Abstract
For the energy shortage in China's coastal areas, which has exerted severe impact on economy development, a growing number of attentions have been paid to ocean energy utilization. In this paper, a review of related researches as well as development of ocean energy in China is given. The main part of this paper is the investigation into ocean energy distribution and technology status of tidal energy, wave energy, and thermal energy, especially that of the tidal energy and wave energy. Finally, some recommendations for the future development of ocean energy in China are also provided. For further research in this field and development of ocean energy utilization in China, this review can be taken as reference.
1. Introduction
China's economy has kept a rapid growth for over 30 years, which, in most cases, means a large amount of energy demands and consumption. In 2001, China accounted for 10% of global energy demand but met 96% of those needs with domestic energy supplies. Nowadays, China's share of global energy use has swelled to over 15% [1, 2]. According to preliminary estimation of 2009, the total electricity consumption reached 3.697 trillion kWh, with an increase of 6.2% from 2008. In addition, before 2020, China's annual GDP will continue to increase at an average rate of 8%. Therefore, China's energy requirement will be rising in the near future with its economy development [3, 4].
China's modern tidal energy development and utilization have experienced three periods so far. The fact is that tidal energy stations growing up in Fujian and Guangzhou in 1955 mark the beginning of development of tidal energy technology, then it gradually turns to the construction period, and now it is the period of improvement and consolidation. China wave energy research rose from Shanghai in 1978, was originally learned from Japan pneumatic principle, and developed a 1 kW air turbine wave energy buoy [5–7]. The 1 kW air turbine wave energy buoy was tested and put into operation in the area of Zhoushan Islands in Zhejiang province, but due to the lack of testing means the exact data was not measured.
In addition, thermal energy and salinity are also discussed in this paper, and some recommendations for the future development of China are provided.
2. Tidal Energy Technology
The long coastline of China contains a large quantity of tidal energy, which is estimated to be 110 MW. Tidal energy is caused by flood and ebb tide, principle of which is similar to that of hydroelectric generation. Tidal energy can be extracted by building a dam (barrage) across an estuary or coastal inlet, with the dam containing turbines to generate electricity.
As has been mentioned above, China's modern tidal energy development and utilization have experienced three periods. The first period started around the year 1958. It is in Shun De County, Guangdong province, that small tidal energy station first appeared, and it soon spread across Zhejiang, Shandong, Jiangsu, Shanghai, Fujian, Liaoning, and other provinces [8]. Up to 1958's national tidal energy conference held by the Chinese Academy of Sciences and the Ministry of Electricity and Water in Shanghai, there had been 44 small tidal energy stations built, such as Da Liang tidal energy station in Guangdong province, but most of the stations were with a small capacity ranging from 5 KW to 144 KW. Besides, there are only two energy stations keeping long-term operation for energy generation, including Sand Hill Energy Station which is in Wen-ling County in Zhejiang province and Chou dong Energy Station located in Chang-le County in Hunan province [9].
In 1970s, came the second period. Construction of tidal energy stations appeared in the coastal area of China, with a total number of more than 20, such as Jin-gang in Shandong province Chen-gang Station [10, 11]. The tidal energy stations in the second period were greatly improved: larger in scale, more standard, and more rigorous in design, operation, and equipments. Most stations possessed an installed capacity ranging from 100 kW to 200 kW, for example, Jiang-xia Tidal Yest Station in Zhejiang province and Bai-Shakou Station in Shandong province, which were constructed by the state and had a larger scale and more regular operation, with a total installed capacity of 320 kW and 960 kW, respectively. During this period, researches on tide resource were conducted in Yue-qing Bay, Zhejiang province, for planning programming, and, finally, four development plans were proposed. Jiang-xia Tidal Test Station is the implementation of the scheme of minimum [12, 13]. Apart from Jiang-xia Station and Bai-Shakou Station, there are other stations keeping long-term running, such as Hai-Shan Station, Yue-pu Station of Zhejiang province, Liu-he Station of Jiangsu province, Gan-zhu Beach Station of Guangdong province, and Guo-Zishan of Guangxi.
