Investor Presentaiton
Energies 2019, 12, 3658
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The hybrid cycle combines both closed and open cycle technologies. Similar to the open cycle
process, the warm surface water is flash-evaporated into steam. The steam is used to vaporize the
ammonia working fluid of a closed-cycle loop and drives a turbine to produce electricity. Afterwards, the
steam is condensed through a heat exchanger, providing desalinated water [142]. Such a cycle can
realize the generation of both electricity and fresh drinking water simultaneously.
3.2.5. Salinity Gradient Energy Conversion
The salinity gradient takes advantage of the power that can be generated by the mixture of cold
and salty water, for instance, at the mouth of a river that flows into the sea. There are two common
methods for generating energy from the salinity gradient: pressure-retarded osmosis (PRO) [143–146]
and reverse electrodialysis (RED) [147–149].
The PRO method is based on semipermeable membranes that allow only the traveling of water
molecules. In this approach, water flows from the diluted solution (freshwater) to the concentrated
solution (seawater) to provide a chemical potential equilibrium on both sides of the membrane.
This occurs only when the pressure difference between the liquids is less than the difference in osmotic
pressure. This flow of water can be used to power turbines that transform mechanical energy into
electricity. The RED method is based on the transport of ions (salt) through membranes. Two fluids of
different salinities (freshwater and seawater) pass through a series of specific membranes. The difference
in chemical potential between membranes results in an electrical voltage. The brackish water is then
discarded into the sea.
Additionally, some hybrid processes, such as the production of electricity from thermal energy
using a closed-loop RED heat engine, low-energy desalination by integrating RED with desalination
facilities, and the use of microbial RED cells with boosted power performance, have been proposed to
facilitate energy extraction from salinity gradient resources [149,150].
3.3. Global Status of Development
3.3.1. Installed Capacity
Despite decades of development efforts, a large amount of the ocean's renewable energy sources
are still untapped [151]. In the last 10 years, the use of ocean energy sources has experienced significant
growth globally. Since 2009, many devices have been deployed worldwide to capture the energy from
currents, tidal ranges, thermal and salinity gradients, and waves. This progress is noticeable by the
gradual increase in installed capacity in some continents, as shown in Figure 9 [152], demonstrating an
expansion of marine energy in the world energy matrix. Globally, this growth has more than doubled
from 244 MW in 2009 to 532 MW in 2018. However, more than 90% of this operating capacity is
represented by two tidal barrages in La Rance, France and Sihwa Lake, South Korea.
The contribution of Asia is led by China and South Korea, where extraordinary progress
has been made since 2011, mainly because of the development of tidal barrage facilities. This is
due to government support, through the adoption of economic policies, the reduction of tariffs
and exemption, which includes financial subsidy policies to encourage scientific research and
development, the development of new renewable energy technologies, prototype demonstration,
and development of the renewable energy industry [153]. After France developed the La Rance tidal
barrage, the United Kingdom led the way in terms of installation capacity followed by Spain, Sweden,
the Netherlands, Norway, Portugal, and Italy. In North America, mainly in Canada and the United
States, the development of these energy sources is in advanced stages, with the implementation of
demonstration-scale commercial projects. Africa, Central America and the Caribbean, South America,
and Oceania are in the early stages of deploying ocean resources as energy sources, with incipient
projects and installed capacity.View entire presentation