Dossier Océan et énergie - Énergie Thermique des Mers
Sommaire IOA News Letters
Questions and Answers of OTEC in Taiwan
Don E. Lennard
Ocean Thermal Energy Conversion Systems Ltd.
1.Would you please comment why the technology of the Ocean Thermal Energy Conversion (OTEC) had been demonstrated, a commercial OTEC Power Plant is not yet available¡H
Comments and Suggestions¡G
- History is full of such examples-canals; railways; aeroplanes. There is nothing new in the situation posed by the question. New ideas are generally not appealing to the established financial houses-or indeed governments.
- In many cases, the generating costs for an OTEC plant are not yet competitive with established energy sources (but see 5. below).
- Funding agencies (as noted in 1) are unlikely to support a first construction, or demonstrator. The total development time (see MOPR) is long.
- Servicing of loans for development/construction is expensive and any significant delay can demolish the financial assumptions e.g. UK/France Channel Tunnel (built); UK Severn Tidal Barrage (not built).
- The statement at 2 is not the whole story. Components of an OTEC plant have been demonstrated e.g. OTEC-1 but no representative scale complete OTEC plant has yet operated. And some parts of the technology have not yet been demonstrated at reasonable scale e.g. the design of a cold water pipe (CWP) which can be launched and installed-and repaired with minimum downtime.
- With the present low oil price, the economy of OTEC is very difficult to justify on its electrical generating cost alone (see 2 above) an banks are only just beginning to take note of environmental impact; and the same is true for other outputs/products from an OTEC plant. Market estimates (see later) have been made for electricity generation from OTEC plants, but little has been done to estimate the market for these other applications. Such market estimates are highly desirable as a part of MOPR.
Everything hinges on building a viable demonstrator: big enough for scaling up (5 to 10 times), but small enough to be funded.
Almost certainly that funding will come from a government and/or an international agency. Not private capital (for the reason given at 4 above).
- The government which supports
such a venture will be one where:
- demand for power is rising rapidly
- existing power sources are less environmentally acceptable e.g. coal, oil, nuclear and
- a good OTEC resource exists within that country's EEZ, and preferably within its Territorial Sea.
There are clear and sensible reasons why an OTEC power plant has not yet become available: the procedures recommended in MOPR are (except for size) a logical way of remedying this.
2. Would you please predict the OTEC potential of the world¡HWill it become a primary or important energy source in the 21st century¡H. When and where are the most possible time and place to develop OTEC power¡H Based on what studies and/or reports that you can estimate the possible OTEC potential along the east coast of Taiwan¡H (Please list out the references, if possible)
Comments and Suggestions:
A 25 year estimate1* of OTEC, for electricity production alone, has been quoted at 57,700 MW from some 1,030 plants. Since that estimate was prepared, the DOWA opportunities for OTEC systems have substantially grown, and that figure of 57,700 can now be treated as conservative.
The potential for OTEC has also been quoted 2 as 40,000¡Ñ106MW. This should be dismissed as a realistically achievable quantity. Whilst it represents the theoretically available resource, much of that is located in inaccessible places, and it also takes no note of the degradation of thermal resource which could result (see Section 4). Estimates of realistically achievable markets have been made by France, Japan, UK and USA. The first three are in good agreement with each other - the US figure is more optimistic. From the date of first operation of a realistic demonstration plant, the total demand met by OTEC in the following 8 years is estimated3 at 8,300MW, with 190 plants at the 10MW size and 160 at the 40MW size - all on a worldwide basis. These figures are similiar for French, Japanese and UK estimates in terms of total MW, with some variation between size of plant. Following the 8 year period, applications are expected to grow rapidly, with 100MW plants being available in another 4 to 5 years. Note, however, that for many of the island locations a plant of 40MW will be the largest required.
In summary: 8,300MW in 8 years and 57,700MW in 25 years may be taken as very achievable targets. OTEC, on these figures, becomes an important but by no means a primary energy source in the 21st century. But for many locations (islands) it could well be the primary source.
