Dossier Océan et énergie - Énergie Thermique des Mers
Sommaire IOA News Letters
Questions and Answers on OTEC in Taiwan
Chairman, IOA Core Group
1. Would you please comment why even if the technology of the Ocean Thermal Energy Conversion (OTEC) has been demonstrated, a commercial OTEC Power Plant is not yet available?
Comments and Suggestions:
To this question one usually answers as follows: In spite the fact that OTEC technology is available, the economy of OTEC are not proven to be competitive when compared with traditional energy sources such as: coal, oil, gas, and nuclear, etc.. This answer might be the right one but until now there was no standard economic model to allow fair and detailed comparison of global costs and benefits of the energy sources. Global costs and benefits means that such a model should not only consider direct investment and production costs but also the development cost and the expenses induced by secondary effects like damage to the environment and to human health, by-products and wastes disposal or reprocessing, docommissioning or dismantlement of old in active plants, sites restoration, military expenses to protect resources, etc..(nota 1)
I reasonably think the lack of such an universal comparison model which would allow detailed and sound comparison is not available for two reasons.
The first reason is that such a numerical model is difficult to built. Technically the evaluation of environmental damages or threats to human health is certainly uneasy and will encounter a lot of controversies ( this means a lot of work for a multidisciplinary. Working Group of experts). Financially the construction of a model that would be accepted world wide as a standard would involve both tenacity and money. The second reason, I believe the most important, is that until now there has been no real interest for the private or public sector to make a fair comparison of various energy soruces.
OTEC's situation can be compared to that of the Electric Car is Industry. Notwithstanding the fundamentals of the technologies for OTEC and Electric Car have been available for more than 50 years, neither Electric Cars nor OTEC plants are commercially developed yet. This is the result of a basic law which rules our present western economy. This law can be stated as follows: In a purely liberal economic system, investors energy tends "naturally" to maximise the ratio of the benefits over the investments and in the shortest possible period of time (nota 2).
Obviously this is a caricature of the mechanism which drives our modern societies. Hopefully there exists for our societies a capacity to generate some antagonist reactions to fling and temper the perverse effect of this "law". This reaction is driven by human wisdom and common sense, religious belief (or sometimes just by survival instinct). It is revealed through what one usually calls the "public opinion" and addressed by "group pressure", "Associations", etc.. Efforts to promote OTEC (as done by IOA) and other renewable energy sources is one illustration of human societal capacity to react to the perverse effect of policies aimed to short term political and financial profits.
To conclude my answer I would suggest to include in the MOPR a task on the theme "Building a model for energy supply global costs assessment". The task would consist of: investigating existing models (there have been probably some sttempts in that sense by USDOE or other organizations). Improve them, and promote the progress and results obtained. The results will probably generate new questions and justify new research actions (nota 3) in various fields.
2. Would you please predict the OTEC potential of the world? Will it become a primany or important energy source in the 21st century? When and where are the most possible times and places to develop OTEC power? Based on what studies and/or reports can you estimate the possible OTEC potential along the east coast of Taiwan? (please list the reference, if possible)
Comments and Suggestions:
During the 1970's many papers have tried to answers to these questions. Some answers are based on the OTEC energy resource potentials (nota 4). This type of wild imaginings lead to an enormoous OTEC potential for base load electric installed power. Potential as high as 14000 GW is given in "Power from the sea" Scientific American January 1987 Vol. 256, No. 1 pp.86-92. See also the 10,000 GW estimated potential in "A guide to OTEC" (nota 1).
These numbers are of no great interest in defining a commercial strategy.
A more realistic approach is the assessment of potential markets for a given situation of the world economy. As an example of this approach for OTEC power plants, see Dunbar's study performed for the US State Department in 1981. This study indicated a market potential of 550 GWe.
Will OTEC become a primary or important energy source in the 21st century?
