As the primary point of interconnection between the generation and distribution sides of a photovoltaic system, thesolarinverter directly affects multiple aspects of solar project development. Consequently, the right inverter has the potential to significantly impact a PV project’s delivered value.
A growing focus for successful integration of PV power on a large-scale, distributed basis has been to add smart features and functionality to inverters. At the same time, other inverter technology advancements are gaining popularity in North America.
Three key trends are making a significant impact in the overall effectiveness of PV installations and will likely gain momentum in the coming years:
- Rapid growth in three-phase string inverter adoption
- Movement toward increased DC voltage
- Shift toward transformerless systems
The rise of three-phase string
Distributed architectures that utilize multiple three-phase string inverters throughout a solar array have been the typical architecture in Europe and are gaining traction in the high-growth U.S. commercial market for distributed generation. IHS predicts that low-power, three-phase inverter shipments will triple over the next four years in the U.S., with annual shipments of nearly 20 gigawatts globally in 2017. As one of the fastest-growing inverter applications worldwide, three-phase string inverters offer a compelling price-to-performance ratio, simplicity in design and ordering, ease of installation, improved uptime, and quick serviceability for commercial applications where flexibility and modularity are essential.
The move toward greater voltage capacity
The industry standard has gradually moved toward 1,000 V models rather than 600 V. Increasing to 1,000 V allows for more modules in each string series. A 600 V inverter can typically only accommodate twelve standard 72-cell modules in a series, whereas the 1,000 V allows for twenty modules of the same type. This results in the use of fewer fuses, disconnects, and combiner boxes, leading to a reduction of up to 40 percent in balance-of-system costs on the DC side. In addition, 1,000 V-rated wire carries more power and reduces conductive losses, providing more efficient output than 600 V-rated wire.
The move to 1,000 V delivers significant improvements in PV system cost and function, but the industry standard continues to advance from there. Inverter manufacturers are already looking at designs and topologies that allow for even higher voltages. For example, one available solution is a 1,000 V bipolar inverter, which enables system cost savings in a range similar to a 2,000 V monopolar inverter.
The shift toward transformerless systems
Since 2007, when Advanced Energy introduced the first transformerless solar inverter available on the market, the industry has seen increasing adoption of transformerless inverter solutions. While transformerless inverters have long been popular in Europe, up until 2005, U.S. regulations dictated that all electrical systems must be grounded. For PV systems, this required the use of transformer-based inverters to create galvanic isolation between the DC and AC sides of the system. Recent code updates allowing for ungrounded systems gave rise to transformerless technology in the U.S.
Without a grounding requirement, project developers can achieve greater energy harvest, lower operations & maintenance (O&M) and balance-of-system costs, and a smaller inverter footprint. The transition to transformerless inverters is also being driven by higher voltage input capabilities and improved DC monitoring tools. Previously, when maximum DC input was limited to 600 V, reaching a desirable AC output required a boost from the transformer. But with the market now moving toward a standard DC input of 1,000 V or more, there is a reduced need for a transformer because the higher DC voltage also boosts the native AC output.
As the brain of the PV system, the inverter is critical in ensuring that solar energy is successfully fed to the grid. And as solar’s role in the North American energy market continues to grow, inverter manufacturers will continue to adapt their offerings to meet and improve industry standards, so as to deliver the greatest possible value to project developers, utilities, and consumers.