feasibility study otec piants - j-stage

The Japan Society of Naval Architects and Ocean Engineers

NII-Electronic Library Service

The JapanSociety ofNaval Architects and Ocean Engineers

(,vlZnt g l# s n tszzinthtaftg4Nenft }a ts v ) -(

"za) 121

Feasibility Study of OTEC PIants in Indonesia

by Donny ACHIRUDDIN', Member Kimio SAITO', Member GErard Claude NIHOUS'

Summary

The present study identifies Ocean Thermal Energy Conversion (OTEC> as an important

power resource for Indonesia. OTEC is a renewable, environmentally friendly, technology

which produces electricity from the temperature difference found between the surface and

deep layers of most tropical oceans. It also offers great opportunities and challenges for

ocean engineers and naval architects. Although capital-intensive floating OTEC plants are

not likely to play a role in the near future, environmental pressures and changing socio-

economic conditions could change this situation in a matter of decades. Before a penetrationof the main Indonesian electricity market becomes possible, it is essential for this technology

to rnature from its present experimental status. The completion of power plants of a iewmegawatts will be required. A strategy is proposed te identify niche markets in Indonesia,such as small remote island communities or new touristic resorts, where these necessary but

costly developmental OTEC systems could be cost-effective.

LIntroduction

Energy is one of the most needed resources in the World today, and without exception for Indonesia, In

Java-Bali, for example, which represents the largest inter-connected electrical grid in the country, peak loacl

capacity is forecast to increase from 7,910.6 MW in 1994 to 14,697.7 MW in 1999, and reach 28,959 MW in 2009

[1]. Even though Indonesia is a major exporter of fossil fuels and also has achieved significant progress in

expanding its domestic electrical grid in recent years, much remains to be done, since currently, about two

thirds of the population have no electriclty. One of the stated goals ef the current governmental strategy, in

order to develop the energy sector, it to use more renewable options, such as biomass, solar energy,

geothermal energy, wind power, and rnicro-hydro puwer. At present, the contribution of renewable alterna-

tives to Indonesian electricity needs is very small, at about O.1%, and further development is hampered by

institutional, financial and operational obstacles[2]. Noticeably absent from the Iist of potential renewable

resources under current consideration are ocean-based technologies. It is believed that this situatien does not

stem from a Iack of corresponding resources, as is discussed below, but rather from a widespread reluctance

to tackle additional engineering ancl investment difficulties associated with large projects at-sea.

Since IndQnesia is a vast archipelago country, ocean energy technologies should play an important role in

the future, although they currently seem to have fallen into relative oblivion because of specific challenges

in their implementatiun, One such technology is Ocean Thermal Energy Conversion (OTEC). As its name

suggests, OTEC aims at converting thermal energy into' electricity by using the temperature difference

between warm water at the ocean's surface and cold water. This concept is viable for seawater temperature

differences exceeding 20eC, since the conversion efficiency would be practically too low otherwise. OTEC

' Graduate Schoolfor International Development and Coorperation (IDEC), Hiroshima University

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The JapanSociety ofNavalArchitects and Ocean Engineers

122 va ss isth as kkW ag 94e

may be unique in the spectrum of possible renewable resources inasmuch as it offers the potential of baseload

(nearly continuous) electricity generation: in other words, there is no obvious reason why OTEC plants

should not have a very high Capacity Factor {COF), of the order of 80 to 9e%.

2. 0TEC Potential in Indonesia

The tropical oceans, approximately defined by latitudes less than 20 degrees, may be thought of as

enormous passive solar collectors, and the amount of available OTEC energy has often been evaluated on the

basis of how much solar radiation is absorbed by the upper layer of the oceans[3]. This method is flawed

in many respects : for example, a strictly renewable OTEC resource should be limited by the supply of deep

cold seawater from the pelar regions[4] ; it also leads to extraordinarily optimistic (large) numbers, with

convertible energy ln one 1-clegree-by-1-degree rnesh element of a latitude-Iongitude grid amounting to the

electricity production of a large developed country (say 5 quads, or 5XIOiikWh, per year). More sober

estimates are typically three orders magnitude smaller, but still represent a potential resource globally

comparable to the World]s current electricity output.

