I was going for a kind of worst case scenario (apart from using the average household), so yes: going completely off-grid using only solar is very doable (in Western countries) today.
- Most European households consume at most half the power of US households.
- The figures I quoted for Li-Ion batteries were on the low end (low power / USD and low power / liter).
- Nighttime+evening power consumption is only part of the quoted daily power consumption.
- Wind power and other renewable sources of power were ignored (although this means being on-grid).
- Efficiency of power generation during the daytime also increases by using batteries as a local buffer (vs transferring excess power to the grid or worse, discarding it)
These oversights with positive influence are of course partly mitigated by these:
- To retain current convenience levels, the batteries and power production must support the worst case. Being left without heating in cloudy winters is not an option.
- The cost of the system regulating the interaction between appliances, solar panels and batteries was omitted.
All in all, though, it seems pretty clear that technically and economically, a society almost completely powered by renewable energy (and specifically solar) is very realistic.