New Energy Course Report - English

南京理工大学《新能源技术》课程报告姓名学号：学院(系):自动化学院专业: 电力系统及其自动化题目: 洋流能的发展状况与最新研究状况组别任课教师硕士导师2017年12月25号The development of marine current energy and the latest research statusE-mail: @ABSTRACT：First of all, this article introduces the basic concepts of marine currents and the basic principles of using marine currents to generate electricity. Then, the article introduces a novel device that uses marine currents to generate electricity: Ocean’s kite. The working principle of Ocean’s kite is expounded in detail, and two kinds of Ocean’s kites with different structures are contrasted. The status quo of their research and development of the actual application are introduced. The article highlights the latest structure of the GEM-Ocean's Kite, developed by Italian scientists, and the latest improvements. The efficiency of GEM-Ocean's Kite power generation before and after the improvement is analyzed and compared, and the efficiency is greatly improved. Finally, the advantages and disadvantages of Ocean’s kites in power generation are summarized, and their application prospects are prospected.KEYWORDS：Marine Current Energy; Ocean’s kite; Working principle; Innovation1. INTRODUCTIONThe marine current is the current of the ocean and it is an inexhaustible source of energy for the ocean. The world on which mankind lives is about 510 million square kilometers , of which the boundless sea accounts for 71%. It is estimated that the total renewable tidal energy, marine current energy, marine temperature difference energy and wave energy contained in the ocean is 76.6 billion kilowatts.Fig.1 Basic distribution of marine currents in the Pacific Ocean Among them, the marine current energy due to its available energy, relatively stable characteristics, attracted the widely attention.As is shown in Figure 1 , the Pacific marine current distribution diagram. Marine current is the seawater in the ocean due to thermal radiation, evaporation, precipitation, shrinkage and the formation of different density of water masses, and coupled with the wind stress, turn to the force, tidal force and the role of relatively stable flow. Therefore, the marine current can essentially be the kinetic energy produced by seawater flow and is a renewable and clean energy source.2. UTILIZATION STATUS AND DEVELOPMENT TREND2.1 The Distribution Of Marine Current Energy Resources in Our CountryThe marine current in our country is seasonal. In addition to the influence of the continental runoff change, the seasonal variation of coastal flow system is also affected by the change of monsoon and consistent with the change of monsoon. The currents of the Bohai Sea, the Yellow Sea and the East ChinaSea are mainly composed of two streams, Kuroshio Current and Coastal Current, which have the characteristics of cyclonic circulation. Among them, the Kuroshio Current consists of the main Kuroshio and its branches. Nanhai, because it is located in the tropical monsoon region, the prevalence of the southwest wind in summer, the prevalence of the northeast monsoon winter monsoon, monsoon direction consistent with the long axis of the sea, is conducive to the stability of the development of the flow system.2.2 Domestic and Foreign Marine Current Power Generation StatusIn the 1970s, the United States and Japan pioneered the study of tidal current and marine current energy generation. In 1974 the United States developed a small umbrella turbine that was tested in the Florida marine current. In 1985, the United States conducted a 2kW turbine test in the Gulf of Mexico. In the same year, another 20kW tidal generator was tested in the New York City river. At present, the United States, Norway, France, Ireland, Britain and other countries have one after another of tidal current and marine current energy generator put into testing. Stand-alone capacity of several hundred kilowatts of generating units in all countries have been more mature models, 1MW above the unit has begun to invest R & D and testing. The trend of the future can be similar to the wave energy in the direction of marine current energy generation. The efficiency and reliability of power generation are the primary problems to be solved. To achieve the level of commercial operation, we must continue to reduce the cost and operating costs of the initial investment.China's marine current energy reserves are very rich. According to the 1989 "China's coastal rural energy resources regionalization" of the 130 national waterways statistics , the theoretical average power of 13,948.2MW. Among them, the coastal provinces in the East China Sea are the major ones, and the marine currents in Zhejiang Province account for more than half of the total in the country. Especially in the Zhoushan archipelago area, the current velocity of some channels is higher than 4 m/s, which is suitable for the construction of large-scale power plants. The trend of China's energy and marine current energy generation technology research carried out earlier. In the 60s has been carried out water turbine test. The mid-1980s, Harbin Institute of Technology developed a 1kW tidal current power generation unit prototype. In 2002 China's first 70kW tidal power station was built in Zhoushan, Zhejiang. Since then, many domestic universities and research institutions have carried out a variety of different characteristics of tidal current and marine current energy generation equipment research, but stand-alone capacity