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The OTEC Thread Ocean Thermal Energy Conversion

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posted on Feb, 26 2017 @ 06:17 PM
Looking back over the work I've posted to this thread so far, I thought that my technical introduction was somewhat lacking. I thought with this post, then, that I would try to provide some infographics explaining OTEC. I also found a photo that provides a good reference of the scale of these devices.
These first two are provided by this website:
which I think are old NREL(National Renewable Energy Laboratory) infographics. The NREL used to maintain quite a few pages on OTEC, but they seem to have gone away in the last few years.
A closed cycle OTEC:

An open cycle OTEC:

The next images were downloaded from Makai Energy's website:
A closed cycle OTEC:

caption: A basic closed-cycle OTEC plant is shown in the figure above. Warm seawater passes through an evaporator and vaporizes the working fluid, ammonia. The ammonia vapor passes through a turbine which turns a generator making electricity. The lower pressure vapor leaves the turbine and condenses in the condenser connected to a flow of deep cold seawater. The liquid ammonia leaves the condenser and is pumped to the evaporator to repeat the cycle.

A schematic design:

This one gives a conceptual visualization of OTEC infrastructure:

This next one is taken from the Hawaii National Marine Renewable Energy Center(HINMREC):

caption: 210 kW Open Cycle OTEC Experimental Plant operated by Vega et al 1993-1998

The large concrete cylinder in the left foreground of this image is where the OTEC assembly is contained. Notice the automobile next to it. I believe from memory of reports I read on it that the enclosure was 14 feet in diameter and 25 feet high.
edit on 26-2-2017 by TheBadCabbie because: to add image captions

posted on Mar, 1 2017 @ 08:02 PM
Now I want to put some more emphasis on the potential positive environmental impacts of OTEC. I think one of the most overlooked potentials of OTEC is its potential to give us a platform to farm our oceans. With that in mind, this post is really about the urgency of this issue, my suggestion that we ought to get around to farming our oceans sooner rather than later, before we've destroyed or depleted some of its resources altogether.

I wanted to be sure and oversource this post to make my point. These are ten of the first thirteen results that I got performing a search on the words declining fish populations, which got me about half a million hits.

Two-thirds of the world's fish stocks are either fished at their limit or over fished. The UN food and agriculture organisation (FAO) has estimated that 70 percent of the fish population is fully used, overused or in crisis.

Marco Lambertini, director general of WWF International, told Reuters mismanagement was pushing "the ocean to the brink of collapse.".

"There is a massive, massive decrease in species which are critical," both for the ocean ecosystem and food security for billions of people, he said. "The ocean is resilient but there is a limit."

It has been some time since most humans lived as hunter-gatherers – with one important exception. Fish are the last wild animal that we hunt in large numbers. And yet, we may be the last generation to do so.

Entire species of marine life will never be seen in the Anthropocene (the Age of Man), let alone tasted, if we do not curb our insatiable voracity for fish. Last year, global fish consumption hit a record high of 17 kg (37 pounds) per person per year, even though global fish stocks have continued to decline. On average, people eat four times as much fish now than they did in 1950.

A video:

But by 1989, when about 90 million tons (metric tons) of catch were taken from the ocean, the industry had hit its high-water mark, and yields have declined or stagnated ever since. Fisheries for the most sought-after species, like orange roughy, Chilean sea bass, and bluefin tuna have collapsed. In 2003, a scientific report estimated that industrial fishing had reduced the number of large ocean fish to just 10 percent of their pre-industrial population.

Faced with the collapse of large-fish populations, commercial fleets are going deeper in the ocean and father down the food chain for viable catches. This so-called "fishing down" is triggering a chain reaction that is upsetting the ancient and delicate balance of the sea's biologic system.

A study of catch data published in 2006 in the journal Science grimly predicted that if fishing rates continue apace, all the world's fisheries will have collapsed by the year 2048.

Few fishing boats head out from Bonavista anymore, and none that fish for cod—there has been a near-total ban on cod fishing in Newfoundland since 1992, when stocks finally collapsed completely.

