ON-GRID SYSTEMS
On-Grid Systems are systems that requires grid connection, where energy can flow two ways. Permanently grid-connected with own consumption plants draw power from the grid during the hours when the PV generator cannot produce the energy necessary to satisfy the needs of the consumer. On the contrary, if the PV system produces excess electric power, the surplus is put into the grid, which therefore can operate as a big accumulator: as a consequence, grid-connected systems do not need accumulator banks.
OFF-GRID SYSTEMS
Off-grid plants are plants which are not connected to the grid and consist of PV modules and of a storage system which guarantees electric energy supply also when lighting is poor or when it is dark. Since the current delivered by the PV generator is DC power, if the user plant needs AC current an inverter becomes necessary.