One of the biggest complaints about solar-electric (also known as photovoltaic or PV) systems is that the energy produced by them is still inaccessible when the electric grid is down. This can be understandably frustrating for people who have invested large amounts of money into their PV systems and still have to put up with no power when the grid is down, even on bright and sunny days. This problem is specific to on-grid. PV systems without battery back-ups. Off-grid systems are fine, but the majority of PV systems in the US are actually on-grid.
Read the full article here: Getting Power from Solar Equipment When the Grid is Down