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Alston Rountree
Dr. Semih Eser
EGEE 101H
28 April 2016
Ocean Thermal Energy Conversion
1. Abstract
Fossil fuels are destroying the environment people, plants and animals call home. To
reverse this concerning trend, more and more time has been dedicated to researching alternative
energy resources. In addition to more traditional renewable methods, over the past few decades
scientists have spent an increasing amount of time and money researching the potential power of
ocean energy. This paper focuses on a single way in which the ocean makes energy creation
possible. The method discussed is called Ocean Thermal Energy Conversion (OTEC).
The first section of the paper explains the two processes through which the machine
generates electricity. It notes the similarities and differences between these different operations,
and details how the natural thermal gradient of the ocean is exploited for electricity production
purposes. Then, a brief history is given as to how the technology has developed and arrived at its
current status.
Furthermore, time is taken to highlight the problems associated with the large-scale
implementation of OTEC. Benefits of the technology are also discussed at length, but findings
indicate that the sheer price of these machines negate the potential benefits. Lastly, it is
concluded that although OTEC is beneficial to the environment in many ways, it remains an
unrealistic substitute or supplement for the energy demand met by fossil fuel powered power
plants due to OTEC’s high cost and low efficiency.
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2. Introduction
The world is facing an increasingly important problem. The growing dependency on
fossil fuels for daily life function is having an overwhelmingly negative effect on the
environment. In just the past 150 years, the emissions from fossil fuels have increased the earth’s
carbon dioxide levels by more than twenty-five percent. Climate scientists predict if this trend
continues, the world could become significantly warmer in the next 100 years. A significant
global temperature increase would devastate the environment. Melting glacial formations and
warming oceans would cause sea levels to rise to the misfortune of coastal populations, permit
the destruction of ecosystems, and make extreme weather patterns increasingly more probable
(“The Hidden Cost of Fossil Fuels”).
In an effort to combat such devastating environmental effects, more and more attention
has been paid to finding alternative resources for energy production. Environmental scientists
have tailored their research efforts to finding and implementing renewable and sustainable
natural resources in place of traditional methods of petroleum based energy production.
Significant headway has been made in the production of energy using solar cells, hydropower,
geothermal and wind power, but collectively, the amount of energy produced using all of these
newer technologies falls significantly short of that produced by petroleum. In 2014, consumption
of energy produced via renewable resources in the United States totaled just around 10% of all
energy consumed (Renewable Energy Explained). This is a strong indicator of progress, but does
not signify a significant potential for large-scale sustainability.
Although hydropower, geothermal, solar and wind power garner much of the public’s
attention when discussing renewable resources, in the past few decades an increasing amount of
time and money has been dedicated to ocean energy research. Also known as marine energy,
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ocean energy refers to engineering technologies that harness the movements of the ocean to
create electricity. Specifically, this aspect of ocean energy refers to tidal and wave power.
However, due to its massive size, the ocean also happens to be the world’s largest solar collector
and energy storage system (“What is OTEC”). Using a third type of technology, called Ocean
Thermal Energy Conversion (OTEC), it is possible to exploit the water’s stored energy for the
clean production of electricity. This technology, OTEC, will be the focus of this paper.
3. Literature Review
In the most basic sense, Ocean Thermal Energy Conversion is “a marine renewable
energy technology that harnesses the solar energy absorbed by the oceans to generate electric
power.” This is achieved through either a closed-system or an open-system OTEC machine. In a
closed-system OTEC machine, a working fluid is utilized to spin a turbine that powers a
generator. First, a pump pulls warm water, approximately seventy-seven degrees Fahrenheit,
from the surface of the ocean into an evaporator where it vaporizes the working fluid. The
working fluid, commonly ammonia, has a much lower boiling point than that of water, thus the
already warm surface water does not need to be heated in order to vaporize the ammonia. Then,
the ammonia vapor travels through a tube where it spins a turbine coupled to a generator. The
generator produces electricity via the turbine, and the ammonia vapor travels through another
tube into a condenser. Here, the vapor is turned back into a liquid through contact with cold
water that is pumped up into the OTEC machine via a separate intake pipe that can extend a mile
or more down into the depths of the ocean. The naturally occurring temperature gradient within
the ocean provides for the manipulation of the working fluid so that it can be reused over and
over again. The warm and cold water taken into the system via the pumps is recycled, and
pumped back into the ocean after use (“What is OTEC?”).
