387
Power and Energy Directly from Water
plant to power delivery cables requires the plant to remain relatively stationary.
Mooring is an acceptable method, but current mooring technology is limited to
depths of about 2000 m (6600 ft). Even at shallower depths, the cost of mooring
may be prohibitive.
13.4.3 oTher uSAgeS oF oTeC
One of the attractions of the OTEC technology is its use for numerous other industries. Both open- and hybrid-cycle plants using surface condensers can desalinate
seawater into potable water. A system analysis indicates that a 2-MW plant could
produce about 150,000 cu ft of desalinated water each day [75].
The 41°F (5°C) cold seawater made available by an OTEC system creates an
opportunity to provide large amounts of cooling to industries and homes near the
plant. In 2010, Copenhagen Energy opened a district cooling plant in Copenhagen,
Denmark. The plant delivered cold seawater to commercial and industrial buildings and reduced their electricity consumption by 80% [76]. OTEC technology supports chilled-soil agriculture. When cold seawater flows through underground pipes,
it chills the surrounding soil. The temperature difference created by this method
allows plants that require temperate climates to be grown in the subtropics [75].
Aquaculture is the best-known by-product of OTEC because it reduces the
financial and energy costs of pumping large volumes of water from the deep ocean.
Nonnative species such as salmon, lobster, abalone, trout, oysters, and clams can
be raised in pools supplied by OTEC-pumped water. This extends the variety of
fresh seafood products available for nearby markets and provides a low-cost refrigeration that can be used to maintain the quality of harvested fish [75]. In Kona,
Hawaii, aquaculture companies working with an OTEC plant (Natural Energy
Laboratory of Hawaii Authority [NELHA]) generate about $40 million annually,
a significant portion of Hawaii’s gross domestic product (GDP) [77]. Deep-ocean
water can also be combined with surface water to deliver water at an optimal
temperature.
Hydrogen can be produced via electrolysis using the OTEC electricity. The OTEC
process-generated steam with an addition of electrolyte compounds to improve efficiency is a relatively pure medium for hydrogen production [75]. While OTEC can
be scaled to generate large quantities of hydrogen, this method is as yet not competitive to other methods of hydrogen production [75].
The OTEC technology can also be used to recover a large number (>50) of trace
salt elements, uranium, and other materials from ocean. Japanese investigators are
pursuing this approach [75].
A schematic of the OTEC process with its other usages is graphically illustrated
in Figure 13.9 [75].
13.4.4 BArrierS To imPlemenTATion
The OETC technology faces several political, economical, and technical barriers.
The stationary surface platforms of the technology may affect the United Nations