Rick Dworsky: A Warm Bath of Energy -- Ocean Thermal Energy Conversion

[editor's note, by Prof. Goose] This is a guest piece by Rick Dworsky--he has been involved in environmental conservation and energy issues for over 30 years in government and private industry.

In 1870, in Twenty Thousand Leagues Under the Sea, Jules Verne wrote: "I owe all to the ocean; it produces electricity, and electricity gives heat, light, motion, and, in a word, life to the Nautilus."

Indeed, the Earth has an enormous natural solar collector - the tropical oceans. "On an average day, 60 million square kilometers (23 million square miles) of tropical seas absorb an amount of solar radiation equal in heat content to about 250 billion barrels of oil."(1) Energy "equivalent to at least 4000 times the amount presently consumed by humans."(2) If we can tap into this renewable source, considering thermodynamics and entropy, approximately 1% of it could provide the entire current worldwide demand for energy. More than enough energy is available, we only need a way to get it - in a practical, cost effective, ecologically safe and sustainable way.

Ocean Thermal Energy Conversion (OTEC) is a technology that can extract useful work from solar energy stored in the sea. Since the sea IS the energy storage medium, OTEC offers 'always on' baseline supply -- during bright clear days and dark nights, in still air and ferocious wind storms -- without the expense and complications of artificial energy storage systems.

In 1881, eleven years after Verne -- 125 years ago -- Jacques Arsene d'Arsonval, a French physicist, conceived OTEC. It operates on the temperature differences between warm surface and cold deep waters - using a heat engine built for the purpose. Wherever a 20 degree Centigrade (36 degree Fahrenheit) difference or greater is readily obtainable between warm surface and cold deep waters, the process can be put to work. In 'Open Cycle' systems, lowering the pressure above warm water turns it into a vapor, effectively 'steam', which runs a turbine before it is recondensed by cold water. In 'Closed Cycle' systems and hybrids, the water heats and cools -vaporizes and recondenses- an intermediary fluid/gas that powers a turbine within a closed sub-system, which enables much larger energy outputs. Basic heat engine physics. The concept, at least, for OTEC had arrived. But the idea preceded the materials technology and manufacturing methods required to make it, and further, make it competitive with fossil fuels.

In 1930 Georges Claude, d'Arsonval's student, built the first experimental OTEC system in Cuba. It produced a gross output of 22 kilowatts (kW) of electricity. Five years later he built a floating OTEC generator in Brazil. Both of these pioneering efforts were destroyed by weather and high seas. High capital investment costs and cheap fossil fuels prevented the further development of OTEC until fairly recently. In 1979, off the coast of Hawai'i, a tiny OTEC generator produced, for the first time, a net output - of 18 kW. A system efficient enough to meet the power requirements of it's pumping systems and provide additional useable energy had been created. A plant which continuously produced more than 50 kW soon followed.

Design and material advances have now reduced the capital investment costs of OTEC to a competitive position in suitable locations, given the expected price of oil over a minimum 25 year life cycle. OTEC facilities can probably be maintained -sustained- far longer than that, perhaps 'forever' - if we reserve enough surplus bio-mass to replace ingredients currently made from petroleum, such as fiberglass resins (synergy with OTEC would return better ERoEI than burning). Currently the Indian Ocean, Caribbean, South Pacific and Hawaiian regions present cost effective scenarios for landed OTEC facilities. If a major OTEC industry develops, costs are expected to fall low enough to justify implementation world wide - at least wherever the process will work - an ocean belt spanning approximately 20 degrees to the north and south of the equator. Land based plants are contracted or under construction in the Cayman Islands and Mauritius. A Japanese company built a 1 megawatt plant in India. Hawai'i has a leading edge OTEC laboratory where working models have been proven, a deep cold water pipe is already in place - better funding could be put to good use.

Large floating OTEC platforms have been designed which would drift and 'graze' warm tropical seas, harvesting the energy, using it to extract hydrogen from sea water, to be picked up by transport vessels and delivered where it is needed. Ammonia, methanol and other compounds could also be produced. At the moment however, only terrestrial and undersea cable transmission of electricity is cost effective - limiting OTEC to land and near shore installations close to waters with sufficient temperature differences.

In no case would critical working parts need to be exposed directly to the ravages of the sea - high and dry on land or safe above sea level on floating platforms larger than super tankers, only the tubes to draw in water would need to endure the difficult ocean environment. The United States has already completed design, production and testing of the required durable cold water intake tubes and their attachment to vessels. The U.S. Navy has proven the use of OTEC generators shipboard.

OTEC can be built with non-exotic materials which do not require expensive secure disposal. While some designs (Uehara Cycle) require titanium, it has also been shown in other designs that the heat exchangers can be made of common aluminum without excessive corrosion problems.

At this time OTEC appears to offer an environmentally neutral energy source. The intermittent injection of minimal amounts of chlorine to prevent bio-fouling of the warm water intakes, and the leaching of metal particles and other materials via erosion/corrosion would probably be environmentally insignificant. Large storage tanks for chlorine would not be necessary - small amounts could be generated 'live' as required to manage the danger to personnel. No bio-fouling within the cold water intake tube has occurred. Although a 100% kill rate for small organisms such as phytoplankton that get drawn into the warm water intakes is probably inevitable, it is believed that this can be mitigated by the pumped 'upwelling' of cold deep fertile waters and the outfall effluent. Only extensive monitoring of an installed mid-size test facility can enable a comprehensive environmental assessment, and find the balance point between bloom and bust. Adjustments of the outfall depth may be necessary, according to local conditions. It may well be the case that OTEC can target some of the energy that causes damaging and catastrophic storms and redirect it into useful work, if large mobile floating platforms become a reality. We should carefully consider when a location can host the process and remain within it's normal temperature gradient range, this would be similar to concerns about the energy absorption effects of solar panels and windmills. OTEC appears to be a vast, renewable, sustainable, safe, 'always on' energy source that does not emit CO2 or nuclear waste.

