Big try at gravity wheel

[TinselKoala]

sounds good, you have admitted that there is usefull energy from gravity.   

Sure... just like there is useful money in a bank.

But how did the money get into the bank in the first place, and what happens when you withdraw it? Or try to withdraw more than you have on deposit?

[MileHigh]

sounds good, you have admitted that there is usefull energy from gravity.   

Not quite.  The energy actually comes from a change in angular momentum.  MarkE did not go down to that level.  Think leap seconds.

There is a certain amount of angular kinetic energy in the solar system.  The planets and the sun are rotating on their axes.  Then the planets in their respective orbits also have momentum also.  Think gravitational sling-shot.

There is even another form of potential energy where you can "fall out" of the solar system and head out into deep space.

Fascinating.

[MarkE]

sounds good, you have admitted that there is usefull energy from gravity.   

When did I ever say that one could not extract the energy in a change of GPE: once? 

[camelherder49]

My question did not involve how the water got into
a reservoir. The hydrology cycle takes care of that
very efficiently. Water recycling on earth is a given.

Water that falls into the great lakes region that passes
thru Niagra Falls moves from higher to lower elevations
by gravity other wise is would be static.

Water that falls into the City of New Orleans is static and moves from
lower elevation to higher elevation by a series of large pumps.

Obviously the water in New Orleans had no where to fall
but yet is was created by the same sun.

If a ball is dropped from a plane gravity crashes it to
the ground. If you pour a glass of water out of a plane
then the sun causes it to crash to the ground.

[MarkE]

My question did not involve how the water got into
a reservoir. The hydrology cycle takes care of that
very efficiently. Water recycling on earth is a given.

Water that falls into the great lakes region that passes
thru Niagra Falls moves from higher to lower elevations
by gravity other wise is would be static.

Water that falls into the City of New Orleans is static and moves from
lower elevation to higher elevation by a series of large pumps.

Obviously the water in New Orleans had no where to fall
but yet is was created by the same sun.

If a ball is dropped from a plane gravity crashes it to
the ground. If you pour a glass of water out of a plane
then the sun causes it to crash to the ground.

And once any of those things have fallen, the GPE is expended.  It is gone it is kaput.  If you want the opportunity to extract GPE again, you have to supply the energy to rebuild the GPE.  In doing so you will expend more restoring the GPE than you harvested.