is still small. In the Outline of National Medium and Long-term Science and Technology Development Plan (2006-2020), the key technologies of 150kW marine current power station have been listed as key projects of ocean energy research and development in China.3. THE BASIC PRINCIPLE OF MARINECURRENT ENERGY AND TYPICAL POWER PLANT3.1 The Basic Principle of Marine Current Power GenerationThe principle of using marine current energy to generate electricity is basically the same as that of using wind to drive a turbine to generate electricity. A certain flow of marine current flows through theblade in a turbine generator to make a turbine to rotate a generator rotor in a stator. The rotor of the generator forms a magnetic field by direct current. After the magnetic field rotates in the stator, the magnetic field lines cut the coils in the stator to induce the potential in the coil. After the potentials of many coils are superposed, a voltage is formed at the generator terminals to supply power to the load. 3.2 A Typical Device that Uses Marine Currents to Generate ElectricityAt present, there are many kinds of devices that utilize marine currents to generate electricity. Here we briefly introduce the working principle of several devices.3.2.1 Horizontal Axis Turbines and Vertical AxisTurbinesFig.2 Horizontal axis turbineFig.3 Vertical axis turbineHorizontal axis turbine, vertical axis turbine is the use of marine currents flow through the turbine blades to rotate their power generation, the structure diagram are shown in Figure 2, Figure 3. 3.2.2 Swing HydrofoilsSwing hydrofoil structure shown in Figure 4.Fig.4 Swing hydrofoilsSwing hydrofoils are based on the study of fluid energy capture technology of swinging hydrofoils. Compared with the existing turbine technology based on rotating vanes, the fluid energy capture technology based on swinging hydrofoils has the advantages of less impact on the environment and less noise , Catching efficiency is high and can be used in shallow water and other advantages, but also has a simple structure of the vane, easy processing andhigher catching efficiency, about 4 times the traditional rotary turbines’ cat ching efficiency. 3.2.3 Venturi Structure DeviceThe Venturi structure is a device that utilizes the fluid pressure differential and was invented by the Italian physicist G . B. Venturi. Venturi are tubes that shrink and then expand, and if the turbines are installed properly, they can effectively utilize the marine currents for power generation. But at present only limited to the laboratory research and developmentstage, have not fully put into use. Venturi structure device is shown in Figure 5.Fig.5 Venturi structure device3.2.4 Archimedes SpiralArchimedes spiral work principle is that when the marine current to drive its axis of rotation, the screw on one hand around its own axis of rotation, on the other hand it rolls along the inner surface of the sleeve, then drive the generator to rotate. Each revolution of the screw, the liquid in the sealed cavity is pushed forward by a pitch, and with the continuous rotation of the screw, the liquid spirally presses from one sealed cavity to the other sealedcavity.Fig.6 Archimedes spiralThe Archimedes spiral is shown in Figure 6. Archimedes spiral is a new type of machinery that drives the generator to rotate, which has the advantages of simple structure, safe and reliable operation, easy maintenance and pressure stability. Also due to its use in the sea floor, by the microbialand other complex environment, large efficiency is limited, is still in the further development stage.4. OCEAN'S KITE: A NEW TYPE OF MARINE CURRENT POWOR PLANT4.1 Ocean's Kite Working PrincipleThe main structure of the Ocean's kite is the wings and turbines. Ocean's kites usually use turbines with apower of about 150 to 800 kilowatts. Generally placed in the sea 50 ~ 300 meters below the sea, with a cable connected to the seabed. It can operate at marine currents of about 1 to 2.5 m / s. When power is generated, the Ocean's kite swings from left side to right side. Its movement path is "八" in shape, just as we saw the kite flying in the air.4.2 The Main Structure of Ocean's KitesAt this stage, the Ocean's kite is mainly divided into two kinds of structures. The first structure is the wing and turbine structure. The second is called GEM-Ocean's Kite, invented by Italian scientists (this new structure was recently developed and not yet in actual use).4.2.1 The First Structure: the wings and turbines The first structure of the Ocean's kite , as shown in Figure 7. It is clear that it consists mainly of two parts: the wing and turbines generator. The wings of the kite are about 12 meters long and serve to adjust the direction and provide buoyancy while the turbineserves as a generator. Because seawater density is 800 times that of air, a small turbine mounted on Ocean's kite produces 800 times more energy in the sky. Swedish Minesto company, successfully developed a Ocean's kite, that is the first structure. It can dive in marine currents, and it looks like a child's toy. Minesto calls the latest technology "dark green" and generates 500 kilowatts of energy, even when thesea is calm. Ocean's kite can increase marine current energy to 80%, and Minesto claims that the first scale model of the "dark green" Ocean's kite will bedeployed on the Northern Ireland coast.Fig.7 Minesto company developed "dark green" Ocean's kite4.2.2 The Second Structure ：GEM-Ocean’s Kite The second structure of the Ocean's kite, GEM-Ocean's Kite, was developed by an Italian scientist and "GEM" stands for the Italian word "Generatore Elettrico Marino", which means marine power generator. Compared with the first structure, the overall space occupied is small, and the efficiency is greatly improved after the structure is improved (we will focus on it in the following chapters), so I will introduce this structure in detail .GEM-Ocean'sKite concept CAD model shown in Figure 8.Fig.8 GEM-Ocean's Kite concept CAD modelGEM-Ocean ’s Kite mainly consists of five parts:1） Two turbines 2） Float body 3） V-tail4） Blade’s cover （Diffuser ） 5） Power transmission deviceThe role of the two turbines is to convert marine currents into electrical energy. The main process of power generation is that when a certain flow of marine current flows through the blade in the turbine generator, the turbine rotates to drive the rotor of the generator to rotate in the stator. The rotor of the generator forms a magnetic field by direct current. After the magnetic field rotates in the stator, the magnetic field lines cut the coils in the stator toinduce the potential in the coil. After the potentials of many coils are superposed, a voltage is formed at the generator terminals to supply power to the load. The Float body, like the wings in the first structure, provides the buoyancy needed for a Ocean's kite to keep it working properly in a suspended state. The V-tail enhances the longitudinal stability of the submarine body when it is impacted by marine currents and changes its direction through an adjustable tail to enhance Ocean's kite flexibility. Diffuser blade protective cover is the latest research results of researchers. Its role is to speed up the flow of the marine current through the turbine. Because the power generated by the turbine is proportional to the cubic power of the ocean current, the turbine capacity can be greatly increased and the efficiency of the turbine greatly increased.The function of the power transmission device is to connect the cables and transmit the electric energygenerated by the turbines to the electric energy collecting network distributed on the seafloor so as to realize the collection and transportation of the electricenergy. It is also a very important part.4.3 The Power Generation Efficiency of GEM-Ocean’s KiteDuring the design and development of GEM-Ocean's Kite, the efficiency of power generation has been a key research issue. How to increase the efficiency at the marine current velocity is a problem that researchers have been trying to solve.Based on the GEM-Ocean's Kite CAD model which had built, the number of observations and measurements by researchers included:1) Assuming the symmetrical operating conditions,the left-hand side turbine torque and angular velocity, from which the total output power can be estimated;2) The tension on the cable obtained through theload cell;3) Acquire the state of the entire underwatersystem through the inertial platform. These parameters are sufficient to characterize the overall efficiency and power generation of Ocean ’s kite systems.When marine currents flow, Ocean’s kites are generally affected by three forces: the cable tension force T, the buoyancy B, and the total horizontal force F. GEM system under steady-state conditionsdiagram, shown in Figure 9.Fig.9 Schematic diagram of GEM system understeady-state conditionsWhen the Ocean’s kite is stable, the three forces are balanced, moving the kite in an "八" shape while the turbine generates steady electricity. Research shows that because seawater density is 800 times that of air, a small turbine that uses an underwater kite produces about 800 times the energy of a small turbine in the air.We define efficiency as, its formula is as follows:312p p C V A ρ=（1）In equation (1), P is the power, V is the velocity of the marine current (at steady state), A is the area of the reference surface (coinciding with the area of the turbine disk), andρis the density of the seawater.Taking into account turbine speed and marine current velocity, we defined the rotor tip velocity TSR as a parameter to explore maximum efficiency during the GEM Ocean’s Kite Efficiency Analysis. TSR calculation formula is as follows:R TSR VΩ= （2）In equation (2), Ω is the turbine speed and V is the marine current velocity and R is the nominal turbine disk radius.The relationship between rotor tip speed TSR and generator efficiency prior to GEM-Ocean's Kite (without diffuser) is shown in Figure 10 below. In the experiment, the V-tail is in a vertical state and the ocean current velocity V = 1.5 m / s.As can be seen from the Figure 10, the original GEM-Ocean's Kite in normal operation, the powergeneration efficiency of only about 40% to 50%, is not very satisfactory.Fig.10 Efficiency and TSR function (turbine without diffuser and fine grids, vertical V-tail, V = 1.5 m / s)Taking into account the complex environment of the seafloor and the high operation and maintenance costs under water, GEM-Ocean's Kite before the structure is not improved seems to have little practical value. Therefore, researchers have been working to improve its efficiency and make it more valuable.4.4 GEM-Ocean’s Kite Structure Innovation and ImprovementIn order to get GEM-Ocean's Kite power generation efficiency has been improved, many researchers have tried, in recent years have a relatively large breakthrough. In summary, there are