Ocean Thermal Energy Conversion (OTEC)
The greatest source of terrestrial energy is the
sun and its greatest terrestrial storehouse is the ocean. The
downside of this thermal buildup is thermal expansion of the
oceans and the melting of polar icecaps.
Robert Stewart, of Texas A&M University points out: “Since the mid
1950s eighteen times more heat has been stored in the ocean due to
global warming than has been stored in the atmosphere.”
Ocean Thermal Energy Conversion (OTEC) is a method for generating
electricity, which uses the temperature difference that exists
between deep ocean water 70, typically at 5oC and shallow ocean
waters 71, typically about 15oC, but as high as 24oC in equatorial
regions, where the largest deserts are found, to run a heat engine
72. The working fluid of the system is a low-boiling-point fluid
such as ammonia 73 or or 1,1,1,2-Tetrafluoroethane, which is
vaporized by the warm water 71, with the vapour driving the heat
engine 72, which in turn drives a dynamo to produce electrical
energy and the cold shallow water 71 then condenses the exhausted
low-boiling-point fluid 73 in a condenser 74.
One aspect of the current invention would generate power using the
principle of OTEC as currently practiced by the Natural Energy
Laboratory of Hawaii Authority. The current invention uses the OTEC process to extract a portion of heat from the ocean that
would otherwise induce thermal expansion of the ocean leading to
sea level rise.
The idea for OTEC dates back to 1881 when the French Engineer,
Jacques D'Arsonval first conceived of generating power utilizing
the temperature differential between warm surface water and colder
waters from the deep.
As with any heat engine, the greatest efficiency and power is
produced with the largest temperature difference. OTEC works best
when the temperature difference between the warmer, top layer of
the ocean and the colder, deep ocean water 70 is about 20°C. These
conditions exist in tropical coastal areas, roughly between the
Tropic of Capricorn and the Tropic of Cancer where the hot deserts
of the world are located.
The Earth is hit with 165,000 terawatts (TW) of solar power every
moment of every day. The ocean absorbs part of this energy causing
thermal expansion and sea level rise. Effectively the world’s
oceans are acting like thermal batteries that are overcharging
storing a potential to seriously harm low lying coastal regions
and their inhabitants.
To give 10 billion people, as is the projected population by the
year 2050, the level of energy prosperity the developed world is
used to, a couple of kilowatt-hours per person, an additional 60 TW of power needs to be generated around the planet. The
overcharging oceans are an available source of this energy
An interesting parallel has been drawn by R Cohen from the US Dept
of Energy :- " a simple comparison may lend some insight into the
energy supply available from OTEC. A temperature difference is
analogous to a hydraulic head; each degree centigrade corresponds
to 427 m of head. Thus, a temperature difference of 21°C would
correspond to having the water at a height of 8967 m if 100%
conversion efficiency were attainable... Thus, a net 2.5%
conversion efficiency would enable a height of 224 m to be
attained... It is as if much of the world's ocean water were
captured behind invisible "thermal dams" of significant heights."
The technology for producing energy by the process of OTEC is well
known in the industry and does not form a part of this inventive
concept. It is an objective of the current invention however to
use OTEC to extract a portion of heat from the oceans that would
otherwise induce thermal expansion and sea level rise.
The Energy Island Group is a partnership of experts in marine
architecture and engineering, infrastructure, project design and
management, applied to all forms of energies available at sea:
wind, wave and solar, with a particular interest in Ocean Thermal
Energy Conversion. Energy Island envisions precisely the
infrastructure required to implement GWMM. Schematics of the
concept and a representation of the Energy Island follow.