Landed OTEC facilities could also provide cold outfall water for reuse in air-conditioning, refrigeration and sea water agricultural projects - 'mariculture'. Some OTEC designs and add on modules produce copious volumes of safe distilled drinking water, a much needed commodity in increasing demand in many tropical locations where OTEC could be based.

Given all the fantastic promise OTEC presents, the amount of useful energy that can be obtained from each cubic meter of sea water is relatively small. The quantity of water that would have to be processed to produce a significant amount of useful energy would be enormous. Deep cold water intake tubes 11 meters (36 feet) in diameter with pumps of the same scale are proposed for 100 megawatt units. "The discharge flow from 60,000 MW (0.6 percent of present world consumption) of OTEC plants would be equivalent to the combined discharge from all rivers flowing into the Atlantic and Pacific Oceans (361,000 m3 s-1)."(3) OTEC is a technology of oceanic magnitude. To ameliorate the enormous problems of Global Warming, Peak Oil, Fresh Water, and Food supplies, we are going to need proportionally large solutions. Our task would be easier if we could reverse Human Population pressures.

OTEC may be one of our best hopes for the environmentally clean, sustainable solutions we need to solve our global energy and environmental problems - or at least a substantial chunk of them. In combination with other renewable sources, efficiency gains, conservation and adequate voluntary population management, we may be able to maintain a semblance of world civilization.

Perhaps we can still save our Nautilus.


  1. http://www.cogeneration.net/ocean_thermal_energy_conversion.htm
  2. http://www.otecnews.org/articles/vega/01_background.html [Note: The seemingly high percentage (1%) of required renewable energy inputs to meet world demand through OTEC is due to entropy and thermodynamics - a basic physical constraint. The theoretical maximum OTEC efficiency is about 8%, but for various practical reasons 3% is more typical.]
  3. http://www.otecnews.org/articles/vega/02_tech_limitations.html

A few links for further research:

National Renewable Energy Laboratory (U.S.) http://www.nrel.gov/otec/what.html
Department of Energy (U.S.) http://www.eere.energy.gov/consumer/renewable_energy/ocean/index.cfm/mytopic=50010
National Energy Laboratory of Hawaii Authority (U.S.) http://www.nelha.org/
OTEC News (U.S.) http://www.otecnews.org/
Wikipedia http://en.wikipedia.org/wiki/OTEC
Sea Solar Power (U.S.) http://www.seasolarpower.com
Marine Development Associates, Inc. (U.S.) http://www.marinedevelopmentinc.com/ocean_energy
Cogeneration Technologies (U.S.) http://www.cogeneration.net/ocean_thermal_energy_conversion.htm
World Energy Council (U.N.) http://www.worldenergy.org/wec-geis/publications/reports/ser/ocean/ocean.asp
Xenesys, Inc. (Japan) http://xenesys.com/english/index.html
Wired Article http://www.wired.com/wired/archive/13.06/craven.html
The National Institute of Ocean Technology (India) http://www.niot.res.in/m1/otec.htm

© Rick Dworsky 2006

This just in

Worldwide production down 400,000 bpd in March to 84,047,000 barrels per day.

Go nuts, peaksters. The end is here.

The EIA released its monthly numbers. That's 700,000 barrels less than December, for those of you keeping track.

OIL CEO This is outta character for you! Ya giving me vthat rush/scare thingee.
Haha. Well, when you add that 300,000 barrels in that the Saudis cut in April, we end up an even million barrels below the peak. I'm headed to the mall right now to stock up on ammunition and bottled water.

I don't keep track of the numbers only the concepts....what percentage of total is this?


1 million barrels is 1.2% of 84 million (total production rate).

On a serious note, I will take this opportunity in light of some of the discussion on production here today, to say that I would have expected this level of production (down so low from its highs last year) to have effected the price of oil much more than it has (which appears to be none).

Whether this is demand-softening, demand-destruction, I don't know. Maybe the Saudis are right. Maybe the numbers are screwy. Maybe it will take 6 months for the effect to come through on inventories.

In 1982 oil hit inflation adjusted highs north of $90. American expeditures on oil hit 7% of GDP that year. We are at 3.5% of GDP now. If this is really TSHTF, I'd expect a little more than $73.

Don't want to rain on your guys parade, but shouldn't off-topic posts like this be in the drumbeat thread? Thats its purpose afterall.

And by the way... (yes I am hypocritcally adding to the off-topic conversation!!) how do you argue with cornucopians who say that production is down because "demand has dropped due to higher prices"??

And by the way... (yes I am hypocritcally adding to the off-topic conversation!!) how do you argue with cornucopians who say that production is down because "demand has dropped due to higher prices"??

I also hesitate to add off-topic material to a very interesting opening essay, but the Drumbeat threads are pretty large by this time of day. It's hard to have a conversation based on new news. Maybe a new thread just based on the new numbers would be in order?

Anyway, I am not a Cornucopian, but it is no suprise at all that demand was down in March. Spring turnarounds were in full swing, and refinery capacity was quite low at that time. You can see a graph of that here:


But mark my words, production will climb from here for at least a bit longer. Mark that prediction down and file it away, and we can revisit it in the summer. You can call me out if I am wrong about that.



Please, no 'down to earth' explanations. It must be the end which is near, otherwise I read this site for nuttin'


For those of you who want to see the EIA numbers...

EIA International Petroleum Monthly

Current World Oil Supply Excel Sheet

Enjoy :-)

Apologies for adding to the off-topic :-/
The EIA number is almost on the 13 month centered moving average Stuart Saniford posted on April 4,2006. Then as now, the question is whether the curve will go up or down? In the same vein, both the IEA and EIA estimates for March have overestimated the actual just released. I don't know CERA's estimate, but I would be interested to know what it was.
I have always liked the idea of OTEC, and this is the most balanced discussion of it I have seen.  The issues of corrosion, chlorine use, and petrochemicals in these projects was appropriately addressed.  (Of note, biofouling of nuclear plant seawater intakes with zebra mussels and such is always an issue requiring attention.)  

