Long Future sustainability & clean technology

Algae Biofuels - Bioplastics - CPV Solar - CSP Solar - Vertical Axis Wind Turbines
Tidal Power - Wave Power - Undersea Habitats - Bubble - Contact

OTEC technology - ocean thermal energy conversion - has been around since early 1900s and is yet to be widely commercialised. It works by exploiting heat difference between the ocean surface and the ocean depth. This is only a small heat difference - 20-30 degrees celcius - so the machines are not very efficient, per se. But if you use vast volumes of seawater, useable amounts of energy can be generated. And herein lies the problem. Drawing vast amounts of sea water from the depths to the surfaces has ecological consequences. So let us hope that the OTEC plants don't solve one problem at the expense of making another.

OTEC - Ocean Thermal Energy Conversion - Marine Renewable Energy - otec - O.T.E.C.

NOAA on Ocean Energy Resources and OTEC

Ocean thermal energy conversion (OTEC) is a marine renewable energy technology that uses the temperature gradients in the ocean to generate a baseload, or constant, source of electricity. OTEC technology uses the temperature differential between the deep cold and relatively warmer surface waters of the ocean to generate electricity. The technology is potentially viable in tropical areas where the year-round temperature differential between the deep cold and warm surface waters is greater than 20 degrees Celsius (36 degrees Fahrenheit).

This is the OTEC News site. Here you will find information about the latest development around Ocean Thermal Energy Conversion (OTEC) and related subjects, such as environmental impact, mariculture, ocean engineering, global climate change, energy policy, alternative energy and global fresh water supply. OTEC is a clean, infinitely renewable and economic way to produce energy, fresh water and food. The intent is to report not only on OTEC development, but also on the context of the development of an OTEC power infrastructure. 
Sea Solar

Sea Solar Power is an innovative company that has designed an economically efficient system to harness the solar energy from the tropical oceans to generate electricity, produce desalinated water, and to grow a variety of food for most of the world's population.

National Institute of Ocean Technology

A Rankine cycle with a working fluid such as ammonia is a first choice for extraction energy from the temperature difference. The essential components of the cycle are an evaporator, turbine-Generator, Condenser and a Pump for circulating the working fluid.

World Energy Council Survey of Energy Resources

Ocean Thermal Energy Conversion (OTEC) is a means of converting into useful energy the temperature difference between surface water of the oceans in tropical and sub-tropical areas, and water at a depth of approximately 1 000 metres which comes from the polar regions.

OTEC Summary

Ocean Thermal Energy Conversion Fact Sheet Hawaii Government

OTEC Summary


Ocean Thermal Energy Conversion (OTEC) system utilizes temperature difference of seawater. This power generation system, which Saga University has been researching, is now attracting attention inside and outside the country.

Xenesys Inc., received an order to conduct the power generation portion of feasibility study for Tahiti Islands from French Polinesian company in February this year.

Bibliography of OTEC information resources Hawaii Government

National Renewable Energy Laboratory

The oceans cover a little more than 70 percent of the Earth's surface. This makes them the world's largest solar energy collector and energy storage system. On an average day, 60 million square kilometers (23 million square miles) of tropical seas absorb an amount of solar radiation equal in heat content to about 250 billion barrels of oil.

OTEC Sites

Ocean thermal energy conversion (OTEC) is perhaps the most exciting world energy resource for the future-the near future. It promises vast amounts of energy (even ten times the current worldwide human utilization) that is cheap (competitive with $25-per-barrel crude oil), naturally self-renewing, and ecologically friendly. As a beneficial side effect, OTEC can turn vast stretches of starved "ocean deserts" into lush "ocean oases" teeming with sea life.

US Department of Energy

Energy Efficiency and Renewable Energy Ocean Thermal Energy Conversion Systems. A great amount of thermal energy (heat) is stored in the world's oceans. Each day, the oceans absorb enough heat from the sun to equal the thermal energy contained in 250 billion barrels of oil. OTEC systems convert this thermal energy into electricity - often while producing desalinated water.

