Sustainable Energy for the Development Strategies in the Maritime Field Phuoc

Along with events like global warming and environmental pollution, fossil energy exhaustion is also a big problem. When people are increasingly dependent on this material while fossil fuels are increasingly depleted. In the face of that risk, many countries around the world have been looking for new types of energy that are capable of regenerating and providing continuous energy. Renewable energy is found from the resources around people like wind, water, sunlight, ... and sea water is one of them. Sea waves and tides are two extremely large sources of renewable energy that have been discovered. According to the study, these two energy sources are capable of providing huge electricity to the world.


I. INTRODUCTION
Renewable energy or renewable energy is energy from continuous sources that, according to human standards, are as limitless as solar, wind, rain, tide, waves and geothermal energy [1][2] [3].The basic principle of using renewable energy is to extract part of the energy from continuous processes in the environment and put it into technical uses [4] [5][6] [5].These processes are often promoted especially from the Sun.Renewable energy replaces traditional fuel sources in four areas: power generation, hot water heating, engine fuel, and rural independent power systems [7][8] [9].
There are about 16% of global electricity consumption from renewable energy sources, with 10% of all energy from traditional biomass, mainly used for heat supply, and 3.4% from hydropower [10] [11] [12].The new renewable energy sources (small hydrogen, modern biomass, wind, solar, geothermal, and biofuels) make up 3% more and are growing rapidly.At the national level, at least 30 countries around the world have used renewable energy and provided more than 20% of their energy needs [13] [14].National renewable energy markets are expected to continue to grow strongly in the next decade and beyond.For example, wind energy is growing at a rate of 30% per year, the global installed capacity is 282,482 (MW) by the end of 2012.Renewable energy sources exist everywhere in many geographic areas , in contrast to other energy sources, exists only in some countries [15][16] [17].The rapid and effective introduction of renewable energy use has important implications for energy security, climate change mitigation, and economic benefits [18].Global public opinion surveys provide strong support for the development and use of renewable energy sources such as solar and wind.While many renewable energy projects are large-scale, renewable energy technologies are also suitable for rural and remote areas and developing countries [19][20][21] [22].
On the planet, 70% is water.Therefore, the ocean is always a great resource for any country which has the sea.In addition, to providing seafood, coral, fossil energy such as oil and gas, many countries are using the sea as a form of renewable energy to provide energy for itself [23][24] [25].The energy supply potential of the ocean is immense.Currently, there are many countries in the world who are exploring and exploiting this renewable energy source to replace fossil energy sources that are gradually depleted [26][27] [28].It can be mentioned that there are a few big countries with strengths in the sea such as the US, some European countries such as Scotland, Spain or Asian countries such as Korea who are exploring and exploiting this energy source.Sea energy is the type of energy generated by ocean waves, tides, salinity, and differences in ocean temperatures.The movement of water in the ocean creates a huge amount of kinetic reserves, also known as motion energy.This type of energy can be exploited to produce electricity to power homes, transport, and industries [29].Ocean renewable energy has many such as Sea energy, tidal energy, flow energy, ocean thermal energy, ... but the most prominent are the two types of energy which are tidal energy and wave energy because they are abundant, continuous and easy to exploit [30].These energies are capable of providing a great source of energy for mankind.Vietnam is a country with great potential in exploiting this type of energy because there is more than 3000 km of coastline [31][32].However, this requires a large amount of investment, so it is also a difficulty.But with the situation of fossil fuels such as coal and gas is exhausted, the investment in developing energy sources Reproduction is an urgent job [33] [34].

A. Tidal energy 1) Overview of tidal energy sources
The tide is the phenomenon of water rising and falling under the impact of the sun, moon and other planets.Tides form and change frequently due to gravity and alternate position changes between the Sun, Moon, and Earth resonating with centrifugal and inertial forces.The relative movement of these planets creates different tidal cycles such as semi-diurnal cycle, spring-reap cycle, half-year cycle ( semi-annual cycle and other cycles longer [35].The highest tide (high tide) when both the moon and the sun lying on the same side to the earth because of the maximum gravity, gravity, including from the moon and the sun.When the moon and the sun are opposite each other from the earth, the gravitational force is minimally known as the shallow phenomenon.In Vietnam, the weakest average energy flow reaches 15kW / m; strongest 30kW / m.Specifically, Ha Long Bay, Quang Ninh, Ganh Rai Bay, Ba Ria-Vung Tau meet all three factors: GWh / km2 energy density; GWh potential; GWh / km performance.Eligible to build tidal hydropower plants.However, due to lack of funds, it was only studied and exploited on a small scale.2) Advantages and disadvantages of this energy source in the production of electricity a) Advantages + Tide is a renewable energy source, does not emit gas polluting the environment, so it is friendly with the air environment.
+ Higher efficiency than other renewable energy sources due to the large volume of water.
+ Zero fuel cost: Energy is kinetic energy and potential of tidal water, so no fuel is needed for tidal power equipment.During operation only cost for maintenance and operation [36].
+ Long life cycle: A hydroelectric dam after construction can operate for up to 100 years, so tidal electricity costs will not be high if this factor is taken into account.
b) Disadvantages + Large investment costs: The cost of tidal power plants is 2-3 times higher than that of hydroelectric dams, so the electricity price is quite high.
+ Depend on geography: Hydrostatic energy can only be exploited in areas with a large and continuous tidal range.
+ Affecting the wildlife of marine life and transportation.