The eastern boundaries of the two majer oceans, i. e. the western ceasts of the Americas and of Africa, are

afiected by strong cold surface currents penetrating deeply into the 20-degree･latitude band. On the other

hand, the prevailing patterns of northeasterly (southeasterly) Trade Winds in the northern (southern) tropical

areas, are known to build up a "lens"

of exceptionally warm surface seawater in the tropical western Pacific,

a situation occasionally interrupted during El Nifio events.

The above arguments make it clear that Indonesia, a country of 1.9 million km2 stretching from latitudes

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35



The JapanSociety of Naval Architects and Ocean Engineers

Feasibility Study of OTEC PIants in Inclonesia ]23

6'08'N to 11'15'S and longitudes 94045'E to 141'e5'E, globally has excellent and potentially significant OTEC

resources. Moreover, the great number of islands included in the Indonesian archipelago define a sea area

about four times larger than the country itself, on the basis of a 200-nautical-mile Exclusive Economic Zone

{EEZ). The seawater temperature profiles for three specific sites are shown in Fig. 1. A dry season occurs

from June to September in western Indonesia, whereas rnuch rain falls from Decernber to March ; the climate

is somewhat `reversed'

in eastern Indonesia. Therefore, the selected profile temperatures, taken in January

and July, are representative ef the whole year since they cerrespond to the two different seasens ef the

Indonesian climate[5] [6].

The development of OTEC resources is also critically dependent upon the accessibil{ty of the deep cold

seawater heat sink, i, e. on the steepness of the coastal seafloor. Coincidentally, a rapidly dropping seafloor

often corresponds to excellent wave power resources as well. Sea depths around southern Sumatra, Java and

estern Indonesia quickly exceed 1,OOO m as one moves away from shore. In some areas, a depth of 500m is

reached within only 2 km from the coast. Global Indonesian bathymetric features are shown in Fig. 2, and twe

particular sites are shown as typical examples in Fig. 3[7].

The absence of typhoons in Indonesia is a very positive point, since the OTEC resource often lies in regions

of active tropical storms. In other countries, such as the Philippines, the frequent occurrence of violent

typhoons represents a major hurdle to the deployment of OTEC plants, whether on platforms (with delicate

Fig. 2 The Indonesian bathymetric features (--- : 1,OOOm depth contour)

Fig. 3 Two sites (near Aceh and Tirnor) where a sea depth of more than 500m is found near the

coast.




124 ut zz inth re ft i? IR ng94g

connections between platform and cold water pipe, or between platform and power cable) or on land, in the

path of storm surges.

Indonesia is a eountry of active volcanism, hewever : earthquakes and tsunamis consequently rnay happen.

Such events are very rare, though they are potentially violent, as historical records show, OTEC prants

deployed on floating platforms would definitely be spared from earthquakes or tsunamis. Land-based plants

can be designed with state-of-the-art guidelines, and should enly suffer major damage during the most

catastrophic events, i,e. when it could be arguecl that virtually no structure on land or near the shoreline

would be safe from destruction : thus, it may be unreasonab]e to rule out OTEC plants in those areas without

ruling out any inclustrial infrastructure at all.

3. State-of-the-art Designs of OTEC PIants

i`Standard"

designs of OTEC systems are proposed below, for different power outputs and market needs.

Even though only one experimental OTEC plant is operated today[8], OTEC electricity generation rests upon

a firmly grounded theoretical framework, since OTEC exhibits many thermodynamic features of such

established technologies as refrigeration, Specific optimizing algorithms tu refine a given design are

available[9]. Several studies also have been published on the issue of the off-design performance of existing

plants, when available seawater temperatures vary[10], [11]. Typically, net OTEC power output increases

by about 15% pereC increase in seawater temperature difference.

The first type of "standard"

designs cerrespends ta net power outputs of about lMW, and is based on

Open-Cycle (OC) OTEC. OC-OTEC consists in bringing surface seawater in a chamber at a pressure below

the saturation value. A$ a re$urt, about O.5% of the warm seawater flashes into steam, which then drives a

turbine for the production of electricity. After incurring a pressure drop across the turbine, the steam is

condensed in a surface condenser fed by deep cold seawater, and effectively provides a source of desalinated

water. Fig.4 represents a simplified schematic diagram of the OC･OTEC concept. There is a residual

temperature difference between the warrn and cold seawater effluents of an OTEC plant, which can be shown

to amount to about one half of the original OTEC resource.

