Centralized & Decentralized PV Power Plants: Vendor Perspectives: Page 9 of 11

How do commissioning and O&M activities compare when considering centralized and decentralized designs? How does the design approach impact plant availability?

“While performing O&M on decentralized plants, you need to shut down only a small portion of the plant at any one time, which provides greater power production compared to a centralized plant.”

Sarah J. Ozga, ABB

“Generally speaking, the commissioning of a central inverter requires more highly skilled laborers who are specifically trained for the equipment you are commissioning. Some manufacturers make it mandatory for the electrical personnel to attend factory training and get certification prior to commissioning. In contrast, the level of knowledge and training required to install and commission a 3-phase string inverter in commercial or utility-scale applications is comparable to that required for a residential installation—installers need electrical knowledge that they can apply to the specific guidelines given in the manufacturer’s installation manual.

“Looking at O&M plans and activities, the decentralized approach presents a potential for additional savings. Although there are differences between individual brands, it is safe to assume that string inverters typically require less preventive maintenance than do central inverters. During a maintenance event, the technician must de-energize the equipment. The decentralized design approach allows the technician performing the maintenance to turn the system off in smaller sections, enabling the remaining sections to continue to operate. This decreased system downtime during a maintenance event translates into overall higher system availability and higher energy yield.”

Verena Sheldon, AE Solar Energy

“Centralized designs follow a repair model, whereas decentralized designs mostly follow a replacement model. Thus, O&M activity for a decentralized power plant is minimal and limited to swapping the inverter in the field. A centralized approach requires regular maintenance of parts and time-consuming repair in the field in case of failure. Plant availability, or uptime, increases significantly when you reduce the mean time to repair field issues. In addition, a centralized design approach can reduce the budget requirements for general system O&M.”

Sukriti Jain, Chint Power Systems, North America

“Commissioning decentralized systems is a simple prospect that experienced solar installers are familiar and comfortable with. Commissioning string inverters one at a time decreases stress and liability. New software and monitoring options allow application of settings to a fleet of inverters from a central on-site or remote location. A major benefit for O&M comes from the ability to field-service inverters. If a central inverter goes off-line, the production lost waiting for a technician to repair the system can have a substantial impact on plant availability. Central inverters come with a shorter standard warranty, and manufacturers usually sell them with additional service packages to cover regular inspections and servicing. Data from independent O&M companies show that central inverters have a 13% higher O&M cost. Decentralized systems provide reliability by eliminating the single point of failure.”

Moe Mahone, Fronius

“There is a significant and measurable difference in central versus distributed architectures when considering O&M and availability. Generally, distributed inverter systems have significantly lower maintenance requirements. This makes the skill level of the required maintenance personnel less important, and it significantly reduces the cost of spare parts inventories. In some cases, the repair program is ‘rip and replace,’ similar to that for small commercial and residential systems. When an inverter fails in a distributed system, the percentage of the total system that goes offline is substantially less than in a typical central project. This, combined with the typically faster return to service on distributed inverters, means that distributed architectures significantly improve availability.”

Bill Reaugh, KACO new energy

“You can generally achieve faster commissioning with string inverters, while central inverters require more specialized, highly skilled technicians to adequately and rapidly commission the larger units.”

Ryan LeBlanc, SMA America

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