Chapter 2
Ocean Water and Its Wonderful Potential
Gold from Ocean Water!
In the First World War (1914-18), Germany was defeated. The country
was ruined, and on top of that, the victorious nations demanded huge
reparations. It was soon recognized that the only way out of this state of
poverty was recovery through technological progress. An Association was
founded to promote this.
The Association took the initiative in many fields of research, but
among one that attracted the nation was an oceanic survey. Its purpose was
to extract the gold dissolved in sea-water, and use it to settle Germany’s war
reparations. Using the warship Meteor, the project was to determine the
concentration of gold at various locations, and to study the structure and
mechanisms of the ocean.
The Meteor carried out its survey, mostly in the South Atlantic, between
March, 1925 and July, 1927 (Figure 4). The results showed that gold was
dissolved in a far lower concentration than had been expected: only 0.003
micrograms (0.0000003 grams) per liter of sea-water. Extracting enough to
make a gold coin would cost far more than the value of the coin. This project,
therefore, was not put into practice, but what is noteworthy about it is the
epoch-making idea of extracting a metal from sea-water, which no one had
thought of before.
What is more, the results were obtained with the latest instruments and
according to a meticulous plan, which made them extremely useful as data
for academic research. For example, the Meteor was the first to measure the
depth of the ocean with sonar waves, rather than the traditional method of a
weighted rope lowered to the sea bottom. The depth sounder measures water
depth by measuring the time taken for a sound it emits to echo back from the
bottom of the sea. With this new equipment, continuous depth measurement
became possible as the ship moved along, and the “terrain” of the sea bottom
could be studied in detail. Sounding techniques are now applied for a wide
variety of purposes, including for instance tracing shoals of fish.
The Meteor’s oceanographic expedition aroused people’s interest in
the ocean, in much the same way as interest was aroused in the Apollo
9
10
Chapter 2
Rio de Janeiro
Walvis Bay
Buenos Aires
Observing station
Current measurement
Figure 4. The Meteor made observations of water mass movement, water temperature, salinity
and plankton at 310 observing stations, as well as obtaining 14 bottom profiles and making a
number of balloon observations.
expeditions and the first man to step on to the moon.
One after another, resources on land are being overmined to the extent
that the minerals we need have become hard to obtain on land. Table 1 shows
the concentrations of a selection of metals in the oceans, and compares total
resources on land and in the sea. As you will see, the amounts of some
metallic minerals are actually greater in the oceans than on land: they include
nickel, zinc, gold and silver.
As more and more of the earth’s land resources are extracted, it goes
without saying that the supply is going to run out; the oceans will be the
Ocean Water and Its Wonderful Potential
11
Table 1. Concentrations of metals in sea-water, estimates of land reserves, and annual
production
Total amount
Concentration
Estimated land
reserves
Annual production
Iron
Aluminum
Nickel
Tin
Copper
Zinc
Lead
Gold
Silver
Mercury
All amounts in megatons; concentration in micrograms per liter
Earth’s greatest reservoir of metals. The German attempt to extract gold
from sea-water in the 1920s may have ended in failure, but we are now at a
stage where the whole world must reconsider the oceans as a storehouse not
only of gold, but of other minerals as well.
It is easy to pump up sea-water in coastal areas. In this sense, extracting
metals from sea-water might seem easier than mining deep down into the
earth for ores whose refining process involves extremely high temperatures
and large amounts of polluting waste. No such problems would arise in the
process of extracting metals from sea-water — as long as large quantities of
chemicals were not used. And so much sea-water is so easily available.
In that case, why not start right away? The problem is that we do not yet
have the technology to extract such low concentrations of metals efficiently.
Some chemists have claimed that, in their expert opinion, it would be
impossible, and have given up the attempt even before starting. But I can’t
help feeling that there must be a method that has not yet been discovered. For
example, there are marine creatures that do effectively concentrate out
metals such as mercury, lead or vanadium (Figure 5). But this process is still
only vaguely known, and has yet to be explained.
To solve this problem, an entire set of new principles, and the epochmaking technology to put them into practice, are required. Mankind has
never tired in the search for new horizons, and surely one great dream for the
future must be how to extract metals from the world’s oceans.