While this value, of the order of 10"C, is too small for

additional electricity generation, it is sufficient to drive a

desalination system consisting of a flash evaporater con-

nected directly to a surface condenser (in other words,

another OC･OTEC type system without turbo-generator), If

this idea is used with an OC-OTEC power plant, the fresh

water output doubles and one has a so-called two-stage

design. If instead, the idea is applied to a Closed-Cycle (CC)

OTEC power plants, described further, some desalination

becomes pe$sible and one has a so-called serial hybrid

design.

Details of a representative example of the 1 MW class can

be found in[12], for a Hawaiian site with very steep subma-

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4 SimplifiedOC-OTEC




Feasibility Study of OTEC PIants in Indonesia 125

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rine slopes, Keahole Point. The complete heat-and-mass balance diagram of this land-based two-stage

OC-OTEC configuration is shown in Fig. 5. Rather than setting a specific power output target, this design is

based on the use of the largest commercially available High Density Polyethylene {HDPE) Cold Water Pipe

<CWP), with a 1.6 m outside diameter, since IIDPE allows a rapicl and effective CWP deptoyment in deep

waters[13]. To adapt this plant design to other locations, a Iengthening of the CWP is likely. It is estimated

that for each additional kilometer in CWP length, a power penalty of 75 kW and an incremental cost ef about

$2,OOe,OOO (7% of the estimated overall project cost) rnust be incurred. These numbers clearly show that the

viability of land-based OTEC plants is extremely dependent upon the existence of favorable sites.

A second type of "standard"

designs approx{mately corresponds to net power outputs of 5 MW. In spite

of the environmental attractiveness and conceptual elegance of OC-OTEC, where the working fluid is

low-pressure steam generated from the surface seawater itself, the very low pressures necessary in an OC-

OTEC plant result in very severe hardware constraints : in particular, the size of the low-pressure turbine

rapidly reaches current technological limits, defined in the lew-pressure stages of large nuclear plants. Using

the largest low-pressure steam turbines available in Japan or in France, a 5MW OC-OTEC plant would

necessitate two double-flow machines ; while this is not necessarily to be ruled out, the idea that the 5 MW

design class should help in scaling up OTEC technelogy toward the higest practical power outputs lead$ us

to select CC-OTEC instead. With CC-OTEC, the fluid producing power across the turbine is chosen tu operate



The JapanSociety ofNavalArchitectsand Ocean Engineers

126 di zz inth nd"rtl va ag94g

at high pressures, of the order of a few atmospheres, and is isorated from the seawater. Thus, no desalination

occurs and a small pump must bring the condensed liquid back to the evaporator. With high process

pressures, ex.isting turbines are available even at large power outputs, Fig. 6 represents a simplified schematic

diagram of the CC-OTEC concept. Ammonia is often selected as a CC-OTEC working fluid, but in principle,

most authorized substances popular with the refrigeration industry would work quite well. Using the same

argument of scalability as above, when CC-OTEC was

selected, a case can be made for floating 5 MW plants instead ,..>-tt,

Turbine

of land-based configurations: the 2,s to 3m diameter cwp is l uaGenerator I L-....-t--7

avery stiff conduit and its deployment on or above several I i

kilometers of seafloor is not deemed practical. on the other EVa

hand, vertical CWPs hanging from floating structures have

]

Pump 4''''"'p

been successfully rnodelled and partially tested at-sea[14].

Since submarine power cable technology is available, a consid. W

erable advantage of floating OTEC plants, aside from their =- -

more promising technical feasibility, is a relative deCOUPIing wann sea.ater Cold Seawater

from bathymetric features:the OTEC site need net be :.::.-- :e(,rPkiCB"FWt".t,edlLv'",ep,,L,.,extremely favorable in terms of deep water accessibility, and --.... (CwOi.d,ii:."gWF"i:I･d)LiquidLine

large offshore OTEC resources could thus be tapped. Addi- Fig. 6 Simplified CC-OTEC

MtstHlmirvator

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Feasibility Study of OTEC PIants in Indonesia IZ7

tionalry, aesthetic concerns could be addresged in very touristic regions by simply locating the plant beyoncl

the coastal line of sight.

