Centralized & Decentralized PV Power Plants: Vendor Perspectives: Page 3 of 11

“Sungrow central units include the 600 Vdc SG500LV and three 1,000 Vdc models, the SG750MX, SG800MX and SG1000MX. We offer three high-capacity string inverters, including the 480 Vac SG30KU and SG36KU, and the 380/400 Vac SG60KU. All inverters feature 10% overload capability at a 0.9 power factor up to 50˚C ambient. The central inverters have customizable dc input options, including fuses or a direct busbar connection, and an optional dc breaker cabinet. The 30 kW and 36 kW string inverters feature 10 monitored dc inputs. The 60 kW unit has eight MC4 inputs. The use of Branch ‘Y’ MC4 connectors in the PV array allows for cable savings by requiring only one homerun to the SG60KU per two strings. The SG60KU is one of the first units to use silicon carbide power components, allowing us to nearly double the power density. This, combined with advanced cooling techniques, allows for a lower cost per watt, as well as lower labor and BOS costs.”

Paul Mync, technical sales manager, Sungrow USA

How has the introduction of high-power 1,000 vdc, 3-phase 480 vac string inverters impacted the design choices available for utility-scale PV plants?

“1,000 Vdc string inverters open up potential sites for utility-scale plants that central inverters previously could not serve due to shading, noncontiguous land segments or uneven land requiring arrays of different tilts or azimuths. The decentralized architecture of string-inverter systems also distributes the weight load, allowing installations on landfill sites with weight restrictions. The 3-phase string inverters allow more flexibility in the PV plant size, so you can size plants in increments of 20 kW and not in 100 kW blocks. Additionally, ABB 3-phase string inverters have a 10-year warranty in contrast to the standard 5-year warranty for central inverters.”

Sarah J. Ozga, ABB

“The availability of high-efficiency transformerless 3-phase string inverters and code changes that facilitate 1,000 Vdc systems make string inverters a competitive option for utility-scale applications. Giving system designers and integrators the opportunity to choose from these different topologies increases design flexibility. The specific system details, financial metrics or site-specific design challenges or limitations drive the decision. With string inverters becoming a viable option for utility-scale applications, system designers and installers can transition more easily from commercial applications to utility scale, since they would be using the same equipment.”

Verena Sheldon, AE Solar Energy

“The impact is positive. We see an increasing number of developers evaluating 3-phase string inverters for utility-scale power plant applications. The adoption of a decentralized approach for projects ranging from 2 MW to 5 MW began in 2013, and we see this trend continuing into the future. CPS is releasing a 36 kW string inverter this year and will follow with higher-power units designed specifically for utility-scale applications.”

Sukriti Jain, Chint Power Systems, North America

“Fronius has been a front-runner in the US solar industry’s shift of consciousness toward a distributed inverter topology. The European market frequently leads design trends, such as allowing 1,000 Vdc residential and commercial systems. The flexibility that string inverters provide makes them an ideal choice for both simple and complex designs.”

Moe Mahone, Fronius

“The introduction of 1,000-volt high-power (30 kWac–60 kWac) string inverters provides more design choices to developers and system integrators. The major benefits of string inverters include improvements in energy harvest due to a larger number of MPPTs, an increase in availability and a reduction in downtime when issues occur. However, the increase in the number of inverters can make interconnection design more complex. The communications and control infrastructure can also be more complicated due to the larger number of devices.”

Bill Reaugh, KACO new energy

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