Unveiled Energy in the Ocean
The ocean is a reservoir not only of metals but also of energy. Dr. J. A.
12
Chapter 2
Tunicates
Metal Refinery
Figure 5. Some marine organisms accumulate metals: tunicates concentrate out vanadium.
d’Arsonval, a French physicist, was the first person to think of exploiting the
ocean’s energy.
It is well known that the waters in deep seas and lakes are warmed up
only near the surface in summer, while their deeper parts remain cool.
Unfortunate accidents sometimes happen when someone dives into a lake in
the mountains: deceived by the temperature at the surface into believing the
water is warm, they are shocked by the cold deeper down, and die of a heart
attack. Generally sea-waters in tropical zones also have a significant
temperature difference between their surface and their depths; there, it is
constant throughout the year because of the high atmospheric temperature all
year round.
In 1881, Dr. d’Arsonval proposed generating electricity using the
temperature difference between the sea surface and its lower depths which,
in tropical zones, is about 30 degrees Celsius. This was a unique idea, and
at first it drew some public attention; but 1881 happened to be the year the
first thermal power plant started operation in the United States. No one
believed that a temperature difference of only thirty degrees could generate
electricity like the high temperatures that were used, by burning coal, to
produce the steam to drive the turbines in a power station. No one even
attempted to experiment with this idea.
It would probably be best to explain here how electricity can be
generated by exploiting the ocean’s temperature difference. It is actually
quite a simple principle.
Ocean Water and Its Wonderful Potential
13
Figure 6. Dr. J.A. d’Arsonval
Generally water boils at 100 degrees Celsius, but this happens only
when the atmospheric pressure is exactly 1, on land near sea level. At the
summit of a high mountain like Mt. Fuji (3,776m), the rarity of the atmosphere
means that the atmospheric pressure is only 0.62, and water boils at only 86
degrees. Therefore, because the water temperature does not go high enough,
rice cannot be cooked well at the top of Mt. Fuji.
This means that water could boil and turn to steam at, say, 30 degrees
Celsius if atmospheric pressure was sufficiently low. Electricity would be
generated if that steam was sent to a turbine to turn a generator. On land near
sea level, the air in a chamber could be reduced to create low pressure, and
then water in the chamber would boil. But the steam made in this way would
turn the turbine only once. The turbine would turn continuously only if such
a condition could be repeatedly produced.
For this purpose, the steam must be turned into water again after turning
the turbine, so that it can be boiled over again. It is easy turning steam into
water. In winter, the water vapor in a warm room is condensed by contact
with the cold glass of a window, and water drops drip down the window.
This is the same principle: air containing water vapor should be cooled
down.
Dr. d’Arsonval thought that generation of electricity would be possible
by utilizing warm sea-water for boiling water, and cool deep ocean water
(DOW) for cooling it down. In other words, the solar energy stored up in seawater could be exploited in the form of electricity.
It is a common misconception that water boils at 100 degrees Celsius
everywhere, since we live normally under conditions of one atmospheric
pressure. The idea of generating electricity by temperature difference seems
strange, because we often do not consider the effects of pressure differences.
It is another misconception that every liquid boils at 100 degrees Celsius. At
one atmospheric pressure, ethyl-alcohol, for example, boils at 78 degrees
14
Chapter 2
Celsius, ammonia at 33.5 degrees Celsius below zero, and propane at 42.1
degrees Celsius below zero.
Dr. d’Arsonval’s idea received attention again in the twentieth century.
In one Italian journal a scientific paper entitled “Utilization of Solar Heat”
appeared: it discussed the utilization of the temperature difference in lake
water. In a deep lake in northern Italy, there is a 16-degree temperature
difference in summer, since its surface temperature rises to 24 degrees
Celsius, while the temperature at the bottom remains at 8 degrees Celsius. A
cost estimation was made for operating an electric generator of 14,000
kilowatts, utilizing such a temperature difference. This would be the first
attempt to estimate the cost of thermal difference generation.
Another paper was published by an American engineer in the journal
Engineering News. In this paper, he discussed the problem of the insufficient
density of the steam produced by sea-water in order to turn a generator. It
is certainly true that steam produced under low pressure is poor, just like air
at high altitudes. Thus, compared with steam produced at a pressure of one
atmosphere, such steam would require an enormous turbine for generating
the same amount of power.
