The Indian solar segment is growing fast and has ambitious targets ahead. With a bustling solar market in the country, developments related to components such as solar inverters have become crucial to achieve greater output from solar installations. The power grid often experiences rapid fluctuations in voltage and frequency, and high levels of harmonic content. This, in turn, impacts power quality. Efficient solar inverters become all the more useful in such a scenario. With technical advancements, increasing modularity and smart technology being implemented in inverters, these devices are becoming smarter, and more capable of handling grid disturbances and optimising power output.
Solar inverter technologies have been evolving over the years. While the central inverter technology was dominant during its formative years, especially in the utility-scale segment, the growth of rooftop solar gave a push to string inverters. These are increasingly finding application in the utility segment as well. While the installation cost of string inverters is higher than that of central inverters, greater modularity allows for lower maintenance costs. The modularity of string inverters offers easy repair and replacement, as any defect in one string of solar panels or one string inverter does not impact other solar panels, thereby reducing project downtime.
With evolving technology, microinverters are a step ahead in modularity. Since these function at the panel level, defects are also dealt with at the panel level with others not being affected. Further, any obstruction or shading on any panel only impacts the associated inverter and not the entire array. These advantages offset the higher cost associated with a greater number of microinverters, in turn, making the system more reliable.
String inverter advancements
Since their arrival in the market, string inverters have constantly evolved to incorporate improvements along the way. For instance, string inverters’ maximum power point tracking (MPPT) software has become better over the years, significantly reducing the power loss from partial shade compared to its earlier versions. Other developments are also taking place for string inverter applications. For instance, the power grid structure in many regions is split phase. Recently, Solis explored the possibility of connecting a single-phase inverter to the grid in the absence of a split-phase inverter while installing a solar PV system. For this, the 120 V/240 V split phase was considered. The 120/240 Vac split phase is a type of single-phase three-wire mid-point neutral power distribution system commonly found in America with a standard phase-neutral voltage of 120 Vac for residential and light commercial applications. As per a study by Solis, while a single-phase inverter can be connected to the split-phase power grid, it is only an emergency solution for extreme circumstances.
An on-grid or grid-tied solar inverter operates with electricity from the grid. Meanwhile, an off-grid solar inverter or a standalone solar inverter is an independent system, which has battery backup and can work without the grid. A hybrid inverter is the combination of an on-grid and off-grid solar inverter. In addition to converting DC into AC, it stores excess power in its batteries. Since intermittency is a concern with solar energy, these inverters have very useful applications. Such inverters work without a grid, store electricity in batteries and export the excess electricity to the grid. These are especially useful in areas with unreliable grid power.
Common hybrid inverters may have some limitations in terms of their ability to handle limited surge as well as restrictions in backup power. However, hybrid inverters can also be used in combination with high voltage batteries to create systems integrating power generation with energy storage. For example, Ingeteam’s hybrid inverter, in combination with batteries, allows for operation in off-grid, backup and self-consumption modes. Thus, the solar energy generated during the day can be stored for night-time consumption, for grid-connected systems, giving the highest possible self-consumption ratios. Moreover, the possibility of operating in back-up mode enables power supply to be maintained in the event of grid outage.
Hybrid inverters use simple energy meters to measure electricity consumption and can have integrated software, which can be programmed to efficiently utilise available solar energy. Intelligent hybrid inverters are emerging as an essential component for synchronising energy consumption and production through the integration of energy storage.
To increase output, especially in small-sc-ale solar installations, microinverters are increasingly becoming a popular option. Microinverters, which are installed under solar panels, perform the same function as string inverters although on a different scale. Some microinverters support two to four solar panels while others support one panel each. Thus, a solar panel installation with microinverters could even have the same number of microinverters as solar panels.
Standard string inverters usually limit the electricity production of each panel by the lowest producing panel in the system. Since microinverters function in a parallel circuit, this limit is not an issue. This feature of microinverters is particularly useful in installations where solar panels face in different directions or are partially covered by shade, thus resulting in different panels producing slightly different currents. Microinverters have several other advantages. Being small in size, these inverters can be fitted at the back of solar panels, and do not even require air cooling unlike central inverters. Their modularity ensures low maintenance and operations costs along with monitoring of output. This, in turn, facilitates the isolation and early rectification of faults. Microinverters also have a rapid shutdown capability embedded in each module, so that first responders and firefighters are safe from high voltage. Despite numerous advantages, the high cost of microinverters has limited their uptake. However, with increasing popularity, their prices are expected to reduce considerably.
Power optimisers for inverters are able to make the voltage even and combat production differences, leading to enhanced solar power output. Microinverters with add-on power optimisers have the ability to track the production of each individual panel, while a standard inverter only allows tracking the production of the whole system. Another key trend in the solar inverter space is the development of smart modules. A smart module is a solar module with an integrated power optimiser embedded in the junction box. In spite of its potential, the uptake of this technology is currently restricted to small-scale projects only.
Smart technology, with smart inverters in particular, are a ground-breaking trend in the solar inverter segment. This is in line with the trend of automation in renewable energy components across the sector. The efficiency gains offered by smart technology are indeed promising. Such inverters can play a key role in stabilising the grid as more distributed solar systems come online.
Smart inverters have an integrated digital architecture and a robust software infrastructure. With their bidirectional communications ability, smart inverters are can have a two-way communication with the grid instead of just feeding power into it. Such inverters can be adaptive, and send and receive messages quickly as well as share granular data with the owner, utility and other stakeholders. This can be useful in diagnosing operations and maintenance issues, and remotely upgrading certain parameters at short notice. The intelligent power electronics can also include the application-programming-interface functionality that provides owners and other partners a way to tie in their own software to create tools.
Smart microinverters combine the advantages of microinverters with smart technology thus offering a unique value addition. Such integrated microinverter systems can help reduce the levellised cost of energy, increase energy production over the lifetime of the system, and increase system uptime. They are also capable of providing advanced grid support functions related to voltage, frequency, communications and controls for grid stability. Instead of simply shutting down upon sensing grid disturbances such as voltage or frequency fluctuations, smart inverters are programmed to respond to the grid in an automated way. This is especially helpful in avoiding too many inverters connected to the grid from tripping. Software-controlled microinverter systems provide grid support services throughout the lifetime of the inverter platform by way of software updates that can be done without any hardware replacement or truck-rolled, hands-on labour.
Solar inverters can be expected to witness continuous improvement in the growing solar market. Earlier, the demand for inverters was largely driven by the utility segments, whereas now its scope in the commercial and industrial as well as residential rooftop segments is now widening. This is expected to be further supported by advancements in inverter technology, improving performance in partly shaded areas, with different panel directions on rooftops, integration of storage, more modularity and smarter control on smaller-scale installations. Although such technologies have helped optimise small-scale installations, there is still a long way to go before they become viable for larger projects.
By Meghaa Gangahar