United Nations Environment Program

Ocean energy draws on the energy of ocean waves, tides, or on the thermal energy (heat) stored in the ocean. Oceans cover more than 70% of Earth's surface, making them the world's largest solar collectors. The sun warms the surface water a lot more than the deep ocean water, and this temperature difference stores thermal energy.

Wikipedia on Ocean Thermal Energy Conversion

Ocean thermal energy conversion , or OTEC , is a way to generate electricity using the temperature difference of seawater at different depths. Nearly all energy utilised by humans originates from some form of cyclic heat engine . A heat engine is placed between a high temperature reservoir and a low temperature reservoir. As heat flows from one to the other, the engine extracts some of the heat in the form of work.

Ocean Thermal Energy Conversion

Ocean thermal energy conversion , or OTEC , is a way to generate electricity using the temperature difference of seawater at different depths. Nearly all energy utilised by humans originates from a cyclic heat engine . A heat engine is placed between a high temperature reservoir and a low temperature reservoir. As heat flows from one to the other, the engine extracts some of the heat in the form of work.

Ocean Atlas

The heat exchangers (evaporator and condenser) are a large and crucial component of the closed-cycle power plant, both in terms of actual size and capital cost.  Much of the work has been performed on alternative materials for OTEC heat exchangers, leading to the recent conclusion that inexpensive aluminum alloys may work as well as much more expensive titanium for this purpose. 


Perhaps the most ambitious and world changing undertaking of the Celestopea Project, is the creation of a grid of Ocean Thermal Energy Converters (OTEC's) to power the world into the 21 st century and beyond.  OTEC's take advantage of the perpetual difference between the temperature at the surface of the tropical oceans and the cooler temperature 3,000 to 4,000 feet below the surface. This temperature variation is used to generate completely pollution free electricity from an inexhaustible renewable source.

5 MW preproduction plant

The literature suggests that the next step is to build a demonstration plant of 5 MWe to establish life cycles of major components.

Much of the design work has already been completed.

See details: by Vega and Nihous, Pacific International entre for High Technology Research. Design of a 5 MWe OTEC Pre-commercial Plant

Image source: Hawaii Govt.

It will then be possible to construct 100 MWe floating plants. Design work by Sea Solar has begun on the 100 MW plant ship. Shown below is the Sea Solar Power 100 MW hybrid cycle OTEC . See brochure: 100 MW OTEC.

Sea Solar OTEC

227 m3/s at 27 �C
142 m3/s at 4.4 �C

100 MW electricity
120,000m3/day fr'sh water

152 m long -  47 m wide
61 m high - 25,400 tons

Images adapted from Sea Solar Power.

Image source: NREL

Potential Locations for OTEC Plants

OTEC plants are ideally suited to areas with a large temperature difference between the surface and deep waters. This map shows the global distribution of there areas.

Ideal locations for OTEC plants rely o not just the water temperatures, but access to the mains power grid and demand for electricity.

Link to larger image.

The OTEC cycle using Rankine Cycle. Image source: Xenesys

Offshore OTEC 3

Image source: Xenesys

Koffi Annan, Secretary General of the United Nations, watches a presentation on the Japanese Uehara Cycle OTEC plant by Xenesys at the United Nations conference for Small Island Developing States, Mauritius, January 10-14, 2005.

OTEC is proposed as a suitable technology to assist in providing water and power for small island states. However, because of the high development costs, the next stages of development would need to be undertaken by industrialised countries.

Surface Condenser for Desalinated Water Production (1993-1998)
Image source: Hawaii Govt.