I have no rational to foresee more than few years ahead. My belief is that OTEC could become a significant source of energy under the following conditions:
a)-severe pressure on oil markets and at least doubling of the present price of the barrel of oil. (Many papers exist relating the price of energy which renders OTEC commercially competitive).
b)-severe pressure from the public opinion against nuclear energy. Such pressure can build up rapidly with repeated nuclear types of accidents such as Chernobyl's.
c)-undertake a rational evaluation of true social and economic costs of the different energy sources, establish a world-wide consensus for a long term policy in matter of energy supply, implement such policy at the inter-national level.
Conditions a) and b) are the most probable conditions that might lead to the take off of OTEC and associated activities. Unfortunately Conditions c) is just mentioned for contemplation and has very little probability to be fulfilled.
Where are the most possible times and places to develop OTEC power?
The most probable places (countries) to develop OTEC are those:
located in a proper geographical zone;
-facing a critical need in energy supply to sustain their economic development;
-where people have democratic means to express their concern for environmental conservation;
-with the investment capacity to support the OTEC capital costs and afford the extra cost which should be normally expected during a developing phase;
-with a relevant political, and scientific level to control the OTEC development phase;
-with an existing industrial capability to fully exploit the political and exonomical benefits that could be generated thanks to the expertise and the technical advances acquired during the implementation of the OTEC development policy.
None of these conditions being by itself and taken separately are prerequisited for OTEC development.
Based on what studies and/or reports you can estimate the possible OTEC potential along the east coast of Taiwan?
My knowledge of the OTEC potential in Taiwan comes from the results of studies executed under the aegis of the ROC Ministry of Economic Affairs.
If we assume the area of the ROC East Coast compatible with OTEC requirement (as defined in MOPR) to be approximately 200km X 34km and referring to chapter 1 of "A guide ot OTEC" (see nota 1 reference), the OTEC potential would range around: 300km X 34km X 0.19 MWe or 1.9 GW. This may appear conservative when compared with MOPR values but the order of magnitude is comparable.
3. What are the implication of CO2 emission with an OTEC power plant? Can you estimate the quantity of CO2 emitted from closed cycle OTEC and from open cycle OTEC? Who has been doing what to have a better understanding or better way of control on this issue?
Comments and Suggestions:
It is very easy to figure out the maximum value of the CO2 emitted, in the worst case, by the degassing of the water flow passing through an OTEC plant of a given installed power. Several results have been presented (see PICHTR, L. Vega) and the CO2 quantities released by OTEC appeared very small in all cases when compared to the global GHGs problems.
In fact the problem to solve at the present state is more fundamental and not really bound to the amount of CO2 emitted by power plants. For fossil fuels, OTEC and others, we know very well how to estimate CO2 conservative values. The most important question to solve is rather "What are the natural processes that control the CO2 balance (nota 5) in our Earth ecosystem. My belief is CO2 environmental threat is not a priority concern for OTEC planners. This does not mean I deny interest in carefully investigating the environmental impacts of OTEC since the "Clean renewable energy" concept is the basic argument to promote OTEC development.
4. What are the considerations of the environmental impacts with OTEC power plants? Can you start by stating all the possible impacts and reach to a conclusion regarding how many OTEC power plants, or how many MW of electric power, can be built along the east coast of Taiwan so that a significant temperature difference at the ocean surface will not occur, and the ecosystem will not be affected.
Comments and Suggestions:
The possible effects of OTEC on the plant's surrounding marine (natural) environment are:
-the effects induced by the temperature changes of water masses on local climate and living marine organisms;
-the effects induced by the chemical contents of the effluent plume.
One can calculate the share of thermal energy subtracted by OTEC from the natural process. If one refers to. the result indicated in ref. nota 1, "OTEC plants can be operated continuously without significant environmental effects, if the power generated is limited to approximately 0.19 MWe per square (km2) the amount of power corresponds to the conversion of 0.07% of the average absorbed solar energy to electricity".
This amount may indeed appear insignificant but this has to be scientifically demonstrated.
Nutrients and others:
For the Tahiti 5 MWe OTEC project a very coarse study was conducted to predict the effects of the effluents on the surrounding environment. A model of the ecosystem was built and run 6. The conclusion was that the potential risks assoicated to OTEC plants of small size (here 5MW) would not be a threat to the marine flora and fauna...". Nevertheless uncertainties will remain as long as long term effect will not be studied in the surrounding of an OTEC prototype of significant size.
