How does the combination of freeze distillation and osmotic power respect the conservation of energy?

Question

So imagine the following system. You're in a cold part of the world. Sea water isn't isn't frozen over due to the ocean moderating temperature, but smaller lakes definitely have by now.

1. Sea water flows into a hypersaline pond. The difference in salt concentration is used to drive osmotic power.

2. In the smaller pond, the water gives up energy to the atmosphere to freeze into ice and brine.

3. More sea water comes in, and the cycle repeats itself. The ice floats to the top and can be skimmed off.

So where does this all go wrong? I've seen the equivalent process for solar power (and normal evaporative distillation) be proposed as an indirect form of solar power. But here, it seems like the system is generating energy by losing it. If say, the sea water needed to be pumped to the hyper-saline pond, would it always use more energy than it gains? Is the energy input "skimming off" the sea ice?

Answer 1

The amount of freezing point depression is a function of the salt concentration in the water. This means that in the given scenario, fresh water will freeze at 0 deg C, salt water will freeze at a few degrees below that, and "hypersaline" brine will freeze at an even lower temperature. Thus, for temperatures low enough to freeze hypersaline brine, the sea water that you are trying to pump into the smaller pond will already be frozen, making it impossible to carry out the plan outlined above.