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Hawaii First to Harness Deep-Ocean Temperatures for Power

scientificamerican.com

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Re: Hawaii First to Harness Deep-Ocean Temperatures for Power

#21

Post by Steko »

sandworm101 wrote: post #4

I have to ask, but since so much of Hawaii's electricity production feeds air conditioners wouldn't it be more efficient to pipe this cold water into houses as coolant? Or to a datacenter?

I'd question how accurate this premise is. There's a comment above that makes this claim but without citation and it certainly isn't my experience and isn't supported in sources I see.

http://apps1.eere.energy.gov/states/residential.cfm/state=HI

https://www.pointclickswitch.com/household-energy-consumptio...

There is a company doing what you are suggesting though, looks like ebay founder Pierre Omidyar is now owner:

http://honoluluswac.com/

Re: Hawaii First to Harness Deep-Ocean Temperatures for Power

#22

Post by deelowe »

Dylan16807 wrote: post #10
dogma1138 wrote: post #9

Earlier quoted context omitted.

It does't work that way crystals will still form, and salts mean free ions free ions mean corrosion.....

If you evaporate half of seawater, you're still down at one quarter of salt's saturation level. That will form crystals even if you keep things mildly mixed? Corrosion is a worry, but isn't that something you can fix with material choice?

> Corrosion is a worry, but isn't that something you can fix with material choice

Not really.

Re: Hawaii First to Harness Deep-Ocean Temperatures for Power

#23

Post by hacker234 »

nashashmi wrote: post #17
Animats wrote: post #6

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.

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?

Re: Hawaii First to Harness Deep-Ocean Temperatures for Power

#24

Post by narrator »

sandworm101 wrote: post #4

I have to ask, but since so much of Hawaii's electricity production feeds air conditioners wouldn't it be more efficient to pipe this cold water into houses as coolant? Or to a datacenter?

Electricity is much easier to move around than water.

Re: Hawaii First to Harness Deep-Ocean Temperatures for Power

#25

Post by Asbostos »

imh wrote: post #18

Man, I really would have expected scientific american to do a better job with their units. Power (watts) is a rate, so a 100 kW facility will power 120 homes, not "120 homes for a year."

Yes. kWh and kW confuse journalists no end. Even with a little common sense and no science knowledge, it's clear that the plant won't stop operating after a year of 120 homes because it's somehow used up all its energy. What did the author expect would happen after that year was up?

Re: Hawaii First to Harness Deep-Ocean Temperatures for Power

#26

Post by stmfreak »

hacker234 wrote: post #23
nashashmi wrote: post #17

Earlier quoted context omitted.

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.

Re: Hawaii First to Harness Deep-Ocean Temperatures for Power

#29

Post by colordrops »

stmfreak wrote: post #26
hacker234 wrote: post #23

Earlier quoted context omitted.

> 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.

Re: Hawaii First to Harness Deep-Ocean Temperatures for Power

#30

Post by dredmorbius »

sandworm101 wrote: post #16
Dylan16807 wrote: post #10

Earlier quoted context omitted.

If you evaporate half of seawater, you're still down at one quarter of salt's saturation level. That will form crystals even if you keep things mildly mixed? Corrosion is a worry, but isn't that something you can fix with material choice?

Corrosion is an immense problem with salt water in large systems. Eliminating dissimilar metals across so many parts is tricky. Even then, unless you're going to plate everything in gold, corrosion will happen. The far easier solution is a heat exchanger between the saltwater and some other working fluid (ie radiator fluid) inside the system. I'm a bit surprised that the hawaii rig is pumping in actual sea water rath…

Indeed, it is. I think I was vaguely aware of them previously, but I ran across a reference to sacrificial (galvanic) anodes a ways back. Fascinating.

https://en.wikipedia.org/wiki/Galvanic_anode

A galvanic anode is the main component of a galvanic cathodic protection (CP) system used to protect buried or submerged metal structures from corrosion.

They are made from a metal alloy with a more "active" voltage (more negative reduction potential / more positive electrochemical potential) than the metal of the structure. The difference in potential between the two metals means that the galvanic anode corrodes, so that the anode material is consumed in preference to the structure.

Essentially, the galvanic anode is "sacrificed" as corrosion attacks it rather than other bits of your mostly-metal structure in salt water.

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