Therefore, in this paper he proposed using some other high vapor
density liquid rather than water in a low pressure chamber. Since high vapor
density liquid turns into a heavy gas, he proposed using propane or ammonia.
Water turns into only 0.337 grams of vapor when it boils at 32 degrees
Celsius under low pressure in a one-liter flask, while on the other hand, the
respective figures for methane, ammonia, propane, and fluorine (i.e.,
chlorofluorocarbon) are 0.64 grams, 0.69 grams, 1.81 grams, and 4.55 grams
under the same conditions. Even air turns into 1.16 grams.
In other words, such liquids are boiled with warm sea-water to produce
vapors heavier than steam, and once these vapors have done their job of
turning a turbine, they are condensed back into liquid form by cold seawater. This cycle of boiling, condensing and then boiling again uses seawater indirectly on some other substance. It is known as a “closed cycle”,
and has been successfully developed. A cycle that actually turns water into
steam is called an “open cycle”.
Professor Claude, the Pioneer and His Challenge
The proposals so far reviewed were no more than proposals, which were
not actually subjected to experiment at the time. It was two French professors:
G. Claude and P. Boucherat, President of the French Electric Society, who
first carried out experiments on electric power generation utilizing thermal
difference (Figure 7). Using the small apparatus shown in Figure 8, they
performed a public experiment at the French Academy of Sciences on
November 15, 1926. The experiment was reported in detail by a leading
Ocean Water and Its Wonderful Potential
15
Figure 7. Professor G. Claude, the pioneer
French newspaper: Paris Presse. With the press in other countries taking
up the story, the world’s attention was attracted.
The British journal The Engineer reported on November 20, 1926:
“The wheel of an ordinary Laval turbine, 15cm. diameter, was
mounted with its spindle vertical inside a glass flask and arranged
to drive a tiny dynamo. The bottom of the glass contained lumps
of ice, and air could be exhausted from it by a vacuum pump
connected to the upper portion. Another flask, containing 25 litres
of water at a temperature of 28 degree Celsius, was provided with
an outlet in the form of a pipe which entered the first flask and
terminated in a nozzle just above the blading of the turbine wheel.
When the system was exhausted of air the water in the second flask
boiled, its vapour passing away through the pipe and driving the
turbine wheel. After leaving the wheel the vapour was condensed
by the ice in the bottom of the flask. It is said that the turbine wheel
was driven by this means at a speed of 5000 revolutions per minute,
and enough power was obtained from the dynamo to light three
little electric lamps for eight to ten minutes, after which the water
had been cooled to 20 degree Celsius or so by its evaporation and
apparently refused to boil any longer.”
This was the first successful experiment to produce electricity from a
small thermal difference. Although it was really a primitive one, it aroused
public interest in thermal difference power generation, which came to be
called in English “Ocean Thermal Energy Conversion,” or OTEC. Generation
ceased soon after the experiment was stopped, but it could have continued if
16
Chapter 2
Vacuum pump
Generator Nozzle
Steam
Lamps
Turbine
20l warm water
(28˚C)
Ice
Figure 8. Generating electricity by temperature difference
the warm water had kept its temperature and cooling had been done
continuously with cold water. This is the principle of the open-cycle model:
supplying warm water continuously to produce steam (the vaporizer) and
cold water to condense the steam back to water (the condenser) (Figure 9).
At a press conference after his experiment, Professor Claude provided
the following figures: The surface temperature of tropical seas is generally
Water vapor
Evaporator
Mist of surface water
Warm surface water
Discharge
Figure 9. An open-cycle
Ocean Water and Its Wonderful Potential
17
between 26 and 30 degrees Celsius, varying within a range of 3 degrees
Celsius throughout the year. On the other hand, at a depth of 1,000 meters
it is 4 to 5 degrees Celsius all year round. If 1,000 tons each of surface seawater and DOW were used per second for OTEC, even using a steam turbine
of 75% efficiency (i.e. a turbine that converted 75% of the energy it
consumed into electricity), it would be possible to generate 100,000 kilowatts
of electricity. Moreover, the cost of construction would be lower than for
the most economically constructed hydropower generation plant.
