Overview
Two-thirds of earth's surface covered with
water, more so for island countries
Ocean energy can be harnessed as
• Mechanical (waves, tides and currents)
•  Chemical (salinity gradients, biomass)
•  Thermal (temperature gradients)
Wave Power
•  The power in the waves, P is given as
P = (p g2 H2 T) / 32ti
H = amplitude of the waves, T = period
P is directly proportional to H and T.
Tidal Power
*   Tides due to gravitational field due to sun and moon
For semi-diurnal tidal regime
E   = 7.09 A r*
E = gross energy production (TJ) A = area of the basin (km2) r = average tidal range (m)
OTEC
OTEC system is essentially a heat engine operating between the 'colď temperature Tc of the water at some substantial depth, and the hot temperature Th of the surface water.
Temperature difference of 20°C between warm, solar absorbing surface water and cooler 'bottom' water can occur.
There are 3 types of OTEC systems:
t Closed cycle - this uses working fluid such as ammonia which is pumped a closed loop,
2.  Open cycle - uses warm sea water as the working fluid,
3,  Hybrid - uses both closed and open cycle system, produces electricity and desalinated water.
Surface Seawater around 25 degrees
Bottom seawater around 4 degrees
100      -
200      -
300      -
d00      -
500      -
GOD      -
ž 7Ď[]   -
^ goo     -
S  900     -
3000      -
ä loo       -
1200      -
1300      -
li 00      -
1500      -
Hawaii Puerto Rico
The Gulf af Mexico
i___i___j____i____i___i___i___j____i____i___i___i___L
ID                                  2D
Temperature ['^C ]
:0
Rankine Cycle
Require a gas that boils at about 20 degrees
T -T T] = -Z-----^xlOO
L
H
Problem
•   As the temperature difference between the hot end and cold end gets smaller, the efficiency decreases
Diesel engine        AT =500 degrees
OTEC                              AT =20 degrees
Diesel Engine Efficiency is about 25%
OTEC Efficiency is at most 7%
Submarine Cable
Moorings
Extreme environment (Salt Water)
Ocear^ Surface
Spilfways
OTEC Power Plant
Warm Surface Water (-78 F} Cold Water from 2700 feet (-50 F) " Mixed Discharge (-64 F)
ELECTRICITY
WARM WATER DISCHARGE
9 bar 20°C
EVAPORATOR
WARM WATER PUMP
25°C
CIRCULATING PUMP
PRESSURE PUMP
GENERATOR
6 bar 10°C
CONDENSER
CONDENSER SUMP
V A
AMMONIA STORAGE & CLEANING
COLD
WATER
DISCHARGE
COLD
WATER
PUMP
5°C
Figure 1. Schematic of a closed-cycle ocean thermal energy conversion (OTEC) system.
OCEAN THERMAL ENERGY CONVERSION CONCEPTUAL DIAGRAM
Consider 1000 MWatt plant
•  Assume 3% efficiency
•  Require 1000 cubic meters/sec flow rate
•  Pipe of radius of 10 m with flow rate of     3 m/s
•  Approximately the same flow rate as the Tully River in moderate flood
•  Energy loss is relatively small as pumping head is equivalent about 6 m.        Perhaps   60 MW