3) Applications of tidal energy a) Tidal dams
Tidal dams are the form of using the potential of the tides, harnessing energy from the difference in tide up and down.At high tide, the sluice gate is pulled up to help the inner catchment area to fill with water.At low tide, the sluice gates are closed to force the water in the dam to escape to the sea according to the turbine system attached below the dam door to make the turbine spin to generate electricity [37].+ Effect on the male level of water at the construction site.
+ Affecting the ecosystem.

b) Tidal fences
The fence is a solid reinforced concrete wall that crosses the strait or estuary, has large gaps to install turbines, usually vertical turbines and forces the water flow through them.The tidal currents make rotating turbines and generating electricity.The principle of operation is to use the kinetic energy of high-speed tidal currents.When the tide turned east, it went down through the turbine to turn the turbine to pull the generator [38].The hydroelectric fence has the advantage of having less impact on the environment like hydroelectric dams and can create roads across the river and the sea.However, it will affect the movement of marine organisms [39].Advantages: + Less impact on the ecological environment, the area, can be used both when the tide is up and down.
+ Less influence of wind and storm because the turbine is located deep below the water surface.
Disadvantage: + Due to high water pressure, the equipment must be under high pressure, need to have a sustainable structure.
+ Difficult to maintain because it is flooded deeply in the water.
+ Marine or garbage can get in and get stuck in the turbine.

B. Wave energy 1) Overview of wave energy sources
A type of renewable energy source based on the use of the power of ocean waves to generate electricity.Unlike tidal energy uses tides and tidal currents.Wave energy uses the vertical motion of surface water to create tidal waves.The wave power converts the periodic ocean's up and down motion into electricity by placing the device on the ocean surface capturing the energy generated by wave motion and converting this mechanical energy into electrical energy.It can be understood that "Wave energy" is a form of wind energy indirectly causing the movement of water on the ocean surface.By collecting wind energy the wave motion is converted into mechanical energy and used to run the generator [42].Sea waves have great potential; the total theoretical sea wave potential in 2010 is estimated at 32000 TWh / year.According to the study, for every square meter of solar panels received from 0.2 to 0.3 kW of solar energy, each square meter of the wind tower will absorb 2 to 3 kW.Meanwhile, every square meter of coast receives up to 30 kW of wave energy.Thereby, it is possible to see the potential of ocean waves [43].2) Advantages and disadvantages of sea waves energy a) Advantages + Wave energy is an abundant energy source.Because waves are generated by wind, waves are also renewable sources.
+ Pollution due to wave energy generated less than other green energy sources.
+ Reduce dependence on fossil fuels.
+ Wave energy is relatively consistent and predictable.+ Wave energy device is a module.Easily combined with additional wave energy devices added as needed.
+ Limit coastal erosion.+ There are no barriers or difficulties in moving fish and aquatic animals.
b) Disadvantages + The devices that convert wave energy depend on the appropriate location where the wave is strong.
+ Continuous power generation when the wave arrives within a certain time.Do not generate electricity during static waves.
+ Offshore wave energy equipment can be a threat to navigation.Cannot see or detect them by radar.
+ Loss of costs for maintenance and repair.The wave collector is a cylindrical float, the inside has air inlet and outlet above and below.Wave in and out below.When the waves rise and fall in the buoy, the water level acts as a piston that pushes air up and down.The air moves in a fixed direction, on the way through the turbine to convert the air flow energy into the turbine rotating energy [44].
In OWC this motion wave creates a two-way air flow transformed into the engine and transmits the generator shaft by a special type of turbine called Wells turbine (turbine injection), which provides a direction.The only movement of this air flow.Wells turbine's properties were limited by a series of phenomena that stopped in turbines.This is a near-shore power converter so there are advantages and disadvantages as follows; Advantages: + As a device near the shore, there is a large capacity of electricity.
+ Voltage has high stability.+ Convenient for maintenance and repair.+ Low cost of electricity transmission.Disadvantage: + High investment costs.+ Impact on the surrounding landscape and impacted coastal environment.

