Over the weekend I went trail running and paid more attention to the pools at the houses below. Most houses don't have pools, so it's likely that the majority of residential electricity use is AC and not pool heating. Of the houses that do have pools, it's hard to tell from a distance the difference between a solar panel and a solar collector, and house with nothing on the roof: hard to know whether the pool is heated or unheated. I did see one pool that was either navy blue or royal blue, difficult to tell for sure on a cloudy day. I thought it looked nice.
Back to the original subject...
According to this site, geothermal heat pumps are about $12,000 to $15,000 for full installation services and $3,500 to $7,500 for DIY route.http://home.costhelper.com/geothermal-heat-pump.html
I think an air-based system (either open loop or closed loop) can be built on an existing AC system for $1,500 in supplies, going DIY. Found a tube fan for $300 here:http://www.qcsupply.com/commercial-indu ... t-fan.html
And possibly a lower price on 1" by 20' PVC pipe:http://hardwareonlinestore.com/index.ph ... t_id=41045
DIY would be a bit of work, but if someone were to mass produce a system that's somewhat easy to install, that would be affordable to a lot of homeowners because it would pay for itself quickly.
A penny saved is greater than a penny earned because you don't have to pay taxes on it.