The American and British press criticized him as too optimistic, but
Professor Claude was not discouraged by such criticisms and attempted with
his own assets a large-scale experiment to collect the necessary data for
putting his theory into practice. First, he experimented with a 60-kilowatt
turbine using warm waste water from a Belgian steel works and cold sea
surface water. Through this experiment, he was convinced that his figures
were right.
Then he proceeded to a real experiment using sea surface water and deep
water.
After a thorough search in his own yacht and amassing as many data as
possible, Professor Claude selected his first experimental site at Matanzas
Bay, Cuba (Figure 10). In 1929, he sank a 2-kilometer-long pipe 1.6 meters
Cold deep water
Turbogenerator
Condenser
Fresh water
Condenser
OTEC generating system
Discharge
18
Chapter 2
Havana
Matanzas Bay
Figure 10. Matanzas Bay is located about 23˚N.
in diameter in Matanzas Bay, intending to pump up sea-water from a depth
of 700 meters. But constant trouble with the pipe prevented water from
being raised. As such, his first experiment failed.
The following year he tried to construct a 1.75-kilometer-long pipe out
to sea from the land, but the pipe was washed away when a connection failed.
He finally succeeded in laying a pipe at his third attempt, but the pipe was
badly damaged in the process, and the water soon stopped flowing.
Nevertheless, Professor Claude did succeed in generating 22 kilowatts
for 10 days, utilizing an actual thermal difference of 14 degrees Celsius in
the sea-water. It was only a small amount of electricity, but it was enough
for an emotional Professor Claude to announce that human beings would
never again need to suffer from a shortage of energy.
Gambling on the Abidjan Project
Professor Claude became convinced through a series of experiments
that the design and maintenance of intake pipes were the key factor of OTEC.
He also found that cold deep water would get warmer than expected during
the pumping up process if the thermal insulation of the intake pipe was not
sufficient. Moreover, he discovered that dissolved gases such as carbon
dioxide (CO2 ) were separated out in the vaporizer and hindered the
maintenance of low pressure.
In order to solve the problems with the inlet pipe, Professor Claude
abandoned generation on land and changed to generation on the sea surface.
For this purpose, in 1933 he converted the 10,000-ton cargo ship Tunisie for
OTEC, and carried his experiment to Brazil. The ship was equipped with an
800-kilowatt turbine generator and had an inlet pipe 2.5 meters in diameter
and 650 meters long. He tried to pump up sea-water from a depth of 120
meters off the coast of Rio de Janeiro, but rough seas made the intake pipe
hard to control, and in the end the ship sank.
Professor Claude was so depressed by all this that for several years he
Ocean Water and Its Wonderful Potential
19
Ghana
Liberia
Côte d’Ivoire
Accra
Abidjan
Gulf of Guinea
To Abidjan
Warm water
lagoon
Warm water supply
channel
Bank
Bank
Warm water
Lagoon
return channel
OTEC power plant
Service zone
Cold water return
channel
Cold deep water intake pipe
Figure 11. Abidjan, the capital of the West African nation of Côte d’Ivoire, is located about
6˚N and 4˚W.
seems to have done nothing. However, he took up the challenge again in
1940 with what came to be known as the Abidjan Project. Abidjan is now
the capital city of the French West African nation of Côte d’Ivoire, which at
that time was a French colony (Figure 11). This is an area where forests have
been cleared for agriculture, and coffee and cocoa are grown. The coastline
drops away steeply into the sea — a favorable condition for pumping up
DOW. What is more, the sea is calm and its surface temperature is 30 degrees
Celsius. Abidjan seemed a most appropriate place for an experiment.
In the Abidjan Project, Professor Claude proposed at the beginning to
20
Chapter 2
Figure 12. Abidjan Project, intake pipe. For scale, see a person standing at bottom right.
pump up cold DOW through a tunnel, thereby avoiding the use of unstable
intake pipes. But he was obliged to abandon this idea, brilliant though it was,
for reasons of cost and the great risks involved in tunnel construction. He
also had to revise output from the originally planned 40,000 kilowatts to a
less ambitious 15,000.