b) Float device
The device is researched and developed by Sweden.Main structure includes: Rotor generator is a permanent magnet connected to a float on the sea surface with a cable, the rotor is placed inside the Stator coil.Stator windings are wrapped in hollow round cylinders fixed on the seabed.Operation principle: when the wave moves through the area where the device is impacted on the buoys moving up and down, these buoys are attached to the rotor of the transmitters making them move up and down at the same speed inside the roll cord.Since it generates electricity inside the transmitter coils, the coils are connected by cables to the in-shore transmission station.This is a far-flung wave power conversion device that has the following advantages and disadvantages: Advantages + Principle of operation is simple, easy to manufacture, high conversion efficiency but often has a small capacity.
+ Larger capacity, power source creates more stable and adjustable.
+ It is possible to supply electricity for offshore equipment such as on islands or lighthouse houses.
Disadvantages + The testing, installation, maintenance and repair had many difficulties.+ Affecting sea traffic.+ Transmission cost loss is very large.Vietnam's sea energy is very large, it is capable of reaching tens of GW of electricity, contributing to national energy security and territorial protection, supplying electricity to islands and coastal areas.Therefore, training of human resources is essential.Integrating marine energy development with socio-economic development.This is a relatively new energy industry in Vietnam, but the benefits it brings are enormous.Therefore, investing in developing this renewable energy source is something Vietnam should do to limit fossil fuel use and reduce environmental pollution.
Ocean waves create endless energy.The calculation results of the wave energy along the coastal strip of our country are very rich.The weakest average energy flow reaches 15kW / m; strongest 30kW / m.Specifically, Ha Long Bay, Quang Ninh, Ganh Rai Bay, Ba Ria-Vung Tau meet all three factors: GWh / km2 density; GWh potential; GWh / km performance.Eligible to build power plants.
In tidal energy, we have two positive regions.The first is Quang Ninh, with the tide of up to 4 meters.The second is in the Southern Delta, the tide is about 3 meters.But actually the tide of 3 or 4 meters of water does not generate electricity to bring it into the grid, but other factors are needed.In Vietnam tidal energy should be exploited locally, for example, small power plants to serve each island.And it is not possible to exploit tidal energy at an industrial scale soon.

A. The project of Tide Island in Co To Island
Quang Ninh area has a tidal energy density of about 3.7 GWh / km2, Nghe An is about 2.5 GWh / km2 and gradually decreases to Thua Thien Hue area with 0.3 GWh / km2.Then gradually increasing south to Phan Thiet with 2.1 GWh / km2 and reaching the maximum in Ba Ria -Vung Tau with 5.2 GWh / km2, Estimated power capacity: 550 MW.With topographical characteristics and the tidal regime, the Northeast Sea is located in Quang Ninh and TP.Hai Phong is the region with the largest potential for developing tidal power in the country with a capacity of up to 550MW, accounting for 96% of Vietnam's potential tidal power technology.However, this energy source has not been paid attention to and exploited, at the early stage of research, there are no specific applications for electricity generation from this energy source.-Create a bridge across the bay, shorten the distance between Vung Tau and Long An. renewable energy sources has helped people reduce their dependence on fossil energy sources.In addition, renewable energy is assessed as a more environmentally friendly energy source than fossil energy.So using renewable energy sources also helps protect the living environment.
Vietnam is a country with great potential in developing renewable energy sources.But the development of this energy source is small while the existing energy source is very large, which can replace fossil energy.Therefore, it is necessary to have more investment in researching and developing renewable energy sources in order to replace fossil energy sources which are exhausted and protect the environment better.
Published on April 20, 2019.Phuoc Quy Phong Nguyen and Dinh Tuyen Nguyen are with Ho Chi Minh city University of Transport, Ho Chi Minh city, Vietnam.

Fig. 2 .
Fig. 2. Characteristics of the sun, moon, earth make up the characteristics of the tide

Fig. 3 .
Fig. 3. Map of tidal energy sources in Vietnam

Fig. 4 .
Fig. 4. The working principle of the tidal dam Advantages of tidal dams: + Create a river crossing bridge that combines electricity production and traffic.+ Reduce coastal and beach erosion.+ Simple operation principle, low operating cost.Disadvantages of tidal dams: + High construction costs.+Effect on the male level of water at the construction site.+Affecting the ecosystem.b)Tidal fencesThe fence is a solid reinforced concrete wall that crosses the strait or estuary, has large gaps to install turbines, usually vertical turbines and forces the water flow through them.The tidal currents make rotating turbines and

Fig. 5 .
Fig. 5.The operation principle of tide fence c) Tidal turbine This is a new type of equipment applied to tidal power.The operating principle of tidal turbines is that the fans are arranged in rows under the sea surface.Tidal current speed when the turbine works about 2-3 m / s.The location of the factory is often in the estuary and the mouth of the bay because of the strong flow of water.The depth of about 20-30m [40][41].

Fig. 11 .
Fig. 11.Construction of cylindrical floats Among them are the parameters: Zc1: Height of piston 1 peak compared to buoy peak (m) Zc2: Height of piston 2 peak compared to buoy peak (m) D: Float diameter (m) d: Submerged part of the buoy (m)

Fig. 12 .
Fig. 12.Average wave energy potential for the East Sea

Fig. 13 .
Fig. 13.Map of tidal power plant project in Co To Island

TABLE I :
WAVE ENERGY POTENTIAL OF REGIONS IN THE WORLD