[birdzoom (OP)]

Is there potential energy in deep ocean or the energy is only there if you do work to put some object there?

[CliffordK]

There are a few gradients I could think of.

• Temperature:  This could likely be exploited.  For example, if you had an insulated pipe leading to a heat (cold) exchange coil at depth, leading to an insulated pipe back to the surface.  You could warm a substance at the surface, and cool it at depth.  Geothermal temperature is available in some deep wells, as well as ocean floor vents.
• Current: Conventional means might be able to exploit deep ocean currents, although I don't know if the deep ocean flow rates are as high as tidal flows are. 
• Pressure: I can think of a few ways to try to get the deep pressure up to the surface, but you would be violating the conservation of energy doing so, and it won't work.

[peppercorn]

See:
http://www.thenakedscientists.com/forum/index.php?topic=31433.msg309266#msg309266

[CliffordK]

The energy required to evacuate a cylinder, or cave would be the same as you would get from refilling it, but it would be a method to store energy.

Although that does bring up a point with the BP oil well. 
Low density oil was located under high density rock pressurizing it.
And, being lower density than the water, it would still come to the surface under pressure.  At least until the well is exhausted.

[peppercorn]

The energy required to evacuate a cylinder, or cave would be the same as you would get from refilling it, but it would be a method to store energy.

Quite.  I assume the OP is aware that the pressure many fathoms down, will (at an idealised best) only represent a means to store energy, not a mean to create it in an unlimited manner.

Without, I hope, being accused of hijacking the thread, I do think this is a unrealised technology that, similar, to pumped-storage, could help balance a distributed electricity grid - by allowing peak generation and demand periods to be managed efficiently.

[CliffordK]

You could likely find some underwater ridges, like on land, that would tend to concentrate the ocean currents.  While I've never been to Baja, I think that would be an excellent place for a tidal generator, or perhaps a tidal dam.

You would likely also get some good current flow through the Bering Straight, and perhaps in some of the channels in Australia/New Guinea. 

If I'm reading this right, here are some deep water channels near Panama/Costa Rica with flows of about 10-20 ft/sec, and a discharge on the order of 1 million cubic feet per second.  The Bonneville Dam has a flow on the order of 100,000 cubic feet per second, I think.  Which would put these channels with potentially 10x the generating capacity of Bonneville if you could only figure out a way to capture the energy.

http://www.marscigrp.org/wildedsr66.pdf

The underwater battery/"reservoir" idea is interesting. 

If you dropped a cubic meter sphere, 5000 meters below the sea surface, it could store the same energy as 50 identical 1 meter spheres elevated 100 meters above the surface.

[peppercorn]

The underwater battery/"reservoir" idea is interesting. 

If you dropped a cubic meter sphere, 5000 meters below the sea surface, it could store the same energy as 50 identical 1 meter spheres elevated 100 meters above the surface.

Yes. Could be handy in an area where there is a steep gradient away from the coastline and power can be transmitted down to the depths over the shortest cable run.  Alternatively the 'equalizer' could lay at depth along an undersea link.

The motor/generator is going to require to run at very high voltage though, as no one wants a sub-station in the middle of the ocean! []

[Geezer]

[diagram=619_0]

No motor required

[peppercorn]

No motor required

I'm liking your thinking, Geez!
You do mean no underwater motor needed, yes?

[Geezer]

No motor required

I'm liking your thinking, Geez!
You do mean no underwater motor needed, yes?

Well, my version uses a manual winch, but I suppose you could substitute a motor/generator  []

[peppercorn]

Well, my version uses a manual winch, but I suppose you could substitute a motor/generator  []

Oh! That's a manual winch - I thought it was a spider going surfing! []

So when you Patenting the design then? After you've notarized ya drawing, of course!