It does not matter to south, west, east or even a little bit towards north. Each roof surface, each partway sunny facade is urgent necessary for the generation of energy.
7500 kWh electric power per year and inhabitant is typical for high industrialised countires. Some consume can bei optimized, but on the other side, new consume by plug-in hybrid cars. This can be calculated like this:
1 car for 2 people
16,000 km per year, 15 kWh for 100km electric power
80% of all travels electric
Makes 1920 kWh per car or 960 kWh per inhabitant. So 80% electric traffic is an additional consume, which can be compensated by more efficient electric power usage in other areas. But this all should be produced in the future with sun, wind, the existing water power plants and biomass.
Alibi solar collector is not enough
This quantity estimation shows: The alibi solar collector on the roof, like a flag to show green convincing, is not enough. Also a roof with solar collectros is not enough. Even a roof with photovoltaic is still not enough.