I wasn't referring to price efficiency, but the general efficiency of the system's use of resources. And I agree that given the house, you are improving that efficiency by adding the solar panel. The point was, the system had to significantly distort the resource scarcity signals to make it look appealing to build the house to begin with, and adding some solar energy doesn't change that calculus.
But most the houses are already built. I live in a house that was built in the 30s. So in my mind the resource cost has already been sunk into homes across the country. Instead a lot of folks are moving into new developments being built in downtown areas.
Perhaps repairing the houses would be less efficient than building new apartment blocks, I'm really getting well beyond my knowledge or expertise. But I'd somewhat presume that instead of building new high rise apartments downtown it would be more efficient overall if we refurbished some of the crumbling residential areas.
Course that only applies to older cities mostly on the East Coast.
Building houses is relatively cheap. The housing stock on top of the land isn't what's so expensive in cities. It's the land underneath.
The cost of the housing stock is of minor importance in these arguments, and nobody suggest tearing down existing houses just for the sake of efficiency. That wouldn't make any sense.
(A house build and paid for once can stand for hundred years or more, but only with a constant expense on maintenance in either money or sweat.)
What we want is denser urban cores. That way there will be less sprawl, and even the country pumpkins would have shorter commutes, because the countryside could start so much closer to the city centres: given the same or even larger number of people in them cities, they would take up less space.