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The second manner in which electricity is produced using this technology is through an
open-system OTEC machine. Unlike a closed-system, this process does not use a working fluid.
Instead, the warm water pulled from the surface of the ocean is the same fluid that evaporates to
turn the turbine. This warm surface water is pumped up into a pressurized chamber where it
evaporates. A vacuum creates a low pressure within the chamber, which allows for the saltwater
to boil at a temperature where it would otherwise remain a liquid. The salt is left behind when
the liquid evaporates, and thus pure water vapor travels through a tube where it spins a turbine
coupled to a generator. The generator produces electricity via the turbine, and the water vapor
travels through another tube into a condenser, just as it would in a closed system. The steam is
then exposed to cold temperatures from the deep-ocean water pumped into the OTEC machine
using an intake pipe like that of the closed-system machine. Just like the closed-system machine,
and open-system machine also pumps the used warm and cold water back into the ocean.
(“Ocean Thermal Energy Conversion Basics”).
The origins of this OTEC technology date back to the late nineteenth century. In 1881,
French physicist Jacques Arsene d’Arsonval first proposed the idea of using the ocean’s
naturally occurring thermal gradient for energy production purposes. It was one of his students,
however, that turned this idea into a concrete technology. In 1930, Georges Claude constructed
the first OTEC plant in Cuba. The very first of its kind, the system produced twenty-two
kilowatts of electricity using a low-pressure turbine. Continuing his conquest, Claude
constructed another plant on board a massive 10,000-ton cargo vessel. Anchored off the coast of
Brazil, Claude recreated his success in Cuba, but the machines were soon destroyed by inclement
weather and ensuring rough surf before they could become net power generators. In 1956, a set
of French scientists designed a 3-megawatt OTEC plant with the hopes of completing the
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installation in Abidjan, Ivory Coast, West Africa. However, due to the cost of construction, the
plant was abandoned and never completed (“Ocean Thermal Energy Conversion Basics”).
The United States first became interested in OTEC research in the mid 1970s. In 1974,
the U.S. provided funding for the establishment of the National Energy Laboratory of Hawaii
Authority (“Ocean Thermal Energy Conversion”). Five years later, the first successful floating
closed-cycle OTEC plant is constructed off the coast of the Hawaiian Islands. This plant
successfully generated roughly fifty kW of electricity without the use of fossil fuels. Since then,
researchers and scientists have tested various heat exchange methods, and have primarily
dedicated time improving the efficiency, and therefore practicality of OTEC machines. Various
studies have received U.S. government funding, but OTEC technology has yet to be installed in
such a manner that would produce sufficient electricity to supplement the demands currently met
by fossil fuels (Johnson).
4. Discussion
Although OTEC remains to be installed on a large scale, there are many benefits to using
this technology in place of traditional fossil fuel powered generators. First, and most notably, this
technology takes advantage of a massive natural resource. Oceans cover over 70% of the earth’s
surface area, and thus provide more than a copious amount of fuel for these machines.
Furthermore, there are no negative environmental repercussions of exploiting this source. The
seas are simply so expansive that massive amounts of power can be generated using OTEC
technology without affecting the temperature of the ocean or the world’s environment. In
addition, OTEC has the distinct benefit of providing baseload power. While other renewable
resources such as solar or wind can only operate under certain conditions, OTEC can operate
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twenty-four hours a day, seven days a week, three hundred sixty-five days a year (“What is
OTEC?”). Therefore, OTEC is one of the most reliable renewable resources.
Two more notable benefits of OTEC technology include the machine’s capability to
provide dispatchable power, and its offshore installation location. With regard to dispatchable
power, OTEC has the unique capability of controlling its level of power production. In a matter
of seconds, power production can be increased or decreased to adjust to inconsistent power
demands. This feature makes it possible for OTEC machines to compensate for intermittent
power supply by other renewables, or even become a supplement for fossil fuel powered power
plants. Lastly, the off-shore installation location of the OTEC machines keeps the constructions
out of sight of the public. Settled land does not need to be purchased, sold or reallocated, and
construction and operation does not interfere with living patterns (Ocean Thermal Energy
Conversion).
Unfortunately installation location also comes with its fair share of problems. The
technology is most efficient in areas where the temperature difference between the surface level
water and deep ocean water is the largest, which means it is only practical for OTEC to be
installed in equatorial areas. At 36 degrees Fahrenheit, the year-round temperature differential in
these regions is the greatest on the planet. However, equatorial areas are primarily composed of
developing nations that lack the funding to support OTEC projects. Even as a developed nation,
the United States struggles to find funding to dedicate to such endeavors (“What is OTEC?”).