Jiangxia pilot tidal power plant (see Figure 1), located in the north end of Yueqing Bay, is the most remarkable one of the three plants, and the other two are La Rance tidal power plant in France and Annapolis tidal generating station in Canada. Jiangxia pilot tidal power plant's construction was started in the year 1974 and completed in 1985, and the plant was installed with one set generator of 500 kW, one set of 600 kW, and three sets of 700 kW, with a total capacity of 3.2 MW [14]. The engineering staff of Jiangxia plant were investigated into industrialization research of tidal generating for many years; remarkable achievements in reliability of the generator sets were gained, such as reservoir sediments reducing, erosion protecting, floating method, operating automation, and optimal scheduling.
Jiangxia pilot tidal plant.
The third period is from the late 1970s to the 1990s. This period is to improve, consolidate, and steadily move forward. Main focus is on the following aspects [14, 15].
Carrying out the investigation and evaluation of tidal energy resources. In the early 1980s, under the leadership of the Ministry of Water, the second national coastal tidal energy resources survey was completed by the water conservancy departments in coastal provinces and cities. In the late 1980s, under the leadership of the State Oceanic Administration and the Ministry of Electricity and Water, the relevant units of the two systems completed the planning of ocean energy resources in the coastal rural areas and regional planning, including the development of installed capacity from 200 to 1000 kW.
The energy plants such as River Tidal test energy stations, Baishakou, and Haishan tidal energy stations have been built.
Building of new energy plants. In 1989, on the basis of Pingtan County tideland reclamation project, Xingfuyang tidal test energy plant with a capacity of 320 kW was built in Fujian province.
Preparation for medium-sized tidal energy plant construction. From the beginning of the 1980s, under the circumstance of rapid national economy construction, the obvious conflicts between energy supply and demand and the great situation of the national call to vigorously develop new energy, leading departments and coastal provinces, especially Zhejiang and Fujian province, to carry out many preliminary surveys on the tidal energy plant construction and plan feasibility. For example, Zhejiang province did an examination on Yueqing Bay, Xiangshan Port, Jiantiaogang tidal energy station dam; the marine group of the State Science and Technology Commission did an examination on the million-kW tidal energy plant in coastal areas of Zhejiang and Fujian; and feasibility study of Bachimen, Dagongban, Jiantiaogang tidal energy plant, and so forth.
Since June 2009, the automation and safety of plant have been improved after technology upgrading. In the National Nature Development and Reform Commission (NDRC) of Medium and Long-Term Development Plan for Renewable Energy in China, there was a target that 100,000 kW tidal power stations would be built by 2020 [16–18]. For the realization of this goal, a series of preliminary work has been completed. The feasibility study of a 10 MW intermediate experimental tidal power station in Jiantiao Port of Zhejiang province and Daguanban Port of Fujian province has been conducted. And the planning of the Maluanwan Tidal Power Plant is under way [19].
3. Wave Energy Technology
Wave energy, that is, the kinetic energy and potential energy in waves, is proportional to square of wave's height and period of motion and is unstable. Wave energy can be used in water drawing, heat supply, seawater desalination hydrogen production, and so forth.
At the beginning of 1970s, the wave energy research activities expanded from Shanghai to Guangzhou, Beijing, Dalian, Qingdao, Tianjin, and Nanjing [9, 12]. There were a dozen units engaged in wave energy research. 1 kW wave energy buoy was successfully developed in 1975 and the test was completed in Shengshan Island, Zhejiang (as shown in Figure 2).
1 kW wave energy buoy in Shengshan Island, Zhejiang.
After nearly 30 year's research and development, the wave energy technology has gained rapid development. Pneumatic beacon lights floating microwave energy device was the first achievement and already put into commercial production. Now there are more than 600 aids to navigation in the north and south coast, and electricity supply was solved by floating microwave energy devices. Elbow buoy wave energy device, developed in cooperation with Japan, has been exported to foreign countries, and the technology is in the international leading level. In 1990, the Institute of Energy in Guangzhou did a research on successful generation test of a 3 kW shore wave energy plant in the Pearl River Estuary Dawanshan Island [20]. In 1996, the successful construction of 20 kW shore-type wave energy experimental energy station, 5 kW wave energy boat, and then the 100 kW shore wave force experimental energy station were accomplished in Shanwei, Guangdong province.
