Talk:Ocean thermal energy conversion

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)

Why so complicated?

kkThe 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)

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. 65.46.169.246 (talk) 15:15, 7 September 2010 (UTC)

Can't get a date

Can somebody confirm the 1930 date? I've seen 1928... 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)

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.

Heda62.68.29.247 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)

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)

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 jameslau2@gmail.com. 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)