2021年3月15日，习近平总书记主持召开中央财经委员会第九次会议并发表重要讲话强调，实现碳达峰、碳中和是一场广泛而深刻的经济社会系统性变革，要把碳达峰、碳中和纳入生态文明建设整体布局，拿出抓铁有痕的劲头，如期实现2030年前碳达峰、2060年前碳中和的目标。“十四五”时期是碳达峰的关键期，大力发展清洁可再生能源成为必然趋势。在海洋这片“蓝色沃土”中，蕴藏着丰富的可再生能源——海洋能，“碳达峰、碳中和”将为海洋能发展带来怎样的机遇与挑战？围绕海洋能的发展，《科技导报》专访了中国可再生能源学会海洋能专业委员会主任、浙江大学教授李伟。

The renewable marine energy provides a solution to the shortage of fossil fuels and the global warming issues. And it serves as an important foundation for the development of the deep sea, the island, and the national defense. Among the various types of the marine energies, the wave energy enjoys its advantages of good quality, easy utilization, high energy flux density, and wide distribution. The wave energy is widely studied and applied. The wave energy device is now a quite mature technology, with diverse forms. In this review of the research development of the marine wave energy, the wave energy devices are classified, and the current research status and development of wave energy are summarized and evaluated. The working principle, the technology, the engineering examples and the development trend of the wave energy utilization devices are analyzed. It is shown that the technique of the wave energy devices has not yet reached the mature state. A device with high efficiency, stability and maintainability is the prime aim. In the development of the wave energy devices, the commercial development on the basis of a large-scale and arrayed layout should be a focus.

Energy is the lifeblood of the technological and economic development. Fossil energy, such as coal, oil and natural gas, has long been the main source of energy for mankind. Although it promotes human progress, it brings about many problems. The ocean contains abundant renewable energy which is inexhaustible. Making full use of the marine energy is an important way for mankind to achieve the sustainable development. This paper designs a novel integrated equipment for generation of the offshore wind power and the ocean wave energy. The equipment can convert these two kinds of random and unstable energies into regular and stable electricity through the hydraulic energy transmission. An integrated generation farm including five units of equipment is established. Through the numerical calculations and the partial experiments, the output of the equipment and the farm is 17 MW and 91 MW, respectively.

The waves contain a enormous energy for exploitation and also invove great forces for destruction. A seesaw-type wave energy converter is proposed for exploitation of the huge energy, with a double-pontoon floater structure, and a vertical damping plate underwater. Waves drive the floater to produce a roll motion, and the relative rotation motion of the floater and the underwater damping plate is used to generate electricity. The structure is simple and reliable. The ANSYS-AQWA hydrodynamic analysis software is used to numerically calculate the power generation performances of the standard module, the large-area modules and the multi-body arrays. It is shown that with the linear wave of 6.28 s in period and 2 m in wave height, the seesaw device generates a power over one hundreds of watts per square meter, and could be adopted in many applications.

In the complex marine environment, there are some nonlinear phenomena such as the wave impinge on the front of the oscillationg buoy wave energy device, the wave run-up and overtopping during the interaction between the wave and the oscillating buoy, with negative effects on the safety and the working performance of the wave energy device. In this paper, the physical model tests are designed and conducted to investigate the wave run-up characteristics of the buoy on the wave-facing side, and the effects of the wave period, the value of constant PTO damping and the buoy motion amplitude on the wave run-up are discussed. Studies show that when the wave period is large and the PTO damping is small, it is beneficial to reduce the wave run-up amplitude on the wave-facing side of the buoy. When the wave period is small, the variation of the PTO damping has a very small effect on the wave run-up amplitude, while the run-up values are significantly affected by the amplitude of the heave motion.

When an array of oscillating buoy wave energy converters is deployed in front of the breakwater, there will be complex hydrodynamic interactions between the buoy absorbers of each converter. This interaction can affect the buoys' motion and the corresponding power generation properties. In this paper, physical experiments are carried out in the wave tank to investigate the hydrodynamic characteristics of an array of oscillating buoy wave energy converters in front of the breakwater. The effects of the buoys' dimension and spacing on the motion and the power generation of each device are analyzed under different wave conditions. It is found that the wave energy converter with a smaller buoy has a higher power generation capability in the considered cases. A smaller spacing arrangement may not lead to a larger power. The incident wave height has a significant effect on the power generation.

To optimize the energy capture efficiency of the oscillating buoy wave energy converter, the effect of the bottom shape of the cylindrical buoy on the energy capture is studied. The commonly used oscillating buoys with the flat bottom, the cone bottom, and the hemispheric bottom are selected for comparison. Firstly, the frequency-domain model of the buoy motion is established. Then, the hydrodynamic parameters of these three buoy types, such as the added mass, the radiation damping, the wave excitation force, and the response amplitude operator, are calculated by ANSYS-AQWA software and compared. Finally, the resistive control is put into the frequency-domain motion model to investigate the energy capture efficiency of the buoys of different bottom shapes under the wave excitation. The results show that the resistive control could significantly improve the energy capture efficiency of the buoys. The hemispherical bottom buoy has a higher energy capture efficiency under wider wave spectrum conditions, while the flat bottom buoy is more suitable when the wave spectrum peak frequency is close to its natural frequency and the wave spectrum is narrow.