As noted elsewhere (Section 1) there are key questions to be answered before any OTEC plant of demonstrator size is built. There has to be financial and political will, and the correct demand circumstances (Section 1, point7). There is absolutely no doubt that an island location must be the first installation for OTEC. Whilst a number of small islands are the best technical locations3, the funding for such plants from international agencies (such as the World Bank and the like) is doubtful. A stronger, more diversified, national economy is needed, and this is where Taiwan becomes a prime opportunity. Support by the Government of Taiwan will have a substantial influence on potential support from international funding agencies, such as the World Bank-but particularly the Asian Development Bank.
References to this proposition are contained in the documents already listed together with the reports accompanying the present invitation to comment6 ,7, and two reports of the mid-nineteen eighties8,9. Together, all these references present a very sound basis for preferring Taiwan as the prime location for early OTEC developments.
In terms of timing, the writer refers to Section 1 and to Section 5 of this note. Taking into consideration these points, the writer believes that the MOPR proposals for Taiwan are appropriate and achievable but (see Section 7) believes the target of moving to a 100MW demonstrator in one step is over-optimistic. The writer has believed for over a decade that a 10MW floating demonstrator is a first target-and continuous to believe this.
3. What are the implications of CO2 emission with OTEC power plant¡H Can you estimate the quantity of CO2 emitted from close cycle OTEC and from open cycle OTEC¡H Who had been doing what to have a better understanding or a better way of control on this issue¡H
Comments and Suggestions:
There is considerable disagreement among "experts" on the CO2 emission-or absorption-in relation to an OTEC plant.
With the present state of knowledge, the writer believes the safest statement is based on a comparison of CO2 benefits/disbenefits from OTEC plants and other forms of electrical generation. Leaving aside nuclear power (on which many other environmental balances and safety balances must be made), a comparison with coal, oil, gas or wood (forest) shows a substantial balance in favour of OTEC. Calculations do exist for all of these (to include for wood, the removal of CO2 absorption capability of forests which have been cut down), and the best approach to obtain the implications for CO2 emission from OTEC plants is to undertake a qualitative, and then quantitative, comparison with these other power (electricity) sources.
This, the writer believes, could be done for closed cycle OTEC. He is not sure that design concepts for open cycle OTEC are yet sufficiently formed to enable and CO2 comparison to be made with reasonable levels of accuracy.
In summary, OTEC does compare favourably with other sources of electricity, except nuclear-for which other constraints exist.
4. What are the considerations of the environmental impacts with OTEC power plant¡H Can you start with stating all the possible impacts and reach to a conclusion that up to how many OTEC power plants, or how many MW's of electric power, to be built along the east coast of Taiwan that a significant temperature difference at the ocean surface will not occur, and the ecosystem will not be affected.
Comments and Suggestions:
Here too, there is not an overall agreement among experts as far as these questions are concerned.
However, it is the view of eminent ocean scientists that the temperature change(s) associated with a 10MW OTEC plant, on a grid of 1 km squares will be insignificant in their effect on the warm water resource and that the waste waters (mixed cold and warm) discharges can be emitted at depths which will cause them to neither sink nor rise-and therefore not affect the stability of the ocean water column; and by the same token not degrade the OTEC thermal resource.
These same ocean scientists maintain that natural phenomena have greater impact on the ocean temperatures, and that the reduction in ocean surface temperatures due to operation of an OTEC plant will be: a.) small and b.) so small that natural solar activity will recover this temperature change as a lesser influence that other natural temperature disturbing feature (such as the mixing due to ocean currents). The WOCE and other international, ocean measuring programs are an ideal opportunity to confirm the natural variations and their causes.
