We present some results of a high-statistics study of the performance and characteristics of NKF OK4E-100 "AC-module"-type inverters under extreme desert conditions. The work was carried out at the Ben-Gurion National Solar Energy Center, located in the Negev Desert. Twenty inverters were monitored for one complete year. Ten of them were each fed by pairs of 40W Solarex SX146 PV modules, in order to provide a set of "normal operation" systems. The other 10 were fed by quartets of similar 40 W PV modules, in order to create frequent situations of extreme overload. The paper addresses hourly, daily and seasonal inverter efficiencies; optimal module sizing; overload penalties; temperature effects; light-threshold effects; quality control issues and failure rates. (C) 2002 Elsevier Science B.V. All rights reserved.