Module-Level Power Electronics

Microinverters and DC Optimizers

When Enphase Energy introduced its first-generation microinverter system in 2008, it revived and reimagined a solar product class that had previously failed to gain commercial traction. In the 1990s, Ascension Technologies and NFK Electronics developed and sold microinverters in the US, but by the early 2000s other companies acquired both these businesses and pulled the plug on their microinverter lines. The potential benefits that these early microinverter manufacturers saw in their products—including performance optimization, shade mitigation, system modularity and the elimination of a single-point failure at a system level—all still hold true today. But contemporary microinverter and module-level dc optimizer systems offer additional benefits, and as the industry continues to evolve and expand, so does the market for these products.

Today, the deployment of module-level power electronics (MLPE) is as much about improving project economics and meeting regulatory requirements as it is about simply increasing a system’s energy generation over its operational lifetime. Microinverter systems can lower the cost of system design, inventory management and O&M. Module-level dc optimizer systems allow integrators to increase the number of modules in a dc source circuit and correspondingly reduce wiring, labor and BOS costs.

Virtually all modern MLPE systems include web-based monitoring that enables technicians to remotely diagnose system performance or equipment issues at the module level and avoid or streamline truck rolls. The granularity of MLPE monitoring can assist integrators with module warranty claims and provide unprecedented visibility into the performance and failure rates of modules and of the MLPE products themselves. Finally, these systems offer potential safety enhancements, especially for rooftop systems, and solutions to meet changes in the NEC, such as the rapid shutdown requirements in the 2014 edition of the Code.


The Resurgence of Microinverter Technology” (SolarPro, October/November 2009) explores some of the early developments in the microinverter product class. The article surveys five microinverter vendors that were active at the time, including Enphase Energy and SolarBridge Technologies. Since then, some manufacturers—such as Azuray Technologies, Direct Grid Technologies and Exeltech Solar—have exited the market. New microinverter manufacturers—including ABB, APS, Darfon, iEnergy and ReneSola—are bringing products to market. Today, nine vendors offer microinverter systems in the US.

ABB. In July 2013, ABB, a global provider of power and automation technologies, completed the acquisition of Power-One to become the world’s second largest manufacturer of solar inverters in terms of revenue, as reported by IHS Technology. In May 2014, ABB transitioned Power-One into the ABB brand. Power-One’s existing inverter offerings and product family names (Aurora Uno, Aurora Trio and Aurora Ultra) remain the same. All of its product certifications remain valid as well.

In 2011, ABB introduced two microinverters developed for the US market. More recently, the manufacturer added a microinverter designed for compatibility with high-voltage modules. Three main components comprise ABB’s microinverter system: the microinverter, the Concentrator Data Device (CDD) and the Aurora Vision Plant Viewer web-based monitoring interface.

ABB’s microinverters include the 250 Wac MICRO-0.25-I, the 300 Wac MICRO-0.3-I and the 300 Wac MICRO-0.3HV-I. All three microinverter models can be integrated with 208 Vac and 240 Vac utility services. Their absolute, temperature-adjusted maximum input voltages are 65 Vdc, 65 Vdc and 79 Vdc, respectively. ABB’s proprietary ac trunk cable, which is compatible with 60-, 72- and 96-cell modules in both portrait and landscape orientation, aggregates the individual microinverters in ac circuits. The maximum number of MICRO-0.25-I units per 20 A circuit is 15 at 240 Vac. The MICRO-0.3-I and the MICRO-0.3HV-I models can be configured in 20 A circuits of 12 microinverters at 240 Vac.

The microinverters communicate wirelessly with the CDD. A single CDD can directly monitor up to 30 ABB microinverters at a maximum unassisted CDD–to-microinverter distance of 164 feet. The system’s Aurora Plant Viewer remote monitoring interface enables free module-level monitoring on the web as well as on mobile devices. ABB provides a 10-year standard warranty that covers the entire system, including the microinverters, the CDD and ac trunk cabling.


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