For Rarotonga, this could be the way to go.  But OTEC won't play any significant role during the world energy crash and dieoff.  It is too late in the game.  OTEC will be a technology adopted by some of the dieoff survivors.

The intermittent injection of minimal amounts of chlorine to prevent bio-fouling of the warm water intakes, and the leaching of metal particles and other materials via erosion/corrosion would probably be environmentally insignificant.

I love it when the techno worshippers say "probably." It usually means the new process, chemical, or machine will destroy yet another vast part of the ecosystem.

The sad thing is, they will probably do it -- right along with the coal and nuclear and burning our food crops.

Why not use our intelligence to get us out of the techno-fix business and work on devolving our tech and reducing our population?

Of course, that will not happen.

Great article, by the way, on the evolutionary basis of war and competition for natural resources at: Evolutionary Psychology, Memes and the Origin of War.

I'm interested to know how intelligence would help to drastically reduce population. I assume you don't mean conceiving and executing schemes of mass extermination.
For the intelligent to avoid having offspring of their own is very feasible, of course. The problem would be getting everyone on earth to do the same. How would you set about it?
I went out to one of those sites that calculates your footprint on earth, and then tells you how many planet Earths we would need if everybody lived that way, and I thought of a new take on Population control.

First, everybody is required to fill out the questions to determine their footprint - not so much how they live, but how they 'pledge' or 'promise' or 'contract' to live in the 'new world'.  After you make your contract agreeing to how you will live, it figures out your expected foot print.  From there you are entered into the 'lottery', with your odds of 'winning' the lottery equal to 1:<your footprint>.  If it is determined that you will live with in a foot print that is sustainable you automatically win.  If you want to live a lifestyle that is 1:30, well, only 1 in 30 will win, and the others are made into fertilizer.  If you break your contract, you have the same fate.


Well, I agree with your sentiment, but I feel one must be realistic. You suggest population reduction. I suggest that if you believe so much in such a solution you should start by reducing yourself out of the population. I agree, the earth has a carrying capacity, and we are probably above it, but to suggest murder of fellow human beings is abominable.
ummm, I think he just meant trying to get our societies on a steady negative fertility rate, not a holocaust...
Are you sure? You must be new. He's just getting warmed up. Give him a chance to horrify you. Negative fertility rate. What the fuck is that? Is that like retroactive abortion?
No, its like keep it in your pants, or withdraw, or get a snip, or take a pill. Hop off that soapbox, the acoustics seem terrible up there.
   Sodium Hypochlorite can be made on location and quickly reacts with organic material to make sodium chloride.  Since the source material is in the seawater your killing plankton in EXTREMELY small quantities.  As for reducing the population will you promise not to breed?  For the sake of the world I mean.
  Matt (AKA Bubba)
Public Radio's Marketplace had a nice little piece on Ethanol tonight.

One third of Americans think they will see a UFO before their car runs on corn-juice

Raises hand
People have been wanking around with OTEC since the 1970s, and it still hasn't gotten anywhere. Perhaps we should ask: why?

It all gets down to the amount of capital investment in relation to the amount of energy that can reasonably be expected to be extracted over the life of the system.

Maybe somebody will make it work more successfully and cost-effectively than it has, but I wouldn't hold my breath.

Yes, a huge amount of energy is bestowed upon the oceans, but the rub is being able to extract it in a practical, survivable, and cost-effective manner.

I wouldn't give up on any of these alternative energy schemes, for the calculus of what's reasonable and what's unreasonable may change quite suddenly should the fossil fuel situation start to tank sooner than expected.

I agree, the capital investment is large, considering the corrosion problems that working with warm seawater involves - which often leads oil & gas companies to invest in titanium heat exchangers and even for regular seawater piping (e.g. Laminaria development Timor Sea).

However considering the low pressures involved relatively cheap GRP can be used for the piping and a titanium heat exchanger, although with a high capital cost, has an extremely long life and useful scrap value.

At some oil price, I am sure OTEC will be worthwhile, however I don't really have a feel what that is.

.. we've been wanking around with Fusion, too.  Is it time to throw in that towel?  No, no, no.. fusion is just around the corner, swear to god..
Warm salt water even at 100 deg. F is low grade energy.  I did a study on green house heat-  During summer they get really hot but it came down to mass. 120 deg air is not the same as 120 degree dirt.  Air has little mass compared to dirt so while is looks like alot it(realatively(SP)) doesn't add enough to justify mechanical systems to try and store it or convert it compared to curent fuel prices. This much energy(4,000 times current use) would attract someones attention.  I would asssume that the scale is off the charts(How many square miles????).  IMUO I think that with todays tech this isn't a viable option.  Better to drink magarita's and enjoy the surf!
Well, I'm not sure it doesn't justify mechanical systems. There is a company in Australia (Enviromission) with plans for a 200 MW solar thermal tower in outback New South Wales, based on a 50kw prototype which successfully operated in Spain during the 80s.
It will look like an enormous greenhouse canopy with a very tall hollow ventilation Tower located at its centre.

The sun's radiation will be collected and trapped under the transparent canopy, creating a massive force of air heated to around 35°C greater than the ambient temperature. The laws of physics will make this air move at 15 metres per second towards the cold air at the top of the Tower located in centre of the canopy. The powerful updraft will force the rising air to pass through large turbines positioned at the base of the Tower. The movement of the hot wind through the turbines will generate up to 200MW of clean, emission free electricity - enough electricity for 200,000 typical Australian homes.

This project has been perpetually in the planning stage for a decade or so, and the height and output of the project has been scaled back by 80%. All the initial funding has been spent, and they are now trying to get huge amounts of government funding and issue new shares according to the link.

