A "grid-tie" solar system is one that ties into the power grid, pulling electricity from the grid when needed, then pushing excess electricity back into the grid when the local customer isn't using the full capacity being generated by PV panels (photovoltaic). As long as the grid stays up, it's a perfect solution because it reduces or even eliminates the customer's electric bills while generating clean energy.

Because of the very fact that these systems are tied into the power grid, however, they all have a safety feature that disconnects them from the grid when the grid goes down. In other words, if the power grid goes offline, your entire grid-tie solar array becomes instantly useless and you can't power a laptop computer even if you have 100KW worth of solar panels installed. In a grid-tie system, they all are instantly shut off