Mercom India hosted a webinar,  ‘Increasing ROI of Utility-Scale Solar Systems Through String Inverters’ to discuss the advantages of string inverters and how they help maximize system performance and reliability and reduce downtime.

String inverters have seen a steady increase in demand, with their market share increasing by 23% since 2018.

The webinar panel included C Chaudhary, Chief Operating Officer-Solar, Amp Energy India; Sudhir Pathak, Head-Design, Engineering & QA, Hero Future Energies; Prateek Sharma, Business Leader, India Key Accounts, Sungrow India; and Rakesh BP, Technical Sales, Solis. The session was moderated by Priya Sanjay, Managing Director of Mercom India.

The panelists discussed and presented their views on the growing acceptance of string inverters and the factors driving their growth in the Indian solar landscape.

Better ROI

Speaking on how string inverters can provide a better return on investment, Chaudhary said, “String inverters will play a significant role in the utility-scale segment due to three main factors. Firstly, direct current (DC) losses can be minimized to a great extent. Generally, DC losses are 1.5% to 2% depending on the cable size used. By using string inverters, you can straight away see a 2% increase in your power generation. Secondly, you can reduce capital expenditure by eliminating the need to construct an inverter control room. This will also help developers reduce their operational expenditure as they can commission the project quicker. Thirdly, when a failure happens, you have a better monitoring system at string level and can root out the cause of the failure quickly by analyzing which modules aren’t performing optimally.”

“Also, when it comes to operation and maintenance, if a central inverter needs to be repaired or replaced, the project’s generation will be significantly impacted as central inverters come in sizes of 2.5 MW to 5 MW. String inverters come in sizes of 25 kW to 100 kW. So, the impact on generation is significantly less during their maintenance,” Chaudhary added.

Speaking on how using string inverters can improve operation and maintenance (O&M), Rakesh said,” With string inverters, if there is any fault in the system, catering to O&M becomes a lot easier as issues are isolated easily from the inverters output statistics. Therefore, issues can be sorted out quickly and efficiently to reduce downtime. Thereby improving project efficiency.”

Replying to how string inverters affect the designs of the solar projects and their generation, Pathak replied, “Many original equipment manufacturers (OEM) have expanded their product line to include string inverters or have completely shifted to manufacturing string inverters. I think this is an obvious sign of changing market preferences. Additionally, as string inverters have multiple MPPTs (maximum power point trackers), where each string can be optimized to its full potential, the energy output from string inverters will be notably higher than central inverters, which have only one MPPT, which caters to a larger array of solar modules.”

“As land availability has become an issue, developers are forced to proceed with whatever land they can get. String inverters offer flexible design solutions in uneven landscapes where panels cannot be uniformly oriented. Also, given the size of utility-scale projects, it is increasingly difficult to troubleshoot isolated issues while using central inverters,” he said.

Better MPPT voltage range

“String inverters have better operating ranges operating between 500V to 1500V, whereas central inverters have a higher operating range starting from approximately 900 V. So, it takes a longer time for the project to be operational in the mornings, and it stops operations early in the evenings. String inverters have longer operational times, as they can produce power earlier in the morning and late in the evening,” Pathak said.

“As more developers start to use bifacial modules, string inverters will maximize the output due to multiple MPPTs virtually capable of tracking the power output from each module.”

BOS bottlenecks

Pathak said, “Only a couple of players provide switchgear for string inverters. Only a few players have gone for 800V molded case circuit breakers (MCCBs), even as string inverters capacities have been increasing consistently. However, this presents a great opportunity for OEMs to develop more compatible MCCBs and low-tension panels.”

CAPEX Vs. generation

Sharma said, “String inverters offer more design flexibility, and therefore, they can be optimized to improve the overall efficiency of the solar project. Hence, the power generation from the project compensates for the initial CAPEX required to implement string inverters. ”

“We have expanded our production capacity from 3 GW to 10 GW. Sungrow is also meeting the government’s mandate to use 50% domestic content requirement. However, we cannot reduce the cost of inverters as the price of imported components, freight charges, and raw materials is significantly high,” Sharma added.