All is not well with this IMHO, it may never get built, despite having cost a fortune so far...


I agree it looks grim, and commercially I think they erred by setting their sights too high (e.g. a 1 kilometre high tower, more than twice any other existing structure). They should have gone with something smaller to prove the concept and economics from the beginning.

However, the commercial failings of Enviromission aside, technically the concept seems to have legs.

It all gets down to the amount of capital investment in relation to the amount of energy that can reasonably be expected to be extracted over the life of the system.

This is an often overlooked aspect of these debates. I have no doubt that coal to liquids, for example, has a far superior EROI to tar sands. But we are developing tar sands instead of turning our coal to diesel because of vastly lower capital costs. Sometimes we just focus on EROI (not that the OP did that) but we also have to carefully consider the capital involved.



I think I buy a smaller car. It's cheaper.

And so does toyota by the way.

I grew up near that OTEC plant in Hawai`i.  My parents still live nearby.  My mom, a science teacher before she retired, took her kids on tours there every year for field trips.  It's been working for a long time...but still is not profitable without government grants.

This is even though electricity in Hawai`i is mostly generated by oil shipped in via tanker.  This is even though they are making money on auxiliary projects (such a lobster farm that uses the cold water brought up from the depths).  

Maybe wave energy will be the answer, but OTEC isn't.


Excellent post. It prompted me to do a quick search for OTEC in Australia... I found a useful overview:
And a working group in Townsville which had a workshop last year on the subject:

Upshot is, Townsville is poorly placed due to the continental shelf being a long way offshore (100km), but points further north in Queensland (e.g. Cooktown) could be suitable due to the shelf being much closer to shore. However Townsville was still seen as a potential engineering base for a future industry to support OTEC applications for pacific islands.

Unfortunately I didn't find any concrete progress towards commercialisation of the technology in Australia.

Thanks for this.

I'm unclear about the mechanism that these systems use.  The beauty of this source seems to be that, since the potential is so enormous, we can consider relatively inefficient generation and still be in the black economically.

how about a Stirling engine or, like the fan on my woodstove, utilize the Peltier-Seebeck effect?

I forgot to mention this site about wave energy which is not only prety cool, but it switches between generation of electricity and reverse osmosis sesalinization.
"sesalinization?"  Wow!
The old second law is pretty ruthless, folks.  20C is a miserably low temp difference for any heat engine.  Carnot efficiency there is something like 6% and you usually actually  get not even  half of that even after a lot of work on minute design detail.  I would rather put the same money into solar thermal run from a flat plate collector on the south side of big buildings in LA.  Would be fairly easy to get 90C delta T. and would not have to worry about salt corrosion except for the tears of the dwellers therein when comes time to shoot their SUV's.
"would not have to worry about salt corrosion except for the tears of the dwellers therein when comes time to shoot their SUV's."

wimbi, that's a great turn of phrase... don't be such a stranger to these parts.

And try to find us some kind of Stirling we can make for cheap and use for years.  It's really important now!

Right you are, Wimbi!

The equation for MAXIMUM theoritical efficiency for a heat engine is:

E = 1 - T2/T1  (T2 is cold temp in Kelvin and T1 is hot temp in Kelvin)

Assuming cold water is 50 deg F (283 deg K) and the "hot" surface water is 85 deg F (303 deg K), maximum efficiency is 6.6%.

Subtract pumping losses and losses for turbines and heat exchangers and you've got a big, expensive device with low output.

But say you've found the world's best site and surface temps are 100 deg and your cold water is 34 deg F.  Efficiency jumps to almost 12%.

Better and maybe even doable in the best case but it sure won't change the world's energy problems.

It might make sense as a sea fertilization system that might give a small electricity bonus. Then you harvest fish and eat them, makes biogas on the left overs for fuel and then fertilize inland fields. Its only intuition but it could probably cycle significant ammounts of nutrients from deep seas too important farming areas keeping both seas and fields in high level production.
Thanks for this nice article on a technology I had never heard of, Rick. I'm going to have to digest all you've said about this new source of energy. I am surprised that the Navy has already done some work on it. There seems to be potential here. I rarely say this being generally a pessimist about our chances.

And now I'm going to say something that some people may not like.

Every day, there is a Drumbeat open forum. But every thread on a specific subject like this one is used as an open thread. I note some comments above that are certainly interesting but completely off-topic. Perhaps TOD commentors could put the off-topic subjects on the readily available open threads and focus on the topic being discussed. Rick has made a serious effort here and it deserves discussion in its own right. I am not trying to stifle TOD comments. I just think they belong where they belong. And the length of the Drumbeat open threads is no excuse.

'nuff said.



I agree, even though I did add a comment myself. But the Drumbeat threads are getting very large lately. If breaking news happens late in the day, it is going to be buried in a Drumbeat thread with 250+ comments. I am not sure what the answer is. The EIA news deserves a thread of its own, in my opinion.

Now for an on topic comment. I found Rick's essay to be quite interesting, and especially appreciated the level of documentation. I knew a bit about OTEC, but not in great detail. I always thought it, as well as generation of energy from waves, made a lot of sense.  I need to look into them a bit more.


I also agree that it is a hard problem, given the length of the open threads. The poster, if he's got hot breaking news, could wait until the next day and post it at the top of the Drumbeat. I know the temptation to post such news is almost irresistable.

I myself will in most cases notice something like the EIA's new low global production numbers. I'm pretty sure Stuart would notice too since he tracks this stuff.

But I'm still sticking to my original point and I'm not quite sure what to do about it. Maybe SuperG has a suggestion? Or PG, et. al.

Thanks for replying, best


Buried or not, I read to the bottom of every thread.

Perhaps a new Drumbeat should start after every 250 comments, pick your number.

