technology is mature and well established, it is critical to ensure that cables are made with top insulation materials, carefully selected and sized according to the project’s technical requirements, installed with all safety considerations and routinely monitored for optimum performance.
