# Talk:Ocean thermal energy conversion

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## Role of Cold Water in the Open System

In the description of the open system it says that the steam is generated by pumping surface water into a chamber that is under vacuum. This lowers the boiling point and causes the water to turn into steam which is then used to power a turbine and generate electricity. If the point is ONLY power generation then what is the purpose of pumping the cold water up? Couldn't the steam simply be released

Recall that this is a heat engine and works on the difference of temperature of two reservoirs. Presumable the surface water and air are at about the same temperature, you need to reject heat to a cold reservoir. The problem with OTEC is generally the lamentably low temperature differentials available, which means vast volumes of water must be circulated to obtain useful amounts of power. Perhaps this needs to be explained better in the article, let me look. --Wtshymanski (talk) 19:19, 27 January 2011 (UTC)
The opening sentences Ocean thermal energy conversion (OTEC or OTE[1]) uses the difference between cooler deep and warmer shallow waters to run a heat engine. As with any heat engine, greater efficiency and power comes from larger temperature differences. look pretty clear. What did you think of them
No I get that its supposed to be a heat engine and that the greater the heat gradient the more energy you can extract with a heat engine. In something like a stirling engine or even the closed and hybrid OTEC systems I understand what the cold reservoir does and why it is necessary (at least I think so). What I don't understand is what the cold reservoir does/why it is necessary in the open system (I imagine it probably is necessary, I just don't understand why from reading this article). The way I'm reading this is that in the open system, a vacuum is used to make the sea water turn into steam at a lower temperature. This steam is then used to turn a turbine. In the closed/hybrid system you would need to cool off the working fluid so that it condenses back into a liquid and can be cycled back to be re transformed into steam again etc. In the open system however, the working fluid is sea water which you have for all intents and purposes an unending supply of.
In summation: If the steam has already imparted its energy to the turbine, and you have more liquid working fluid ready to be transformed into steam, why do you need condense the steam back into a liquid? Why can't you just vent it and start over with new sea water?Sxoa (talk) 21:45, 27 January 2011 (UTC)
What makes the steam flow through the turbine? If you don't condense it, there's no reason for the steam to continue flowing. This is another problem with OTEC systems, any dissolved gases in the cold water come out when the water warms, increasing back pressure in the condenser. But even an open system is still a heat engine and still needs the temperature difference to work. --Wtshymanski (talk) 03:15, 28 January 2011 (UTC)
The steam flows through the turbine because its heat energy makes it expand giving it increased pressure. A turbine in a hydroelectric dam for example is an open system that uses a turbine that is not a heat engine. Ok looking at surface condenser I think explained it. Since the stuff is boiled under vacuum you need vacuum on the other side as well for the steam move. Condensing the steam with cold water helps create the vacuum on the other side. A vacuum pump I think could also do this (i.e. venting it) but presumably would not be energetically productive anymore. — Preceding unsigned comment added by Sxoa (talkcontribs) 07:30, 28 January 2011 (UTC)

## Jules Verne

In the french version of this article it is said that the first mention of the OTEC technologie is from Jules Verne (in Twenty Thousand Leagues Under The Sea). Is it true ? —Preceding unsigned comment added by 82.243.242.13 (talk) 19:24, 20 December 2007 (UTC)

French WP makes the claim it is from 20,000 leagues under the sea. However search of public domain copies of the book yield no occurrence of electricity and variant combinations- surface water, cold water etc. Credit appears to properly go to French physicist Jacques Arsene d'Arsonval. J JMesserly (talk) 19:12, 28 May 2012 (UTC)

## Why so complicated?

The process presented here looks pretty complicated. Why would someone want to do this when the same thing could be accomplished by something simpler, like a stirling engine? Is there some subtlety that I'm missing that makes this process more efficient at extracting energy than the Carnot cycle? Flatline 19:47, 2005 May 25 (UTC)