I think TOD could benefit from a better forums system, perhaps ancillary to the existing rolling headlines publisher.  Maybe something like phpBB running on forums.theoildrum.com?
The answer is simple.  Tree structure.  Get blog software that supports it.
I just have to say this. More has been written about the fact that I posted on a couple of off-topic, yet totally relevant subjects than is actually written within those "off-topic" comments.
No specific criticism of you, Oil CEO, was intended. And I don't really follow your remarks here. How is something "off-topic" and "totally relevant" at the same time? Either the subject written about is on-topic and totally relevant or it's off-topic and therefore not relevant to the specific thread. I will admit there is a subjective judgement here but most cases are obvious. Hell, in every thread lately, there's a big section on this ethanol bullshit we're being handed regardless of the subject. RR took care of that subject a few posts ago. Lack of memory is one of the failings of a forum like TOD. I didn't write anything about you posting off-topic and did not single you out above. Maybe others did but I didn't see those comments.

Ironically, I've started a discussion here that belongs on tomorrow's Drumbeat. So, I'll repost my original comments there and say nothing else on the subject here--which should be devoted to Rick's OTEC technology. So, that's my final word on this subject on this thread.

again, best,


I know you weren't singling me out, but I think it was pretty obvious I was the only guilty party, or the ringleader at least.

I meant off-topic to thread, relevant to oil. I think being relevant to oil is important here, but I often seem to be in the minority on that one.

As far our our little "system" here. I think it works just fine. Good posts will get responses regardless of off-topic comments that are really annoying just a small percentage of readers. If I were to tweak one small detail, I would run two open threads per day. One at 7AM EST, one at 3PM. But I don't care. Somebody's always going piss everybody off, and unless you make it the law and institute a force of thread-police, people like me are always going to bend the rules. I certainly don't make it a habit.

The EIA numbers are important and should not be put off for one minute. They are already two months old.

Always happy to stir up contraversy,
Oil CEO ;)

I agree with this. The system isn't perfect, but who says the replacement would be any better.

I do frequently complain about non-peak oil topics - like today's posting of a road rage article in two different threads. I think a tighter focus on the subject would help solve the clutter problem. However, I think it needs to be a commenter culture, not editing or censorship.

I do understand that those obsessed with George Bush, Americans, the faults of capitalism, our consumer society, death, doom, etc. do have a near medical need to vent. Let's give them a permanent topic and consider it charity. I know it will make me feel better.

As far as road rage and that "intermittent explosive disorder" it does have relavance in that those people represent those most likely to get violent first as hard times worsen. It will be a consequence of the stress after all. Best left in open threads of course. As far as OTEC goes, a problem could result caused by people with IED using IEDs to sabotage OTEC plants if built.
I just use the find function in Firefox, and search for "[n" which takes me directly to each new post.  By doing this, I feel TOD is the best system I've ever used.  I can't believe no one else does this... anyone?
Methane Hydrate Effects ?

If used on a large scale the potential for warming the water enough to cause signifcant. The interaction of ocean current with water thats several degrees warmer is unpredictable.

I suspect any large scale deployment would have to be far from
methane hydrate deposits and even then the effects on currents
could cause the water to move a significant distance before cooling.

Since we've already caused enough GHG related climate change to alter (reduce) the thermohaline oceanic heat transport mechanism, all that frozen methane is just a ticking time bomb anyway.

How about combining the 2: build an OTEC thingy that processes the clathrates, using the temperature difference to run stirling cycle generators, and producing natural gas as an increasingly valuable byproduct?

Maybe I'm just saying pumping large volumes of warm water over frozen methane mud is probably not a solvable engineering problem the system is chaotic. Even in nature the methane muds are unstable with landlides mud volcanoes belches etc.

The fact that we not doing it today just to caputure the methane without even considering the power from the temp differential.

We might take that as an indication that OTEC is going to be another niche energy source, to be used in such places as tiny isolated Pacific islands.

I have heard that the major hydrocarbon companies have investigated the frozen methane. Like OTEC and Pelamis, or maybe more like the oil shales, frozen methane has promise as a niche source once we get further downslope. Currently, like the oil shale, it is spread over a large area and requires more effort to collect than 'conventional' sources.

I envision a floating production platform with a lot of flexible plumbing stretching to the bottom -- kind of like a giant Physalia.

I'm surprised that no one seems to be concerned with the impact to the ecosystem of inducing a large-scale disruption to the marine thermocline. When a few degrees of surface warming induces the severe and detrimental effects that we've already observed happening to the biota in the top layer of the oceans, why wouldn't we expect something similar in the deeps?

It's not just the lifeforms that will react to warming - The solubility of CO2 declines dramatically with increased temperature, given constant pH. But the most nightmarish possibility is the initiation of an instability event like that seen in Lake Nyos, Cameroon, in, when was it, 1980? Only in this case, it might be methane hydrate that triggers runaway deepwater convection, releasing all that greenhouse gas at once.

Natural upwellings of deep cool "nutrient" rich water are seen as some of the best fishing grounds.

Any deepwater fish or organism sucked up will likely become "nutrient".

I will need to Google Lake Nyos.

But I think the volumes mentioned will have a localized effect, but one that should be investigated.

At the risk of being off topic, I found out that Lake Kivu (between Rwanda & DR of Congo) has large amounts of dissolved carbon dioxide and methane.  A large energy source if they can tap it without blowing it all up !