Cold water would be pumped up from 430 meters deep; for this, a pipe
four kilometers (4,000 meters) long would be necessary (Figure 12). He
planned to connect sections of metal pipe with durable rubber joints, and
suspend his pipeline in the sea with special floats. Forty-two tons of 30degree Celsius surface water and 14 tons of 8-degree Celsius deep water
would have to be pumped up every second to achieve the target of 15,000
kilowatts. To meet this condition, it was estimated that 4,000 kilowatts
would be required for pumping up the water, and 1,000 kilowatts for
removing gases from the air and sea-water.
The generator turbine was to be 14.25 meters in diameter and to operate
at 332 revolutions per minute (Figure 13). Professor Claude also hoped to
condense 14,000 tons of water per day by cooling the steam that had turned
the turbine, and by preventing it from mixing with sea-water, produce the
added bonus of usable fresh water. He also thought of extracting salt,
magnesium and bromine from condensed warm water after evaporation, and
to use the remaining cold water for cooling. The pumping system for cold
water would take up 55% of the construction cost.
The French government was interested in Professor Claude’s project
and offered it joint support and promotion: in 1948 an organization named
“Energie des Mers” (Energy from the Seas) was set up. This organization
Ocean Water and Its Wonderful Potential
21
Generator
Turbine
Evaporator
Evaporator
Pump for cold
deep water
Flow of water
vapor
Warm
surface
water
Cold deep water
Condenser
Figure 13. Open-cycle OTEC system developed for the Abidjan Project
was to carry out research and development for implementation of the
Abidjan Project. Research and development covered various fields, such as
the evaporator, condenser, gas drainage, intake pipe, total design, etc.
Even so, construction of an OTEC plant was never completed. In the
1950s, large amounts of oil became cheaply available, and it was thought that
thermal difference electricity generation would cost much more than oilfired generation. There were domestic political problems in France, too, and
the Abidjan Project was abandoned in 1955. In this way, the development
of OTEC was completely halted. Professor Claude passed away in 1960 at
the age of 90 without seeing his 30 years of determined efforts reach fruition.
The name of Professor Claude will always be linked with ocean thermal
energy conversion. But he was a man of many other achievements. Born
in France in 1870, before he became interested in OTEC, he did much
important work on liquefaction of oxygen, air and nitrogen; production of
ammonia; industrial uses of gases such as argon, neon and helium; production
and storage of acetylene. He was the inventor of the neon lamp and had a
large income from the patents he held. But from the time he became
absorbed in OTEC in 1926 at the age of 56, he devoted all of his fortune to
it.
On 22 October 1930, Professor Claude received a commemorative
medal from the American Society of Mechanical Engineering for his research
on OTEC. At that time he said that when he started on his work he had not
known about the research previously done by others, including his own
respected professor d’Arsonval, the American engineer Campbell and the
22
Chapter 2
Figure 14. Dr. J.H. Anderson (second from right)
Italian engineers Dornig and Boggia. This ignorance, he claimed, had been
fortunate, for he might not have embarked on his attempts if he had known
someone else was already concerned. A well-trodden path, he said, is not
attractive to an inventor.
There is an important message here for all scientists.
The 1960s: Efforts at National Level
After the Abidjan Project was abandoned, no more attention was paid
to OTEC for several years. Then in the 1960s in the United States, Dr. J. H.
Anderson turned his attention to Professor Claude’s work, re-examined it
thoroughly and identified some of its problems (Figure 14). On 31 August
1964, Dr. Anderson applied to the US Patent Office for a patent on a “Seawater power plant”.
Dr. Anderson pointed out three problems in Professor Claude’s project:
First, it was too costly. The reason was the low-pressure vapor used to
turn the generator turbine. The gas used for jobs such as turning a turbine
can be called a working fluid. As has already been explained, if we use weak,
low-pressure vapor as a working fluid, large amounts will be needed to turn
the turbine blades. This requires a gigantic turbine with huge blades.
Second, warm sea-water raised at low pressure by Professor Claude’s
method releases the gases dissolved in it, and they are hard to eliminate.