During the 10th Five-Year Plan period, with the support of the national “863” project and the Chinese Academy of Sciences Innovation directional project, the Chinese Academy of Sciences in Guangzhou Institute of Energy did a study on the independence and stability of the wave energy generation system. On January 9, 2005, the first low-energy test under real sea condition in Shanwei wave energy station proved wave energy generation system to be good in independence [21]. According to the test results, expected results of impact resistance, stability, and energy generation have been achieved by the wave energy generation system, which consists of three parts: independent energy system, fresh water, and floating charging system. An independent wave energy supply system, with a total installed capacity of 50 kW and the maximum wave peak energy of 400 kW, was developed in Zhelang Town, Shanwei City. However, after a 29 h typhoon, the device was wrecked by giant waves.
China's wave energy generation system still remains in 10–102 kW level, and the long-term goal by 2020 is 102–103 kW level. According to the current technology development, China's wave energy development can step into the demonstration operation stage, but commercializing is difficult to be realized in the near future. For the next stage, building of 102 kW devices and problems of costs, efficiency, and reliability are of priorities. By 2020, an MW level wave power plant farm will be constructed and connected to the grid [22].
In short, research on wave energy in China has a short history, but with the support of the “863” planning and the development of science and technology, it develops rapidly [20, 23, 24]. Microwave energy generation technology has gained maturation and commercialization. The small-shore wave energy technology has gone forward to the international market. However, the scale of the wave energy device demonstration test in China is much smaller than that in Norway and the United Kingdom, and the type of test development approach is far less than that of Japan. The small device is far from being put into practice, and its running stability and reliability remain to be further improved.
4. Thermal Energy Generation Technology
The temperature difference between warm surface ocean water and cold deep ocean water leads to the formation of thermal energy. As a result of heating effect of solar radiation, temperature difference in most tropical and subtropical oceans can reach 20°C or more. For utilizing the temperature difference, the Ocean Thermal Energy Conversion (OTEC) technique is adopted to make a thermodynamic cycle through heat engine to produce power.
In China, thermal energy generation technology began in the early 1980s, and the research was carried out in Guangzhou, Qingdao, Tianjin, and so forth [14]. In 1986, the thermal energy conversion test analog devices were completed in Guangzhou. In 1985, Guangzhou Institute of Energy Conversion made a study on open-cycle ocean thermal energy conversion by using a method called droplet elevating cycle, which increased potential energy of the seawater and density of thermal energy and reduced the size of the system. It is estimated that seawater will be elevated to a height of 125 m by releasing heat and driving the turbine when its temperature decreases from 20°C to 7°C [24].
Since 1980, Taiwan has carried out a research on the ocean thermal energy resources in the east coast of Taiwan island and an evaluation and program design of the natural environmental conditions of Hualien County Heping river, Shihtiping, and Taitung County Zhangyuan and also gave a plan of constructing a 40,000 kW demonstration energy plant in 1995 [25].
Another promising way to utilize thermal energy is Seawater-source Heat Pump (SWHP) technology. The first plant adopting SWHP system in China is Qingdao Power Plant in November, 2004 [26]. It is proved that the cost of winter heating by using SWHP is much lower than that of coal heating, which are 15 CNY/m2 and 25 CNY/m2, respectively. Therefore, air conditioning in Olympic Sailing Venue in Qingdao adopts this system.
5. Marine Salinity Gradient Energy Technology
Salinity gradient energy, the potential chemical electrical energy caused by difference in salt concentration between seawater and fresh water or between seawaters with different salt concentrations, mainly exists in the area where river meets the sea. Usually the potential chemical electrical between seawater (35% salinity) and fresh water has an energy density of 240 m water head, which can directly drive the turbine to produce power [13].
It is calculated that the total amount of salinity gradient energy resource along China's coast can reach 3.58 × 1015 kJ, but the distribution is uneven. It is relatively scarce in northern China, while that in the southern region of Yangtze River accounts for 92.5% of the total amount [14, 27], especially in the estuaries of Yangtze River and Pearl River. Shanghai and Guangzhou are located in the estuaries of Yangtze River and Pearl River respectively, and those two areas are the most developed in economy and with large energy consumption.
In 1980s, research on salinity gradient energy generation and semipermeable membrane in China began, and laboratory device of Salt Lake concentration energy generation was successfully developed in 1985 in Xi'an. In the test, the solvent (water) to the solution (brine), penetrating the water column of the solution increased to 10 m hydrogenerating unit generating energy from 0.9 to 1.2 W. Obviously, salinity gradient energy generation research in China is still at the preliminary stage of the laboratory principle.
