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Ocean Thermal Energy Conversion

Discussions of conventional and alternative energy production technologies.

Unread postby Andy » Tue 16 Nov 2004, 17:20:27

Don't forget the most prodigious marine renewable of all Devil. It is called OTEC. The main problem is that it is only available in the tropics and subtropics. (far from markets) It utilizes the natural temperature gradient of tropical waters, about 20 degrees celcius. This is enough to drive turbines using closed cycle (ammonia, ammonia/water, propane or some other refrigerant type working fluid) or open cycle (direct seawater vapour turbines). Of all the renewables, it has potentially the largest scale, it can operate 24/7/365 like fossil plants and can accomodate complementary systems like aquaculture etc. For tropical islands, it is without question the most promising alternative energy source.
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Unread postby tmazanec1 » Tue 18 Jan 2005, 21:29:49

OTEC might be restricted to tropics and sub-tropics, but a lot of people live in those areas. Maybe it could help develop the Third World some?
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Unread postby tmazanec1 » Thu 20 Jan 2005, 10:39:54

OTEC would be in mid-ocean, not rivers, IIRC.
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Unread postby Andy » Thu 20 Jan 2005, 11:56:01

Tmanzec, I think they are referring to the tidal technologies and not OTEC.

OTEC is a completely different animal operating either on shore with long pipes or floating far offshore in deep water. The environmental risks are primarily with the scale of water being moved and stuff like ammonia used in some of the cycles. I agree however that it is extremely promising for tropical island nations in SE Asia, Caribbean, Pacific, especially if combined with open ocean mariculture. It is one of the few renewables with 24/7/365 capability without energy storage.
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Deep Sea Water Applications - OTEC Plantships

Unread postby EnergySpin » Sun 31 Jul 2005, 21:20:22

It has been evident to all POilers that the decline of availability of fossil fuels will have an impact on multiple fronts: energy production, transportation and agriculture. The latter would lead to a decrease in the available food production due to a decrease in the available nitrogen (in fertilizers). Is there a way of mitigating this mess that is dependent on using or imitating the biogeochemical cycles of this planet? I decided to embark on an ambitious mental masturbation program :P to see what might be possible. No zero point energy but probably a lot of BS :P
Background

During the last century agriculture and industry disrupted the Nitrogen Cycle through the ICE, and fertilizers. The net result was the transfer of significant amounts of nitrogen from the atmosphere to the land and finally to the oceans leading to eutrophication phenomena (i.e. algal blooms and subsequent anoxic marine life die-offs). When the fertilizer input is cut, agricultural production will fall and it will take a lot of time for it to recover. One of the problems with topsoil loss is that regeneration takes a very long time .... in fact total nutrient recirculation between marine and terrestrial systems on the planet is dependent on a) geological phenomena like the movement of tectonic plates, and volcanic activity b) biological phenomena (i.e avian species feeding on aquatic life, bringing back to the land nutrients with their hmm bowel movements :P)
Even though we cannot do anything about mechanism a) we certainly screwed up mechanism b) with the depletion of fisheries around the globe. Simplification of food webs in the aquatic ecosystems means that a big proportion of carbon/nitrogen that would exist in complex life forms exist either in inorganic form or in micro-organisms. Eventually all material irrespective of whether is "locked" in life forms or not ends up in the deep sea waters, and is slowly recycled through upswellings of waters along the western US , Peru, Ecuador, Central Pacific and the Atlantic Coastline of Europe. This upswelling is responsible for the increased net primary production in marine ecosystems (and numerous fisheries) in those places. Disruptions of those upswellings is responsible for the El Nino phenomenon. Note that these upswellings are naturally occuring phenomena that are dependent on solar radiation. Solar radiation creates a thermal differential between the deep sea and the surface waters, which under certain conditions drives naturally occuring cycles that stabilize the climate across the Pacific. This thermal differential is also utlized in Oceanic Thermal Plants which are currently used in Hawai for AC, electricity generation, mariculture, and water desalination. The interesting thing about OTEC plants is that the energy to run them is provided by the oceans. Deep Sea Water is used to power the plant, generate base load electricity 24-7, provide water for mariculture, desalinate water and drive industrial chemistry reactions generating ammonia, methanol and hydrogen from the water (check the OTEC NERL page). The problem with island based OTEC is that they are based in land ... you cannot move them and hence their applicability is limited at first sight. When the Carter administration kick-started the OTEC program in the 70s they considered both stationary and floating OTEC (OTEC plantships). Are these ships one possible answer to the creation of liquid fuels and or fertilizers to support agricultural production and recycle stuff from the Deap Sea? Lets see