History of OTEC - a proven technology

1881 - J. D’Arsonval first proposed the concept of driving turbines with ammonia using temperature difference of the oceans. 1930 - George Claud makes a small Open Cycle OTEC plant in Cuba. It is functional but produces no net power output. 1979 - Mini OTEC Hawaii constructed on a a barge. This produced 50 kW gross and 18 kW output. 1982 - Land based plant in Nauru developed by Toshiba. This was 100 kW gross and 16 kW output. It was only built as a demonstration plant and was decommissioned after running successfully for 12 months and exporting power to the mains grid. 1993/8 Hawaii 220 kW OC-OTEC Experimental Plant (1993-1998) and 103 kW output. The largest and most efficient unit to date built on land.
1994 - Dr Uehara develops the Uehara Cycle Cycle with an efficiency of 5-6%. See comparison with rankine cycle. 2002 - Designs for 100 MW OTEC Plantship by SEA Solar.

see .pdf report on history of OTEC

Image source: Stanfor
OTEC Workshop Sustainable Townsville Townsville Port Authority Board Room
29 September, 2005, 5 - 7pm

Ocean Energy for Sustainable Townsville Is Townsville positioned to become the leading international centre for the research, development and commercialisation of the ocean based renewable energy technology, OTEC? OTEC (Ocean Thermal Energy Conversion) is an technology that has long been considered a potential source of low-cost, carbon-neutral, base-load electricity as well as bulk desalinated water. Whle OTEC technology has been under development for over sixty years, the commercialisation of the technology has not yet been achieved. As the global price of energy increases in step with concern for reducing greenhouse emissions, perhaps a valuable opportunity presents itself for Townsville to take the lead in forming an international consortium to complete the excellent work commenced by OTEC researchers and developers around the world.

Illustrators' impression of a
North Queensland OTEC plant.
By Dean Willey, Townsville.

Ocean Energy for Sustainable Townsville Townsville held its first OTEC workshop on 29 September, 2005. Sponsored by SEA O2 Sustainable Development and under the aegis of the Society for Sustainability and Environmental Engineering (a Society of Engineers Australia), the workshop considered the opportunities for Townsville to become an international centre for the development of OTEC technology, and the potential for OTEC to solve Townsville's energy and water needs. The key elements of the workshop were a presentation on the engineering and environmental aspects of OTEC by Dr Peter Ridd (pictured right) from James Cook University.

Special thanks to Townsville Port Authority for use of their excellent conference facilities.

Download OTEC Workshop Agenda

Dr Peter Ridd discusses OTEC in Townsville

Townsville OTEC workshop supported by:
Society for Sustainability and Environmental Engineering
Download Dr Peter Ridd presentation
(right click save as, 1.5 Mb)
Engineers Australia

Special thanks to the attendees to the OTEC workshop
Caryn Anderson Manager Planning and Environment Townsville Port Authority
Peter Chapman Project Manager SMEC
Wayne Hickey Principal Jabiru Management Consultants
Engineers Australia
Damien Sweeney Environmental Scientist SEA O2
Guy Lane Principal and Manager SEA O2
Shelley Templeman Environmental Scientist Connell Wagner
Chris Williams Environmental Scientist Connell Wagner
Frank Dallmyer Manager Economic Development Townsville Enterprise
Jake Pienaar Mechanical Engineer GHD
Peter Ridd Senior Lecturer James Cook University
Adam Smith Manager Environmental Impact Management GBRMPA
Russell Reichelt Chief Executive Officer Reef CRC
Craig McLintock Mechanical Engineer MGF NQ

Minutes from OTEC workshop Guy Lane as new chair of North Queensland Society for Sustainability and Environmental Engineering Chair introduction how he came to know OTEC technology
review of agenda for evening introduction to Dr Peter Ridd Presentation by Peter Ridd background, interest in renewable energy
OTEC interest in 1975/76 during energy crisis global interest collapsed after oil prices fell
OTEC not well known renewable compared to solar, wind etc
Guy Lane, Adam Smith, Jake Pienaar and Craig McLintock listen to Peter Ridd discuss the technical and environmental aspects of Ocean Thermal Energy Conversion technology.

