Gotta power the new electric cars somehow...
Seriously, Japan is a country that already has its people living in tiny homes, uses tiny cars, and has excellent mass transit. But those efficiencies do not offset a very high population. If Japan wants to be sustained by renewables, it will need less people drawing energy.
https://www.nytimes.com/2020/02/03/climate/japan-coal-fukushima.html
Fortunately, thanks to Japan's smart immigration policies, their population is expected to fall.