Photovoltaic (PV) systems form two groups: grid-connected ones and stand-alone ones. The first group can be divided into: centralised systems with large power (PV farms), and decentralised systems with low-power (especially prosumer ones). The second group includes systems with electric buffer sources (especially with electrochemical batteries), and those without electric buffer sources (possibly with non-electric buffer sources). Due to significant decline in price of PV modules, both of these groups are becoming increasingly common in Poland, especially grid-connected ones. Additional factor for prosumer systems is economic and legal support in a form of exemption from fees for connection to grid, lack of additional required licenses for such connection, and possible support in a form of guaranteed sale prices to grid (feed-in tariffs) of electrical energy generated in system. However, in case of systems not covered by economic benefits, increasing, or even ensuring, their cost-effectiveness, requires the number of ventures regarding areas of proper installation and operation rules of PV generator from installer/user/owner of system, as well as selection of suitable tariff and rational restructuring of energy demands. Detailed analysis and conclusions of these ventures, especially for prosumer systems, is discussed in paper.