two innovative points that play an important role in enhancing GEM-Ocean's Kite efficiency, as follows:1)Install the turbine blade guard with diffuser structureThe first structural improvement of GEM-Ocean’s Kite, is to install the turbine blade guard with diffuser structure. In the past there was no installation of turbine blade protection device, resulting in easy damage blades, efficiency is not improved. On the other hand, it can form a low pressure area at the exit of the turbine, which is equivalent to letting more marine current flow into the turbine, thus increasing the marine current velocity V, Which in turn increases the power output. From formula (1), we can know that the turbine power generation P is proportional to the cube of the flow velocity V, and a small increase of the flow velocity can greatly improve the power generation P. The GEM-Ocean's Kite with a diffuser-mounted turbine blade guard is shown in Figure 11 (the yellow part is the diffuser shield):Fig.11 GEM-Ocean's Kite with blade guard2)Fine Grids On Blade and Blade’s cover Surfaces The second structural improvement of GEM-Ocean's Kite structure is based on the calculation of fluid mechanics, with fine grids on the inner surface of theblade and boot, as shown in Figure 12.Fig.12 Fine grids on blade and b lade’s cover surfaces Similarly, after hydrodynamic calculations, the addition of fine grids on the inner surfaces of the blades and shrouds also effectively increases the marine current velocity V, thereby increasing the output of electrical energy. At the same time, theincreased fine grid structure can also effectively reduce the impact of high-speed marine currents on Ocean ’s kites, greatly improving the overall stability of GEM-Ocean's Kite. A large number of experimental data show that all aspects of the improvedstructurehavegreatlyimprovedperformance.4.5 Comparison of Power Generation Efficiency Before and After I mprovement of Ocean’s Kites From the pre-retrofit Ocean's kite power efficiency picture, Figure 10, we can see that the original GEM-Ocean's Kite is not very efficient in normal operation and the overall efficiency is only about 40% to 50%. After the structural improvement and installation of the diffuser structure of the turbine blade guard, and use the fine grid structure on blade and the protective cover inner surface, the improved Ocean's kite power efficiency C and the TSRfunctional relationship shown in Figure 13:Fig.13 Efficiency and TSR function (turbine with diffuserand fine grids, vertical V-tail, V = 1.5 m / s)As can be seen from the figure 13, after installing the protective cover of the diffuser structure and adding the fine grids structure to the inner surface of the blade and the protective cover, the steady running (vertical V tail, V = 1.5 m / s) turbine power generation efficiency increased to 60% to 80%,compared to the pre-improvement of the structure efficiency has been greatly improved, greatly enhance the practical value of Ocean's kites . Precisely because GEM-Ocean's Kite has greatly improved in its structure in recent years, it has aroused everyone's attention. I believe in the near future, the ever-improving structure of the Ocean's kite will become the most effective marine current development equipment and more widely used. 4.6 The Advantages and Disadvantages of GEM-Ocean’s KiteThe main advantages of Ocean’s Kites (mainly for GEM-Ocean's Kite) are as follows:1) Under the same marine current velocity, itssteady-state power generation efficiency is very high, reaching 60% ~ 80%;2) With the structural improvement, the requiredstarting flow rate of the turbine is reduced so that the turbine can work in a larger flow rate range, thereby increasing the power generation of the turbine;3) The increased blade guard can protect the bladeto a certain extent and prolong the service life of the turbine.The main disadvantages of Ocean's kites (mainly for GEM-Ocean's Kite) are as follows:1) The blade structure of Ocean's kite requires theuse of high-strength materials to ensure that the turbine can work normally in complex and changing seabed environments;2) Ocean's kites work on the seabed and need toconsider the problem of equipment sealing, which will greatly increase the running cost; 3) The problem of seawater corrosion will placehigher demands on the maintenance of Ocean's kites. Many microorganisms in the seawater canattach to the surface of the turbine, causingdamage to the equipment on the one hand andgreatly reducing the power generation efficiencyof the turbine on the other hand, requiringfrequent maintenance work and increasingoperating costs.5. PROPOSALS FOR THE DEVELOPMENT OF CHINA’S MARINE CURRENT ENERGYThe history of the renewable energy industry in various countries in the world proves that decades of time have to go through from research and development to industrialization and commercialization. Most of the renewable energy technologies are high-tech and require large amounts of capital for development and application. It also has big development and market risk. At the same time, the protection of resources and the environment is the primary goal of renewable energy industry development, which makes these industries face more prominent difficulties than conventional industries in how to adapt to the characteristics of the market economy. Government support is to develop new energy sources and renewable energy industry indispensable basic conditions.According to the