The depth contours in relation to distance offshore for candidate ocean sites of East Taiwan suggests to the writer that 1 km linear distance between 10MW plants parallel to the coastline, and adjacent to each candidate site, would be entirely adequate spacing. The writer notes that this is at variance with the proposals in MOPR, but remarks that those are for no-current conditions.
Since (see elsewhere in this note)the time to reach the full operation of a 100MW plant is at least 10 years, there is a clear need to ensure that modelling of water flows around an OTEC plant should be carried out at the same time as WOCE data relevant to Taiwan is gathered. Regarding the overall ecosystem, the writer does not believe that we at present have enough information to comment on overall impact at any specific sites- off Taiwan, or elsewhere. That comment refers only to temperature effects. Other effects are CO2 emission (mentioned at Section 3) and the danger associated with the release of working fluids (ammonia). The potential damage to ecosystems from ammonia at the concentrations which would be derived from a leak are small-due to immediate dilution with sea water. Moreover, it is suggested that modern sensing technology would enable such leaks to be discovered, located and contained to at very early stage. It is the writer's opinion that, if ammonia is used as the working fluid (and that is very much to be preferred) then the environmental impact assessment for ammonia effects would be shown as entirely reasonable and acceptable.
In summary, the environmental impact of an OTEC plant appears to be not only superior to that of most other energy systems, but also to be acceptable on present estimates. As noted above, time is available to check on these statements for specific sites, and this should be done.
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 (50MW up)¡H If not, what are the possible good designs¡H For these designs, can you suggest who has the best technology and/or experience to do the design and/or fabrication¡H You are absolutely welcome to provide us any organization and/or private sector for our reference.
Except platform and cold water pipe, is there still any technologically uncertain or unavailable components, for instance, the heat exchanger, pumping system, or the power transmitting system.
Comments and Suggestions:
The writer has firm views on preferred items and these have not significantly changed since 19841 (note:References not otherwise available e.g. 1,3 and possibly 10 can be made available to the IOA office, for the purpose of this study, if required.)
Regarding the questions posed, in summary:
the best platform is a spar with demountable power pods, which is particularly appropriate for the demonstration plant where a "spare" power pod can be provided for development work, and to provide full contract power capability if one of the operational pods develops a fault.
the best cold water pipe (which will require development work) is a segmented composite pipe, incorporating a technique to replace damaged pipe sections without having to demount the complete pipe. (This latter point appears not to be possible in the concept put forward in the MOPR).
For the platform construction, any contractor who has manufactured offshore oil and gas platforms of the floating variety will be capable of undertaking the work, and should be considered. Such contractors are well versed in entering into joint ventures with the host country which requires a facility. The writer would particularly name Brown & Root, UK Division, who deal with the Asia-Pacific zone; specific names can be provided if desired.
For the CWP, substantial development work is still required. The key sub-contractor will be a composite materials fabricator, probably working already in a number of other industrial sectors. Such an organization would then work with a pipe lining contractor, and here Netherlands or Norwegian operators may be the best option. A new possibility which may now be worthy of consideration is the flexible pipeline firm Coflexip Stena, but the problem which would remain in that case is the replacement of damaged parts.
The CWP is the crucial element on which more work has to be done for a commercial OTEC plant to operate successfully. Its stability/location is likely to be associated with the mooring system. Other components which will benefit from further development include;
heat exchangers: their cost and size has decreased considerably in the last decade. The size reduction is particularly important as it has considerable Knock-on effects for the size (and therefore cost and mooring requirements) for the whole OTEC plant. It is the writer's view that plant-fin HEX are preferable to shell-and-tube HEX as quoted in MOPR.
moorings, and power take-off. These two features are inter related. Further development of (probably) Kevlar mooring lines is required and also development of the power cable, the latter supported via a stand-off buoy1. The CWP is likely to be designed integrally with the mooring system1.
Notwithstanding the list of items given above for further development, it is stressed that a very large part of the total floating OTEC plant consists of an assembly of well proven items.