Details of a representative example of the 5 MW class can be found in[15]. The corresponding heat-and-

rnass balance diagram is shown in Fig. 7. The CWP is made of Fiberglass Reinforced Plastic (FRP), a strong

sandwich structure which was successfully developed for OTEC applicatiens[14]. The most noteworthy

positive characteristics of FRP are buoyancy control and no corrosion.

Finally, CC-OTEC p!ants housed on platforms and capable of producing 100 MW should be envisioned as

a feasible cemmercial goal[16], This coulcl represent a practical limit for OTEC since CWPs as large as 10

ni in diameter would be needed. One must stress the importance of environmental pressure as a future

potential incentive in developing large-scale OTEC systems. The only obvious envirenmental concerns about

OTEC are the avoidance of working fluid leakage (for CC-OTEC systems), and the possible thermal shock

incurred by species exposed to the seawater effluents. Very large OTEC se'awater flow rates actually would

minimize the impact of even moderate working fluid leakage, while exacerbating the question of effluent

discharge. A discharge depth of 60 m has been deemed environmentally acceptable[17] : the discharge plume

would stabilize in a neutral buoyant state below the photic layer, i. e. where biological activity is sharply

reduced, and weuld undergo significant dilution by ambient seawater.

4. Matching OTEC with Indonesia's Needs

Different scenarios corresponding to various levels of the cost effectiveness of OTEC have previously been

identified[18]. Due to significant expected economies ef scale, the cost effectiveness of projected OTEC

systerns sharply improves as net power output increases : doubling the diameter of the CWP, for example,

al]ows approximately a quadrupling of the power output ; other critical components, the cost of which does

not increase linearly with power output, are the power cable and mooring system. Unfortunately, smalTer, less

cost-effective plants are necessary as experirnental stepping stones, although their financing would be

problematic. This situation can be ca]led the "OTEC

Paradox", iTlustrated in Fig. 8 i in order to safely deploy

large OTEC plants, with the promise of cost-effectiveness, smarler capital-intensive units must first be built

with little hope of competing in the current energy market.

These difficulties have led to an investigation of so-called

niche markets, that is small isolated electricity markets where

an otherwise uncompetitive system, by mainstream standards,

could appear economically attractive : this approach could be

compared to the search for an easier climbing route up an

otherwise too steep mountain. The notion of niche markets

implicitely underly the positive conclusiens of Uehara et aL, in

their a$sessment of the feasibility of OTEC in the Philippines

[19]. With these preliminary remarks, the potential role of

OTEC in Indonesia can now be briefly discussed.

From past trends, electricity consumption in Indonesia as a

whole will grow at a swift pace in the next 15 to 20 years.

MAIN MARKET

Possib]yCornpetitive

A : : ,

-Cos- Nec

NICHE MARKETS

Competitive

VerySmall,Experimental

(<250kW)

Fig. 8 OTEC Paradox.

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128 th zz isth wa ft tt rv ag 94 e

'Forecasts are based on the estimation of several pararneters, such as GDP growth, population growth,

electrificatjon ratio and share in industry,

Mkein Gn'd : The Java-Bali system is considered to represent the main grid, as demand outside is far lower.

The Java-Bali peak load capacity is forecast to rapidly increase frem 7,910.6 MW (1994) to 28,959 MW in 2009

[1]. Since the population and industry growth rates should then slow down, the percentage growth of

electricity demand also should decrease. Under the assumption that the percentage growth of electricity

demand will stabi]ize at 20% for each five-year period, starting in 2009, the peak load capacity in Java-Bali

would reach about 125,OOO MW in 2050. By that time, the development of conventional power plants in

Java-Bali may beconie difficult for a number of reasons which may not easily be predicted today: land

availability and environmental pressures are likely to play a role in this extremely densely populated region.

