Investor Presentaiton
Energies 2019, 12, 3658
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compared to that of air, the blades of current turbine devices have smaller dimensions and move slower
than those of wind turbines while still providing a significant amount of energy. The main difference
between tidal and ocean currents is that the tidal currents have bi-directional flows in contrast to the
ocean currents which are unidirectional. This has implications for the design of a tidal current turbine,
which must act in both directions of the water flow [59].
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The four major types of current energy conversion devices are as follows, as shown in Figure 8:
Horizontal axis turbine [116-118]-blades, driven by current energy, rotate around the
horizontal axis;
Vertical axis turbine [119–124]—blades, driven by current energy, rotate around the vertical axis;
Oscillating hydrofoil [125–128]—currents passing the hydrofoil result in the lift force, which can
drive the motion of the hydraulic system to generate electricity;
Venturi effect turbines [129]—harness the kinetic energy of the current by amplifying the current
velocity by the Venturi effect in the strangulated section of a tube [63].
Additionally, ducted channels are utilized to induce a sub-atmospheric pressure within a
constrained area and, consequently, increase the flow velocity around the rotor [130–132]. The tidal
kite is a novel technology, which uses wing carrying and pushes a turbine in an "8" shaped trajectory,
sweeping a large area with a relative speed of more than the local current speed [133-135]. A review of
the tidal current technology is presented in [136].
(a) Horizontal axis turbine
(b) Vertical axis turbine
Sea bottom
(c) Oscillating hydrofoil
(d) Venturi effect turbine
Sea bottom
Figure 8. Primary types of tidal and ocean current energy conversion devices.
3.2.4. Ocean Thermal Energy Conversion (OTEC)
OTEC is a technology that converts the difference in temperature between the sea surface and large
depths (around 1000 m) for use in heating, cooling, or to generate electricity. Closed-cycle technology
requires a minimum temperature difference of 20 °C, which is possible in equatorial marine regions.
Warm water from the upper layers is used to vaporize a secondary working fluid (e.g., ammonia),
thus driving an electric generator. The resultant steam is then condensed by the cold water, which is
brought, using pumps, from the bottom of the ocean and then discarded. Some works that studied the
closed-cycle OTEC can be found in [137-139].
Open cycle technology uses the warm surface ocean water as the working fluid, which is drawn
into a vacuum vessel, causing the working fluid to vaporize. The main benefit of the open cycle process
is that it produces both electricity and desalinated fresh water. An investigation of the performance of
a shore-based low temperature thermal desalination using an open-cycle OTEC is presented in [140].
Recently, a novel optimal open-cycle OTEC plant using multiple condensers was designed in [141].View entire presentation