OTEC Plantships
Much of the following is supplied from web searches on the issue, web diving on OTEC webpages at NREL and the Hawaii OTEC website and a few random articles. Issues in Science and Technology had an interesting article back in 1997 on the technical feasibility of an OTEC plantship which can be read here
Analysis of the OTEC cycle indicates that equatorial OTEC plant ships slowly "grazing" on warm surface water at 1/2 knot could continuously generate more than 5 megawatts-electric (MWe) of net electric power per square kilometer of tropical ocean. The electricity generated would be converted to chemical energy on board the plant ship by electrolyzing water into hydrogen and oxygen. ..... Engineering studies indicate that OTEC plant ships designed to produce 100 to 400 MWe (net) of electricity (which is between 10 and 40 percent of the output of a large conventional power plant) would be the optimum size for commercial operation.

Note that the electricity is available 24-7 ... and is used to power the ship.
The U.S. Department of Energy (DOE) sponsored engineering designs that were developed between 1975 and 1982 by industrial teams under the technical direction of the Johns Hopkins University Applied Physics Laboratory (APL). Designs are available for a 46-MWe pilot OTEC plant ship that would produce 15 metric tons per day of liquid hydrogen (or 140 metric tons per day of liquid ammonia) in a conventional chemical plant installed on the OTEC vessel. It would use the same synthesis process that produces ammonia on land but would eliminate the costly methane-reforming step of that process.
An APL conceptual design is available for a 365-MWe commercial OTEC plant ship that would produce 1,100 metric tons per day of liquid ammonia. Used as a motor vehicle fuel, this could replace approximately 150,000 gallons of gasoline. If operating experience confirms the utility of this conceptual design, 2,000 OTEC ammonia plant ships could supply enough ammonia fuel per day to match the total daily mileage of all the automobiles presently in the United States. If these plant ships were distributed uniformly over the tropical ocean, an area of about 60 million square kilometers, they would be spaced 175 kilometers apart

Although I have a distaste on arguments of the kind : it will take X amount of something to replace all the energy consumed in the US/world etc, we should take into account the following:
1. An ammonia ICE prototype has been built (it is not a lot different from the ICEs currently in use). In fact the ICEs that burn hydrogen or ethanol can burn NH3 as shown here
2. A distribution network for anhydrous NH3 already exists in the US and the world (i.e. tankers, pipelines etc) which can deliver NH3 directly to farms both as fertilizers and as fuel for agriculture
3. Emissions from an NH3 ICE are Nitrogen and Water (with the use of catalyzers to get rid of NOx as in current vehicles
4. NH3 can be stored as liquid (using the same kind of materials found in propane tanks)
5. NH3 is not flammable under transport conditions
OTEC ships are feasible; the following was copied from the article in Issues in S&T :
Competitiveness and financing. OTEC systems are "low" technology. Operating temperatures and pressures are the same as those in household air conditioners. About two-thirds of the required OTEC system components and subsystems are commercially available. Another 10 to 15 percent need to be scaled up and optimized for OTEC use, which adds some cost unpredictability. Only the cold water pipe construction, platform attachment, and deployment will require new types of equipment and procedures. If we assign l00 percent cost uncertainty to these items, the overall investment uncertainty of the OTEC system is around 15 to 25 percent. This relatively low uncertainty permits cost estimates to be made with reasonable confidence.