Third, if a power plant is constructed on land as Professor Claude
originally planned, the long intake pipes lead to high construction costs and
other troubles.
Dr. Anderson worked out how to solve these problems:
The first problem would be solved by using high-density fluids which
boil easily under relatively low pressure. In other words, the system should
be changed from open cycle to closed cycle.
Ocean Water and Its Wonderful Potential
23
The second problem would be solved if both evaporator and condenser
were immersed in sea-water at the same pressure as the working fluid. Then,
the dissolved gases could not be released, since the pressure of the surrounding
sea-water and working fluid are the same.
The third problem would be solved to a great extent if the power plant
were located in the sea, near the coast.
Based on this plan, Dr. Anderson estimated the cost of OTEC and the
unit cost of electricity produced by that method. The figure was $166 per
kilowatt: for the first time, a clear idea of the cost had been gained. From
this point, more and more people began to show an interest in OTEC and to
do further research in it. Until then, Professor Claude had been alone, but a
number of scientists in different countries now started their own research and
development, with support from their own countries.
In Japan, OTEC was described in detail in the evening edition of the
Asahi Shinbun newspaper on July 3 1959. An article entitled “Generation
of Electricity from Limitless Sea Water” by Professor Tadayoshi Sasaki
introduced Professor Claude and the French project. Eleven years later, in
1970, Dr. Kenzo Takano pointed out six advantages of OTEC in his book The
Ocean and Energy: First, temperature difference is the most stable natural
energy source compared with solar or wind power. Second, ocean energy
does not pollute the atmosphere or produce radioactive waste. Third, since
it does not require the high temperatures of thermal power plants, it does not
need special materials for its facilities. Fourth, sea-water is a limitless
resource, so that there is no need to worry about supplies running out, or to
transport it over long distances. Fifth, fresh water can be obtained as a sideproduct, and also the salt and other minerals in sea-water can be extracted.
Sixth, pumped up water can be utilized for both cooling and warming.
Research and Development in Japan
A Committee for a Comprehensive Survey of New Electric Power
Generation was set up in Japan in 1970. The committee surveyed various
alternative types of electric generation to thermal power generation, and
OTEC was among them. The ideas of Professor Claude and Dr. Anderson
were examined in detail. At the same time the committee studied the seawater temperature surrounding Japan and considered possible materials for
the working fluid. After the disbanding of the committee, a planned Leisure
Center took over part of the project to utilize ocean thermal energy. The
Center examined a project to build an OTEC power plant on a South Pacific
island and develop a leisure land around it.
Universities and governmental research institutions also started basic
research on OTEC around 1972. Private companies showed great interest,
too. Among them Toden Sekkei (Tokyo Electric Power Services) in 1971
24
Chapter 2
Dr. T. Kajikawa
Prof. H. Uehara
Prof. T. Honma
Figure 15
set up a plan to build an OTEC plant in the Pacific island Republic of Nauru,
and in 1973 surveyed the geographical features of the planned site, sea
conditions and climate. The fact that the power generated was actually used
for normal purposes means that this was the world’s first practical OTEC
power plant. The story will be described later.
Japan was badly hit by the oil shock, or energy crisis, of 1973, in which
the price of oil soared after concerted action by the oil-exporting countries.
The following year the “Sunshine Project” was started up by the Industrial
Technology Agency of the Ministry of International Trade and Industry
(MITI) to develop new energy sources.
This project was initiated by the government to examine alternative
energy sources to fuel and atomic energy and to exploit any viable ones. A
Figure 16. #2 experimental closed-cycle OTEC generator at the Institute for Comprehensive
Electronic Technology
Ocean Water and Its Wonderful Potential
25
decision was made to utilize solar energy, geothermal energy, coal energy
and hydrogen energy, and to research and develop technology for exploiting
them.
Other potential energy sources remained as subjects for
“comprehensive study.” These were new energy sources whose immediate
practicality was not clear, but which appeared to have potential for the
future.
OTEC was classified for “comprehensive study” at this early stage of
the Sunshine Project since it was considered an unrealistic idea. However,
serious research was started because it was included in the project. Many
Imari #3, completed in 1985, currently Saga University’s main experimental generator
Imari #3 turbine, using ammonia as its working fluid. The generator is at back right.
