Geothermal Heat Pumps

Thinking for some now about the feasibility of geothermal heat pump for our house and have decided that with our small plot of land it probably isn't feasible. Apart from that there is the cost:
As a rule of thumb, a geothermal heat pump system costs about $2,500 per ton of capacity. The typically sized home would use a three-ton unit costing roughly $7,500. That initial cost is nearly twice the price of a regular heat pump system that would probably cost about $4,000, with air conditioning.

You have to add the cost of drilling to this total amount. That will depend on whether your system will drill vertically deep underground or will put the loops in a horizontal fashion a shorter distance below ground. The cost of drilling can run anywhere from $10,000 to $30,000.

When energy costs are figured in, however, geothermal systems are probably cheaper. If the extra price for the geothermal system is included in an energy efficiency mortgage, the homeowner could have a positive cash flow from the beginning. The extra $3,500 cost of the more efficient system may add $30 per month to each mortgage payment - an amount more than offset by the savings on the homeowner's utility bill.

Added to an already built home, an efficient geothermal system saves enough on utility bills that the investment can be recouped in two to ten years.

The technical limitations for us seem to be:
Horizontal Ground Closed Loops
This type is usually the most cost effective when trenches are easy to dig and the size of the yard is adequate. Workers use trenchers or backhoes to dig the trenches three to six feet below the ground in which they lay a series of parallel plastic pipes. They backfill the trench, taking care not to allow sharp rocks or debris to damage the pipes. Fluid runs through the pipe in a closed system. A typical horizontal loop will be 400 to 600 feet long for each ton of heating and cooling.

Vertical Ground Closed Loops
This type of loop is used where there is little yard space, when surface rocks make digging impractical, or when you want to disrupt the landscape as little as possible. Vertical holes 150 to 450 feet deep - much like wells - are bored in the ground, and a single loop of pipe with a U-bend at the bottom is inserted before the hole is backfilled. Each vertical pipe is then connected to a horizontal underground pipe that carries fluid in a closed system to and from the indoor exchange unit. Vertical loops are generally more expensive to install, but require less piping than horizontal loops because the Earth's temperature is more stable farther below the surface.

There just isn't enough yard to do horizontal and I'm afraid of what we'd find if we start drilling that deep. Most definitely not oil.

It seems like there might be a case to be made here for neighbors pooling their yards together to share the cost of installation and thereby the savings from geothermal heating and cooling. I'm trying to think why I would not enter into such an agreement if my neighbor were to propose it and I guess there might be some free riding concerns: Even though we may split the cost equally we may not use it equally? I don't know. Some market failure here that perhaps the new administration could work to change (or part of fiscal stimulus?). Yes, I am still waiting for change to happen.