Xi'an University of Architecture and Technology made an experimental research on elevated tank system in 1985. The upper tank in the experiment was about 10 m above the permeator and 30 kg dry salt was used for a work of 8–14 h and to generate 0.9–1.2 W electricity. Unless the permeation flux was improved by one order of magnitude and the seawater could be used without pretreatment, the technology of osmotic energy development would be commercialized [14].
Although marine salinity gradient energy exploitation is simple in principle, lots of difficulties remain to be solved to achieve commercialization and industrialization. Some experts reckon that commercial exploitation of salinity gradient energy is difficult to realize, investment would be unadvisable, and the environment impact should also be taken into consideration under present conditions of technology and process. Therefore, after some theoretical researches and putting forward of energy conversion devices, few further research on it are made in China [28].
6. Ocean Current Energy Technology
Ocean current energy is the kinetic energy of flowing seawater, mainly caused by the relatively steady ocean flow in strait or channel and the regular tides current flow. The power of current is in proportion to velocity cubed and flux. Therefore, the higher the speed, the more powerful the current.
From the Bohai Sea to the South China Sea, distribution of ocean current energy resources is uneven. Current velocity in most areas of Bohai Sea is less than 0.77 m/s, except for water channels in Bohai Strait, among which the highest speed can reach 2.5 m/s. Current velocity in the Yellow Sea coast is larger than that of 0.5–1.0 m/s in Bohai Sea.
Ocean current energy technology in China can be traced back to 1978. At the year of 1987, He Shijun, from Dinghai, Zhejiang, made a tidal current conversion testing device and harnessed 5.7 kW electricity at a velocity of 3 m/s in Xihoumen channel. In January 2002, the first floating moored tidal current turbine in China was built by Harbin Engineering University, and installed (WanXiang I) in Guishan channel (Daishan, Zhejiang), as shown in Figure 3. The “WanXiang I” consists of two vertical axis rotors, driven systems, control mechanism, and floating platform, and every 2.2 m diameter rotor is composed of four vertical blades with variable pitches.
The tidal current pilot plant in Guishan channel.
In 2009, a project of National Key Technology R&D Program (NKTRDP), research and demonstration of 150 kW tidal current power station technology was launched, which aims to test the prototype turbine and to demonstrate technology and will be finished in 2014.
7. Suggestions
With years of development, ocean energy harnessing technology has gained maturity. In terms of technical maturity, tidal power generation technology is the most mature one, but it may cause possible environmental impacts. Therefore, careful consideration should be taken in its development. For the short term, China's ocean energy development mainly focuses on tidal power generation and construction of 10 MW-level tidal power plant. At present, technical problems of reducing costs in devices and improvement of reliability should be the point disscussed. In the near future, construction of hundreds of kW level demonstration generation devices and accumulating experience for commercialization should be the task. For this, the following measures should be taken.
Increasing financial support in science and technology. Social forces and nongovernment capital must be introduced into researches on ocean energy development as well as investment in national science and technology development planning.
Establishing a strategic position for ocean renewable energy, incorporating it into national planning and improving its development by preferential policies and economic means of tax cuts, feed-in tariff, and so forth.
Making efforts to its industrialization and commercialization, seeking a combination of low cost and large-scale development to improve economic returns and market competitiveness.
It is predicted that China's energy demands will increase year by year, and the total energy consumption in 2050 will be 3 times as much as that in 2000. Such a huge demand cannot be satisfied by conventional energy and we must make full use of ocean energy, and gradually reverse the energy structure and the structure of electricity supply. Only in this way coordination of China's energy, economy, and environment can be accomplished.
8. Conclusions
In this review, different types of ocean energy and related technologies in China are introduced and evaluated. Ocean renewable energy faces a good opportunity for development and China has offered a favorable environment, especially for the tidal energy and wave energy, so there is much reason to believe that ocean energy will get greater development in the future and contribute more to national economy.
However, to realize the commercialization of ocean energy is not an easy work. Many inventions still need to be made, and many challenging problems remain to be solved. In general, cooperation of research institutions in ocean energy technology and collaboration between governments should be strengthened to remove difficulties, reduce cost, and improve ocean energy utilization rate.
Footnotes
Acknowledgment
This research was supported by Science Technology Department of Jinxing State (no. 2013AY21034).