This article is written in an over detailed way. An encyclopaedia needs to give the reader an initial introduction to a subject. This early resort to mathematics only serves to obscurify the subject and put off the general reader. A more qualitative approach is needed. Lumos3 16:30, 27 May 2005 (UTC)
I've tried to start doing that by making a first shot at discussing the economics. How about a simple diagram showing a rig with a big pipe and the flow of water? Are there better estimates out there for cost? --Kris Schnee 08:08, 5 May 2006 (UTC)
I skiped over most of the math, but the text just before and after the math was helpful as were the other details. Generalities are near useless ie I have no idea how Flatline expects to run a Stirling engine on hot and cold water. Please keep and add more detail. The complications are essential to get net power out, otherwise the auxillary systems use all the power produced. Ccpoodle 17:00, 24 October 2007 (UTC)
OK, with the new info on history and the pictures, this article is looking better! I also worked again on the opening, but the wording is still kind of repetitive. Is the total energy really that much greater for OTEC than for wave power? Even if so, the real issue is how much of that energy can be extracted at a profit, same as with any other energy source. --Kris Schnee 03:11, 6 May 2006 (UTC)

## Stirling Engine

Why not use a Stirling Engine using surface and deep water to create the two temperature zones? I get the feeling I am missing something but cannot pinpoint it.

Wow. Slashdot has linked to this article today ... and still noone can answer this. Somehow, somewhere there is a moral to this, possibly in the same day Slashback article.
A sterling engine would be more complicated, not less. You need two heat exchangers both for a sterling engine and a closed-cycle turbine. The turbine itself is much less complicated then a sterling engine (at least IMHO). Both require a working fluid (probably hydrogen for the sterling engine and ammonia for the closed cycle turbine). Economically speaking, a sterling engine might make more sense for a very small scale installation, but there's a reason large power plants use the rankine cycle instead of the stirling cycle. Toiyabe 20:12, 5 January 2006 (UTC)
Also Stirling engines are very inefficient at the low temperature differences available in OTEC. Lumos3 12:28, 11 November 2006 (UTC)
The Low-Tempurature Differential Stirling Engine that would be able to run on the tempurature spread could be theoretically more efficient than a vapor turbine but only in small applications. The problem most of the engineers I've researched cite is the exponentially lowering heat transfer rate per volume of heat transfer fluid as you enlarge a Cylinder bore or Displacer. Basically, the same reason the heat in the ocean doesnt migrate to the lower thermoclines. As the sheer volume of working fluid space grows, the surface area required to contain that fluid becomes less and less, therefore providing less heat transfer surface area per volume of working fluid and slowing the flow of heat through the engine to a point where the mechanical motion required to keep the engine running is impossible to achieve. Solutions for this have been suggested, but basically need to increase the rate of heat transfer to and from the working fluid at the heat exchangers. -JamieG 28 May 2012

#### Patents Issued for Stirling OTEC

FYI, patents have been issued internationally for an OTEC platform based upon the Stirling thermodynamic cycle. See http://www.google.com/patents/US8429913

My research has shown that the capital investment costs of deploying an OTEC platform based upon stirling cycle OTEC can cost 85% less than existing OTEC designs based upon the rankine cycle generating the same amount of gross power output. Rankine-based OTEC's net power output suffers when 30% of its gross power production is needed to access (pump) large amounts of cold water to the surface.

This design has also placed in the top 100 innovative ideas submitted to the GE Ecomagination Challenge . See submission here. — Preceding unsigned comment added by 134.174.140.32 (talk) 20:21, 18 November 2013 (UTC)

## Or a Minto wheel

Imagine a 30' wheel with 50 gal drums on each end half full of seawater for weight and a mixture of butane and propane (LPG gas) for the propellant. The bottom of the wheel sits in the surface water, and deep water from far enough down to be cold is pumped to the top of the wheel to cool it. Hang the efficiency, it's low-maintenance, built out of trash, and generates a steady kilowatt or two: It's the perfect thing to operate the home appliances on your postapocalyptic mid-ocean floating village. Minitrue (talk) 16:26, 7 September 2010 (UTC)

## Can't get a date

Can somebody confirm the 1930 date? I've seen 1926... Trekphiler 03:00, 29 December 2005 (UTC)

## Aquaculture

Can we get an expansion of the Aquaculture entry as it applies to the OTEC? What advantages does an OTEC supply to aquaculture?