Figure 17
26
Chapter 2
experts from governmental institutes, universities and industries participated
in the research group and examined in detail the possibilities of OTEC from
1974 till 1979. Their conclusion was that ocean thermal difference power
generation was relatively economical compared with other energy sources,
could generate large quantities of electricity, and would be an important
means of providing energy in the future.
When the Sunshine Project started, research on engineering systems for
OTEC was initiated at the same time. Dr. Takenobu Kajikawa from the
Industrial Science and Technology Agency’s Institute for Comprehensive
Electronic Technology, Professor Haruo Uehara from Saga University, and
Professor Takuya Honma from the University of Tsukuba carried out this
study (Figure 15).
The Institute for Comprehensive Electronic Technology completed its
first model system for a basic experiment in September 1975, and succeeded
in generating 100 watts of electricity. The system, built at the Institute, was
a closed cycle with 500 grams of fluorine (chlorofluorocarbon) as the
working fluid and circulated a maximum 50 tons of temperature-controlled
warm and cold water per hour. Although it generated only 50 watts of
electricity when the temperature difference was 19 degrees Celsius, this was
increased to 600 watts when the difference was raised to 27 degrees Celsius.
With this system, experiments were carried out for various conditions and
basic data were collected for designing the most efficient system. The
Institute for Comprehensive Electronic Technology completed its second
model system in 1977 for further advanced studies (Figure 16).
Saga University was busy, too, and built experimental facilities Nos. 1
to 5 on its campus. These models were called Shiranui, which is the Japanese
word for marine luminescence. Shiranui No. 1 was a small one made with
flasks, and generated one watt of electricity. It was open cycle, similar to
Professor Claude’s first experimental model. All later ones were closed
Keahole Pt
Island of Hawaii
Figure 18. Hawaii, the largest volcanic island of the Hawaiian Islands
Ocean Water and Its Wonderful Potential
Ammonia pool
Ammonia storage
tank
Condenser
27
Control operation room
Diesel generator
for starter
Cold water pump
Warm water pump
Turbine generator
Evaporator
Connection for water
discharge pipe
Figure 19. Mini-OTEC. The water intake pipe is located in the ship’s bottom, and cannot
be seen in this figure.
cycle, and Nos. 3 to 5 produced 1,000 to 1,200 watts. The university also
constructed experimental systems, Imari Nos. 1 and 2, on the coast in Imari
city. Imari No. 2, completed in 1980, is capable of generating 50 kilowatts
and as an actual operating OTEC system has been used for various
experiments. For Imari No. 3, see Figure 17.
American Attempts
While all previous experiments had been basic, elementary ones, the
experiment named “Mini-OTEC” carried out off Hawaii Island from August
to November 1979 aimed to produce surplus electric power beyond just what
was necessary to operate the pumps and other components of the system
itself (Figure 18). This experiment was implemented by the State Government
of Hawaii in cooperation with enterprises including Lockheed and the
Dillingham Corporation. After preparations lasting 13 months and
expenditure of $3 million, a 268-ton raft 37 meters long and 10 meters wide
was positioned off Keahole Point where the sea was 1300 meters deep
(Figure19). A generator with ammonia as the working fluid was installed,
and a 60-cm diameter polyethylene tube (57.5 cm in inner diameter) was
used as the cold water intake. The experiment succeeded in generating 53.6
kilowatts of electricity by pumping up 50 liters per second of about 5-degree
Celsius cold water from a depth of 650 meters. The system used 35.1
kilowatts to operate its own water pumps, so that its net output was 18.5
kilowatts. This corresponds to 34.5% of the total output of the generator.
Governor Ariyoshi of the State of Hawaii was delighted with the
success of this experiment, comparing it to the first flight by the Wright
28
Chapter 2
Helicopter deck
Cold water pump
Environmental laboratory
and control room
Warm water pump
Thruster
Mixed cold and warm
water discharge
Cold water pipe
Evaporator
Condenser
Warm water intake
Figure 20. Converted tanker for OTEC-1. No generator is installed.
brothers. Generally speaking, in OTEC the rate of surplus power generation
increases with the size of the system, and will approach 75-80% with a
100,000-kilowatt system. For practical power generation, it is necessary to
increase this rate by enlarging the system, but a number of problems remain
to be solved.
