Centralized & Decentralized PV Power Plants: Vendor Perspectives: Page 10 of 11

“Decentralized system designs simplify the maintenance process, which becomes similar to that for maintaining a residential inverter. These designs also enable the installation of replacement inverters on-site. Furthermore, they allow for greater visibility into plant operations with string-level or module-level diagnostics. We can do some of the commissioning on the fly by using the SafeDC feature to check voltages before connecting to an inverter. Finally, decentralized designs allow phased commissioning, such as 20 kW at a time, which is a huge advantage when you are dealing with large installations.”

Dru Sutton, SolarEdge

“A 10 MW centralized interconnect could use 10–20 central inverters. For the same project, a decentralized system design would require 350–450 string inverters. That is significantly more inverters to maintain and service, which means higher annual O&M costs. Commissioning can take longer for string inverters because each and every inverter needs attention. Every inverter needs the dc input and ac output voltages verified, terminal torques confirmed and Modbus communications ID set. Additional time is necessary if the interconnection agreement requires specific voltage and frequency settings or power factor settings.”

Eric Every, Solectria

“O&M and commissioning are key factors when looking at decentralized design. Three-phase string inverters offer quick installation and relatively simple commissioning procedures. With built-in combiner boxes, you can do string testing essentially after wiring up the inverter. You can set parameters via the LCD screen or remotely via Modbus. The commissioning of 3-phase string inverters does not require specially trained technicians. Central inverter commissioning can often require manufacturer technicians and an on-site supply of spare parts, and it can take more time than commissioning string inverters.”

Paul Mync, Sungrow USA

What implications do centralized and decentralized designs have on inverter-based grid management and control?

“Comparing the grid management capabilities and limitations of the inverters themselves, there are no significant differences between central and string inverters. The main difference lies in the system control structure, which at first sight can be more challenging using a distributed approach. For system coordination, it is critical to provide a control structure that allows communication with and control of several inverters at once. Readily available equipment ensures this coordination. One of the benefits of distributed designs is the added granularity, which can be beneficial for certain requirements, such as a controlled staged ramp-up.”

Verena Sheldon, AE Solar Energy

“Decentralized designs offer better granularity of control than centralized designs. While it is true that these systems have more inverters to control, modern communication methods and the use of a plant control scheme can support and control a large number of inverters.”

Sukriti Jain, Chint Power Systems, North America

“Decentralized systems allow a more granular and flexible system for grid management and control. Combining output from multiple units allows a plant-level controller to offer multiple options for controlling power. For example, reducing power from all units, or alternatively, taking some units off-line completely, could meet a power reduction command. Intraplant communications could be more specialized and possibly more complex in a distributed system.”

Moe Mahone, Fronius

“From the KACO perspective, choosing a distributed or central inverter has no significant impact with respect to grid management, support and control. Distributed inverters have a smaller range of reactive power support than central inverters, but for projects within the Americas, the available range even from the distributed inverters is more than sufficient for most projects.”

Bill Reaugh, KACO new energy

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