Hawaii First to Harness Deep-Ocean Temperatures for Power | Hacker News Reader

Hawaii First to Harness Deep-Ocean Temperatures for Power

scientificamerican.com

46 pointsdeegles34 comments

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?

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.

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/...

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...

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.

It's a question of local vs global optimization. Do we only consider energy generation tech on its current path, or explore other possible paths to lower cost tech? It's unknown if some alternate energy tech could provide lower costs per KW unless they're explored. Even if prototypes cost more, one must try to at least imagine what the costs are at scale.

Beyond the direct costs there's also to cost of the new tech vs direct cost + external costs of current tech. One knows that burning natural gas has an externalities of adding carbon to the atmosphere.

Considering that LM and other companies are also building multi-MW installations in other regions like the 10MW installation that LM is building for China I'm not quite sure what the value of this project will be since it doesn't really being scaled up by any account.

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 ...

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?

> 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.

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.

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?

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. :)

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?

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.

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

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?

Don't know most system that use that use the cold water for heat exchanging and have a closed / open sweet water loop for the actual cooling. But from every thing I've seen salt tends to accumulate on any surface under the right put a lid on a salt water container and the salt will form on the lid just with the internal evaporation/condensation cycle through sublimation

But there's only a handful of such systems in the world https://en.wikipedia.org/wiki/Deep_water_source_cooling

The largest is in Canada and they use sweet water, Norway and Finland have salt water systems that use water from the baltic sea but they seem to be simpler as they pump it into large water reservoirs under the city which won't really work for Hawaii.

Other limitations like the fact that the US builds with wood and drywall/plaster while Europe (and many other parts of the world, which were either deforested centuries ago or wasn't that much forested in the 1st place) uses concrete and concrete like blocks/materials almost exclusively even for internal walls might make it not that applicable for residential cooling.

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.

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.

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

Not really.

The OP states that the cold water intake is a 5c. That would seem cool enough to either directly cool houses, or at least greatly increase the efficiency of their air conditioners. For the later you wouldn't need to evaporate anything. Just cooling the air conditioner with water rather than external air.

< since so much of Hawaii's electricity production feeds air conditioners

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/

Electricity is much easier to move around than water.

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.

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

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

It makes the water mode dense, the opposite of this

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

Unintended consequences of deep sea ocean warming.

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

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.

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