[mattmaroon]

You have had to spend energy to get the floating container to the bottom.

If you filled it with something heavier than water, or left it open to the elements to sink, you still would have to spend a bunch of energy to pump it clean at the bottom.

Probably still easier to just pump the water up.

[sikonomial]

The container doesn't have to float. The container could have density of 1020.00001kg per m3 and it will sink. Saltwater is 1020kg per m3

Then when you fill container with fresh water 1000kg per m3 it will float.

[patall]

I think I see what you do not understand. Your freshwater is at surface pressure, not at depth pressure. You cannot just displace the salt water from your container, you need pressure to displace the saltwater and put the freshwater out of the filter chamber and in the container. That does not just happen because you cannot do it in the filter chamber as else, that filter chamber would lose its pressure differential and not work anymore. Sorry, but your idea is not made for reality :)

[mattmaroon]

The idea is a perpetual motion machine (the water of the ocean is just part of the machine) and I’m trying to show OP that. They’re just skipping an energy intensive step in their heads with every idea.

[mattmaroon]

It has that density when full of air? What about when it’s full of highly pressurized salt water?

Or, if it’s open to the environment on the way down, how does it evacuate the salt water and how much energy does that take?

Even if all this wasn’t a perpetual motion machine, which it is (the sea water is just part of the machine), wouldn’t it be easier to just float some solar panels to power a pump?

[sikonomial]

The container can be similar to a hydration bladder (Google what it looks like) that is slightly more dense than salt water.

1. At bottom you fill it with fresh water

2. It floats to the surface

3. At the surface you just empty it and remove the fresh water

4. It starts sinking

5. Jump to step 1

[mattmaroon]

Right. You’re glossing over the energy required to fill a bladder at sea depth with enormous pressure on it. That requires a pump and a lot of power, just like pumping it to the top does.