Developers Prefer String Inverters for Bifacial Modules With Trackers_ Mercom Webinar

Mercom hosted a webinar to discuss how solar inverter technologies impact project performance.

The webinar shed light on the technological trends pushing the market and how Indian developers decide which inverters would be used for their projects.

The panelists also discussed the inner workings of the solar inverter industry and spoke about developments that can improve efficiency and boost healthy competition. The panel included- Nataraja M S, Head, Technical, Support (Asia-Pacific), Sungrow (India); Sudhir Pathak Head – Engineering, Hero Future Energies; Shantanu Sirsath Technical Head – India, Growatt New Energy; and Gaurav Wadhwa, Head – Engineering, ReNew Power, and Priya Sanjay, Managing Director, Mercom India.

Although inverters account for 5% of the total project cost, their impact on project performance, stability and the levelized cost of energy (LCOE) is substantial, making quality and technology the prime movers in this segment. Here are the session highlights:


New Technologies Entering the Market

According to Nataraja from Sungrow, the solar inverter segment’s focus was on utility- container solution – for both string and central inverters. Technology related to container solutions is on the rise, and now, the focus is shifting towards outdoor inverters. Outdoor inverters, these days are strong enough to combat corrosion, C5 corrosion in coastal areas as they come with an IP65 rating.

Nataraja said, “We are reducing the size of the inductor, thereby reducing the size of the inverter while improving output and reducing costs. We will also use heat exchangers, especially in coastal areas and dusty terrain. A heat exchanger is not a new technology, but it will be introduced in inverters. It is a closed-loop control system and doesn’t need any maintenance. These additions will improve power density, performance, and balance of system cost.

He further added that string inverters nowadays come with intelligent air-cooling systems with a compact design. Nataraja also added that string inverters need to be updated with changes in module design, which is not an issue that central inverters face.

Another innovation that has come in handy with string inverters is battery energy storage system (BESS) connections in the inverters, which can store the excessive energy in batteries.

As Growatt supplies string inverters to the C&I and residential solar market, the company’s technical head, Shantanu Sirsath, said, “We have reduced the size of new inverters we released in the range of 70-80 kW. We have reduced the weight by 40%. A 50 kW inverter that weighed 80 kgs now weighs around 50 kgs, all thanks to a new compact design. The new inverters make life easy for EPC contractors and developers for rooftop applications and small utility-scale projects up to 2-3 MW.

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As a solar developer, Sudhir Pathak from Hero Future Energies gave his take on the new inverter technologies and said, “Let’s consider the lowest capacity 1 MW central inverter with one maximum power point tracking (MPPT) and a 250 kW string inverter with 12 MPPT. Cleary, one has 48 times more MPPT in a 1 MW AC block when using string inverters. Meanwhile, earlier in central inverters, we had issues with string monitoring with poor power density.”

He said that string inverter technology had advanced a lot, and it can even pinpoint issues and errors in one particular module in the project. As project sizes grow and resources on the ground are limited to 4-5 individuals, it becomes easier to locate faulty modules using string inverters.

However, he also threw light on both string and central inverters’ latency issues, which need to be addressed for the projects to prosper.

According to Gaurav Wadhwa, Head – Engineering, ReNew Power, a lot of focus is needed in the industry regarding grid integration of inverters, “Consider a 1 MW plant that uses four 250 kW central inverters. If you use a 10 kW or a 115 kW string inverter, the power density is still higher than 1 MW, four 250 kW central inverters. The number of products connected with the grid is more. So the stability of the grid with relation to the product is critical.”

Are inverters equipped to work equally efficiently with new age modules?

According to Nataraja, central inverters won’t face any issues with new technologies as the latest ones come with multiple MPPTs. “However, when it comes to string inverters, it will be quite critical, especially when it comes to bifacial modules, due to back-end radiation which will make each string inverters’ performance unique.”