Some of the methane is from volcanic origins (CO2 + bacteria = CH4).  If a dormant volcano on the lake bottom goes off, a massive release into heavily populated areas.

yes, a whole village died when such a bubble enveloped a village:
"In the middle of an August night in 1986 in the west-African country of Cameroon a misty cloud of carbon dioxide bubbled out of a lake and swept silently down the surrounding valleys - thousands of animals and 1700 people died, many in their sleep." (http://www.mala.bc.ca/~earles/nyos-feb01.htm
I agree, changes on a massive scale are %100 certain to have unintended consequences. There is more life in a square centimeter of sea water than most people know and when you start disrupting that cycle on a large scale ..
Would it be possible to use the warming effect to convert methane hydrates to useable natural gas? It strikes me that the electric transmission loses would make this impractical for many human inhabited areas, and the gas could provide storage and effective transmission, but I lack the math to figure it out.
Your concern over the hydrates and OTEC plants gives me an idea. If some methane hydrate exists along the Gulf Coast, you're in luck. Place a giant plastic tarp over the deposit, and manoeuver the OTEC device over it and start it up. You get electricity, but warm the water between the plastic sheet and the deposit. As it warms, methane is unleashed by that heat and collects under the plastic sheet. Set up a hose to harvest the NG that results.

A problem is weighing down the edges of the plastic. Use a lot of rocks from digging up shale and cooking the shale, using the rock waste to weigh down the plastic. You get kerogen oil too! ERoEI? Anyone's guess but each part helps to add energy to the system. You get shale oil, the waste weighs down plastic, and the OTEC makes electricity as it uses waste heat to get NG. Would it work? Maybe. Is it desperate? YES!

... or you lower a gigatic bell into the water over an area of hydrates, then start warming them.

Collect the methane as it bubbles up into the bell, and also run a turbine generator on the flowing water dragged up with it. Come to think of it, you probably don't need the OTEC plant now, but you do need a nearby market for the methane, and some hope of controlling the release once it starts.

A Note: Methane hydrate beds are believed to be the cause of some mysterious cases of ship suddenly disappearing into a 'boiling' sea -- the bubbly water does not produce as much buoyancy as normal water, and anything floating is likely to sink into the bubbles.

At the same time the methane puts the crew to sleep as the ship starts to go down! If it's CO2, the crew gets put down completely as it sinks.
I remember the Popular Mechanics drawings of OTEC in my childhood.  Little since then.

This seems to be a technology that responds to economies of scale.  Significantly lower pumping losses with larger pipes.    Some square/cube advantages in the turbines & pumps.

Many islands (Hawaii) burn oil for electricity.  (Cheap low quality oil for larger islands, diesel in smaller ones).  So the economics can change.

Add a pumped storage unit and wind, and a 100 MW unit MIGHT just "pencil out" at $70+ oil and eliminate oil use.

But how many islands in the tropics (that are close to deep cool water) need that much power ?  If one has to use 80 MW or larger units ?

Not many IMHO.

If small OTEC does not work economically (probable IMHO), and only larger units are economic, they have to be within 20 degrees of the equator and have a close in access to deep cold water, and they are only economic when compared to oil, then the world may not need more than 1,000 to 2,000 MW of OTEC.

Wind and batteries/load management may work better for many oil dependent islands.

Hawaii may be home to half or more of the feasible OTEC demand.

The problem with almost all renewable energy sources is the low power density. The calculation of the total available energy is usually intoxicating. Sobriety sets in when you estimate the capital cost of the plant required to harvest this energy.

Reading some of the quoted references does not give you much confidence in the ability to use this technology for appreciable contribution to global electrical generation.

The literature is awash with grandiose schemes but actual achievements are modest. According to OTEC News the best to date produced 40kW of net power for 8 days. It produced a nominal 210kW gross power but most of that was used up driving the pumps. Under good conditions there was some net power, under poor conditions there was none.

This and the other problems and abandoned projects listed in that reference show the difficulty of working at energy conversion efficiencies of 3% or so. When your usable output  power is the small difference between huge input and waste rejection energies small changes in conditions can reduce your output to little or nothing. Corrosion, marine fouling, blocked filters, reduced dispersal of cold water at the surface and other practical problems can all destroy the small net benefit.

Extrapolating these projects to the size where they will have any effect on global electricity (10's of gigawatts or a million times the biggest so far) in the face of such precarious energy balance is uncertain to put it at its very mildest.

The energy returned to energy invested ratio is heavily dependant on the working life and maintenance requirements of vast flimsy structures in deep and often tempestuous seas. The thought of 11 metre diameter thin walled tubes a kilometre long in deep tropical water just to obtain 100kW net power seems just the sort of thing to cause running financial problems.

Although there are places where special conditions will probably make OTEC economic I have the greatest difficulty imagining a globally significant contribution from huge numbers of huge OTEC generators offshore in deep tropical waters to power needs in the existing centres of consumption.

Were OTEC to be developed on this scale the vast induced thermal churning of the oceans might have significant environmental effect.

There is no such thing as a free lunch, per the 2nd law.  While there is lots of low-density energy around, transforming it into high-density energy poses severe problems of scalablility due to the enormous volumes entailed, low efficiency, and high capital costs.  To put the brakes on our runaway entropy we need to adapt to low-capital modest yield renewable energy sources.  Anything else is an entropy wreck.
This is an excellent point. I always wonder when wave energy, OTEC or other low-density energy "solutions" are mentioned--where is the venture capital for this?

I'm assuming that the "theoretical" venture capital isn't venturing very many places... It's kicking back and having a cold one with BP, Chevron, Shell, ExxonMobil, et al. Wikipedia (not that I am saying this is fact, just mentioning it) says, and it's sourced,

"One study [1] estimates power generation costs as low as $.07 USD per kilowatt-hour, compared with $.07 for subsidized wind systems [2] and $.0192 for nuclear power."

I'm waaaay to lazy, and tired, not to mention delirious, to see how those estimates are calculated. From looking at those numbers a few things are clear:  

  1. no one is going to put large sums of money into OTEC to even see how feasible it is when you scale it up.

  2. Nuclear (even with it's pitfalls) is a technology we've had (and used) for the last half century--so investors and private equity are very comfortable with it.