On a more global scale, the crucial economic parameter is the price of hydrocarbons, which should increase

oyer such a long period of time, whether in a gradual inflation-like fashion, or in more chaotic steps

reminiscent of the past "oil

shocks". Even though Indonesia has vast hydrocarbon resources, much higher

market prices should induce the country to strengthen its cash reserves through exports, or to preserve a

significant amount of these rnineral resources for strategic purposes. Whatever scenario will unfold in this

leng-term perspective, the OTEC technoiogy should be developed to a mature level over the next half century

as a matter of strategic planning.

IViche Markets : In this sectien, net rated OTEC power outputs of 1 to 10MW are enyisioned, and the

technology required for the implementation of these designs is available in the near term. Outside of the main

islands (Sumatra, Java, Bali, Sulawesi and Kalimantan), many small islands are inhabited by only 1,OOO to

5,OOO peopre, a figure appropriately cempatible with electricity need$ of the order of a few megawatts. Most

of these islands have no (or limited) access to electricity, OTEC systems could help such island communities

in reducing their dependence on fossil fuels, while also producing fresh water if necessary. Moreever,

Indonesia's government has been planning to improve the infrastructure of Lornbok island and Nusa

Tenggara archipelago to promote these locations as major resort destinations after Bali. The bathymetry

along the southern coasts of these islands is favorable for OTEC[2].

In addition to the possibility of OTEC electricity generation, deep cold seawater also can be used to supply

the cooling fluid for air conditioning AfC in hotels, cottages and other buildings in resorts, since one major

source of electricity consumptien in tropical resorts is cemfort ceeling : typically, 800 kW could be saved for

every 1,OOO air-conditioned hotel rooms[20]. If one defines efficiency in using cold seawater by the ratio of

net OTEC power or net (AfC) electricity savings, respectively, over deep seawater flow rate, the result is one

order of magnitude better for A!C than fer OTEC. In other words, it would be very unwise to generate OTEC

electricity in order to supply a local A!C load. This point has even led to the formulation of a phased

financing scheme for small land-based OTEC plants, which would spread the cost and risk of the OTEC

sy$tem by first implementing a deep-seawater AfC system equipped with the <oversized} OTEC CWP[21], In

the case of larger OTEC systems housed on floating platform$, the idea of using other Deep Ocean Water

Applications <DOWAs), such as deep-seawater AfC, to boost OTEC cost-effectiveness while sharing the same

CWP may not be feasible. A smaller separate CWP deployed on the seafloor may be required for the

non-OTEC, more cost-effective DOWAs, and a case could be made to consider the energy budget of the resort



The JapanSociety ofNavalArchitects andOceanEngineers

Feasibility Studyof OTECPIants inIndonesia 129

No MatehingNo Costeffective

?

No Matehng

No Costeffective

?

Yes

Matching

Yes

Matching

No Matehing

No Mateliing

Estlinate indonesia's Long-term

Energy Sii

No Costeffective

?Yes

Matclimg

Fig. 9o'rECPotential inIndonesia :a possible implementation scenario.

from an integral viewpoint in an effort to promote the OTEC technelogy preper.

All points presented so far, in an attempt to match OTEC with Indonesia's electricity future needs. have led

to a conceptual strategy illustrated in Fig. 9. Central to this strategy is the understanding of the "OTEC

Paradex", whereby using OTEC to supply significant power to the main grid of a large country like Indonesia

is not possible in the near-term. Instead, the strategy focuses on the identification of niche markets, which




13e di zz inth th ft R W ag 94e

are supposed to exist either as sma!1 remote communities or as new touristic resorts : this assumption is

compatible with the geographic reality of Indonesia, a vast archipelage, and with its claim to grow "beyond

Bali" as a major touristic destination. The flow chart then proceeds in a step-wise, logical fashion in

tentatively deploying small OTEC systems adapted to the niche markets. If this first developrnental phase

succeeds, and pending favorable long-term socio-ecenomic conditions, the OTEC technology would then be

mature to penetrate the rnain Indonesian electricity market in Java-Bali.

5. Conclusions

Indonesia has excellent ocean thermal energy conversion technology resources, especially along southern

Sumatra, Java, Bali, Nusa Tenggara archipelago and in eastern Indonesia.