The cost of these machines is not cheap. Construction and installation expenses for one single
machine can total upwards of $250 million (Bechtel and Netz). Not only are governments unable
to provide these sorts of figures domestically or externally, but it has also been extremely
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difficult to entice investors. As OTEC is still in its infancy in comparison to other renewable
technologies, investors hesitate to provide funding for an unproven technology (Lacey).
Without sufficient funds, it becomes increasingly more difficult for OTEC to compete
with subsidized fossil fuel energy sectors (Leary and Esteban). Per kilowatt-hour, coal fired
power plants generate electricity at about three cents. The bits of electricity that have been
produced using OTEC technology cost around forty cents per kilowatt-hour (Lacey). The thirtyseven cent difference between these two energy sources is an incredible cost discrepancy. On a
large scale, it would mean the difference in millions of dollars. In addition, customers would be
paying more to exploit a process that does not vary drastically in efficiency from that of fossil
fuel combustion. Around ninety percent of the thermal energy extracted from the ocean is wasted
with each cycle of the machine, and the efficiency of the entire process maxes out at six to eight
percent in the most state of the art machines (Masutani and Takahashi).
5. Conclusion
Ocean Thermal Energy Conversion is undoubtedly one of the most reliable renewable
resources. In the quest to lessen dependency on fossil fuels, OTEC’s ability to provide constant
power while adjusting to demand separates it from competing renewable resources. The
technology does not interfere with established human developments, and does so in an
environmentally friendly manner. The sheer size of the oceans prevents their temperatures from
increasing despite its status as fuel, therefore lessening the effects of global warming without
significantly impacting the ability to meet energy needs of consumers.
However, although OTEC has very evident benefits, large-scale installation remains
nearly impossible. The disinterest of investors has put an increasing amount of pressure on
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governments to provide funds that they simply cannot deliver. Maintaining current allocations of
energy spending is a fiscally responsible move for most governments, but it simultaneously
inhibits the growth and development of OTEC. Without proper funding, there is next to no way
for this technology to grow past infancy. Other renewable resources like solar, wind, geothermal
and hydropower will continue to grow at the expense of OTEC. Additionally, the current price of
energy produced using this technology is unreasonable given the cost of energy produced using
fossil fuels. Unless funding increases, or the price of construction, installation and operation is
reduced drastically, the financial drawbacks will continue to significantly outweigh the
environmental benefits. In the current moment, OTEC is not a practical substitute for energy
produced by fossil fuels.
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Works Cited
Bechtel, Maria and Erik Netz. “OTEC – Ocean Thermal Energy Conversion.” PDF. 26 Apr.
2016
"Fossil Fuels." Fossil Fuels. Environmental and Energy Study Institute, n.d. Web. 24 Apr. 2016.
Johnson, Ted. "Research, Development and Testing: A Timeline." OTE Corporation. Ocean
Thermal Energy Corporation, n.d. Web. 25 Apr. 2016.
Lacey, Stephan. "Ocean Renewable Energy Has Huge Potential But Not Without Giant
Hurdles." Renewable Energy World. Renewable Energy World, 24 June 2009. Web. 17
Apr. 2016.
Leary, David, and Miguel Esteban. "How Things Work: Ocean Energy Making Waves - Our
World." Our World. United Nations University, 5 Oct. 2009. Web. 17 Apr. 2016.
Masutani, S., and P. Takahashi. OTEC. Manoa: Academic Press, 2001. PDF.
"Ocean Thermal Energy Conversion Basics." Office of Energy Efficiency & Renewable Energy.
U.S. Department of Energy, 16 Aug. 2013. Web. 17 Apr. 2016.
Ocean Thermal Energy Conversion." Makai Ocean Engineering. Makai Ocean Engineering,
2010. Web. 17 Apr. 2016.
"Renewable Energy Expalined." Energy Explained. U.S. Energy Information Administration, 27
Mar. 2015. Web. 24 Apr. 2016.
“What Is OTEC?" OTEC News. OTEC Foundation, 2016. Web. 22 Apr. 2016.
"The Hidden Cost of Fossil Fuels." Coal and Other Fossil Fuels. Union of Concerned Scientists,
n.d. Web. 24 Apr. 2016.