Off grid solar systems are standalone units independent of the solar energy distribution network. Off grid solar homes and establishments do not need public utilities for their power supply. They can independently generate, store and use solar energy for their needs.
The essential difference between these systems is that one has a battery backup system and is not necessarily connected to the public utility (off-grid) and the other does not have a battery system (grid-tie). There are some pros and cons to each:
Most homeowners do not buy entirely off-grid systems due to the high cost of battery backup systems (they can double the price of going solar). There are also some environmental questions to answer concerning the use of caustic battery chemistries, as well as the fact that if the system is completely off the grid there is no backup if something goes wrong.. Most people who choose this option live in the countryside where self-sufficiency is a no-brainer.
Grid-tie systems are generally the rule, not the exception and, in most cases, make the most sense.