The OTEC technology, however, is capital intensive and lacks a credible operational record for large power

systems. Since OTEC appears to be potentially cest-effective at-large for power outputs of 50 to 100 MW, the

financing of smaller quasi-experimental plants is an extremely difficult hurdle. Only the identification of

niche markets for smaller OTEC plants could break this developmental paradox.

Among promising niche markets in Indonesia, two candidate groups have been discussecl. On one hand, two

thirds of Indonesfa's population have no electricity, and most people not yet supplied with power live in

remote valleys and small islands. OTEC systems can provide communities of a few thousand people, in small

islands, with electricity and fresh water. On the other hand, OTEC systems can supply electricity to resorts,

for example in Lembok and Nusa Tenggara, whereas using deep cold seawater as a coolant for air condition-

ing in hotel, cottages and other buildtngs could additionally result in drastic energy savings.

In the long term, perhaps by the middle of next century, the necessary slowdown in the present period of

rapid growth experienced in Java and Bali, combined with modest inflation, may allow the OTEC technology

to play a significant role in supplying renewable, environmentally-safe, and indigenous power to the main

Indonesian electricity grid. In order to make such a goal possible, it would have been necessary to acquire

as much operational and engineering knewledge as possible through the development and operation of the

smaller OTEC plants (pilots) clepioyed in the near-terrn fer the niche markets.

References

[1] Mitra Technology Indonesia Foundation, Electnjication & Renewable Ene2gy Development Plan in 2nd

Long-71e?7n Development, Jakarta, 1994.

[2] Endro Utomo Notodisuryo, "Experiences and Thoughts Regarding the Current and Potential Role of

Renewable Energy in Asian Economic Development (Indonesian Case)", Technical 651, APEC Renewa-

ble Energy for Sustainable Development Workshop, Hawaii, 25'27 September 1995.

[3] Kamogawa, H., "OTEC

Research in Japan", Enei2gy, 5, pp. 481-492, 1980.

[4] Johnsoll, F. A., `LCIosed-Cycle Ocean Thermal Energy Conversion", Chapter 5 in Ocean Ene?gy Recove}y,

R, J. Seymour editor, ASCE publishers, pp. 70-108, 1992.

[5] Ocean Thermal Energy Conversion Association of Japan, "Other

Sites in Pacific Islands", Report dated

25th October, 1989.

[6] Hydrographic Department of Japan-Oceanographic Data Center, 1994.

[7] Jones, M.T., A.R,Tabor and P.Weatherall, "General Bathymetric Chart of the Oceans", British



The JapanSociety ofNaval Architects and Ocean Engineers

Feasibility Study of OTEC PIants in Indonesia 131

Oceanographic Data Center, 1994.

[8] Vega, L.A., and D. E. Evans, `COperation of a Small Open-Cycle OTEC Experimental Facility", Proc.

Oceanolc}g], international '94,

5, 1994,

[9] Uehara, H., T. Nakaoka and Y. Ikegami, "Optimization

of OTEC", Proc. Ist KSME -ISua T7zennal and

Flzaicls Engineen'ng Conjbrence. 1, pp, 1-4333 to 1-438, 1988.

[10] Masutani, S.M,, C,Nihous and M.A.Syed, [`A

Discussion of the Effects of Seawater Temperature

Variations on the Performance of an Open-Cycle Ocean Therrnal Energy Conversion System", Proc.

intemational Solar Ene7g]r Conj??rence, pp. 117-124, 1991.

[11] Ikegami, Y,, and H. Uehara, "Performance Analysis of OTEC PIants at Off-design Conditions : Ammo-

nia as Working Fluid", Solar Engineering 1, pp. 633 638, 1992.

[12] Nihous, G.C., M.A.Syed, and L.A.Vega, "Design

of a Small OTEC PIant for the Production of

Electricity and Fresh Water in a Pacific Island", Proc. international Conerence on Ocean Ene7{gy

Recove,),, pp. 207'216, 1989.

[13] Vuirlemot, F. L., J. C.Van Ryzin and A.M. Resnick, `'The

HOST-STF (OTEC) Project in Hawaii:

Planning, Design, Construction':, Proc. A4CON 88, OST5, Henolulu, 1988.