The ultimate sales price of fuel from OTEC plant ships depends on the cost to amortize plant investment (including construction costs) over plant life, plus operation and maintenance costs, including shipping to consumers. For a range of scenarios, the cost of OTEC-ammonia delivered to U.S. ports is estimated to vary from $0.30 to $0.60 per gallon (in 1995 dollars). Adjusting for the lower mileage per gallon of ammonia, this would be equivalent to gasoline costing $0.80 to $1.60 per gallon. These estimates are strongly dependent on assumed interest rates, amortization times, and whether tax credits and other subsidies that are available to gasoline users would be available to ammonia producers as well.


This text was written in 1997 BTW ..... and to provide additional fuel to the interaction between government and technology, the concluding paragraphs from the same articles (emphasis and emoticons added)
The seven-year DOE R&D program provided positive answers to doubts about OTEC. It demonstrated at a reasonable scale that the OTEC concept for ocean energy production is technically feasible. The next step was to have been construction of a 40-MWe (nominal) pilot plant that would provide firm cost and engineering data for the design of full-scale OTEC plant ships. Planned funding for this step was canceled in 1982 when the Reagan administration, with different energy priorities from those of the Carter administration, took office. :( Since l982, government support of OTEC development has been undercut further by the drop in oil prices that has reduced public fears of an oil shortage and its economic consequences, as well as by the opposition of vested interests that are committed to conventional energy resources. :twisted:

Lack of support for OTEC research is part of a general lack of interest in energy alternatives designed to address fundamental problems that will not become critical for several decades. :x If and when the need for measures to forestall energy shortages and/or severe environmental effects from present energy sources becomes evident, the long lead times needed for the costly transition from fossil fuels to sustainable energy resources may prevent action from being taken in time to be effective. :( It is prudent to renew OTEC R&D now.

Well that's here in the US ... India is launching a prototype OTEC plantship (I'm not using the word "pilot", the work by NREL in Hawaii proved the concept 20 years ago) by modifying an available cargo ship (read here)
SeaSolarPower produced a design of a 100MW ship back in 1996 (link is here)
It is interesting that OTEC plants are already regulated in the US (link)
and that the environmental impact is much less than other technologies (OTEC removes nutrient rich water from the deap sea where it is underutilized anyway due to lack of photosynthesis.
However the environmental impact of wide scale deployment of OTEC ships would be interesting at the very least and impossible to predict without extensive modelling. There are legal issues as well regarding the commercial exploitation of the oceans (i.e. the EEZ of 200 miles places certain restrictions on the utilization of this source by everyone, but at least 99 nations can utilize this technology without legal problems, and the rest of world wide community could use international waters or engage in cooperation about this resource)
However they could be used to at least provide enough fuel and fertilizers for agriculture (forget about electricity, they just need to produce enough to stay afloat) to offset or mitigate the PO effects in this area.
It is interesting that the OTEC community have been telling everyone about the future of fossil fuel energy (the following was written in 1999 by L. A. Vega
At present, the external costs of energy production and consumption are not considered in determining the charges to the user. Considering all stages of generation, from initial fuel extraction to plant decommissioning, it has been determined that no energy technology is completely environmentally benign. The additional costs associated with corrosion, health impacts, crop losses, radioactive waste, military expenditures, employment loss subsidies (tax credits and research funding for present technologies) have been estimated to range from 78 to 259 billion dollars per year. Excluding costs associated with nuclear power, the range is equivalent to adding from $85 to $327 to a barrel of fuel oil, increasing the present cost by a factor of 4 to 16. As a minimum, consider that the costs incurred by the military, in the USA alone, to safeguard oil supplies from overseas is at least $15 billion corresponding to adding $23 to a barrel of fuel - equivalent to doubling the present cost. Accounting for externalities might eventually help the development and expand the applicability of OTEC, but in the interim the future of OTEC rests in the use of plantships housing closed (or hybrid) cycle plants transmitting the electricity (and desalinated water) to land via submarine power cables (and flexible pipelines).

