Solar is still not free or unlimited. A well designed house will be more comfortable and save energy over its whole life while costing a fraction more than a badly designed house.

It's better no matter the heat source really. And it allows you to do without central heating and/or complex heating techs which are more annoying to maintain and replace

> expensive mechanical ventilation

A top of the line heat recovery ventilation unit cost the same as a shit tier air/air heat pump and has no moving parts besides the fans, which are cheap and easy to replace.

You can even make reasonably efficient heat exchangers at home with corrugated plastic sheets...