The AC module: An overview and update on self-contained modular PV systems

The concept of attaching a small complete inverter designed for grid interconnection to each photovoltaic (PV) module of an array has been pursued for about 20 years. National Grid began supporting development of this novel concept in 1992, designating the complete system as an “AC Module” (ACM). Technical success was achieved around ten years ago, but commercial success has been achieved only within the last two years. Now there are a number of companies (to be described) with products in the final stages of development, undergoing independent laboratory certification testing or on the market. There are numerous advantages to employing AC Modules in PV systems from 2 to several kW, in comparison to a typical PV array comprised of two or more series strings of standard PV modules with dc output, all feeding one grid-connected inverter. These advantages will be discussed. A final comment is that the term “microinverter” has been used increasingly in recent years, but the combination of a microinverter with a commercial PV module is in essence an AC Module.