The paper deals with distributed photovoltaic (PV) systems capable of accepting reference values for the reactive power generation and active power curtailment. The aim of the performed research is to analyze to what extent can the use of controllable PV systems increase the total share of PV systems in electric grids and to what extent can controlled PV systems increase the yearly net self-sufficient electricity supply. In the case study the analysis is performed from the viewpoint of the distribution grid, considering the voltage profile, conductor loading and grid losses. Problems related to the power system stability are not discussed.