Conventional power plants pollute the environment more than an OTEC plant would and, as long as the sun heats the oceans, the fuel for OTEC is unlimited and free. However, it is futile to use these arguments to persuade the financial community to invest in a new technology until it has an operational record.

The article in PDF format can be donwloaded here
Considering that OTEC plantships:
1) can be based on existing tanker desings,
2) that they could synthesize chemicals i.e. fertilizers without burning gas 3) that the technology is low intensity, well understood (it is a Carnot engine)
4) the marine industry already has tankers that can shuttle the output of OTEC plants (clean water, NH3), especially now that the fossil fuels wil become obsolete (from my understanding one does not need expensive LNG design to transport NH3 or water :P
it is amazing how greed, shortsightedness did not enable this technology to be deployed 20 years ago.
In any case for what is worth ... it is technically feasible to avoid the carbo cycle and prevent the decline of food production when we will no longer be able to convert fossil fuels to food. The energy to start that industry is available by the sun, we know how to build tankers and deep sea tubes but I do not think that the corporate-military-political complex will ever let this fly.
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Unread postby MicroHydro » Sun 31 Jul 2005, 22:28:58

As I understand it, electricity generation efficiency from small temperature differentials is pretty poor.

The Tuapo geothermal plant in New Zealand produces mainly steam heat energy for local heating, with electricity as a trace byproduct.

The arguments for the viability of Pacific OTEC have been mainly:
1) Cold water to provide cheap air conditioning
2) Fresh water (through condensation)

So if one was doing OTEC primarily for electricity production, what would be the cost/kwh? Does someone think that OTEC electricity would cost less than the offshore wind cost of $0.05/kwh?
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Unread postby EnergySpin » Sun 31 Jul 2005, 22:39:04

World Energy Council Assessment of OTEC plantships (back in 2001)
In short, the key breakthrough now required for OTEC/DOWA is no longer technological or economic, but the establishment of confidence levels in funding agencies to enable building of a representative-scale demonstration plant. Given that demonstrator, the early production plants will be installed predominantly in island locations where conventional fuel is expensive, or not available in sufficient quantity, and where environmental impact is a high priority. Both simple OTEC and OTEC/DOWA combined plants will feature, depending on the particular requirements of each nation state.

Full Text is here

A PDF by one of the big Japanese players can be read here
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Unread postby EnergySpin » Sun 31 Jul 2005, 23:06:55

MicroHydro wrote:As I understand it, electricity generation efficiency from small temperature differentials is pretty poor.

The Tuapo geothermal plant in New Zealand produces mainly steam heat energy for local heating, with electricity as a trace byproduct.

The arguments for the viability of Pacific OTEC have been mainly:
1) Cold water to provide cheap air conditioning
2) Fresh water (through condensation)

So if one was doing OTEC primarily for electricity production, what would be the cost/kwh? Does someone think that OTEC electricity would cost less than the offshore wind cost of $0.05/kwh?

Electricity generation has been calculated to be from 7- 22c/Kwh for an 100MW offshore OTEC plant (as the distance from the shore is increased from 10 to 400km page 21 of the paper by Vega found here here) .
The major difference with offshore wind farms is that OTEC plants provide base load electricity (i.e. the gradient is stable)
The potential for OTEC is not limited to electricity generation (although it can be used for that) but extends to deep sea mining for fresh water and ammoniagenesis using a carbon less cycle but for that one would need offshore plants. To give you an idea of the size .. a 400MW plant would be the size of one of the supertankers.
Note that the environmental impact could be considerable. A 100MW plant essentially recycles a volume of water equal to the outflow of the Colorado River, but the impact could be positive (at least for the epipelagic zone) with unknown impact on the bathypelagic abyssal and hadal ecosystems (even though it is felt that the bathypelagic, abyssal and hadal zones are of low biomass).
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Unread postby MicroHydro » Mon 01 Aug 2005, 00:13:24

Ok, if you make electricity at 7 cents per kwh (your best case) then (BOE=1600kwh, assume hydrogen generation 40% efficient) hydrogen will cost $280/BOE and ammonia somewhat more than that. Maybe ammonia at $420/BOE or $10 per gallon?

