Centralized & Decentralized PV Power Plants: Vendor Perspectives: Page 7 of 11

“The cost of string inverters in recent years has declined significantly—more rapidly than that of central inverters—due to increased power classes and improved production methods. Therefore, LCOE has seen a convergence in recent years to a point where distinguishing factors are project specific, with the costs of decentralized systems equaling—and then perhaps improving upon—centralized system costs. Some sites favor one approach, while other sites are more favorable to the other. What the solar industry is experiencing today is almost a push at the CAPEX level, but modestly improved performance and lower O&M costs improve LCOE for string inverter systems.”

Ryan LeBlanc, SMA America

“The biggest change we notice is a greater appreciation of factors such as risk, O&M and system lifetime. Previously, most of the attention was on the initial capital investment; now this has shifted to considerations such as O&M stipulations, warranty period and system uptime calculations.”

Dru Sutton, SolarEdge

“Owners who are just becoming familiar with decentralized systems are finding that commissioning costs and operating costs are higher than they originally expected. Consider a system with string inverters that have an uptime three times better than that of a central inverter. For the same array size, a decentralized array would require about 30 times more inverters. This means the decentralized array would require 10 times the number of inverter service calls. Since LCOE accounts for operating costs, additional service visits increase cost per kWh. The reality is that developers and investors should evaluate both solutions, and they will find they have two good options to choose from.”

Eric Every, Solectria

“String inverters still cost more than central inverters, but that difference continues to shrink rapidly. Fortunately, the market is advanced enough to where the dollar-per-watt cost is not the only consideration. When you factor in the other benefits of decentralized designs—such as built-in combiner boxes with string-level monitoring; multiple MPPTs; savings because you do not need cranes, skids and in many cases concrete pads; and lower downtime and O&M costs, especially in remote locations—we have seen string inverters deployed in larger and larger projects.”

Paul Mync, Sungrow USA

How do centralized and decentralized designs affect the BOS requirements and construction costs for the dc and ac sides of the system?

“Centralized systems have higher dc BOS costs due to the need for multiple dc combiner boxes to feed into the central inverters. Most string inverters used in large plants include an integrated dc combiner that reduces the dc BOS costs. In addition to eliminating external dc combiner panels, string inverter systems eliminate large PV output conductors and conduit. Designers can achieve additional savings on the dc side by placing the string inverters closer to the arrays, which minimizes the length and size of PV source-circuit conductors and conduit. Reducing the size of these conductors reduces the associated labor costs as well. Decentralized systems require the use of ac combiner panels to parallel the output of the string inverters to one point of connection with the utility. While this is an additional cost that centralized systems usually do not require, the cost of ac combiner panels is lower than that of dc combiners and offers a net BOS savings.”

Sarah J. Ozga, ABB

“For decentralized systems, the majority of the BOS cost is on the ac side for collecting and combining ac runs from the individual inverters. However, these systems have dramatically reduced dc BOS compared to centralized systems because they do not require external dc combining if the inverter comes with this capability integrated, as does the AE 3TL product. The cost for dc wiring including conduits generally exceeds the wiring cost on the ac side. Also, the costs for fused dc combiners with disconnect, which centralized designs require, run higher than for the panelboard typically used to combine and protect the ac side in decentralized designs. Overall, there is a potential for BOS savings using the decentralized approach.”

Verena Sheldon, AE Solar Energy

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