Using photovoltaic (PV) systems connected in distribution and even transport grids increase the need for energy supply security. Energy Efficiency of PV power plants is a performance indicator as well as a fault detection method. Control system topologies for grid connected PV power plants can increase the overall generation performance. Three types of plant control topologies with their benefits and drawbacks are compared. The paper also synthesizes the control requirements for each of the plant components cells/panels, inverter and grid connection point. The PV panel faults issue is tackled practically by designing a PVPP test bed for further application of the proposed fault detection algorithm. A 80kW rooftop PV plant is proposed for efficiency evaluation. A decision tree algorithm for power plant efficiency and fault detection is designed. Computation of the capacity factor is an energy efficiency indicator, as well as a detector for PV panel fault initiation by dust or objects covering the cells. A hierarchical control system architecture with a central level PLC and 4 inverters, each with several MPPT modules, one for each string is proposed. The fault tree algorithm will be implemented on the practical PV power plant test bed.