Microinverters and Power Optimizers
Most manufacturers agree: reliability is the most critical challenge of the solar industry and paramount to its long-term success, particularly because these devices are installed on a rooftop where temperatures reach 140°F.
“Now that the solar industry has finally come into its own and become a viable alternative to fossil-fuel electricity, we absolutely have to ensure that our products are every bit as reliable as we say they are,” says SolarBridge’s Craig Lawrence.
Other critical factors, such as serviceability, truck roll costs (hard costs and opportunity costs) and service frequency, should also be considered in any operations and maintenance plan, says Brad Dore, director of marketing for SMA America. Additionally, module-level technologies are often unable to scale cost effectively.
Michael Ludgate, VP of business development at APS America, identifies one ongoing challenge to increase the “ease by which the installer can map the microinverters in an array and communicate UIDs to the system.”
In markets where higher levels of PV grid penetration are prevalent, evolving interconnection requirements are crucial to addressing these issues. Dore (SMA America) points to the European market, specifically Germany, for these types of grid management solutions.
“Germany’s local industry developed the technical blueprint for solving these issues,” he says. “These solutions are found within string and central inverters and can be relatively easily implemented domestically.”
Transversely, Raghu Belur, co-founder of Enphase Energy, recognizes a global shift from traditional inverters to microninverters, exhibited by the replication in global markets, such as Europe and the Asia-Pacific, of microinverter dominance that originated in the United States.
The Red Oak Park, a neighborhood in Boulder, CO, features renewable energy design. (Photo by Dennis Schroeder / NREL)
Central Inverters
With the continually growing solar market comes the increased concern over grid stability issues. As a result, codes are being devised to address this concern, says Josephine Tsen, product manager, utility scale and large commercial, Schneider Electric Solar Business.
“When this happens, manufacturers have to continually keep up with code changes and try to anticipate what these changes might be, or else they may face expensive upgrades to existing equipment or changes to their designs,” she says.
These code changes include increasing acceptance of 1000Vdc facilities and a trend toward 1500Vdc designs, but Tsen says it could take several years for these changes to gain acceptance in the U.S.
However, as more scrutiny is placed on the impact to the distribution lines, those studies are both costly and timely when it comes to the interconnect agreement process. Peter Gerhardinger, vice president of technical sales at Nextronex, thinks it would be interesting to develop a generic solar inverter model that could be used by all manufacturers.
Since price is always a continuing challenge for central inverter manufacturers, Gerhardinger’s idea might not be that far off. Higher penetration of PV in the U.S. has resulted in the call for developing smart inverters that can improve grid stability and help alleviate power quality issues.
“Adding smart inverter capabilities, such as voltage requirements and fault ride through, will free up the grid for more PV installations and allow the U.S. market to continue growing,” says Mark Goodreau, Solectria Renewables.
Additionally, as more brands become available, customers are carefully examining the value offered in a particular design and considering the long-term cost of ownership versus a lower initial purchase price. Now more than ever, there’s a need for an inverter to be more than just a power converter, but also offer services like reactive current control and power factor control, says Lou Lambruschi, marketing services and E-Business manager for Parker Hannifin.
“As advancement in technology becomes more predominant in the central inverter market, evaluation in terms of levelized cost of energy also becomes one of the key assessment factors,” adds TMEIC’s Ryuta Ray Saka.
String Inverters
Downward pricing pressure, constantly shifting global trends, shifting subsidy markets, energy prices and the global finance market all affect the solar industry, and string inverter manufacturers are no exception. As such, they must be “nimble” and innovative to regularly enhance products and product features to the latest standards, according to Chavonne Yee, in the Product Solar Group at ABB.
“Demands by customers and regulatory bodies have continuing, evolving requirements that are costly to implement and support,” says Alan Beale, general manager, SolarMax USA. “Inverters are complex devices that need to produce reliable power year after year and continue to report energy production via integrated monitoring technology in challenging environmental conditions.”
Those requirements include multiple AC grid standards and changes to building codes on a country-by country basis. For example, according to Susanna Huang of Ginlong USA, the AFCI requirements in California and Canada put a temporary roadblock for new comers to those markets.
“On one hand, the pricing competition becomes more intense, pushing string inverter manufacturers to lower cost, while maintaining quality,” Huang says. “On the other hand, technical innovations are important for us to stay ahead of the game and protect our margins.”
Technical innovations are becoming even more necessary as string inverters are being applied to larger projects with large scale features that are usually reserved for central inverters and ground mount projects.
“The solution,” says Tucker Ruberti, director of strategic marketing at Advanced Energy, “includes offering more autonomous grid support functions and also offering higher level master control devices to operate groups of inverters as a single plant.”
The U.S. market is poised for record growth in 2014 and Beale points to two interesting areas to watch in the next couple of years: silicon carbide component advancements and energy storage.
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Microinverters vs Traditional Inverters: Do Microinverters Pose A Threat?
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