
Hawaii First to Harness Deep-Ocean Temperatures for Power - deegles
http://www.scientificamerican.com/article/hawaii-first-to-harness-deep-ocean-temperatures-for-power/#b09g04f20b15
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Animats
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.

~~~
nashashmi
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.

~~~
hacker234
> 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?

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stmfreak
From evacuating the water at the top of the pipe.

~~~
colordrops
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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dogma1138
Seems kinda pointless this only doubles the original pilot which was 50KW....
The plan was to build a 40-50MW plant within 3-5 years and expand it to 100MW+
over the following decade.

[http://www.bizjournals.com/pacific/print-
edition/2010/11/12/...](http://www.bizjournals.com/pacific/print-
edition/2010/11/12/ocean-thermal-energy-conversion.html)

This tbh looks less like any type of commercialization but more of a
consolation prize to LM since the Navy paid for the original pilot and was
supposed to pay for the expansion but due to the drop in oil prices it never
came off the ground.

Also the average household consumption in Hawaii is 2.3kW/h (gotta love air
conditioning) so looks more like 40 houses with peaks averaging at almost
double that.

BTW in comparison most commercial Gas Turbine power plants produce 400 MW per
unit, or 600 if coupled with a traditional non-critical steam turbine which
harness the excess heat.

Low power Gas Turbines small enough to fit in a sipping container which can be
delivered by truck average at around 5MW, so this whole apparatus will produce
produce 50 times less power than something that can be fit into a container,
other unites like the TM2500 by GE which can be towed by a single truck can
provide as much as 30MW of power. [https://www.ge-
distributedpower.com/products/power-generatio...](https://www.ge-
distributedpower.com/products/power-generation/mobile-units/tm2500)

So besides catching some headlines and paying some dues to LM i really don't
see this being any thing but a waste of money.

~~~
Steko
Your own link explains why it's not 'pointless':

 _There is no data on maintenance costs, possible environmental impacts on the
marine environment or potential engineering problems that could arise with a
full-scale model — not an enticing combination for private investment. ... The
pilot is needed to produce the information necessary to attract investment for
a large-scale model ..._

~~~
dogma1138
Old link was for announcing the original pilot and they've built that one,
they are already scaling it in China and other places why not scale it in the
US?

~~~
Steko
> Old link was for announcing the original pilot and they've built that one,

You seem confused about something, that link is announcing a 5-10 MW system
they didn't build. Or rather what they built is the system that you're calling
useless.

> they are already scaling it in China and other places why not scale it in
> the US?

That question is answered in the comment you replied to. China doesn't care
about things like marine life and runs on giant government capital
investments.

~~~
dogma1138
Well you sure seem to think so, while everything pointing to the fact that
they are just bringing the initial pilot to full capacity rather than
developing or scaling the technology further.

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imh
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."

~~~
Asbostos
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?

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cpeterso
Arthur C. Clarke wrote about an ocean temperature power generator like this in
a short story back in the ~1950s. Reading this article, I now understand why
systems like this haven't been more common. :)

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sandworm101
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?

~~~
dogma1138
The temperature of the littoral water in Hawaii isn't cold enough (77f/25c
during winter an 85f/28c during summer) for efficient transmittance cooling
not to mention that salt water can't be used for evaporative cooling like the
one being used by commercial AC units for fairly obvious reasons.

~~~
Dylan16807
Is it hard to evaporate half of saltwater and dump the rest back?

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dogma1138
It does't work that way crystals will still form, and salts mean free ions
free ions mean corrosion.....

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Dylan16807
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?

~~~
sandworm101
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 rather than dropping a radiator into
the depths. That intake pipe will corrode eventually.

~~~
dredmorbius
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](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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hadeharian
Good to see that the concept which was first presented to me in an ACT problem
is finally becoming a reality. It would have been nice to have heard about
this before taking a timed test. Much too fascinating and time consuming.

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caseyf7
Meanwhile in Hawaii, solar power is generating more power than the grid can
handle.

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duaneb
What are the environmental impacts of sucking the heat out of the ocean?

~~~
SixSigma
It makes the water mode dense, the opposite of this

[https://en.wikipedia.org/wiki/Effects_of_global_warming_on_o...](https://en.wikipedia.org/wiki/Effects_of_global_warming_on_oceans)

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sitkack
Unintended consequences of deep sea ocean warming.

~~~
stmfreak
No one worries about these things when the numbers are big. I say the same
thing about geothermal energy.

~~~
sitkack
Just like the ocean and the atmosphere is an infinite sink for carbon. Look at
fraking causing earth quakes, things we can't internalize will never effect
us. The crust of the earth is an eggshell floating on liquid rock, we should
take care of it.

