Well, an extension cord to your neighbor's garage meets
the "free" criterion. ;p
This, like renewables, depends greatly on the local environs.
Legal, geographic and meteorological.
Hydroelectric is the best if you happen to have a year-
'round stream and a substantial fall or flow on your
property. Old-school and fairly cheap conversion to
electric, no interruption of supply every night or on
still days, no waste and compact plant for the power
output.
But this is not a common resource. A good one to bear
in mind if you're planning to get away from it all, though.