The Return of the AC-Module Inverter

AC-modules offer a lot of advantages compared to traditional photovoltaic systems with string or central inverters. These do not only relate to safety, but also to economics, especially of smaller systems. AC-modules are especially interesting to use for the integration into buildings, as the independent operation of AC-modules prevents that a PV system will function poorly due to partial shading of one or more PV modules. Research and development into AC-module inverters started in the early nineties, and have resulted in AC-module inverters ranging from 100 to 300 Watts. AC-modules disappeared from the market mainly due to the (relatively) high costs and failing AC-module inverters. Recently however, several new AC-module inverters have been introduced on the market. For a successful return of AC-modules costs, performance, reliability and lifetime should be comparable or better than that of central and string inverters. This paper discusses whether and how these design targets can be reached in the newly designed inverter by OKE-Services, called the OK4All, of which the technology has been sold to SMA.