Heating and cooling are the primary energy use and decrease faster than roof area increases for low rise apartments. Average apartment size is about 80m^2 so i

Heating and cooling are the primary energy use and decrease faster than roof area increases for low rise apartments. Average apartment size is about 80m^2 so in a 3 story building that's about 30m^2 each or roughly 5kWh/day. 200W doesn't allow you to be wasteful, but it's plenty for a 1-2 bedroom apartment. Hybrid cells with slightly better efficiency and low light tolerance would get you to 10kWh/d Tokyo is around 7000 people per km^2. A 2 bedroom apartment can happily house two or three people, so with a reasonable amount of roof area per apartment you have 80-90% of your area available for not-housing. High density just means not dedicating a freestanding house worth of land area per resident to force them into cars, it doesn't need to mean highrise. Even with manila levels of density you can still get lighting, climate control (if well insulated), a washing machine, a few entertainment devices at 10-20W and basic cooking (nothing for the ground level commercial or infrastructure though) with about half your area left for not-housing. So that's some level of semi-decentralisation even in the worst case. Mid-winter in high latitudes you might struggle without long term storage, but it's not unsolvable. Batteries take up approximately 0 space. If the better part of a month's worth of energy can fit in a car it's fine.