A Direct Comparison between a Central Inverter and Microinverters in a Photovoltaic Array

Microinverters, successfully introduced to the market in 2008, have the potential to transform the PV landscape. They offer many advantages over central inverter topologies, including potentially increased power output compared to a central inverter. Many manufacturers claim up to 25% energy enhancement. The largest claimed enhancements are under conditions of partial shading. These claims have yet to be verified in peer-reviewed literature. This research effort used a total of eight Sharp NE-170U1 PV panels in conjunction with a single SMA Sunny Boy 700U central inverter and two Enphase D380 microinverters. All panels were on a pole mounted rack with a clear view of the southern sky in Boone, North Carolina. AC power output and POA irradiance (direct and diffuse) were logged for over two months. The experiment was conducted under both unobstructed and partial shade conditions. Conclusions from the experiment are similar to a 2011 Enphase study. Preliminary results suggest that when irradiance is greater than 650 W/m2, microinverters outperform central inverters by 20% and 26% in unshaded and shaded conditions, respectively.