My suggestion would be for a 48 volt DC system. Plain
old telephone service uses 48 volts DC for battery and
PoE, power over Ethernet is usually 48 volts DC. The
wire size could be smaller than that for a lower voltage
system and the 78xx type regulators are very inexpensive
and come in a variety of wattage ratings for stepping
down the voltages. The technology to pull it off is not
exotic and can be done with all off the shelf parts.
Solar and wind power could integrate quite easily with
such a system.

TDD



And what would be the advantage? The 78xx series are linear regulators,
they are in effect a regulated resistor that burns up the excess voltage
in the form of heat. On top of that, they max out at 37V input at which
point a substantial heatsink is required to dissipate the heat. The end
result is FAR less efficient than even the lousy iron class II
transformers found in most wall warts and small appliances.

You could use a switchmode regulator to get decent efficiency, but once
you've gone that route, you may as well just use 120V or 240VAC since
the additional components required are trivial.

Solar and wind power can easily integrate with the existing grid, with
the additional advantage of being able to sell excess capacity back to
the utility. The cost of the special inverter is low compared to what
the panels cost, and dropping all the time. This proposed DC system is
just reinventing the wheel with something inferior to what we already have.