I cannot help you to minimize your electricity bill but I will show you why your idea won't work.
If I understood correctly, your system will be like the following:
simulate this circuit – Schematic created using CircuitLab
Suppose 220Vac/12VDC converter has an efficiency of %95 (heavily optimistic expectation) and 12VDC/220Vac inverter has an efficiency of %90 (ultra-heavily optimistic expectation). Since they are cascade-connected, total system efficiency will be the multiplication of those two:
\$e = e1 \cdot e2 = 0.95 \cdot 0.90 = 0.855\$
What does this number mean? If your home appliances use, say, 1000W then total power drawn from power grid will be 1000/0.855 = 1170W.
See? A terrible idea!
I'm not an expert about energy efficiency but at least I can say:
- Use LED lamps instead of fluorescent or incandescent lamps.
- Avoid over-usage.
- We Turks have a motto: "Lüzumsuz ise söndür" which means "Turn it off if not using".
- We have an infinite source: Sun light. Make use of it.
- Finally, google "minimize electricity cost".