The prediction technologies of the power generation from the wave energy converters (WEC) are an urgent and crucial problem in the renewable energy planning, the power grid dispatching and the economic operation. Besides the statistical modelling, this paper presents a novel hybrid DDM for very short term (15 min-4 h) and short term (0-72 h) predictions of the wave energy power, based on the long-short term memory (LSTM) network and the results are compared with those obtained by the Artificial neural networks (ANN) and the support vector machine. The experimental results indicate that the proposed deep learning models enjoy a better performance with a high accuracy in the WEC power prediction than other related models. Furthermore, the proposed DDM methods are shown to be robust and timesaving in training and deployment, with advantages over the statistical methods in very short term and short term WEC power predictions.

The energy and fresh water resources restrain the development of the hydrogen production by the electrolysis of the water. The production of the fresh water and the hydrogen by using the ocean energy can best use the marine resources. An integrated system is proposed for generating the fresh water and the hydrogen from the tidal current energy to meet the daily requirement of the fresh water and also the demand of the hydrogen produced from the water by the electrolysis. A simulation model is established to verify the feasibility of the system. The control strategy of the power generation equipment and the operation mode for high efficiency is discussed. The simulation results of a 60 kW tidal current power generator integrated with the reverse-osmosis units and the electrolyzers show that the system enjoys a good stability and can theoretically produce about 90 tons of the fresh water and about 55 Nm³ of the hydrogen per day.

This paper studies the influence of the array arrangement of the tidal farm on the power generation, by considering different row and column spacing combinations. Based on the Delft3D-Flow module, a hydrodynamic model of the Zhaitang Island's waters is established, the site of the tidal farm is selected according to the annual average TSE index distribution, and the vertical placement is determined according to the tidal current characteristics of the Zhaitang Island's waters and the EMEC standards. And through the comparative study of 25 different arrangements, it is shown that within a certain range, the increase of the row and column spacing will reduce the total power of the array, and the changes gradually tend to be flatened.

This paper investigates a low-speed direct-driven small generator for the marine energy under the ocean conditions in China. The final dimensions of the generator are determined by analyzing and optimizing the key parameters, such as the length-diameter ratio, the air-gap length and the inner stator diameter. Then the characteristics of the cogging torque and the varying speed and loads are calculated by the 2D FEM and the analytical formulas to analyze the running performance. Further, a prototype is fabricated and the manufacturing test is conducted to validate the design. The experimental results show that the designed generator can meet the requirements of the rated output power 200 W, and enjoys a good performance under the conditions of the varying speed and loads. This research may serve as a reference for designing and controlling the low-speed direct-driven generators for the marine energy.

In the new type thermodynamic cycle for the ocean thermal energy conversion system, the Guohai cycle, a lean ammonia solution and the steam extraction of the turbine heat recovery branch on the basis of the Kalina cycle are adopted in order to increase the thermodynamic efficiency. This paper applies the principle of the energy conservation and the equation of the heat balance to calculate the efficiency of the Guohai cycle under different steam pressures at the turbine inlet, in warm and cold water temperatures, and with various concentrations of the working fluid. The results show that the concentration of the ammonia and water mixture has a significant effect on the efficiency. When the temperatures of the cold and warm source are fixed, there is an optimal concentration of the ammonia and water mixture, with a higher cycle efficiency. If the temperatures of the surface warm water and the deep cold water are 26 and 5℃, respectively, the maximum efficiency of the system is 4.56% as the concentration of the ammonia and water is 92%. The cycle efficiency first increases and then decreases with the increase of the steam pressure at the turbine inlet, with a maximum value in-between. The deep cold water temperature has an influence on the cycle efficiency, while that of the surface warm water has little effect on the cycle efficiency.

In view of the the low efficiency of the ocean thermal energy conversion(OTEC), this paper makes a theoretical analysis of the Rankine cycle based on the first law and the second law of thermodynamics, and a mathematical model for the individual equipment of the cycle is built. Through the calculations of the cycle thermal efficiency and the net power output, the variations of the thermal efficiency and the net power output against the turbine inlet pressure, the superheat and the condensation temperature are obtained. A 15 kW ocean thermal energy conversion system with the Rankine cycle is constructed and tested, and the variations of the thermal efficiency against various parameters under the simulated working conditions of the ocean temperature difference are obtained through analyzing the experiment results. The consistency between the theoretical calculations and the experimental results is verified.

In order to improve the cycle efficiency of the ocean thermal energy conversion (OTEC), the performance of a radial inflow turbine is studied. Based on the 1-D thermodynamic design of the turbine with the main parameters determined by experience and modified by a genetic algorithm, an aerodynamic model of the turbine is built through the 3-D design of the volute, the nozzle and the impeller. The performance of the turbine under the design condition is studied by the computational fluid dynamics (CFD) and the numerical results show that the turbine efficiency is 86.5%. Finally, it is shown that the turbine has a good performance when the nozzle-impeller relative radial clearance is 0.04 and the nozzle stagger installation is about 37°. Therefore, the nozzle-impeller radial clearance and the nozzle installation angle can be fine-adjusted to obtain a higher turbine efficiency under the design condition; and under the non-design conditions. An adjustable nozzle mechanism can be used under the off-design conditions to put the turbine in a good working state under various working conditions.