As I understand it, deep water is relatively rich in nutrients, so bringing water up from below would be a way of fertilizing aquaculture operations in the shallows. This article [1] mentions such an experiment, which was unsuccessful. This book [2] has lots of info on aquaculture. Also, kelp grows best in cold water, so bringing cold water towards the surface would be good for shallow-water kelp farming in warm areas. --Kris Schnee 07:35, 5 May 2006 (UTC)
At high tide, there is water pressure that OTEC wastes, unless it can bring the still cool nutrient water to plants and kelp. Without OTEC considerable energy is used to deliver water to the plants and the water is typically less nutrient rich. Ccpoodle (talk) 14:12, 22 November 2007 (UTC)
OTEC, not OPEC. --Wtshymanski (talk) 21:32, 22 November 2007 (UTC)
The primary advantage to OTEC is that with the cold deep sea water and the warm surface water, you can create proper environments to grow anything. Thus most of the company's that use the OTEC infrastructure in Hawaii are growing things like Maine Lobsters in captivity. Also in the case of Crustaceans like crabs and lobsters, temperature affects how much water is saturated in their flesh, so while ocean caught lobsters are susceptible to the temperature changes and you could be paying for water weight. Using OTEC, you can raise crustaceans at the optimal temperature to reduce the amount of water in the meat. —Preceding unsigned comment added by 64.75.249.5 (talk) 01:48, 26 July 2009 (UTC)

haha well yes this is trueee . — Preceding unsigned comment added by 75.72.108.231 (talk) 03:28, 13 November 2012 (UTC)

## Thermocline Transducer

I was wondering if this technology is or resembles the thermocline transducer base facility from SMACX. If so, shouldn't the article make a mention of it?

## Link not working?

Hi, just tried to retrieve reference no. 1, but the link does not seem to work. Heda 62.68.29.247 13:09, 7 September 2006 (UTC)

## Geography 101

"The limited geographical area in which it is available"? Have you seen the size of the Pacific Ocean? The Indian Ocean? We're talking about millions of km². Can't access it? Good reason to develop Power Relay Satellites... Trekphiler 06:31, 29 September 2006 (UTC)

By limited geographical area I'm pretty sure they are referring to the fact that this only works if the temperature difference between the cold deep sea water and the warm sea water is high enough, which limits the geography of OTEC to tropical climates. Also in order to keep the construction to a reasonable amount, the location also needs to be near a deep drop off when you look at the underwater topography. —Preceding unsigned comment added by 64.75.249.5 (talk) 01:37, 26 July 2009 (UTC)
Near the poles, or anywhere that has a winter, there's a huge delta-T between water and air. Minitrue (talk) 16:30, 7 September 2010 (UTC)

## Global warming?

Wouldn't that greatly contribute to global warming? For one, the deeper, colder ocean layers would be heated and could dissolve less CO2, liberating it into the atmosphere. Also the upper sea levels would be cooled and so be able to take up more heat from insolation. Of course there would be no such effects from only a few such power plants, but the effects should be visible if this technology would be used on a large scale. 84.160.255.160 11:28, 11 November 2006 (UTC)