Either way, more electricity is def. needed. I personally think that the electricity situation in this country (the US) is in much better shape than the liquid fuels situation. It would certainly be extremely useful if we could come up with a way to generate massive amounts of electricity--and perhaps this is one of the roads we must go down to see how viable it is... However, I fear that OTEC may help at some point, but (as liferaft said) the capital costs, scalability and the low-density natute of the beast will prove difficult. Bill Gates is actually just invested a boat load of money into Canadian trains (I guess he read Matt Simmons book--I heard this somewhere)... I wonder, where are the Bill Gates of the world when it comes to energy investments? I'm sure they're out there investing in ideas here and there--but my real curiousity is why doesn't some bazillionaire finance some experimental energy solutions. Actually come to think of it, this seems more like something  Paul Allen would do, and should do...
Have approached Paul Allen.

Sometimes focus is overdone.  OTEC is about more than electrical energy.  For Example:

The World trade Organization is requiring all single hull petroleum tankers to be replaced with double hull tankers to reduce political hazard. This results in numbers of relatively new ships being scrapped as the only accepted alternative use is as FPSO (Floating Production, Storage and Offloading Units), stationing the redesignated tanker over submarine wellheads to collect low production for shuttle tankers.  That's a designated future environmental disaster (we used to call it abortion engineering).

All the existing OTEC research is based on a very expensive and difficult to handle "pipe" to bring deep ocean water to the surface, creating the condensation side of the thermal energy conversion system.  There is now a Norwegian polyethlene pipe producer that extrudes directly into a coastal channel in unlimited lengths to two meters diameter.

The whole of the Antilles island chain is subject to a prolongued dought, but the country on the west side of the Windward Channel is worst-off, though it's coastline is so steep that 1000 meter depths may be found 1500 meters from shore.  That point may easily access six nations that import water at least sometimes.  Their refugees cost the region significantly.

A single hull petroleum tanker might be reconfigured as an OTEC desalinator plant. In the short term, the ships are available at an extraordinary discount. While not extraordinarily powerful, OTEC generators could certainly provide station-keeping propulsion to the ship. Desalination requires degassing the seawater which produces Hydrogen, Nitrogen and Oxygen, which may be sold or combined to produce ammonia fertilizer or propulsive gasses.  OTEC installations have also provided refrigeration, agricultural and aquacultural byproducts.

US port facilities have been underemployed for decades and some are currently abandoned.  The port cities have need for employment/workforce  training, but there's no marketable product for that labor. An OTEC plant may be assembled almost entirely with commercially available equipment, though some engineering firms, especially government contracors, have a vested interest in "optimizing" performance.

I have located a "social entrepreneur" who is venture funding an engineering firm with a design concept for a floating Ocean Thermal Energy Conversion Plant (OTEC).  Being an engineer, he proposes to engineer the ship as well.  The social entrepreneur is interested in supporting job creation in his depressed port city.  OTEC research has always concentrated on electrical energy production, though it produces vast quantities of desalinated water as a "by-product."  

Naturally NOBODY in this chain is talking to each other, most don't believe they're on the same planet.

And since it starts off with a recycling/social welfare premise, even tho it might become profitable, it scares capital away.  There are commercial OTEC ventures in the works today.

Hello TODers,

If one believes the basic economics of taxation as: concentrating the benefits for a select few, and diffusing the costs to the unfortunate taxpayer collective, then OTEC has a viable future.  Huge taxdollar sums can be diverted to build these OTEC gensets with the future output only going to a select few living lavish energetic lifestyles.  PostPeak defending of OTEC installations anchored way off the continental shelves can be energetically done very cheaply.  At night, as seen from space, future America might be largely dark, except where the OTEC gensets power the baseload demand for the elite few [along with the remaining hydro and wind power sources].  Detritus Entropy rules: we should seek to match our population decrease to the Hubbert Depletion Rate to maximize energy/capita.

One possible way to increase the efficiency of OTEC gensets might be to harvest deep-sea frozen methane clathrates at the same time the cold, deep water is being sucked up.  I am not an engineer to know if this is feasible or not, but it seems the closer the intake tube is to the ocean floor, the less likely you are to suck up every variety of swimming lifeforms.  Just my two cents.

Bob Shaw in Phx,AZ  Are Humans Smarter than Yeast?

OTEC is interesting and certainly deserves some continued testing, but there are so many better alternatives.  Until we have a solar water heater on every home we shouldn't be diverting a lot of funds to OTEC.  A solar water heater is in effect an electric generator.  About 20% of our electric bills are for hot water.  See www.tctsolar.com for some more info.      

The most pertinent part of this interesting article is to be found at the very end - Our task would be easier if we could reverse Human Population pressures.

Low quality energy (i.e. low temperature differentials) are to found almost everywhere. The trick is to extract this energy without a monumental investment. At present, the most ambitious and extravagant way of extracting energy is through the use of offshore structure (e.g. Sakhalin). Does it make any sense to make much greater investments for far lower returns?</font>

The quality of energy can be improved, on land, by using concentrators for solar energy, for example. I know of no way of doing that with ocean currents.

Controlling population growth is a much more effective way of getting the necessary return. There are perhaps around one billion women on this planet would like to be able to access safe and convenient contraception.

Making contraception safe and cheap is a big help. A government can more easally subsidise cheap-to-make contraception so women can get it free for the asking OTC. That's the trick. Even if people figure out how to make estrogen into meth, free OTC no questions asked contraception would be worth it. Fun problem: How do you get the clerics of all the religions to SHUT UP?
HA!  The return of the Pol Pot solution.
In spite of the Environmental issues discussed above (which I do not know enough to contribute to) and of the low density energy problem, it has to be stressed out the fact of OTEC being an "always on" renewable energy source. And boy do we need that!

Counting on a greater than 1 EPR this project should deserve the proper attention.

By the way, will it work during the less hot days of the year?

The prototype systems described by OTEC News were not always on. Because they were fighting to make any net energy small changes in conditions meant that they sometimes gave no net energy.

