Can orbital energy be a source of perpetual power? A thought just came to me, and I want to comfirm it here:
If we figured out a way to harvest the energy from the orbit of the Moon, would that be perpetual?
The Moon has been orbiting the earth for billions of years without disappearing for any reason. The problem of the Moon losing 4 meters per year might be able to be solved by the energy of its orbit.
Would this form of energy be perpetual? What if it happened elsewhere? What if this planet with a Moon is in a hydrogen cloud?
 A: You could harvest lots of energy from the moon but not an infinite amount.  Taking orbital energy from the moon will cause its orbit to decay with time.
This offers its own problems.  The closer the moon got to Earth, the more extreme tides would become on Earth with potentially destructive consequences.  And, in the end, if you continued to take energy from the moon's orbit, it would collide with Earth.
A: If you could take from orbital energy, then it would decrease, until at some point in the future it would zero. Hence, it can't be perpetual.
A: We already harvest energy from the Moon. It causes the tides and stress and strain and motion throughout the Earth. As a result, the Moon keeps getting farther away. (And it causes some heating in the Earth).
The Moon at one time had a spin that was not locked to the Earth, and the tidal bulges in the Moon's shape caused by the Earth generated heat in the Moon's interior, and the rotation slowed. That rotational energy has now been used up. 
In other words, work was done on the Moon through deformations of the rock or friction of the regolith, which required energy which was lost to heat. If the Moon were an ideal elastic, and did not get hot from being bent, it would not have changed. But also no work could be extracted from the rotation.
As the Moon gets further away, the gravitational effect gets less and the rate at which the Moon retreats gets less. Sorry, I don't recall if there is a stable end-game for this scenario, at least before they are engulfed by the expanding Sun.
So, the direct answer is no, you can not use the motion of the Moon as a perpetual source of energy.
A: The first law of thermodynamics (through conservation of energy) precludes that there can ever be an infinite energy source. However one must consider infinity as theoretical. We humans might consider an energy source that could power the whole of our society for a million years infinite, but on a cosmic timescale it is merely a dot on a very, very long line.
There is also the matter of efficiency. In order for a power source like the moon to be even usable, you must be capable of extracting at least as much energy from it as you used up extracting it.
A: If the moon generates a magnetic field, then theoretically you can generate an electrical current simply by having a conductor within the magnetic field. This is called "Flux". When a conductor exists within a changing magnetic field, then a current will be generated based on the rate at which the field is changing. 
Then, because the moon is in constant motion, the strength of the field will constantly be changing based on your location, albeit SLIGHT. 
I think that the most effective, granted non-viable solution, would be to create a network of orbital wires that are arranged perpendicular to the pathway of the moons orbit, as close to the moon as you could get them, without having their structure compromised by the gravitational force of the moon. As the moon passed over the wires, a current would be generated in the same way that a car's alternator functions.
I apologize if my explanation is inadequate, or unclear. I'm sure the physics grads could explain it better.
edit: I was thinking more on this, and had a thought: because these conductors would cause the moon and the conductors to attract(magnetically), could the slow change in the moons average distance from the earth be counteracted, while simultaneously harvesting energy?
A: The answer from the mid 1700s has been that the tides are caused by the Moon,
and the tides move the Moon away.
Well maybe, but, probably not.
Both the Moon and the Earth gain mass by accretion, so both have increasing
cummulative gravitational force. The Earth is just over 81.3 times the mass
of the Moon, so it gains more mass at a faster rate. This gradually changes
the balance of power. That is, the Earth applies a gradually increasing force
on the Moon that is far larger than the gradually increasing force that the
Moon applies on the Earth. There would be four equations to solve, but, 
two (Lunar) are very small, and 2 (Earth) are large.
The result is that the Moon moves away from the Earth at a net increase in 
distance of 38.2 +/- 0.7 mm per year. A simplified equation that uses the 
81.3 / 82.3 and the 1 / 82.3 would be Earth moves about 0.5 mm down plus 
the Moon moves about 38.7 up, so the net change is the 38.2 up (away).
When using the concepts of conservation of (anything and everything), we always forget to use the limitation "in a closed system".
The Earth and the Moon, as well as all other objects orbiting a larger
sphere anywhere in the Universe, are all exposed to an "open system".
The exposure to "open system" conditions to both materials, and energy
means that conditions, and "ratios" of things change. The mass ratio changes,
the applied gravitational force ratio changes, the orbital distances change,
the angular momentums change, the kinetic energies change. The potential
energies change.
What must remain relatively constant is that the alignment must remain
co-linear. That is Earth, E-M Barycenter, Moon must remain co-linear, 
while at the same time the orbital distances and velocities are changing due to 
the changing mass and gravitationally applied force ratios.
Back to the original question, we can use the Solar and Lunar applied forces
as they create winds, and waves, and thermal heating, but there is an upper
limit to how much we can use. We could never reach the point of
using all that is available, so it would never reach the definition of
perpetual motion machines. There are always inefficiencies and losses
in any and every system.
