i'm missing something

with just trying to figure the wind power thing out . there is something i am missing. here is what i understand so for. turbine spins, 24 volts goes into a charge controler, from there it goes into batteries for storage. from there it goes to invertor, from invertor it goes to circuits. what i am lost about is when the batteries run low does that circuit go dead? or is there a switch that will switch it back to the grid? and if there is such a switch can it switch back to battery when they are charged? i guess what i am getting at is, does all of this switching happen manualy or can i by a transfer switch that works oppisite of a backup generator transfer switch. that switch switches when utility is lost.