characteristics of the marine current resources distribution and the local social characteristics, we can formulate the corresponding plan of marine current resource development. For example, in the southeastern coastal areas, the temperature in summer is high and the time is long. The energy consumption of refrigeration is quite high. If the abundant marine current resources in the area are used for cooling, the contradiction between the shortage of electricity supply in summer in southern China can be drastically alleviated. In the northeast and north China, the pressure of heating in winter is very large. The current heating mode is mainly coal-fired, and the air pollution is very serious, seriously affecting the quality of life of local people. As a high-quality and clean energy, The marine current energy supply is steady, which is the best alternative energy for heating in the north. To this end, make the following suggestions:(1) Increase government funds to support the exploration, development and sustainable utilization of marine current resources. Find out the potential of marine current resources in various areas and conduct scientific evaluation. China has a vast coastline and a huge prospect of marine current resources. However, the degree of investigation and research is relatively low. Only a few provinces and cities have completed the exploration of a small amount of marine current resources. It is very important and necessary to strengthen the exploration of basic marine current resources.(2) Establish a special government fund to support the development of marine current heating projects in the southeastern coastal areas. Support the research of the core technologies of large-scale marine current power generation equipment, such as the research on the advanced design methods of Ocean’s kites and efficient structures, and industrialization so as to facilitate the development, utilization and large-scale popularization and application of marine current energy resources.(3) Strengthen the research on marine current energy exploration technologies and expand the discovery of marine current resource reserves; strengthen the research on technologies to improve the efficiency of marine current energy generation and realize theefficient use of marine current resources and make extensive use of them.(4) Formulate economic incentive policies. The adoption of economic stimulus measures such as finance and finance by the government is one of the key measures to achieve the planning goal. It is also an important policy measure to promote the commercialization of renewable energy technologies and increase market penetration and economic competitiveness. Especially in the early stages of commercialization, government policy support is often a key factor in market development due to the gap between the technology's affordability and government promotion goals. Such as: tax relief policy specializing in the development and utilization of marine current resources enterprises; the implementation of price subsidies to users who reasonably use marine current resources; investment subsidies related to the development and utilization of marine current resources, low-interest loans and credit guarantees, the establishment of venture capital funds, Polluter pays system.(5) Adopt the policy support, financial subsidies, venture capital and other means to build several large-scale group companies that specialize in the development of ocean current in the whole country to promote the development of marine current utilization and gradually promote the development of marine current energy to industrialization and commercialization.6. CONCLUSIONSAs the world economy grows, people's demand for energy is also on the rise. As a new type of renewable green energy, the ocean is extremely rich in reserves. If it can be effectively exploited, the ocean can completely solve the problem of long-term energy shortage in the world. With the continuous depletion of onshore oil and gas resources in recent years, the exploration and development of oil and natural gas have also gradually moved toward the sea and to the deep sea. The oceans can not only take this opportunity to be developed, but also provide convenient and cheap energy for offshore oil and gas development. China has a vast sea area and abundant marine energy resources. Making rational use of this resource can not only promote China's economic development but also effectively protect the environment and eventually achieve social sustainable development.Marine current energy, as a kind of high-quality, high-stability and wide distribution Ocean energy, increasingly gets the focus of scientists. In the future, with the rapid development of high-efficiency equipment that uses marine currents to generate electricity such as Ocean’s kites, the prospect of marine current energy will become broader. REFERENCES[1]夏登文.“十三五”海洋可再生能源开发利用战略研究[M]. 北京：海洋出版社，2017.[2] D. P. Coiro , G.Troise, F. Scherillo, A. De Marco andU. Maisto, Experimental Tests of GEM- Ocean’s Kite,an Innovative Patented Submerged System forMarine Current Energy Production . IECCP,International Conference on Clean Energy Production,June 2011, Napoli, Italy.[3] D. P. Coiro, A. De Marco, F. Scherillo, U. Maisto, R.Familio, G.Troise, Harnessing Marine Current Energywith Tethered Submerged Systems: ExperimentalTests and Numerical Model Analysis of an InnovativeConcept. IECCP, International Conference on Clean。