> High density housing is unlikely to be compatible with that.

To the level of total energy independence? Indeed. But even an apartment can get some PV.

There's even PV specifically designed for renters in apartments.

> Also rental dwelling owners and people with limited economic resources tend to be less likely to make those kinds of capital investment.

Not so: https://www.lidl.de/p/tronic-balkonkraftwerk-860-wp-800-w-to...

As per my first line, 800 W is not going to be total energy independence.

But it's €249, cheaper than all but the cheapest phones.

In the best case, it can pay for itself in the first year; though obviously a north-facing apartment gets almost nothing from it.