The systems your speaking of dont use battries. The inverter will feed the grid the whole time, or if your home and using power, it will utlise what your making and send or use the grids to suplement your useage. You can go a bigger inverter, but this would only be for having more panels installed on your roof. I cant tell you about the rebate and electricty bill just yet as I only got my solar smart meter, after pumping 320kwh back into the grid...f*cking *beep*