Utility-scale installers can opt to use either central or string inverter solutions, but one choice usually remains the same for both options: high-voltage.
Higher voltage inverters allow installers to condense systems while achieving the same power output. An increase of 500 volts from the typical 1,000 lets contractors use fewer inverters because each one can process more energy. They’re especially advantageous in large utility-scale arrays, where cost savings are greatest.
The 2018 “International Technology Roadmap for Photovoltaic” found from 2021 onward, the market for 1,500-V systems will be greater than 50%, and these high-voltage systems will attain a market share of greater than 75% from 2026 onward.
The choice of this voltage is common for utility-scale projects at this point, but after making that decision, developers must choose between 1,500-V central or 1,500-V string inverters.
ABB says high-voltage string inverters work well for utility-scale arrays because of their ability to optimize power through modular, combiner-free design. String inverters also make O&M easy — they can be diagnosed, repaired or replaced without much hassle or expertise. Central inverters are more challenging to troubleshoot and often require a high level of technical knowledge to diagnose and fix problems.
However, when developers are working on larger utility-scale systems, the number of string inverters needed to convert all that power is often prohibitively costly. Central inverters can process much more power per unit, and even more so in the case of high-voltage central solutions. Fewer central inverters means less labor and fewer combiner boxes needed to consolidate wires in these high-voltage installations.
Sungrow offers both 1,500-V solutions. “We don’t maintain that one string inverter [at] 1,500 V has an advantage over a central inverter [at] 1,500 V, so we’ve been offering both at the same level,” said Naveed Hasan, director of marketing and strategic initiatives at Sungrow.
Hasan said almost every C&I and utility project for the past year was developed using 1,500-V inverters. From market research, Sungrow expects that number to increase even more in the coming years, with about 95% of projects over 1 MW using 1,500-V inverters by 2023.
There are some risks to using high-voltage inverters in utility-scale arrays. More voltage passing through fewer inverters means more power loss if an inverter fails, so developers need to carefully consider the pros and cons of easier serviceability with string inverters vs. decreased upfront cost associated with central inverters.