Investor Presentaiton
Energies 2019, 12, 3658
5 of 37
2.2. Model Description
2.2.1. Ocean Current and Thermal Gradient Energy
The datasets for ocean current velocities and temperature were obtained (surface down to 5500 m)
from the numerical model product available for the CMEMS (Copernicus Marine Environment
Monitoring Service) center. The applied product is a high-resolution global analysis and forecasting
system that uses the NEMO (3.1) ocean model [27]. It consists of part of the Operational Mercator
global ocean analysis and forecast daily system, which was initiated on December 27, 2006. The dataset
has one regular horizontal grid with a 1/12° (~9 km) resolution based on the tripolar ORCA grid [28],
50 vertical levels with 22 layers within the upper 100 m from the surface, bathymetry from ETOPO1 [29],
and atmospheric forcings from the ECMWF (European Centre for Medium-Range Weather Forecasts).
Additionally, it uses a data assimilation scheme, in which the initial conditions for numerical ocean
forecasting are estimated by joint assimilation of the altimeter data, in situ temperature, salinity vertical
profiles, and satellite sea surface temperature.
Ocean current energy
Near-surface (~5 to 50 m) u and v components of velocity from January 1, 2007 to December
31, 2017 were used as a subset of the area corresponding to the Brazilian coastline (25°W-55°W and
6°N-34°S).
The ocean current power can be calculated as the amount of marine-hydrokinetic energy that
flows through a unit cross-sectional area oriented perpendicular to the current direction per unit
time [30] expressed as follows:
P
=
2PS3
(1)
where P is the current power density in (W/m²), p is the density of seawater (defined as 1025 kg/m³),
and S is the flow speed (in m/s). In practice, only a fraction of this energy can be harnessed.
The underwater turbine efficiency has a typical range from 35% to 50% [31]. Additionally, a mean peak
current of more than 2 m/s is necessary for commercial power generation [32].
Thermal gradient energy
Gridded daily seawater temperature (°C) model output with 50 vertical layers and ~9 km in
horizontal resolution was used to analyze the temperature difference (AT (°C)) between the surface
warm water and the deeper cold water. It was assumed that the superficial water intake pipe was
located at about 20 m and the deepest point in the vertical depth stratification was approximately
1000 m. At specific locations (each grid cell), we calculated the gross power (P gross) following the
methodology described by [33,34]. The OTEC gross power can be expressed as the product of the
evaporator heat load and the conversion efficiency of the gross OTEC [34]:
P gross
Qcwpcp3&tgY
16(1+y)T
-AT²,
γ
Qww
Qcw
(2)
(3)
where y is the flow rate ratio calculated for a 10 MW OTEC plant in which Qww = 45 m³/s and
Qcw 30 m³/s are the warm surface water and the cold deep water flow rates, respectively [35]. AT is
the difference in temperature between the surface layers and deeper layers, and T is the absolute
temperature at the surface (in Kelvin) (20 m). p and εg represent the water density, which was equal
to 1025 kg/m³, and the turbo-generator efficiency fixed at 0.75, respectively. Cp is the specific heat of
seawater and has a value of 4000 J.kg¯¹.K¯¹.View entire presentation