[141 Vega, L. A., and G. C. Nihous, "At-sea

Test of the Structural Response of a Large Diameter Pipe

Attached to a Surface Vessel", Proc. Qffshore Tlachnolagy Cova1itence, No.5798, pp.473-480 pp.25-29,

1991. pp. 25 -29,

1991., 1988.

[15] Vega, L,A., and G.C.Nihous, "Design

of a 5MW Pre-commercial OTEC PIant", Proc. Oceanolqg),

International '94,

5., 18 pp., 1994.

[16] Nihous, G. C., and L, A. Vega, "Design

of a lOO MW OTEC-Hydrogen Plantship", Mdrine StTuctura 6, pp.

207-221, 1993.

[17] Niheus, G. C., and L. A. Vega, "A

Review of Some Semi-empirical OTEC Effluent Discharge Models",

Proc. Oceans gl, 1, pp.25-29, 1991.

[18] Vega, L. A., "Economics ef Ocean Thermal Energy Conversion (OTEC)", Chapter 7 in Ocean Energ]y'

Recove,:y], R. J. Seymour editer, ASCE publishers, pp. 152L173, 1992.

L19] Uehara, H., C, O, Dilao, and T. Nakaoka, "Conceptual

Design of Ocean Thermal Energy Conversion

Power Plants in the Philippines", Solar Ene,g:y. 41, No. 5, pp. 431-441, 1988.

[20] Syed, M. A., G. C. Nihous and L. A. Vega, "Use of Cold Seawater for Air Conditioning", pp. 25-29, 1991,

pp.25-29, 1991., 1, pp. 60-64, 1991,

[21] Nihous, G. C., and M. A. Syed, "A

Financing Strategy for Small OTEC PIants", Ene,g], Conversion and

Mdenqgemen4 38, No. 3, pp. 201-211, 1997.

Discussion

Question (by Koji Otsuka, Osaka Prefecture University)

(1) In your paper, the OTEC by-products discussed are desalination and A!C. Cl"he cold seawater is also rich

in nutrients and has few pathogens, "rhich makes it attractive fer aquacu]ture. If you condider the benefits

of aquaculture, the total cost of your project could be reduced. What are your ideas on this issue?

(2) Do you have a plan to identifly a location with a favorable eeonomic environrnent ?

Answer

(1) No decision has yet been rnade about the possible Deep Ocean VLrater Applications (DOWAs) which could

help OTEC attract investors for smaller (but needed) plants in Indonesia. This decision depends on the site,

on the market-side needs (e. g. which aquaculture species could be profitable) and on the overall investment




132 pt at iath wa a R w eg g4g

capabilities. It is safe to say, however, that only deep-seawater AIC has a very strong payback potential

for smaller $ystems. AIso, the future of OTEC relies on the development of platform-based systerns, and

the compatibility of DOWAs with that objective should be kept in mind.

(2) The next step, as discussed in the paper, will be the tentative iclentification of niche rnarkets in Indonesia.

It is expected that resorts in islands like Lombok or Nusa Tenggara may provide the answer. We hope to

be able to perform a simple economic analysis, using, as much as possible, the same approach and

algorithms as the Indonesian power companies (utilities). Only then weuld the existence of niche markets

for OTEC in Indonesia be confirmed.

Question (by Hiroshi Watanabe, Ishikawajima Harima Heavy Industries, Kure)

What percentage of the electricity produced by the OTEC plants is consumed by the seawater pumps?

Answer

All design studies of "commercial"

OTEC systems show that about 60 to 70% of the electricity produced

at the OTEC turbo-generator terrninals Cgross power) is available fer export to the grid (net power). This is

why our standarcl designs are labeled according tQ their net power rating. Of the 3e to 40% consumed within

the plant, called parasitic losses, the lion's share belongs to the seawater pumps. For eur standard 1 MW (net)

design and a Hawaiian site, 577 kW are consumed by the two seawater pumps, which represents 32% of the

1,800 kW produced by the turbo-generater. In the case of our standard floating 5 MW {net) design, 2,470 kW

are required to power the seawater pumps, i. e. 34% of the 7,92e kW expected gross power.

feasibility study otec piants - j-stage

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