The study found that global fish catches peaked at 130 million tonnes in 1996 and have declined by around 1.2 million tonnes per year since then as a result of overfishing exhausting the supply.

In contrast, the official figures compiled by the UN’s Food and Agriculture Organisation state that the peak in 1996 was 86 million tonnes and has since then been declining by a relatively modest rate of about 0.38 million tonnes per year.

Following World War Two, industrial fishing rapidly expanded with rapid increases in worldwide fishing catches. However, many fisheries have either collapsed or degraded to a point where increased catches are no longer possible.

It is clear that marine fishes have experienced extraordinary declines relative to known historic levels (figure 1). These data are based on populations for which time series extend at least 10 years, with a mean of 25 years and a maximum of 73 years. Taken as a whole, the median maximum population decline among the 232 populations for which data are available is 83%; well over half of the populations (58%) exhibited maximum declines of 80% or more. The strong negative skew in the data, and the high median decline in abundance, are also evident at lower taxonomic levels. Among 56 populations of clupeids (including Atlantic herring, Clupea harengus), 73% experienced historic declines of 80% or more. Within the Gadidae (including haddock [Melanogrammus aeglefinus] and cod [G. morhua and other species]), of the 70 populations for which there are data, more than half declined 80% or more. And among 30 pleuronectid populations (flatfishes, including flounders, soles, and halibuts), 43% exhibited declines of 80% or more.

These results are sobering for two reasons. First, many of them have occurred in spite of an enormous effort to prevent them from happening. Second, as noted above, they are based on “historic” maxima that are not really historic at all, most fisheries having been well under way decades or centuries before the time series of data began. In the absence of longer-term data, researchers' perceptions tend to scale to time periods that they, or perhaps their parents, can remember. This results in the “shifting baseline syndrome” (Pauly 1995), whereby scientists accept data from more and more recent periods as baselines, forgetting that this allows drastically reduced populations to substitute for the much higher baselines that occurred before humans began having major impacts on populations.

All the world's oceans are at risk, but the Pacific Ocean is of particular concern. There are fewer regulations in Asia, and they are fishing more waters...

...Many of the species that are dying are vital food sources around the world -- especially for poorer countries who rely primarily on the fish population for food. Also, the ecology of the oceans is greatly impacted.

Widespread mariculture can fix this problem of declining fish populations. Offshore OTECs are ideal platforms for large scale fish farms. You can power your operation and fleet with the energy produced. Not one acre of land needed for this ultra-efficient means of livestock production. Out of room!
edit on 1-3-2017 by TheBadCabbie because: edit

edit on 1-3-2017 by TheBadCabbie because: (no reason given)

edit on 1-3-2017 by TheBadCabbie because: (no reason given)

posted on Mar, 1 2017 @ 09:06 PM
Thought I should write some more on this, so I'll start back in with that last paragraph:

Widespread mariculture can fix this problem of declining fish populations. Offshore OTECs are ideal platforms for large scale fish farms. You can power your operation and fleet with the energy produced. Not one acre of land needed for this ultra-efficient means of livestock production. Fossil fuels need not be mined or used to fuel this effort. With enough money and a little time, you can make most of the ocean pollution and species population decline issues go away utilizing this technology.

Deep sea water discharged into a pond at the surface will naturally bloom algae, the base building block for a polyspecies mariculture. You grow a little of everything in other words; or, instead of growing and feeding a link in the food chain, you grow the whole food chain. It's not quite as simple as just building a pond, of course. The proper habitat needs to be set up, but this is a doable process. It doesn't have to be a really high maintenance affair, either. You have to maintain your culture, and harvest at the appropriate times, sure. You're essentially getting your livestock feed for free though, or rather as a by product of the OTEC reaction. Done in the right location, there is no negative environmental impact, and environmentally beneficial side effects are a part of the process (like increased salp proliferation and regeneration of coral reefs!).

posted on Mar, 9 2017 @ 04:26 PM

[Andy] Baker says there’s a common misconception that heat pumps circulate corrosive seawater. Not true. The seawater raises the temperature of a coolant loop through a heat exchanger, and then is returned to the ocean.

And for corrosion-resistance, the heat exchanger — like the one in Seward — is made from titanium.

