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

“Only very minor differences in grid management and control are present with respect to SMA’s solutions. SMA offers both small and large inverters with advanced grid support functionality. In Europe, the industry often requires system sizes down to 3 kW to provide fault ride through capabilities, among other factors, to help support the grid in the event of a fault rather than drop off and make it worse. With string inverters, there are more nodes on the network, but both designs can meet the features just about any project requires.”

Ryan LeBlanc, SMA America

“While both topologies offer great grid-management functions and value to the utilities, decentralized systems have significantly more inverters to monitor and control. These projects will typically use a plant master controller to provide a single communication interface with the utility. That controller then distributes commands to all of the inverters. System control becomes more complicated and costly as the number of inverters increases. Also, anti-islanding coordination is more difficult with a higher inverter count.”

Eric Every, Solectria

“Most available 3-phase string inverters have the advanced grid-support features that have become standard with central inverters. These include LVRT, reactive power injection, power curtailment, remote shutdown and frequency response. The interconnection standards in Germany have driven this functionality, so if an inverter manufacturer is active in the German market, its inverters most likely have these capabilities. Communication capabilities are also important, and both central and string inverters offer Modbus RTU and TCP/IP as standard offerings, required for communication with utility plant controllers.”

Paul Mync, Sungrow USA

How do you see the relationship between utility-scale project requirements and centralized and decentralized designs evolving in the next few years?

“Due to the economy of scale, very large utility-scale projects will continue with central inverters and migrate from 1,000 Vdc to 1,500 Vdc systems for BOS cost savings. As developers build out large 100 MW utility-scale projects on available, primarily flat desert parcels, decentralized string inverter systems will be more common for smaller utility-scale plants on less homogeneous sites that are better served by more granular MPPT optimization.”

Sarah J. Ozga, ABB

“String inverters are packing more power into smaller enclosures and becoming smarter with their utility interactive control features and commands. With increased plant availability and ease of installation, as well as replacement, decentralized power plants will become the norm rather than an exception over the next few years.”

Sukriti Jain, Chint Power Systems, North America

“At Fronius, we see a continuing trend toward decentralized systems in utility-scale projects. With the availability of larger and more efficient string inverters and the introduction of favorable new building codes, the goal of driving down system costs and decreasing the LCOE is now more attainable than ever.”

Moe Mahone, Fronius

“The biggest evolution in utility-scale projects going forward will be the change to 1,500 Vdc and the concurrent change to 690 Vac output. These changes will impact the BOS costs on the dc and ac sides of the project, but will not necessarily affect any of the points discussed above when comparing the benefits of central and distributed inverters.”

Bill Reaugh, KACO new energy

“With each new record year for solar, in North America in particular, the industry develops the low-hanging, easiest sites first, and then tackles the more difficult sites, which in turn increases the demand on manufacturers to innovate even more flexible and robust equipment. In the next few years, SMA anticipates that utility-grid management requirements will drive increased interactivity and a broader range of applications. Both string and central inverters can take this on without either having a particular advantage, but we expect the flexibility of string inverters to become a more important trait as project sites become more remote and oddly shaped, and owners become more cost conscious. SMA’s 2 MW Sunny Central 2200-US is feature rich, cost effective, compact and efficient. This will be a difficult machine for string inverters to compete with on cost alone. However, where site access for larger machinery and higher-skilled labor is limited, or where O&M needs to be lean, we can expect to see some very large projects installed with some modestly sized inverters.”

Ryan LeBlanc, SMA America

“Expect to see more-advanced inverter controls implemented more often. California Rule 21 and amendments to IEEE 1547 will remove restrictions on grid support features that inverters are capable of performing. Solectria will be able to meet these needs with both system designs, which are reasonable and have strong futures.”

Eric Every, Solectria

“The evolution of utility-scale project requirements will likely involve storage systems integrated into the PV plant. Large-scale storage will help with the intermittent nature of PV and provide ancillary services that customers can monetize on the utility level. These developments may lead to the combination of 3-phase string inverters with a central, four-quadrant inverter that allows for battery-bank charging and discharging. Communication and control will also drive utility-scale project requirements, because utilities will need to monitor and control these generation assets through advanced communication schemes. For both centralized and decentralized designs, the plant controller will evolve, as well as the on-board web servers inside the inverters.

“Asset availability will also play a deciding factor in utility-scale plant design as we gather more data from existing systems. Three-phase string inverters provide more redundancy, which developers will find compelling as they execute PPAs based on performance. In addition, 3-phase string inverters offer increased energy production due to the number of MPPTs and the ability to generate power early in the day and late in the afternoon—the ‘shoulders’ of the daily power curve get wider. As utility-scale systems become more advanced, uptime and control will become paramount, and 3-phase string inverters provide less risk in terms of downtime. Additionally, 3-phase string inverters will also increase in size, eventually breaking the 100 kW mark, while remaining lightweight enough for a two-person installation. Finally, 1,500 Vdc 3-phase string inverters will hit the market in the coming years, which will increase efficiency while further lowering the LCOE.”

Paul Mync, Sungrow USA


Joe Schwartz / SolarPro magazine / Ashland, OR / solarprofessional.com


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