For grid-tied systems, check the local regulations and requirements for grid connection. Obtain necessary permits and approvals to interconnect your solar system with the utility grid.
In an off Grid configuration as the name suggests there is no grid connection at all.
The systems design must therefore be capable of providing all of the power needs of day and night and make provision for low sun days.
This often results in a hybrid solution where a generator is also employed to provide power for high loads and low sun situation.