CHAPTER 1 INTRODUCTION
1.1Motivation
With the improvement of the industrial techniques, our lives become more and more convenient; however, technology advancement leads to high energy consumption by using the fossil fuels, resulting in the tremendous increase of carbon dioxide in ambient. Therefore, our living atmosphere is being deteriorated by the accompanied global warming mainly due to the carbon dioxide emission. This phenomenon is called Greenhouse effect. The principle of its effect is shown in Fig. 1.1. Firstly, the sun emits short-wave ultraviolet radiation passing through the atmosphere to the earth surface. Then the long-wave infrared radiation is reflected from the surface and may be absorbed by greenhouse gases, like carbon dioxide, methane and water vapor. This cause the atmosphere temperature to increase as the greenhouse gas emission intensified continuously due to enhanced industrial development.
The global temperature variation is shown in Fig. 1.2. The criterion of zero degree is an average temperature from 1901 to 2000. About 90%
of energy consumption is from the combustion of fossil fuels, including coal, petroleum and natural gas, which its produces carbon dioxide.
Figure 1.3 shows the annual record of carbon dioxide’s emission from 1959 to 2014. Apparently, the emission is getting higher and higher. In this situation, the traditional energy usage concept has been evaluated and concerned in recent years. Obviously, the target is how to achieve the
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balance between the technical development and environmental protection.
Since scientists have reached a consensus that carbon dioxide emissions from human activities are the major cause of global warming, therefore, it is necessary to replace fossil fuels with renewable energy. Figure 1.4 shows the carbon dioxide emission from different types of power generating systems. It is clearly illustrates that the carbon dioxide emission from fossil fuels is apparently much greater than the one from renewable energy, such as the wind power and solar energy. Although nuclear energy emits very low carbon dioxide during power production as well, its waste would cause damaging impact on the environment that is more severe than the one from emission of greenhouse gases. Moreover, the incident and disaster of 311 Fukushima nuclear power plants in 2011 make the people reconsider the safety of nuclear power. Because of the above reasons, it is worthy to focus on the research of renewable energy.
Moreover, the climate in Taiwan belongs to both tropics and subtropics island climate, which makes good wind condition in advance. Therefore, this study is interesting in the wind energy, which plays an important role in the present Taiwan government energy policy.
In view of the energy supply related to national security and the protection of environment, the development of the renewable energy has been recently emphasized. Taiwan government policy has set that the emission of carbon dioxide down to that at 2005 by 2020, and down to the one of 2000 by 2025. In order to reduce carbon emissions and establish a nuclear-free homeland, the government has announced to popularize the alternative energy, including the policy of “Thousands of
3 planned to install 2120 MW solar panels by 2020 and 6200 MW by 2030.
Due to the support from the government, the technologies of the Development of High-Performance 3kw Hybrid Wind and Solar Integration System”. The background is that although Taiwan has such application and commercialization for such distributed power generation system at an order of 3kW. In this project, the power was generated by installing four Savonius wind turbines in system. With this arrangement,
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the positive interaction between the turbines can occur due to the flow interference; consequently, it enhances the momentum of nearby rotor and so on. As mentioned previously, a pilot plant was proposed to set up, a conceptual design should be carried out in advance that it needs a corresponding numerical simulation to aid to complete the experimental task. This numerical research intends to fit the purpose.
Generally speaking, there are two kinds of wind turbines. One is the horizontal axis wind turbine (HAWT) and the other is the vertical axis wind turbine (VAWT). The difference between the two is the orientation of rotational axis. Normally, the power coefficient of HAWT is ranged from 0.30 to 0.45, whereas the one of VAWT is from 0.15 to 0.30.
Although the power coefficient of HAWT is higher than the one of VAWT, the latter still holds certain advantages against HAWT. First of all, the main advantage is that VAWT can generate electricity in low wind speed.
Second, the installation and construction are simple and cheap. Third, its operation is independent of the wind direction. Moreover, HAWT can cause low-frequency noise at high tip speed ratio, which is a problem that VAWT does not happen. Because of these reasons discussed above, it is worthy to engage in the research of VAWT.
This kind of device belongs to VAWT and drag-typed wind turbine.
The advantages include its low cost with simple construction, wind acceptance from any direction, operation in low wind speed and low operation noise, etc. Its application is suitable in suburban regions, remote districts or even the telecommunication stations.
The reasons to utilize the drag-typed (Savonius) wind turbine in the
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small-scale pilot plant instead of life-typed one are given as follows. The VAWT system can be roughly classified into two categories, the lift-typed and drag-typed wind turbine. The typical drag-typed wind turbine is Savonius (see Fig. 1.5) used in this study, and the lift-typed is the H-type (see Fig. 1.6) wind turbine. Generally, the power coefficient of drag-typed wind turbine is a little bit worse than that of the lift-typed one;
however, its starting torque is so large that it can generate electric power in low wind speed. Therefore, this study adopts Savonius drag-typed wind turbine.
In previous studies, both Feng [1] and Huang s’ [2] works show that each rotor in the parallel system, consisting of three and four two-blade Savonius wind rotors arranged in matrix, can have a higher performance than a single one. The present work will extend their research by considering more parameters, including blades’ thickness, overlap ratio and turbine’s height, for analyzing the difference between H-type and Savonius wind turbines by simulations using the computation fluid dynamics (CFD) software, FLUENT.