If you've ever driven by high tension, high voltage electric lines
with your AM radio on you will note that there is a rapid furious increase
in radio hiss and roar as you drive by.

That's wasted energy....Radio energy radiating from those power lines
that can be converted back into electricity.
Simple large parabolic dish antenni, or halfpipe trough antenna,
near or parallel to those lines can soak up that radio energy and by grounding the
antenni you can siphon off kilowatts of electric power converted from the captured radio
emissions coming off those lines.

My mother still owns rural property which has high-voltage power lines cutting through.

Warm ground at night for a couple of hours after sunset?...Maybe in southern California or Florida?
It might be pitch black and your silicon solar-cells are useless, but that ground warmth emits
microwave and infrared radiation and energy.
I think it's possible to develop devices to convert those microwaves and infrared radiation into electric power
for individual use or for beefing up, increasing the power supply in your city's power grid.

Lightning?....Florida has a resource that is untapped.
One lightning storm has enough potential energy to light a city all night.
One lightning stroke can charge up a WalMart-sized building full of super-capacitors that can
be gradually drained to rev up large flywheels for energy storage that would be useful.

It would be interesting to get actual numbers and values.