6. What is the comparison between land-based and offshore floating OTEC¡H
Comments and Suggestions:
A thorough evaluation was carried out by the writer1, as a result of which the closed-cycle floating variant was shown to have a clear advantage. Since the date of that study, the additional applications for an OTEC plant-the DOWA dimension-have become more important, but the floating variant remains the preferred option.
Significant factors include:
|the CWP is shorter (with fewer Hydrodynamic lossed, does not have to cross the surf/intertidal zone, and is not subject to seabed currents). The cold water entry is also in the centre of the resource, as opposed to having only a 180¢X access-with the additional possibility of ingress of seabed materials. However, the CWP of a floating plant also has to be stabilized.|
demands on land space are much reduced.
the plant can be relocated fairly readily to take advantage of medium to long-term changes in the position of the cold water resource; we do not yet have enough detailed long-term information on the stability of that resource i.e. to what extent could it vary with ocean currents (for example, is there an "el nino" type variation).
Whilst these are major plus points for a floating plant, the following potential advantage of a land-based plant must be recognised:
electrical transmission costs will be lower.
use of the cold, deep pathogen-free water for other purposes (see for example Reference 1 Figure 25).
Overall, a floating plant has advantage, particularly at this early stage of OTEC development. Much relevant expertise can be transferred from floating offshore oil and gas equipment. The final bullet point above is the only substantial reason for considering land-based plants. It is a significant factor, and therefore a significant secondary effort should be devoted to development of a land-based option. Note, though, that it should be a secondary effort.
7. What is your overall impression on MPOP and MOPR ¡H Do you think it is possible that either MPOP or MOPR can be promoted as an internationally co-operated project, instead of just a project promoted by the Taiwan government¡H and why¡H What will be the best strategy that Taiwan government must consider in order to enhance the achievement of the MPOP or MOPR? Can you also recommend the possible organizations that we should get in touch with¡H
Comments and Suggestions:
MPOP recommends a land-based plant. MOPR a floating plant. As noted in Section 6, the MOPR recommendations should be Priority 1, with the land-based option as Priority 2.
These priorities reflect both the status of OTEC development and the likely markets10. Also, the fact that a CWP for a floating variant has fewer developmental problems than that for a land-based plant.
A further caveat on MOPR is that (see also Section 2) the goal of a 100MW plant as the first demonstrator is not realistic in the view of the writer. A 10MW demonstrator with (say) 5MW power pods is much more realistically achievable. Morever, the incorporation of such an additional step will certainly not delay the timescale given in MOPR for the 100MW unit. It could even shorten it, since confidence levels of funding organizations will be greater a.) because of the lower capital cost of the 10MW plant and b.) the lower risk by the time the 100MW plant is commenced i.e. the 10MW variant will by then be proven technology. Reference to such a possible shortening of timescale is made on page 67 of the MPOP report-in a somewhat similar context, but not an identical one.
Certainly, MOPR could be promoted as an international co-operative project. The disadvantage to Taiwan is a sharing of the cost. The disadvantage to Taiwan is a sharing of the intellectual property and, therefore, the loss of significant and substantial export opportunities. Taiwan must decide which it prefers. Other proposal for international co-operation have been made4. The growing environmental concerns make the development of benign energy systems more likely. The fact that such a large porportion of OTEC market opportunities are the Asia-Pacific region suggests that any co-operation should be focussed with that in mind, but it should be noted that could still include the European Union under its Lome programmes.
However, this writer's view is that-if he were a member of the Taiwan government-he would be seeking to maximise the medium to long term benefit for Taiwan in relatively high technology, high added-value, activity, which is a characteristic of most maritime systems including OTEC. Therefore the funding system should allow most of the intellectual property to reside the remain with Taiwan. An optimum funding scenario would therefore seem to be Taiwan government funding, plus Asian Development Bank finance (rather than finance from the World Bank or other international funding organizations). The ADB is therefore the key recommended organization with which to explore funding opportunities.