Nowadays, in Albania, several photovoltaic plants are in various stages of construction. The main problem encountered is the power quality, because in spite of the energy production, PV Power Plants inject into the electrical grid voltage harmonics from the conversation of DC to AC through Power Electronic devices like inverters. Except for the fundamental harmonic, the voltage and current spectrum of the inverter output contain high-order harmonics. In this work, we will present a virtual instrument built in the LabVIEW software, which is customized to measure THD and to notify in real-time for the voltage signal harmonics present in the electrical grid PoC (Point of Connection) besides the fundamental 50 Hz harmonic, generated from a small-scale PV Plant in its AC side and to allow the remote user to implement the most suitable passive filter needed to be connected to reduce the THD to the allowed value by respective standard. This virtual instrument can be upgraded easily to automatically calculate and to select a passive filter and to connect it to the electrical grid to filter a specific harmonic of the voltage and current which is detected by the same instrument. This solution can be used to reduce the voltage and current THDs generated from PV Plants and other electrical devices.