Sure, but the same would be true if you bought solar panels and lead-acid batteries, which are cheaper (but less compact). Or if you bought just the solar panels, and sold the excess power back to the grid (assuming your utility provider allows that).
If you buy enough solar panels and one of these, you can remove yourself from the power grid and pay 0 with conservative nighttime usage (for an American home) buy two and you don't need to be so conservative.
Your utility company is going to want to charge you a fee (or take a cut of what you sell to the grid) for not buying any electricity from them, so that they can maintain the power lines and substations to your home.
A solar array would expedite charging, but I believe they intend to monitor energy supply rates and charge based off that as well. eg. When rates dip, it charges at a higher rate.
