In this work an investigation of a low performing grid-connected PV system was conducted. The system totally consists of 72 PV modules of 45Wp each and two inverters. The investigation showed that the inverters were the main cause of the bad performance. One of the inverters performs more than 10% below the manufacturer’s specifications while the other one has completely stopped working. The PV modules in the system perform well and all installations have been properly conducted. To improve the system the best solution would be to buy a new inverter and connect all the modules to that one. Today the array is oriented to 30? south-east and the tilt is set to 60?. The output from the system could be increased with approxemately3.3% by changing the orientation of the modules directly to south and the tilt to 42?.