I think we get only benefits the first 1000 years, even if OTEC supplies 1/2 of all the world's energy needs. Electric pumps would leak some waste heat to the deep water, likely about the same heating if cool water is pumped to great depths to power the pumps that bring the 5 degree c water to the surface, the water thermocline is warmed very slightly. Only trivial amounts of CO2 bubles at great depths would reach the surface in the first 1000 years. This is more than offset by cooling the surface water slightly, which allows the surface to absorb more CO2 and more heat. The CO2 which is disolved in the water brought up from the depths, does not have to be dumped/much of it could be sequestered at moderate extra cost. Ccpoodle 17:33, 24 October 2007 (UTC)
I'd like to see some numbers on this idea. I suspect that the oceans are so fast that it would make no difference. OTEC releases zero green house gases, its these which alter the thermal equilibrium of the earth not flows of existing heat within the atmosphere, oceans and the earth's crust. Lumos3 12:33, 11 November 2006 (UTC)
I think I have a source (in print on the book shelf) that discusses why this is not a problem. From memory is much as you say, the oceans are too big and replenishing too fast for anythign less than tens of thousands of these to even have any noticable impact. Plus the contribution to reduction in CO2 would actually come from the nutrients in the deeper water being pulled up in the middle of the ocean which is the oceans equivlent of a desert. It would cause a boom in growth of biomass which if allowed to die and sink or enter the food chain (rather than being harvested) would act to sequester that carbon in biomass. I will see if I can dig up the source and mention it here on the talk page, if it is relavent enough we can work something into the article. Dalf | Talk 12:54, 11 November 2006 (UTC)
Me too, I'd like to see some serious numbers there, but I don't have any. From first thought, I doubt that OTEC would not release CO2, by heating up sea water in which CO2 is dissolved. And algal blooms are generally not mentioned with a positive ecological connotation. Naturally, the effect of a few such plants on the oceans would be neglectible --- just as the effect of a few thousands of carbon based firings would not significantly change the composition of earth's atmosphere. 84.160.255.160 21:58, 11 November 2006 (UTC)
Well, basic thermodynamics tells you that when you extract energy (here in the form of mechanical or electrical energy) you correspondingly reduce the energy in the system you extracted the energy from. So you heat the cold part of the water and you cool the hot part. Net effect then is a net cooling of the oceans. As for circulation it is well known that the Gulf Stream is flows fast, warm water on the surface towards the Arctic where the cooling (plus the salt pump) make sthe water sink and return to the Gulf along the sea floor. From the North Sea oil operations it is known that the cold return water is colder than 0 degrees celcius, which is the reason anti freeze is injected into the undersea gas pipelines. All in all I cannot see that there is a danger of heating, quite to the contrary. And if you are extremely efficient in the Gulf of Mexico you might just reduce the incidence of damaging hurricanes. that appear when the surface water is above ca. 27 degrees celcius. --17:01, 27 January 2007 (UTC)
OTEC taps into the hydrologic cycle which is driven by solar radiation incident upon the oceans. To put it into perspective, each day, the solar radiation incident upon, and absorbed by, the tropical ocean is significantly more than 1000 times the current global energy consumption over the same twenty four-hour period. Thus, even anticipating the eventual industrialization of the rest of the planet, we will likely never consume more energy than the _natural_daily_fluctuation_ of this enormous thermal resource. This is significant. Basically, OTEC is tapping into the background noise of energy that is absorbed by the ocean and is then used to generate steam from a thermal differential which drives a generator. Co-products from this process can be used for aquaculture, desalination and hydrogen production. OTEC technology has a slightly high initial cost but a low operational cost and most importantly, has no cost of the seawater itself, other than the cost of building the OTEC system itself which delivers the seawater through a large pipe. Therefore, efficiency of the OTEC process isn't a good determining factor for whether the technology should be implemented. For example, a coal power station needs to have an efficiency rating to determine how much energy it will output for a given input of coal over a given amount of time. Coal costs money to extract from the ground and to sell to the market. OTEC only has an extraction cost of the deep ocean water itself, and the extraction method (pumps) gets energy from the OTEC process itself. The other important consideration is that an OTEC plant can provide base-load power. Once the plant is operational it can function, uninterrupted for extended amounts of time. This is due to it's low pressure, low temperature operation.
It's not too good to be true. Thermodynamics are obeyed and it really isn't that complicated. It generates a net positive which is enough to drive electrolysis and to power pumps to take water to various subsystems such as hydrogen production, aquaculture, agriculture (island based), sea-water air conditioning and desalination holding tanks. Once you get it started, it keeps going. Yes it works, yes there is hard scientific data on it. The US government has spent millions of dollars perfecting this technology in conjunction with Universities, NREL and DOE.

## Ecological impact

A more thorough analysis of ecological impact of global OTEC implementation would greatly benefit this article, IMHO. People here stated some generals about negligence of energy magnitudes involved in the process relative to what is supplied by solar radiation, but it sounds like "Ahh, don't worry..." to me. Suppose a massive OTEC production is concentrated in a region - what would the impact be on the region's sea life? Might a slight artificial regional change in natural water thermal cycle trigger a bigger, global unexpected change? —Preceding unsigned comment added by 84.94.63.75 (talk) 14:40, 27 January 2008 (UTC)

Short answer: yes. Just 1 case: alter PacOc temp in tropics by 0.5°C, you could trigger a Dustbowl & decade-long drought; that's all it took in the '30s. You'd have to pump up a bunch of cold water, tho. Trekphiler (talk) 02:04, 28 January 2008 (UTC)
You are completely wrong. It will not damage the marine ecosystem. Excess effluent would be returned to a location within the ocean matching the temperature of said effluent, which is, of course, sea water. —Preceding unsigned comment added by 71.117.98.55 (talk) 18:22, 15 July 2008 (UTC)
If you're bringing cold water up & extracting energy... As I said, it would take an enormous volume to change the surface temp in any case. Want to guess how much it would take to lower the surface temp of the Pacific Ocean by even 0.5°C? And how long you could run the entire world on the amount of power you'd generate doing it? TREKphiler hit me ♠ 23:55, 15 July 2008 (UTC)
Impact on sea life? Compared with, say, releasing a dozen cubic miles of toxic slime every few years? Mixing the layers oxegenates the depths, causing all kinds of goodness and glory by increasing the carrying capacity of the water. —Preceding unsigned comment added by Minitrue (talkcontribs) 16:35, 7 September 2010 (UTC)