overview of heat engines - OTEC is a very large heat engine
all engines need is a cold end and hot end, and take energy out of system
classic engines, rankine cycle (type of system needed for OTEC, as well as organic rankine cycle engine at use in the artesian basin - Birdsville)
use ammonia as working fluid - at right pressure, liquid phase or vapour
overview of rankine cycle
require 20 degrees celcius difference between hot and cold end
OTEC requires pipe down to depths - 500 to 700 m deep
the ocean is on average 4 km deep and cold about 4 degrees
there is a tiny bit of the ocean, the surface waters in the tropics where the water is warm
queensland coast - temperature outside shelf always over 24 degrees, and has cold water in depths
after 700m, rate of temp drops less steeply, 750m a good number
temp drops similar in all oceans
Townsville, at latitude 19, is at southern end of ocean temp range required for OTEC
karnot efficiency - limits efficiency of heat engines (differential between hot and cold end)
OTEC efficiency around 3-4%
other problems is power cable to mainland, moorings and permits, salt water environment floating OTEC, or OTEC on continental shelf (or on land) consideration of the figures for a 1,000MW plant

assume 3% efficiency, require 1,000 cubic meters/sec flow rate, pipe of radius of 10m with flow of 3m/s - approximately the same flow of Tully river in moderate flood
energy loss is relatively small as pumping head is equivalent about 6m in air - perhaps 60MW
waste water plume - high nutrients, plume must be discharged below thermocline to prevent mixing of nutrient rich waters with warm surface waters
small OTECs have been built, Taiwanese are looking into bigger ones
Taiwanese proposals for 400 MW offshore OTEC plants
Taiwanese have deep water close to their coast
environmental impacts have to be considered
as well as consider costs

Frank Dallmyer , Wayne Hickey and Peter Chapman consider the potential opportunities for OTEC in Townsville.

Group Discussion
risk assessment - thousands of litres of ammonia, size of structure would be much greater than what is currently on reef (pontoons), more like the size of an oil rig consideration of environmental risks
1. installation esp. pipes and moorings 2. operation eg. water discharges 3. accidents ( eg spill of ammonia) ammonia should evaporate quickly from the sea surface if spilt
structure not necessarily the killer, but nutrients on the reef (community interest)
effect of nutrient on fishing (esp game fishing- black marlin, off Cairns) building into development discharge at equivalent ocean temp
what lives in the ocean 750 metres below sea level?
Giant squid? Billfish?
life of structure, and maintenance costs
20-30 year life - same as a ship
cf. power station life of 50 years
What about using waste discharge from power plants and industry to create the heat differential for power production - less flow, but already flow rate, or temp differential between rivers and ocean
hybrid scheme - heat water using the sun and use cold water
what about using cold water to cool surface water - as a potential solution to coral bleaching
GL- describes discussions with Sea Solar about fully funded plant 100 MW - just needs needs power purchase agreement
Unlike most renewables, OTEC runs 24h a day and thus could be used as base load power
120ML of freshwater a day
what about using the system to use with cooling water of coal power stations, like at mt isa
use this as proof of system - eg 10MW
Cooktown needs 40 MW and has its own grid need energy demand, Cooktown and Cairns would not use up 100MW possibility of putting an OTEC plant on shore and running the pipe to the shelf consideration of the size of the water pipes? 10 metres diameter
the recent water pipe laying process between Pallaranda and Magnetic Island
8 km pipe costs many millions of dollars and was only 30cm diameter
Solomon islands - only want 50MW, prove system at smaller scale

reviewed history of OTEC, Sea Solar, Indian and Taiwanese proposal Potential to have Sea Solar President in Townsville to discuss suitability of Townsville as a base for Pacific OTEC
use discharge plume as artificial reef, other uses for OTEC platform
could you circulate ammonia rather than sea water - yes, but need same flow rate
OTEC would not be supported in NQ because of costs - needs large proponent, security of investment and returns, cost of contractors - salt water environment, infrastructure costs, (cable costs around $8000/m), transmission loss - no more than 5km from generation site, cannot run AC cable for very long, need to convert to DC, cost of energy going down with deregulation of energy market
Caryn Anderson, Shelley Templeman, Chris Williams and Russell Reichelt watch the OTEC presentation by Dr Peter Ridd from James Cook University.

