Commenter Pangolin made a point about the cost of ground source heat pumps, an energy-saving technology, in his comment about Hansen’s open letter: “If I cluster installation of my geo-exchange systems (4 homes) I can realize significant savings in the greatest cost of the system, the drilling for the ground loop. If I bundle systems into neighborhood or block thermal-service units unit costs go down again.”
Just so. To take an extreme example, a neighbor of mine had a ground source heat pump installed for $15,000 in a single-family residence (her home was ideal for the technology in a number of ways). Normally such systems run $20,000-$40,000. However, that cost can drastically be altered when shared. In 1992, a HUD Oklahoma apartment complex, Park Chase Apartments [PDF], installed heat pumps for 348 units for a cost of around $6,800 per unit — about $10,000 per unit in 2009 dollars.
Even on the four-unit basis Pangolin mentions, the price could be lowered not only by a shared ground loop, but by shared pumps, and by timing installation to coincide with road repair, and placing the loop under the street. I suspect that done on the block level or even along a single street the length of a block, this could lower costs to $15,000 per unit.
This is not a technological change in the usual sense. But it makes use of smart cooperation to use technology more effectively. And this is only one of many cases where we can use cooperation to drastically lower the cost of the investments we need to make to replace fossil fuels. You can look at it as a form of technology if you want to. Certainly it is innovation — an innovation in social relations rather than machines.