Hello all, I have added what I can about the recent environmental studies done for OTEC in the Environmental impact section. Hope this is acceptable & helpful. Mechengineer2012 (talk) 06:47, 27 March 2013 (UTC)

## Size matters

"Very small temperature difference"? Pournelle compared it to a 90' head. Can somebody offer some perspective? Trekphiler (talk) 01:12, 6 April 2008 (UTC)

The temperature difference to keep the cycle going is about 20˚ —Preceding unsigned comment added by 64.75.249.5 (talk) 01:41, 26 July 2009 (UTC)

## Merge suggestion

Someone suggested deep lake water cooling be merged with this article. I strongly oppose this suggestion. These are two distinct processes. In the Toronto system -- the largest installed to date, the cool water used to cool the city is not in a closed loop. Once it goes through the heat exchanger it supplies the cities fresh water needs. This is totally unlike any salt water project. In general, merging distinct articles, merely because they are related, is a great disservice to readers, because it erodes the value to their watchlists. In this particular case a reader can choose, as I have, to have "deep lake water cooling" on their watchlist, and not have "Ocean thermal energy conversion" on their watchlist. Once an ill-advised merge takes place, readers will have to update their watch lists. And, having done so, they will be advised of changes on topics they are not interested in, because the resulting omnibus article would really be about two topics, not one. Cheers! Geo Swan (talk) 15:28, 21 June 2008 (UTC)

Better reason: "the resulting omnibus article would really be about two topics, not one." Trekphiler (talk) 20:39, 21 June 2008 (UTC)

## Contradiction

If OTEC can function at high latitudes, it's clearly not limited to within 20deg of Equator... TREKphiler hit me ♠ 23:46, 6 August 2008 (UTC)

I don't understand where the contradiction is -- the thermal energy source is not available outside of the tropics, because the surface water is too cold. —Preceding unsigned comment added by 206.75.202.177 (talk) 19:01, 1 September 2008 (UTC)
Except (as I seem to recall the article says...) it's not the surface water temp, but the temp differential, which counts, & air temp is often lower than water temp in hi latitudes. TREKphiler hit me ♠ 21:37, 1 September 2008 (UTC)
The temperature difference between surface water and deep sea water is not enough to keep the cycle when you get above the tropics. —Preceding unsigned comment added by 64.75.249.5 (talk) 01:43, 26 July 2009 (UTC)

## Cost of electricity from OTEC

OTEC should be able to provide electricity at 2 cents per kilo-watt hour. This is much lower than the consumer price in USA of between 6 cents to 17 cents per kilo-watt-hour. All the OTEC designs described in this write up are not cost effective. Anybody interested in a cost effective design can request information from me at [email address removed to protect privacy -- Rehman]. I hope to get some people to listen. NREL is useless because the old project the are involved in is at least 20 times less cost effective than my design. —Preceding unsigned comment added by 96.251.110.220 (talk) 00:36, 19 November 2008 (UTC)

## Requested move

The following discussion is an archived discussion of the proposal. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

No consensus to move. Vegaswikian (talk) 00:40, 12 December 2010 (UTC)

Ocean thermal energy conversionOcean thermal energyRelisted. Rehman 02:57, 5 December 2010 (UTC) Ocean thermal energy is an alternative to the above title. Simplifying to that would increase accessibility. We could always use a redirect too. Rehman 06:50, 24 September 2010 (UTC)