In "A Guide for OTEC"(nota 1) the author gives also some relevant comments about nutrients and others (CO2) components' impact, including the effect of Ammonia in case of failure of a close cycle OTEC plant.
In all cases the potential risks will depend strongly on the local geography and the oceanographic characteristics of the site. Also the risks could be drastically reduced by a careful design of the platform and pumping and exhaust system.
But one should not only consider impact on the marine environment: Impacts on social "environment" will be revealed as much more important in the long run.
5. Is it possible at the present time that one can state what will be the best platform and cold water pipe design for a floating commercial size OTEC power plant (50 MW up)? If not, what are the possible good designs? For these designs, can you suggestion who has the best technology and/or experience to do the design and/or fabrication? You are absolutely welcome to provide us any organisation and/or private sector for our reference.
Except for the platform and cold water pipe, are there still any technologically uncertain or unavailable components, for instance, the heat exchanger, the pumping system, or the power transmitting system.
Comments and Suggestions
For floating OTEC plants in general it is wise to consider no one can predict what will be the best designs for future OTEC platforms and CWP. Many new concepts will be generated during the first decades of the commercial OTEC development.
For the first commercial demonstration plant the maximum of experience should be taken from the offshore oil industry:
- the semlsub platforms concept
with minimum of submerged equipment and easy access tot he installations should
considered in priority;
- I anticipate difficulties before
mastering the non-self statically rigid CWP technology. For big plants the CWP
designed more as a tower than as a pipe, and I will recommend to carefully examine in priority a modular prestressed
CWP design using light cellular concrete material.
Huge concrete semisub oil field reservoirs have been built and experienced on site in the last decade and companies with this type of expertise7 should be questioned on the limits and the prospects of this technology for building demonstration OTEC Platforms and CWP.
This topic brings a general remark to be considered by MOPR promoters. In the chapter 1.1.4 page 12 of MOPR Volume 1 "OTEC as contributor to (ROC) National Economy" it is written: "By creating an OTEC industry and infrastructure, it raises the level of technology and expands heavy industry...,etc., which further stimulate economy". This chapter is very important and it might be worthy to be more fully developed. The question should rather be formulated as: "How MOPR efforts can also contribute to global ROC development policy" (or "How to maximise the return of MOPR investments").
What is the comparison between land-based and offshore floating OTEC?
Comments and Suggestions:
This comparison between land-based and offshore floating OTEC was the object of detailed and lengthy debates during the 1975-1985 period. The main advantages for offshore plants are:
- minimise the length of CWP, and facilitate its construction installation and maintenance; allows construction of the supporting platform and energy subsystem in an industrialized zone, with the plant being towed to offshore site prior to the pipe installation;
- eliminate the problem of the investment costs for land ownership and the potential conflicts with neighbours and surrounding land users; this can become important in case of development of OTEC and energy consumption on site (to produce hydrogen, or other industry products);
- it is the unique solution compatible with the "Grazing concept",
and drawbacks are:
- increased running costs; this can be partly solved by designing a highly automated and/or remotely controlled plant.
- length of connecting cable for the electric plants connected to a distribution network.
- lack of maturity in the design of multiproduct offshore plants. (How to use fully the DOW on an offshore plant? Think for instance on how to develop DOW applications for aquaculture or open ocean fertilisation).
For large OTEC plants (greater than few tens of MW seems the upper limit) there are not really alternatives to floating solutions8 for the next decades. Completely submerged OTEC plants could be considered in the future.
7. What is your overall impression on MPOP and MOPR? Do you think it is possible that either MPOP or MOPR can be promoted as an internationally cooperated project, instead of just a project promoted by the Taiwan government? and why? What will be the best strategy that Taiwan government must consider in order to enhance the achievement of the MPOP or the MOPR? Can you also recommend possible organisations that we should get in touch with?
