Harvesting the energy of sea waves using capacitance

[tarakan]

Thank you.
I am not trying to build a power plant.
I just want to understand the order of magnitude of the output.
So I can compare it to mechanical harvesters of sea wave energy.

Can we leave out the algae and storms and all the other environmental factors and imagine an ideal setting:

Ideal average sea water, electrode plate in a 0.2mm polyethylene bag with an insulated lead, some circuit that measures power output. The circuit is somehow connected with a "ground" to the sea water.

I submerge the plate in a container of sea water.

How do (micro)Farads convert into centimeters squared of an electrode, inside 0.2mm plastic?
Is it the rate at which I submerge or the force that I apply when I submerge the plate that charges the capacitor?

That original video with a static plate illustrates the work of a Wimshurst machine.

What is their efficiency, if there is any way to compare them to electromagnetic generators?
Would more (and smaller) segments lead to lower voltages and more current output?

I am looking for ways to compare methods of energy harvesting,
not for concrete engineering advice on why this would not work as a power plant.
I am not building a powerplant.

Thank you.

 

[Baluncore]

...
The circuit is somehow connected with a "ground" to the sea water.
I submerge the plate in a container of sea water.
How do (micro)Farads convert into centimeters squared of an electrode, inside 0.2mm plastic? ...

Capacitance is a parameter determined by the geometry and dimensions of the conductors and dielectric.

It takes two conductive plates to make a significant capacitor.
What area of metal plate is directly opposed to the other metal plate?
What is the separation distance between the metal plates?
The relationship between area and spacing is described here;
https://en.wikipedia.org/wiki/Capacitor#Parallel-plate_capacitor

If you have only one metal plate then the capacitance could be approximated by a spherical capacitor. The inner sphere being the size of the electrode, the outer being the distance to the ground connection.
C = 4⋅π⋅k⋅ε / (1/ri -1/ro)

Describe the geometry and the size of the two electrodes of your capacitor.

 

[tarakan]

One plate is a 1m^2 metal plate, another "plate" is sea water around the first plate.
Sea water is conductive.
This is the whole point.
Some layer of plastic between salty water and metal acts as a dielectric.
For now, I would assume that the dielectric is 0.2mm polyethylene.

 

[Baluncore]

Sea water is conductive.
This is the whole point.

That does not compute. Either you treat seawater like liquid mercury, a good conductor, not a dielectric. Or it is a dielectric, with poor conductivity, so cannot be a conductive capacitor plate. You cannot have the best of both worlds.

 

[tarakan]

That does not compute. Either you treat seawater like liquid mercury, a good conductor, not a dielectric. Or it is a dielectric, with poor conductivity, so cannot be a conductive capacitor plate. You cannot have the best of both worlds.

Yet a signal cable that runs beneath the ocean experiences capacitance, acting as a capacitor "plate" surrounded by another capacitor "plate".

Why would resistance matter for the sea water if we are accumulating charge and not current?
What about bottle capacitors that were used in Tesla era, where bottles were placed in a container of salt water and filled with salt water?

If we are talking about resistance, what is the thickness of the conductor?

It is the whole ocean around the plate. Plate resistance matters a little more. Plate lead resistance matters even more because cross section is small. What is ocean water conductor's cross section? The entire surface area of the plate electrode. (Or the "ground".)

 

[Baluncore]

Yet a signal cable that runs beneath the ocean experiences capacitance, acting as a capacitor "plate" surrounded by another capacitor "plate".

The cable is a balanced twisted pair or coaxial transmission line. All the currents are balanced and internal. It is inside a steel wire armoured case. The seawater is quite irrelevant.

Why would resistance matter for the sea water if we are accumulating charge and not current?

Because you are not accumulating charge. Capacitor charge is constant while the capacitance and voltage are changing. Charge is being pumped by the change of capacitance. The flow of charge takes place at two different fixed voltages.
A flow of charge is called a current.

What about bottle capacitors that were used in Tesla era, where bottles were placed in a container of salt water and filled with salt water?

The static voltages were measured in thousands of volts, the current was less than 1 mA. Resistance was not important as insignificant power was being handled, uneconomically.

If we are talking about resistance, what is the thickness of the conductor?

It should be sufficient.

What is ocean water conductor's cross section?

It is irrelevant and unmeasurable.

 

[sophiecentaur]

If you don't like those numbers

Can we leave out the algae and storms and all the other environmental factors and imagine an ideal setting:

Basically, it looks like the OP wants to be told that he has a great idea and it's strange why it's not already being used. He wants to discuss an Engineering project but not to consider Engineering reality. Many ideas have been aired in this thread but the OP is clearly not reading them.

It's a waste of time to continue with this.

 

[Baluncore]

It's a waste of time to continue with this.

I was originally exploring the possibilities myself, then I felt I was entertaining a silent crowd who maintained a safe distance, but now I am inclined to agree with you, it is getting very repetitive.

 

[russ_watters]

...then I felt I was entertaining a silent crowd who maintained a safe distance...

You have been, and we thank you for that. It has been both entertaining and more importantly, informative.

 

[berkeman]

It's a waste of time to continue with this.

I was originally exploring the possibilities myself, then I felt I was entertaining a silent crowd who maintained a safe distance, but now I am inclined to agree with you, it is getting very repetitive.

You have been, and we thank you for that. It has been both entertaining and more importantly, informative.

This is a good time to tie off this thread. Thank you all who were trying your best to help the OP.