Oppose. The article isn't about the heat energy sitting in the ocean, it's about turning that heat energy into something useful to humans. If you think "ocean thermal energy" is a common search term then make that the redirect. --Wtshymanski (talk) 13:02, 24 September 2010 (UTC)
Well, this article itself says that it is an alternative (Ocean thermal energy conversion (OTEC or OTE) uses the...), sourced by this website. So I just thought it would be more accessible or simpler with a shorter title... P.s., the title is already a redirect. Rehman 13:10, 24 September 2010 (UTC)
Weak Support - the corresponding articles Solar energy and Wind energy (which redirects to Wind power) both refer to the human application rather than the energy itself, so this would bring it into line. I say "weak" because perhaps this whole model is wrong and each of these energy sources should be qualified... but on balance there's not much to say about the energy itself, except in connection with human usage.  — Amakuru (talk) 12:06, 1 October 2010 (UTC)
Oppose. The heart of this is "conversion". "Ocean thermal energy" makes me think of a natural system or process. What about a move to Ocean thermal power (which was the term Jerry Pournelle used)? TREKphiler any time you're ready, Uhura 08:54, 7 November 2010 (UTC)
That'd be alright too. My main reason for the move is to remove "conversion", which doesn't seem to fit in, at lease to me. Rehman 10:47, 7 November 2010 (UTC)
OPPOSE again. Keep relisting it if you like, but what the world calls this is OTEC. Rename it and you will mystify anyone who stumbles across this article. --Wtshymanski (talk) 05:12, 5 December 2010 (UTC)
The above discussion is preserved as an archive of the proposal. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

## Introduction

The introduction should give a concise easy to understand view of the subject for an intelligent lay reader. I have had a go at rewriting the introduction with this in mind. Lumos3 (talk) 11:23, 28 January 2011 (UTC)

## Closed cycle image

I have swapped the closed cycle image for the one from German Wikipedia with English annotation. The old image showed a temperature difference of only 10 degrees , showed the apparatus as submerged which is not necessarily the case and was not in colour. Lumos3 (talk) 10:18, 31 January 2011 (UTC)

## Total insolation received by the oceans

Re this sentence:

"The total insolation received by the oceans (covering 70% of the earth's surface, with clearness index of 0.5 and average energy retention of 15%) is 5.457 x e10 Megajoules/year (MJ/yr) x .7 x .5 x .15 = 2.87 x e10 MJ/yr".

This calculation is apparently based on 5.457 x 10^16 joules/year incoming solar energy. This seems incorrect/too small, and there is no citation.

And http://en.wikipedia.org/wiki/Solar_energy says "The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year."

This is 3.85 x 10^24 joules/year. Vastly greater than the 5.457 x 10^16 joules/year on this page.

I have no expertise in this field, but this seems like an enormous discrepancy that should be checked by someone. 60.242.229.250 (talk) 09:48, 10 March 2012 (UTC)

"I have no expertise in this field" Nor I. A quick calculation, based on surface area of earth & 1400W/m2 at the top of the atmosphere, gives 1.09x1020W/yr. Helpful to anyone? TREKphiler any time you're ready, Uhura 18:30, 10 March 2012 (UTC)
I am an expert at the multiplication table. Watts per square meter times square meters gives watts, not watts/year. 6378000 (Earth's approximate radius in meters) squared time 4pi times 1300 watts/square meter solar constant times 1/2 (only one side faces the sun) gives 2.55 x 10^14 watts, there's pi times ten million seconds in a year so that's 8 x 10 ^21 joules/year. We need a reference that calculates this to cite here. --Wtshymanski (talk) 23:53, 10 March 2012 (UTC)
Does anyone know (= have a citable reference for) the albedo of the Earth? Not every watt that falls on the Earth's surface gets absorbed. --Wtshymanski (talk) 23:55, 10 March 2012 (UTC)

Deep Water Condenser

In Vega and Michaelis' paper, First Generation 50 MW OTEC Plantship for the Production of Electricity and Desalinated Water, they concluded a 53.5 MW Closed Cycle OTEC plant would employ 2750 kg/s (4 cubic meters liquid - 2750/680)of anhydrous ammonia as the working fluid and would flow 264.4 m3/s of warm water and 138.6 m3/s of cold water.

How is it more efficient to circulate 138.6 m3 of cold water than it is to flow 4 m3/s of ammonia to the the cold water heat sink and then pump it back? Particularly when this is a closed system with no impact on aquatic life and also the condensation takes place in deep water where the biofouling problem is minimal to non existent.

Dominic Michaelis has in fact a patent GB 2395754 for such a deep water condenser.

