The sun is not sustainable. In a few billion years it will collapse on itself and implode, destroying our solar system (and beyond).
Self-sustaining energy is, by definition (in our current understanding of thermodynamics in this universe), not possible.
So the question becomes, like with the sun, HOW sustainable can we get? How long can it continue producing energy, with how much waste/exhaust, and how much cost?
My knowledge on this topic is extremely limited...I only know enough to know that it's foolish to claim to know too much.
And that the Next Big Thing always looks like Magic to those who don't understand what makes it work.
So even though my first reaction is to say that the mystique around Tesla is overhyped, and most of his ideas -- although admittedly surrealistic genius -- were non-functional and lacking in complex knowledge of practical applications (aka "Don't work")....
...I would be very quick to qualify that reaction by saying, I'll be the first in line to congratulate you for proving everyone wrong, should you actually make it work.
"Sustain itself for 50 years..." on what? Like...a nuclear power plant is considered "sustainable energy," when sustainable energy is defined as "meets the needs of the present without compromising the needs of future generations." (of course that's only true if you're not worried about the pollution to groundwater/from spent rods/potential of fallout).
So for example, fossil fuels are not considered sustainable because, although they meet our needs fairly satisfactorily, we can easily imagine a time within only a few generations where fossil fuels alone will not satisfy the planet's energy needs.
On the other hand, solar power is (in the current iteration of the technology), also NOT SUSTAINABLE, because it doesn't come close to meeting our CURRENT energy needs (even though it has little negative effect on the needs of future generations).
Usually when you say "energy source" you're talking about a raw material that is put through a technological process to become "work." So gasoline, expanded by measures into controlled explosion chambers becomes kinetic energy and heat, which is harnessed by pistons and transferred to rods and wheels to do "work" (the work of moving your car forward). The gasoline is the energy source, the internal combustion engine is the technological process through which the gasoline is put.
With wind power, the wind is the "energy source" and the turbines are the technology. But do we really have a full enough understanding of the complexities of fluid systems on a scale as large as global weather patterns to be able to say that carpeting the ground with turbines would be sustainable? In fact, we do know that the very very large turbines DO change the weather systems near the ground...for all we know, enough turbines to power the globe would also create freakish storms and floods and snowstorms...it's just too complex, anyone who says they know with ABSOLUTE CERTAINTY is lying (or doesn't know what absolute certainty means).
So ... are you talking about a new energy source? Or a new technology to harness a already-known energy source (which may or may not be currently underutilized)?
If you thinking of a variation on the old theme of a waterwheel fed by water siphoned from the bottom of a shared tank (so the same 500 gallons of water fall on the wheel to move it, then into the tank, then is gravity syphoned back up to turn the wheel) then...well, I was going to say you're chasing a dragon, but then again the next big thing might very well be harnessing the power of gravity. (Or, like in that waterwheel, harnessing two sources in tandem; in that case, the energy sources are water to turn the wheel, gravity to feed the syphon, and air pressure to feed the syphon).
Maybe, MAYBE, there are synergistic effects that we haven't explored yet (synergistic meaning the result being equal to something greater than just the sum of the parts)....maybe the answer to our energy disaster lies in understanding how to make 1+1 = 30.
Interesting...but it has to be cranked by hand? I won't ask you to give any more details, and I definitely don't mean to discourage you from exploring/experimenting. Only meant to remind you that you will need to convince much more cynical people than me.
My plan is to have a few small windmills and my roof covered in solar pannels...