According to Shantanu, the module’s increasing size will not affect the overall performance of the inverter. “However, when it comes to the voltage, the inverters need to be upgraded regularly as a high-performance module because even inverters in utility-scale can take current up to 30 Amp and the new modules can put out 75-80 Amp. If not fixed, it can lead to a loss of energy.”

Speaking on the challenges when new module technologies are matched with inverters, Sudhir said, “There are way too many module variants, which makes life difficult for string inverter manufacturers because they need to adjust their ports to meet universal requirements. Module sizes will keep going up, and the string inverter manufacturers need to cope with these changes. The manufactures need to ramp up their research and development to meet these challenges.”

Meanwhile, Gaurav said, “Module tech is changing so rapidly that we need to sync it with other aspects of the project, including inverters.”

String or central inverters – which one and why?

The choice between string and central inverters should be made carefully, keeping in mind the project size, finances, and performance expectations.

Nataraja said, “It all depends on the project design. If the land is a little undulated, we prefer string inverters, and if it is flat, we opt for central inverters. String and central both have their advantages- grid support is stronger in central inverters, while string inverters incur some loss. However, when it comes to multiple MPPT features, string inverters perform better than central inverters. Meanwhile, in terms of BoS (balance of system), central inverters fare better than string.”

Gaurav, too, shared a similar sentiment and said, “It is the LCOE that determines the kind of inverter we use in our projects. Earlier project sizes were small; now, it’s massive, which means more land is needed. There is no telling how the land will be. Thus, string inverters play the lead here. However, if the land is flat, and not undulated, central inverters make for a better option than string.”

Sudhir said that with the introduction of bi-facial modules, string inverters would have an advantage in the battle of inverters.

What is the trend with container/outdoor solutions for inverters?

Sudhir said that container solutions are always a better option; however, in India, costs determine such decisions. When it comes to outdoor solutions, it has several negative points. “It’s like driving a car for years outdoors. It does require maintenance. The same goes for outdoor inverters, which lasts as long as it does, but will have issues eventually.”

While agreeing with Sudhir, Gaurav said, “We need some sheds that can protect the inverters from sunlight and rains.”

Inverters are getting smarter with time?

Nataraja said that smarter inverters are the future, focusing more on efficiency, performance, and temperature management. “As the market moves towards the Internet of Things (IoT), the new technologies will be integrated into the inverters, making them much smarter. Even now, several features can assist our consumers, but our consumers are not applying all of them.”

Shantanu added that “Artificial intelligence is playing a vital role in the rooftop segment. In case there are voltage fluctuations and power surges, AI will drive the inverters to function accordingly and keep the project and the grid stable.”

Gaurav stated that smarter inverters would help, especially with IoT, by capturing vital data. With the right kind of integrated innovation, it will be easier to pinpoint faulty modules or string inverters and can fix them and save valuable time and money.”

Meanwhile, Sudhir said, “After 5-10 years, solar projects will be unmanned. New inverters with their machine learning can help fix several issues facing the project, especially when it comes to module maintenance and assist in robotic cleaning.”

Predictions for 2021

In conclusion, Nataraja commented that the new age modules will force string inverter manufacturers to innovate. He further added BESS would be a significant factor in future solar projects- i.e., PV with BESS. According to him, future coastal areas will need more analysis before setting up projects, especially regarding component selection.

Shantanu opined that 125-150 kW inverters with 400 V could come in faster than expected. Hybrid solutions across the globe led by Africa and Southeast Asian regions will be in demand.

Bifacial with trackers are the future trend and string inverters will be the choice for this was Gaurav and Sudhir’s view.

Sungrow, FIMER India (formerly ABB), and Sineng Electric were top solar inverter suppliers overall to the Indian solar market in the first half (1H) of the calendar year 2020, according to Mercom’s India Solar Market Leaderboard for 1H of 2020. Several international players have their solar inverter manufacturing units in India.

Click here to view the webinar recording.