Wednesday, 5 March 2025

ocean buoys gravity battery

It starts as a buoy, then tethers to the ocean floor and pulls itself under.

It can go down and up to store and release energy, since it wants to float.

The Shell

Could recycle out of two scrap ships, decks facing each other.

Needs to be some size and thickness, and shape.

a diving bell?

Gas filled chamber open to the water at the bottom.

The tether winding onto a drum above the water, fairly high, because:

The air in the chamber compresses by 20x over the first 200m.

At 10m depth pressure is ~2 atm, volume halves.

At 50m is 6atm, 100m is 11atm, 200m is 21atm. 

It will need charging with air as it descends to 100m, then should handle the volume halving by design.

This means no pressure differential on the shell - it simply weighs less than the surrounding fluid.

There is negligible extra buoyant force when deeper.

Electrics

Could recycle out of elevator machinery, arrayed.

Inside each buoy

Generator/motor (probably permanent magnet)
Brake control solenoids
Pawl control motors/solenoids
Sensors for speed/position/tension
Control computer
DC-DC converters for control voltages
Probably around 1000V DC for main power to minimize cable losses

Along the seabed

DC cables linking multiple units

Shore

DC to AC inverters
Grid synchronisation equipment
Control system to coordinate multiple units

Control

The Drum

How to clutch it? To walk a large ratchet wheel? Generating while walking downstairs, etc. A little vague on how to make this efficient and reliable but someone has surely solved it.

Centrifugal brake or something to stop an uncontrolled ascent suddenly tugging on the end of the tether.

Scale

8-12m shells look quite manageable:

Forces: 200-650 tons
Cable: 155-285mm diameter
Hydraulic cylinders: 22-40cm diameter
Power: 200-640kW

15-20m getting challenging but possible:

Forces: 1,300-3,000 tons
Cable: 400-600mm diameter
Hydraulic cylinders: 56-87cm diameter
Power: 1.2-3MW


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