Tasmania, DC cable for around 250km, to keep loss down
build onshore, big plastic pipe, 20-30MW, may get up (pacific island ideal)
what takes less energy to transmit - electricity or water
heat water with solar, and use difference between bay water and heated solar water - go down south
ratio between hot and cold water required roughly equal (1.5:1)
what is running costs? Peter Ridd says he thinks it would be relatively high
cost of installed power cheaper - maybe OTEC comes later when RECs, or carbon trading mechanism becomes established
demand in pacific island, where they have to import fuels
talk finished at 6:30pm

Outcomes of the OTEC Workshop

The workshop provided a thorough consideration of the OTEC technology, its application to Townsville and North Queensland and the opportunities for an OTEC base in TOwnsville with focus on the South Pacific Islands.

Townsville an unlikely location for OTEC plants because distance between land and the continental shelf would make costs of transporting power to shore prohibitive, plus, Townsville has more easily exploitable energy sources close to hand, ie gas fired power stations.

Cooktown and North, OTEC would make more sense as the shelf is much narrower and energy sources not so apparent.

Smaller plants could play an important role in the sustainable development of the South Pacific Islands.

Rigorous environmental management would necessarily be mandated and a view that the risks could be managed.

Operation impacts on coral reefs of particular concern.

Costs of OTEC water and power are unknown and a missing factor from the conversations.

Townsville identified as a very suitable location for base of OTEC considerations for the South Pacific because of

  • the City's proximity to tropical South Pacific
  • existing expertise in South Pacific development resident in Townsville firms and institutions
  • extensive marine science capabilities
  • sophisticated marine environmental management capacity
  • energy engineering expertise at hand
  • resident capacity in ammonia engineering

There is sufficient interest amongst members of the group to form an informal OTEC working group.

Agreement for Chair to make a CD of all the available OTEC information and make available for the workshop participants and others.

Special thanks to SEA O2 support.

Workshop co-ordination, minutes and photography by Damien Sweeney.

OTEC Internet Resources

size="1">Schematic of OTEC system
Image size="1">source: WEC

Townsville is considered a potential base for OTEC technology because:

  • Warm-surface and cold-deep ocean waters only 100 km from Townsville
  • Research institutions with marine / engineering capabilities
  • Existing expertise in global marine management projects
  • Industrial base to support development of the technology
  • Deepwater port to support installation of technology Demand for large amounts of low cost energy
  • City-wide support for sustainable development
  • Spiralling demand for base-load power

A vision for Townsville's Energy Future might include an ocean energy farm of 100 OTEC plants located 100 km offshore each producing 100 MW of base load power with a subsea cable feeding into the mains grid near Townsville. We call this vision one hundred by three.

Additional uses of OTEC Infrastructure Around the world, OTC plants have been considered for a range of uses adittional to producing electricity. An assessment of the potential opportunities associated with offshore OTEC plants might include:

  • Production of bulk fresh water
  • Aquaculture and Mariculture
  • Marine Adventure Tourism
  • Marine Research Platform
  • Platform for Wind Power
  • Navigation Marker
  • Emergency Rescue Centre

Impression of an OTEC plant
image source: Ocean Power Plant

Potential Ecological Consequences

The ecological impacts of OTEC plants would need to be thoroughly considered given the proximity of the Great Barier Reef Marine Park. Here are some preliminary considrations. The flow of water from a 100-megawatt OTEC plant, would equal the of a large river. Since the salinity of the ocean is nearly uniform, these large discharges will not significantly affect the salinity of the receiving waters. The temperatures of the seawater discharges will be some 3�C (6�F) above or below their initial temperatures. If the warm and cold discharges are mixed, they will have an temperature near 18�C (64�F). The water will need to be discharged at a depth below the bottom of the surface layer in order to avoid contaminating the surface water intake. At that depth, somewhere below 100 m, the discharge will be denser than the water at that depth and will disperse gradually downward, having little impact on the surface layer where most life exists. Information source: Ocean Atlas