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Hawaii is a chain of seamount islands, so the deep ocean isn't far away. That's unusual. Continents have a continental shelf, and it's usually a longer pipe run to the deep ocean, which means the 4°C cold water warms up along the way, plus pumping costs are higher.

Solar works so well in Hawaii that the power company there is trying to stop it. Once batteries get a little cheaper, Hawaii will be mostly solar.

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Pumping costs would not be higher due to depth. There is a whole lot of pressure at greater depths. That by itself can bring the water up. There might be a slight difference in density of warmer water over cooler water that could add to pumping costs.

But I agree with the first point: water warms up along the way unless they were to use insulated pipes like heat exchangers.

> There is a whole lot of pressure at greater depths. That by itself can bring the water up.

The pressure inside a deep pipe will be the same as that outside the pipe. Where will your differential pressure come from?

From evacuating the water at the top of the pipe.

How does that differ from standard run-of-the-mill pumping?

Edit: ok, I get it, there's no suction, just removal of the water, and the pressure of the ocean pushes it back up to sea level.

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