The temperature difference is so small and the thermal efficiency so low that even a small reduction in that difference causes drastic drops in output. If the cold water pumped up in vast quantities in any large system is not swept away quickly by warm surface waters the hot end will be cooled.

This is probably less of a problem with the tiny systems that have been built so far but it further restricts the usable sites to those that not only have high temperature gradients and deep water near the coast and near centres of consumption but also have predictable strong tides.

Interesting article.  Reminds me of closed cycle Stirling engines.  Does this only work in the large?  Or can a micro-hydro implementation on land be had for summer months?  So say a lake, or artifical pond, when the surface gets hot in the summer might be enough of a temperature differential as noted in the article.

another possibility would be those tall tripod water reservoirs dotted around towns and cities perhaps?  

just a half baked idea

nope, I'm sorry, too much water required.  ignore last post.
OTEC and other solar technologies ought to have their efficiencies measured in $/btu. Carnot efficiency is irrelevant to OTEC just as it is irrelevant to windfarms. Being less than 3% thermally efficient doesn't matter when fuel is free.
I've looked at OTEC systems as a way of generating electricity from solar ponds. With bottom layer temps of 80-90C and air temps of at most 40C thermal efficiencies of 8-10% are possible which is on par with thin film PV without the need for storage batteries and inverters.
Cost/unit energy is is a reasonable criteria even if you have  low efficiency provided that efficiency is stable as in some photovoltaic units. Reading the literature quoted in the main article shows that the 3% often quoted for OTEC easily slips to zero or negative values.

It is very unlikely that a large enough OTEC plant capable of comfortably generating net energy will have sudden changes in performance as the sea water temperatures do not change rapidly. The critical factor is keeping the whole fluid circulation system tight (few leaks) and heat exchanger surfaces (only applies to warm side by the way) working effciently (ie free of biomass)

OTEC is a technology that reacts strongly to economies of scale. The efficiency is low at 3% or so but it is 24/7 energy thus making it effectively 10 - 12% as compared to photovoltaics. The reason the prototypes struggled to have net energy was that they were too small to overcome the inevitably large pumping losses inherent in the system. It is unlikely that they will be net energy feasible below about 5MW. At that scale, the parasitic losses are about 25- 30% of power produced.

For the person who says that only Hawaii can benefit from larger plants, that is not the case. I can think of countries like Jamaica, Dom. Republic, Mauritius, Barbados, Cuba, Costa Rica, Taiwan etc. etc. where a 50MW to 100MW floating plant would be ideal for their power grid. Total capacity in Jamaica is in the 700 MW range for example.

With newer cycles like the Uehara/Kalina ammonia that get 3.5% or Sea Solar Power propene Rankine, also around 3.5% and able to use every efficient aluminium exchangers, I am confident that after the first few proving commercial scale plants, OTEC will be competitive, especially versus slow speed diesel or low efficiency steam that is predominant in the 50MW size range predominantly employed.

When the possibility of fresh water is added to the equation and maybe the possibility of massive protien production via plankton, things get very interesting. There is not another technology out there with these valuable combination of potential byproducts.  

Taiwan gets cheaper power from it's nukes.  Costa Rica would be better served by more hydroelectric dams.  Cuba is a candidate for nukes as well once Castro dies, and some small hydro (I think wind as well). Jamaica has some hydro potential left in the Blue Mountains + wind ?.  Dom. Republic has some wind potential and perhaps some hydro as well.

Basically, OTEC is likely as option when the alternatives are PV solar with batteries or oil.  Most other renewables (or nuke) will be preferred otherwise.  Only once those are exhausted, will OTEC have a place IMHO.

Worldwide potential ?  Somewhere between 1,000 & 2,000 MW seems an optmistic view.

For me and a plurality of humanity, nukes are not a credible long term option when all the issues surrounding them are appropriately considered, including GEN III and GEN IV. They are especially not likely in smaller countries where the technical expertise to handle them is limited and will likely remain limited. I will not get into another argument here where that is concerned.

I know that the remaining hydro potential in Jamaica is not more than another 100 MW with the Back Rio Grande project the biggest at about 50 MW. Costa Rica may have more but even there, it is limited. Geothermal is also a candidate I think for Costa Rica.

Of course wind, solar, biofuels etc. will also be looked at and implemented where applicable. The issue though is that OTEC has some attributes that are valuable, 24/7 energy like nukes, coproducts that can be extremely valuable (possibly even moreso than the energy) and the fact that they need not use any land, very good for land starved islands. Your total market of 1000 - 2000 MW worldwide is way too little. A company called Sea Solar power is claiming they can build a 100MW plant for US$300 million with figures corroborated by reputable engineering establishments. If they are off by US$100 million equating to $4 per Watt, that still makes the technology competitive with diesel and BUNKER C steam that is rampant in these areas. Compared with GEN III and GEN IV nukes and definitely Fusion, the technological risk is much lower being principally tied to the pipes, (Cold Water in particular) , heat exchangers and storm survivability. The oil industry is already dealing with some of these ssues in their offshore engineering.

Remember, we are not talking about competing with Australian coal plants generating at 3c per KWH, so the hurdle bar is much lower.

A big problem with OTEC is that all the good spots are prime targets for the hurricanes (no matter what they're called locally) and the rough seas. As shown by the Gulf Coast/Katrina debacle, the OTEC plants have to be sturdy, costing extra.

As far as geothermal, I thought of an idea as a teenager: Drill for volcanoes! You drill, like for oil, but you drill for magma, let a volcano form, and you get plenty of geothermal. But alas, it will be limited to areas already active like Iceland. Hawaii has a pre-existing volcano so they can get like the Icelandic. But for civilisation-wide power, I bet it won't cut it. Geothermal is fairly limited whether you drill for volcanoes or not. But it is already used and is just another addition to the portfolio.

Renewables in general will end up being a whole portfolio where what works here is used, what works there is used, but with no one major workhorse of a solution.