Awl --

PBS's World Focus had a little ditty on Denmark energy efficiency -- $15
per YEAR heating bills! Holy ****....

ROI on these systems seems to be about 10 years, whose initial cost is about
10% of the house value -- which was either $60,000 or 10% of 60,000 -- heh,
just a zero....

But inyway, one method was a heat pump/AC that uses buried coils (3 feet
underground) as the heat exchanger. I don't know if it's a formal heat pump
as in a minisplit ($15 wouldn't go very far, even with inverter technology),
or if the underground is just a passive equalizing heat resevoir, with water
as the transfer medium.

One home-moaner smartly distinguished "solar heating" from "solar cells",
and uses the solar heating for direct heat transfer for hot water, and solar
cells/panels (photovoltaics) for electricity -- a separation that allows
much bigger bang fer yer photonic buck.

The diff between Denmark and the US in all this is that there seems to be
much more government interest, ergo more apparent development and
progress -- depending on the PR spin. It's not clear whether this stuff is
in the "every man's" home, or still for experimenting arkytecs.

Rainwater is collected in underground tanks, as well, for less critical
water usage.

You might be able to catch archives on pbs.org.
--
EA, and PV'd with $15 per DAY utility bills.....