Ammonia from natural gas costs 33500 cubic feet of natural gas per ton. At $9/ thousand cubic feet for natural gas, the feedstock cost is $300/ton of ammonia or about $42/BOE ammonia

I can see why the World Bank and venture capitalists haven't jumped on this bandwagon.

For generation of hydrogen (or ammonia), the varying nature of wind power doesn't matter. That is probably why the 2003 Imperial College study on future aviation fuel for the UK mentioned hydrogen from offshore windfarms. With OTEC plants very capital intensive and high maintenance (corrosion of heat exchanger) and requiring plastic (oil based) pipes, I see a very limited future for OTEC as an electricity or fuel source.
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Unread postby Andy » Mon 01 Aug 2005, 01:16:24

Microhydro wrote:For generation of hydrogen (or ammonia), the varying nature of wind power doesn't matter. That is probably why the 2003 Imperial College study on future aviation fuel for the UK mentioned hydrogen from offshore windfarms. With OTEC plants very capital intensive and high maintenance (corrosion of heat exchanger) and requiring plastic (oil based) pipes, I see a very limited future for OTEC as an electricity or fuel source.


I agree that plantships producing hydrogen or ammonia might not prove to be viable. I disagree however that OTEC for electricity and possibly fresh water is limited. For developing and even industrialized tropical island areas, it is extremely promising. Studies have been carried out on heat exchanger surfaces and shown that corrosion and biofouling are not the problems that were once feared. The problem only occurs on the warm water side and was found to be readily controllable with small amounts of chlorine and aluminum or titanium heat exchangers.

The pipes represent the greatest uncertainty but they do not have to be plastic. They can be rubber and even strong fabric has been proposed. In any case, other materials can provide the plastic ingredients like hemp, coal, nat. gas etc. for instance.

I can easily see, if we get serious about alternative energy OTEC providing countries like Jamaica, Cuba, Puerto Rico Dom. Republic, Haiti etc. with 40 - 50% of their electricity needs and also supplemental fresh water, coastal AC, mariculture sufficient for a significant fraction of protein needs etc. You name me one other energy technology that has this many potential byproducts save for biomass and I will give you a prize.
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Unread postby MicroHydro » Mon 01 Aug 2005, 02:45:28

Andy wrote:if we get serious about alternative energy OTEC providing countries like Jamaica, Cuba, Puerto Rico Dom. Republic, Haiti etc. with 40 - 50% of their electricity needs and also supplemental fresh water, coastal AC, mariculture sufficient for a significant fraction of protein needs etc.


If
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Unread postby EnergySpin » Mon 01 Aug 2005, 10:14:10

Ammonia from natural gas costs 33500 cubic feet of natural gas per ton. At $9/ thousand cubic feet for natural gas, the feedstock cost is $300/ton of ammonia or about $42/BOE ammonia

I can see why the World Bank and venture capitalists haven't jumped on this bandwagon.


But there will not be any natural gas to serve as feedstock in a few years . But even if the natural gas was out there this is a carbon-free method, that requires no new technology. In fact the technology components have been out there for years.

Just by having a carbon free method that does not compete with onshore or offshore wind for space, can generate water, fertilizers and potentially transportation fuel is a feature that none of the other technologies have.