“And so this is really the star of the system. There’s no moving parts. That’s a $28,000 unit. It’s about 7-feet tall. There are 126 plates in it. In advance of it is an in-line filter that traps particles, so we don’t have clogging in the plate exchanger. And the Science Center here is looking at having a similar system — similar hardware, but on a smaller scale. And this is one of the most important investments. If you do this right and size it right, you’ll have plenty of heat coming into your system.”

Baker also discussed expanding a seawater system beyond a single building — into a neighborhood district. The concept is already in use in Scandanavia. It functions like any utility, electricity or drinking water, but it this case it would be a coolant loop. Residents could connect heat pumps to it, or not. And cities understand pipes. (Sitka, AK), Aug. 2014 - Heat pumps tap ocean’s thermal energy to warm buildings, neighborhoods.

I was watching public TV the other day and had a little video/news item about local issues. I watched in amazement that there is a variation of OTEC in use at the Alaska Sealife Center! The exchange is not between warm sea water and deeper, colder sea water, but from the air and warmish sea water. The heat exchange is geared to happen around 32°F and as noted in the article, the ocean water off of Alaska is 50°F until deep winter.

The above article is about Sitka and does a bit of explaining on why they should go the OTEC route. The guy they talk to in Seward envisions a neighborhood wide (maybe even city wide) series of pipes circulating cold sea water that your household could tap into using a smaller heat exchange unit to heat your home. The article says "it is already in use in Scandinavia" which I also did not know about!

I did not know that about the Seward Sealife Center! Figured I would share something that is close to my home and an idea that has potential and application in many northern costal areas!
edit on 9-3-2017 by TEOTWAWKIAIFF because: spelling and highlights

edit on 9-3-2017 by TEOTWAWKIAIFF because: typos galore

posted on Mar, 9 2017 @ 05:50 PM

That's interesting, I was not aware of Seward Sealife Center either. I shall have to give them a closer look.

Sea Water Air Conditioning(SWAC) is being used in a number of locations around the world. This report by OTE Corporation lists a number of them:


Since August 2004, a deep lake water cooling system has been operated by the Enwave Energy Corporation in Toronto. It draws water from Lake Ontario through tubes extending 5km into the lake, reaching a depth of 83m. The SWAC system, part of an integrated district cooling system that covers Toronto's financial district, has a cooling power of 59,000t (207MW). The SWAC system currently has enough capacity to cool 3,200,000 m2 of office space, making it the largest system in North America.

In addition to the SWAC system in Toronto, Canada has two operational systems at Halifax, Nova Scotia. The original system at Purdy’s Wharf was the world’s first and has been operational since 1986, cooling a 700,000-ft2 office complex. The second system at Alderney 5 became operational in February 2010, cooling a 330,000-ft2 office building. The Directors report that the two systems offer an annual $400,000 cost saving when compared to traditional air conditioning systems.

According to this blog at the New York Times:

Hawaii has used cold seawater to air-condition a few buildings at the Natural Energy Laboratory of Hawaii Authority on the Big Island. The lab “has been saving up to $4,000 per month since it switched its three buildings to deep seawater-based cooling,” according to its Web site.

Hawaii is well cognizant of this potential for major energy conservation. Downtown Honolulu has a SWAC project in the works according to this article:

"Nature gives us endless amounts of cold sea water that we have access to. We've got hot buildings and cold sea water really close to each other, so why not bring those two things together and really just cool using Mother Nature essentially?" explained Murray.

Honolulu Seawater Air Conditioning's district cooling system is designed to collect seawater from more than 1,700 feet below sea level. It will pump back to a cooling station in Kaka'ako, where it will transfer the coldness to freshwater that will be distributed to customer buildings through underground pipes.

"Buildings can see savings of about 70 - 80% in their electricity costs that they normally would be spending on air conditioning," described Masutomi.

Project developers say it will reduce Hawaii's dependency on oil by eliminating the need for 178,000 barrels per year, while also saving about 260 million gallons of fresh water each year.

There is a huge potential for energy conservation in coastal cities around the world here that has so far remained practically untapped...

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