Comments and Suggestions:
To answer these questions one needs first an exhaustive and detailed assessment of the technologies and expertise needed for OTEC development, and if any, possible alternate solutions. Choicing between alternate solutions can be influenced or determined by non-OTEC technical criteria.
For example there are different possible answers to the question:"Is it realistic to envision all the expertise and industrial needs for MOPR implementation can be satisfied at ROC national level? and, if not, what are the alternative? The possible laternatives would probably offer different advantages and drawbacks from the various points of view to be considered. This remark has to be assoicated with the point evoked in my answer on chapter 4: 1.e. In addition to the impact on the marine (natural) environment, other impacts such as the Economic, Social and probably Political impacts have to be inventoried and evaluated before any strategic decision.
I have not the expertise to answer these questions related to international co-operation. Notwithstanding this limitation my present belief is as follows.
The minimum cost of the programme for the MOPR intermediate 100 MW demonstration plant shall range around 700 million $US. Because the probable economic and industrial consequences of the results of this MOPR demonstration phase would have so much importance, any significant foreign participation to its funding (a share of 10% seems the minimum) can't be envisioned without a very strong and long term agreement between partners. Presently the political links between ROC and the European countries do not favour such long term agreement. This situation might change in case of major events would happen, related to the political situation in the Republic of the People of China.
The istuation might be quite different when one considers the possibility of international co-operation for the MPOP programme. And (not only) because the costs involved in MPOP are much lower than those ofr MOPR but for the reason that the MPOP programme can be presented with a strong political reference to the contribution of industrialized countries for relieving small developing countries from oil dependency. The first targets of possible organizations to get in touch with are then the regional organisations for the economic development and international co-operation in the sub tropical zone (where OTEC is feasible). The second targets are the international organisations distributing the funds devoted to the assistance to economic development. UN conferences such as the recent conference organised in Berlin or Climate Convention may offer an interesting framework and opportunities.9
In all cases, to build up a sufficient lobbying force among developing countries, the Taiwan government will have to demonstrate its strong determination to go ahead for OTEC development. Obviously such a policy cannot be justified bearing in mind with only the objective of financial returns.
1 Chap. 8 of "Renewable energy from the Ocean" W. H. Avery and Chih Wu, Oxford Univ. Press. 1994.
2 Here, "Investor energy" means essentially the money invested by private and public (political) decision makers. "Benefits" are harvested in term of moneyor political returns. "Short term" should be understood scaled at a human life time. I do not intend to make here a value judgment; this "law" has been in some ways a strong motor of progress.
3 Just as an example of identified problem raised already concern the CO2 emission; a better understanding of CO2 storage capacity and CO2 balance between the land vegetation, the ocean and the atmosphere is obviously a prerequisite to the forecasting of CO2 impact on the environment and the comparison between fossil fuel, nuclear and OTEC. Other obstacles will arise from difficulties to assess and quantify social costs with relevant units.
4 Proceed as follows: delineate a volume of surface water of the tropical ocean, assume a given thermal energy extraction compatible with harmless(?) impact on the environment, inject Carmot's and other efficiency ratio, compute on OTEC net power potential....
5 What are the storage capacities of the main components the Forest, the Ocean and the Atmosphere, etc... to my knowledge scientists cannot exdplain the fate of 20% of the carbon dioxide circulating in the Earth ecosystem. In other words 20% of the gas is missing in their global evaluation of CO2 emissions.
6 "A van project Tahiti Centrale ETM 5 MW: Etude des impacts sur I'environnement IFREMER December 87". Publication internee.
7 as: the company DORIS in France, as an example.
8 Building a 20 or 30 metres diameter pipe from a land based site down to -700 or -1000 metre has never been seriously envisioned (as far as I know). A land based OTEC of hundreds of MW could be conceivable if there existed by some geological fluke an atoll island with a vertical volcano chimney or a submerged lava-tunnel type of structure which offers a possibility to pump deep water through a "natural tunnel. Unless nuclear explosive become in the long term a common tool for civil engineering work and allow cheap tunnel excavation techniques to be developed...
9 Read the interesting articles reporting on the Berlin Conference in "the Economist" April 1st 1995.