Most current efforts turn their nose up at this approach and claim the thermodynamics don't work but this is dispute by others and a heat pipe is proof that vapour will flow downward drawn by the drop in pressure resulting from the condensation of the fluid. — Preceding unsigned comment added by Bairdjr (talkcontribs) 16:19, 28 May 2012 (UTC)

Carbon Dioxide as working fluid

A plot of the vapour pressure of carbon dioxide over the range of 4 to 28 degrees Celsius - the typical OTEC range - shows an increase from from about 570 PSI to 1000 PSI.

For Ammonia over the same temperature range the pressure change is from 73 to 163 PSI.

What are the obstacles to using CO2 as a working fluid in OTEC?

And does the increase in power production from the use of CO2 not more than compensate for the increased parasitic losses? — Preceding unsigned comment added by Bairdjr (talkcontribs) 16:34, 28 May 2012 (UTC)

## Flammability of Ammonia

Ammonia is only slightly flammable. At least the flammability is not a significant danger associated with it. Under Ammonia#Combustion it says: "The combustion of ammonia in air is very difficult ...". The HCFCs are not that different: under special conditions like higher pressure they burn to. So I would suggest removing the flammability of ammonia here. --Ulrich67 (talk) 09:52, 21 July 2012 (UTC)

See the Wiki Ammonia article, it has been used as a fuel and will have a explosion limits to stay outside of. Matheson Gas has them listed. Fire hazards are detailed by the Canadian Centre for Occupational health and Safety.Vancouver2 (talk) 00:21, 24 February 2014 (UTC)

## Link to solar pond

User:PeterNetsu undid revision 574477045 by User:Liotier that linked this article to solar ponds, claiming that "they are a confined seawater mass, with a much higher temperature difference, therefore linking these technolgies is incorrect". While this is true, the low pressure Rankine cycle engines used to take advantage of the heat gradient are similar and solar ponds can be combined with nearby cold ocean currents to reach a much higher temperature gradient. So I claim that there is indeed a link between ocean thermal energy conversion and solar ponds, worthy of a "See also" entry. --Jean-Marc Liotier (talk) 09:00, 26 September 2013 (UTC)

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## Bluerise OTEC variant, and other improvements

Appearantly, the OTEC variant used by Bluerise is up to 20% more efficient by using both seawater as well as ammonia. I think it's called the Kalina cycle, see https://webcache.googleusercontent.com/search?q=cache:ck4Hn6UQPOYJ:www.irena.org/DocumentDownloads/Publications/Ocean_Thermal_Energy_V4_web.pdf+&cd=1&hl=en&ct=clnk

Also, at bluerise curacao, the air conditioningswater from the airport is reused, reducing the energy requirements by 90% making the financially profitable to raise an OTEC plant.

Other improvements are:

• combining with solar thermal collector to preheat the seawater use to boil the ammonia. A reasearch paper was made on this by Paola Bambarda of the Politecnico di Milano. A cheap solar thermal collector can appearantly increase power production by 200 to 300% during daytime[1]
• having the vaporiser placed in the deep sea rather than on the surface. This eliminates the need pump nutrient rich water to the surface and eliminates the chance of algae growth. Patent by Energy Island, Dominic Michaelis.
• use of OTEC on a ship. A design has been made by SBM Offshore.

Perhaps worthy of mentioning in article ? KVDP (talk) 15:47, 25 October 2014 (UTC)

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## Confusion of thermal efficiency and economic efficiency.

The article suffers from a confusion of thermal efficiency and economic efficiency.

In the lead it says:- "However, since the temperature differential is small, the efficiency is low, decreasing the economic feasibility of ocean thermal energy for electricity generation."

Low thermal efficiency only means that a small fraction of the heat processed is available for human use. Since large volumes of water are available significant amounts of useful energy can still be extracted. The running cost is minimal, once the initial capital has been spent, since the ocean provides the temperature difference free and forever. A low thermal efficiency can therefore still provide a high economic efficiency. Lumos3 (talk) 09:48, 20 September 2015 (UTC)

## Major reversion proposal

On the 14 November an anonymous editor deleted a major part of this article and replaced it in my opinion with a poorer and lighter weight version

The edit was (cur | prev) 12:57, 14 November 2016‎ 185.82.187.37 (talk)‎ . . (25,141 bytes) (-55,152)‎ .

I propose reverting all changes to the version prior to this. Some of the images and text that have been added since then can then be incorporated in to the article. Any comments? Lumos3 (talk) 21:58, 21 February 2017 (UTC)

1. ^ Journal of Engineering for Gas Turbines and Power, number 135 page 42302, april 2013