The areas where plantships could be deployed do not compete with wind (in fact the lack of wind is those places prevents the deployment of wind turbines). Small onshore plants make sense for island communities, big plants will be used for chemical generation. In addition the EEZ of 200 miles make cooperation between big players and natural communities a big plus. The ships could be deployed close to the islands and transfer the surplus electricity and water via wires or tubes(ships).

The reason that none of the venture capitalists have jumped on this was detailed in the article in Science and Technology. In fact market mechanisms will never "save the day" on time (isn't this what Hirch told us?)
The environmental impacts have to be studied on two fronts:
1) the impact on bathy-abyssopelagic ecosystems and epipelagic ecosystems (if chemicals used to prevent biofulling are kept at minimum, then it is likely that we will see an explosion of fish life in the epipelagic region)
2) the potential impact on the thermohaline currents that maintain the Gulfstream. In fact in those regions that OTEC makes sense have "natural" deep sea water upswellings (in the opposite direction than the water columns in Northern Europe where the Gulf Stream ends). We might end up speeding up the gulf stream, which seems to be shutting down anyway due to the polar ice melting). Anyway this needs a composite oceanographic/atmospheric modelling and a supercomputer to answer ... no answers possible from my Compaq Pressario :-D
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Unread postby Andy » Mon 01 Aug 2005, 19:30:30

Microhydro wrote:If


You are so very right. IF!!! Most likely, we are going to wait until the last minute and then it wll be too late.
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Unread postby EnergySpin » Mon 01 Aug 2005, 20:16:52

For what it's worth there is a web site with OTEC news. I found it a few days ago. Those guys are bitter :-D Every news or science article they post starts with a nice opening section about the evil of fossil fuels and the industry that supports them
The webpage is OTECNews
Another web page of interest is Green Ocean
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Unread postby EnergySpin » Thu 04 Aug 2005, 00:21:25

An antidote to glooming and dooming. A presentation on potential application of the opean oceans for energy production, food production and vision for peace for the 21st century. Could it be that the oceans be the answer to climate stabilization, energy and food production?
The presentation was given by the people at the Renewable Energy Lab of Hawaii in the 2003 Paris UNESCO conference. Was commisioned by the Intergovernmental Oceanographic Commission. Can be read here
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Unread postby bjelkeman » Mon 15 Aug 2005, 17:33:45

EnergySpin wrote:For what it's worth there is a web site with OTEC news. I found it a few days ago. Those guys are bitter :-D

What us bitter? Nahhh....
It is just part of our chosen editorial style really. :)
OTECnews - http://www.otecnews.org/
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Unread postby EnergySpin » Mon 15 Aug 2005, 18:36:08

bjelkeman wrote:
EnergySpin wrote:For what it's worth there is a web site with OTEC news. I found it a few days ago. Those guys are bitter :-D

What us bitter? Nahhh....
It is just part of our chosen editorial style really. :)

You should be bitter mate.
They should not have killed the program.
Your average OTECer :)
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Re: alternative energy future

Unread postby mkwin » Mon 25 Feb 2008, 07:08:13

You forgot ocean technology. I like the energy Islands. :)

http://anz.theoildrum.com/node/3643#more
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Re: Energy from Ocean

Unread postby anador » Tue 28 Sep 2010, 10:40:50

Temperature Variation, you mean like using a giant thermocouple to generate power?

How could you construct one that can utilize differences in temperature which only manifest themselves meaningfully on gigantic scales?
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Re: Energy from Ocean

Unread postby RankineCycle » Thu 30 Sep 2010, 13:08:13

Ocean thermal electricity generation is in most cases a losing battle, the temperature difference is so low that the work required to pump the water is greater than the work that can be extracted from the differences in temperature of said water.

I've done an idealized analysis on this. It will only work at all where the cold and warm water bodies are close to one another. The turbine efficiency is still horribly low (less than 5%) and must use a low-boiling point working fluid like R-134a.

Using ocean water as a source or sink for a heat pump, however, is a more reasonable proposition.
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