budget. It usually costs a couple of hundred dollars for a simple circuit installation, compared to the thousands laid out for a basic grid tie solar system.
However, a grid tie solar system is preferred when generating over one kWh of electricity. Anything less would favor the grid fallback solar system. If you are not going for a heavy investment on a huge grid tie system, then a grid fallback system is the more feasible option when a lower amount of hourly power is required.
Grid failover
The grid fallback system is also useful in that it can be configured as a grid failover system, which kicks in during a power cut. This allows contingency power, but the solar power provided is wasted if it is not used on a daily basis.