GravBuoy(TM) from admin's blog

In recent years, linear generators have been employed to harness wave energy.

This actually uses gravity for power. But the most effective way to tap gravity would be to orient the generator vertically, underwater.

Buoyancy is actually produced by gravity, which makes water pressure increase as depth increases. Instead of accelerating, objects decelerate as they sink. If the water is deep enough, and density of object is not too high, the object will stop before it hits bottom. At this equilibrium point, the object is weightless!?

Any decrease in density of object will cause it to float up. Potentially faster than it sank!? The amount of energy required to pump in enough air would be very low, overcoming deep water pressure notwithstanding.

This provides an idea of the potential energy associated with buoyancy.

The challenge is to design an object (container) that can change its density reliably and efficiently. Via expansion (air spring), or by pumping air from above the surface into a cowling under the object. Then releasing it at the top of the cycle. Thus causing it to sink.

Depending on the design of density-changing object, it might be possible to use steel cables to transfer the force above the surface where it could drive a standard rotary generator. ? Using pulleys with two buoyancy objects, one at each end of cable. One in sink mode while the other is in buoyant mode. Two pulleys anchored to ground underwater (to provide tension), and the third above water to spin generator shaft. The cable would thus take on the shape of the letter W.

Using a submerged vertical linear generator provides magnetic lubrication, thus durability reaching into decades without maintenance or repair. Placed in a tank above ground, the generators could be also installed anywhere, using non-salinated fresh water, for even greater durability. Liquids other than water might also reduce maintenance requirements, while increasing efficiency. Only the ballast/buoyancy mechanism would require periodic maintenance -fast, easy, low-cost.

The system moves slowly, meaning the potential energy available underwater is less than something in free-fall above water.

Finding the resonant balance between mass of the buoyancy device, and its density change potential is the challenge.   

Large scale systems are probably practical for oceanic installations. Low budget, small-ish versions might enable households to produce more energy than they use, thus generating income by feeding excess into grid, as with solar systems. Think 30ft tank with several generators in staggered synchronization for smooth energy flow and uninterrupted production if one generator breaks. Using an array of generators in staggered synchronization would flatten the power output wattage, making it easier (cheaper equipment needed) to feed power into grid.

The vertical generator does not require sunlight, wind, fuel, etc., and quietly works away 24/7.

Cheap high mass, low power, iron magnets might be advantageous. ?

Use of aluminum pipe as core, rather than copper coils (with magnets in container), would be cheaper, and still work?

My guesstimate is that the ballast power consumption will be on the order of 1% of the total power output of the system.

It might be easier to service some large oceanic designs if the up/down container has the coils and the core tower is made of magnets. Magnets in container might interfere with crane extraction of the container onto iron hull ship. ? Magnets in container would require many times fewer magnets, thus reducing cost. ?

Thanks for your interest. Please pass this around, especially if you know any mechanical engineers, or DIY folk!