The biggest problem of OTEC is the capacity and durability of the
evaporator and condenser which are the heart of the system. In the United
States, the Energy Research and Development Administration (ERDA) led
attempts to make various types of evaporators and condensers, and gathered
them all together for tests at the Argone National Institute. Still more, a
series of experiments to examine their performance at sea were carried out
at the same location on Hawaii Island between April 1980 and November
1981.
A converted oil-tanker was used for this experiment, which was called
OTEC-1 (Figure 20). Surface sea-water was taken into the vessel from the
stem, and cold water was pumped up from 686 meters deep through three
intake pipes installed in midship. These pipes were made of polyethylene
and were 1.2 meters in diameter; the pipe walls were 5 cm thick. They were
closed at both ends and towed by a ship to the site, where they were sunk with
weights at the end.
However, a generator was not installed in this experimental system:
studies concentrated on the capabilities of evaporators and condensers, ways
of connecting intake pipes, means for removing marine creatures and other
unwanted materials that fouled up the system, and the effects of sea currents.
Furthermore, the United States instituted a long-range plan leading up
to the year 2000, whereby practical OTEC is achieved by the power industry,
nation-wide research and development is promoted for systems other than
Ocean Water and Its Wonderful Potential
29
Japan
Taiwan
The Phirippines
Republic of Nauru
Plant location
Figure 21. The island Republic of Nauru is located just south of the Equator. The plant
location is about 166˚55’E.
closed cycle and those with ammonia as the working fluid, and other
technology is improved.
OTEC Lights Up a School
The Mini-OTEC experiment in Hawaii was the first to generate more
electricity than was needed for operating the system itself; but the amount
was only small. The following story is about the world’s first instance of
practically useful power generated by OTEC. This happened over a period
of about one year in the Republic of Nauru. It was implemented by Tokyo
Electric Power Company and Toden Sekkei with the support of the Japanese
Government, and in cooperation with the Toshiba Corporation and the
Shimizu Corporation.
The Republic of Nauru is an island country on a coral reef in the South
Pacific, located about 5,000 kilometers southeast of Tokyo and not far south
of the Equator (Figure 21). The country covers an area of 21 square
kilometers and has a population of 8,000. Australia, New Zealand and the
United Kingdom governed the country in the past, but it gained its
independence in January 1968 as the smallest country in the world. Fourfifths of the area of the islands are covered by guano, the solidified droppings
of sea birds. The country’s economy is maintained by exports of guano,
from which high quality phosphorus can be extracted. For this reason,
medical care, education and electricity are all free and life is prosperous.
30
Chapter 2
Figure 22. View of the Nauru OTEC plant. Three pipes extend into the sea: one each for
DOW intake, surface water intake, and discharge.
However, it was estimated in 1983 that guano reserves had fallen to no more
than 38 million tons, which would be exhausted by the end of the twentieth
century if extraction continued at the rate of 2 million tons per year.
The sea surrounding Nauru plunges at a steep angle of 40 degrees
toward the open ocean, and what is more, water from a depth of only 500
meters is an impressive 20 degrees Celsius cooler than water at the surface.
These two factors alone provide the great advantage of the need for only a
short intake pipe. The islands are hardly ever hit by typhoons, winds are
light and the waves are not so high; the islanders are friendly toward Japan.
All of this made the islands ideal for the experiment.
The photo shows an overview of the whole OTEC station (Figure 22).
A generator was situated on land and was designed to generate 100 kilowatts
with fluorine-22 as the working fluid. The intake pipe for cold water was
70 cm in inner diameter. Twenty-two tons per minute of cold water were
pumped up from a depth of about 580 meters, 1250 meters off-coast, and 24
tons per minute of surface water were pumped every minute from 150 meters
off-coast. A maximum of 120 kilowatts of electricity was generated. Out
of this power, about 90 kilowatts was used at the plant, and the rest was
supplied to a local elementary school and other places in Nauru. The first
day OTEC electricity was delivered to that school in Nauru was 14 October
1981.