The Motivation Behind Renewable Energy Development Environmental Sciences Essay

The demand on electrical energy has been significantly increase due to the technological and economical developments over the world. In the Past 30 years, the global economy has increased by 3.3% yearly. In the same period, the electrical energy demand grew by 3.6%. In 2007, the electrical energy production of the world was 16,429TWh. It is predicted that the world consumption will be 28,930 TWh in 2030. Thus, thousands of new power plants must be built to cope with the required electricity demand. [1]

Non-renewable energy source such as; coal, natural gas, and oil is efficient energy sources due to the ability of produce large amounts of electricity with small amounts. They have been the conventional energy source until now. However, they have many drawbacks such as; the limitation in supply and the concentration of reserves in a few countries; in this manner raising energy security concerns. Moreover, the major source of pollution is a fossil fuel. It estimated that the Power stations account for 32% of NOx and 72% of SO, emissions, which cause environmental issues such as climate change and lead to global warming [2] . In addition, according to [4], “In 2005, the total of greenhouse gases emissions [EEA] was 5177 Mt CO2 – equivalent comprising: 82.5% CO2,8.1% CH4, 8% N2O and 1.4% fluorinated gases. Energy related emissions continue to be dominant, representing approximately 80% of total emissions, particularly in production and transport of energy (Fig. 1.1).” [4]

Figure 1.1: Structure of total greenhouse gas emissions

Source of image: [4]

Thus, governments are considering the ample use of renewable energy sources, as a result of the security of the energy supply and the growth of the global environmental issues. For instants, the UK government goals are to reduce emissions of carbon dioxide to 20% below 1990 levels by2010 and to put the UK on path to reduce carbon dioxide emissions by 60% compared to 2000 levels, by 2050 with real progress by 2020[3]. Such goals cannot be achieved without a deployment of alternative energy sources. Thus, many studies on electrical energy production with renewable have carried out in order to substituted the conventional energy source by renewable energy source

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1.2 Renewable Energy sources:

“The practical definition of renewable energy is a flow of energy, that is not exhausted by being used”[5]. The renewable energy sources like wind, hydroelectric, biomass, solar , tidal waves and geothermal and solar are clean and in large quantities Available in nature. Moreover, they also have the advantage of having low or no emissions of carbons and that means they are environmentally friendly. In addition, renewable resources can be categorized into two main categories: dispatchable and non-dispatchable. Wind, solar and tidal waves are classified as non-dispatchable resources. On the other hand, hydroelectric, biomass and geothermal are classified dispatchable resources. The difference between them is how electric power can be control. Generally, the dispatchable resources have the energy stored and ready at any time to produce power, whereas, the non dispatchable resources naturally uncontrolled input energy which cannot stored be used when needed later. The main drawback of using renewable resources such as wind and solar is their ability to produce power on demand. Moreover, these renewable resources are more variable than fossil fuel plants. Moreover, the uncontrollable input of wind and solar energy is the main causes of the changeability in power output[6]. However, among these energies, wind energy production has rapidly increased in the total electricity production in the last decade as shown in figure (1.2).

Figure 1.2: global wind power capacity (GW)

Source of image: REN21 Renewable 2007 Global Report, WWW.ren21.net

This increasing is encouraged by Kyoto Protocol and supported by European Union (EU) Government such as Germany, Denmark and Spain[7]. According to [8], it is predict that the wind farms will contribute by 12% of total electricity generated in 2020.

1.3 Wind Energy:

It has been reported that the wind power were used to pump water for irrigating crops in the seventeenth century B.C by The Babylonians. In addition a uncomplicated horizontal axis wind turbine was described in the third century B.C by Hero of Alexandria, Moreover, “The earliest recorded English wind turbine is dated at 1191″[9] . However, When the sun heats an earth land, the surrounding air temperature affected by this heating and as a result the wind is caused. According to freris, the world needed of electricity can be met, if 10% of raw wind utilized. Many factor has an effect on wind intensity, such as; altitude, wind speed and location. However, open area, mountain, oceans and specific hill have a good wind a viability trend. In addition, the wind energy can be converted into electrical or mechanical energy is by using wind turbines, which will be discussed next.

1.4 Wind Turbine:

”The most efficient way to convert wind energy into electrical or mechanical energy is offered by wind turbines that operate as a lifting-device” [10] .Generally, wind turbines come in two types, which depend on the direction of their rotational axis.

Horizontal – Axis Wind Turbines (HAWT): have a parallel rotational axis to the direction of the wind and capture kinetic wind energy with a propeller type rotor. in addition, three bladed concept ”Danish” is usually used in this type but there is two bladed design which contribute in the reduction of cost and weight of the turbine.

Vertical – Axis Wind Turbines (VAWT): have a perpendicular rotational axis to the wind stream and use straight or curved bladed (Darrieus type) rotors in order to capture wind from any direction.

Figure (1.3) shows wind turbine configration of the both types. It is clear that they are composed of a generator, a gearbox and a tower. Moreover, the both types have the same ideal efficiency, however, the (VAWT) type is more common [10].

Figure 1.3: wind turbine configration

Source of image: The encyclopaedia of alternative energy and sustainable living

When the wind passing throws the swept area of the blades, it turns and as a result, the shift turns. The rotational energy converted into electrical energy by the generator which produce alternative current (AC). A transformer is used to ensure that the voltage suitable for the distribution system of a grid. The size of wind turbine is the most important factor of the amount of the produced energy . The typical wind turbine size was less than 100 kW, In the early and mid-1980s. Nowadays, capacities up to 3.5 MW turbines are available[11]. Moreover, usually wind turbines is a grouped in the same location to form wind farm.

1.5 wind farms:

“THE FIRST application of wind power generation of electricity was by the Danes in 1890 “[12]. Since that , the development in the wind technology has led to introduce a large on shore wind farm. However, a lack of the suitable onshore sites has an effect on this development and is considered as the main motivation behind the implementation of off shore wind farm. Moreover, the offshore option is based on the higher and constant of the wind speeds which is the main advantage compared to the onshore sits . Figure (1.4) shows that by 2030, the main gain of wind energy is going to be from offshore in Germany[13].

Figure (1.4): the predicted scheme of the capacity of the wind power installed in Germany until 2030

Source of image: [13]

In these conditions one of the most important questions is the transmission concern, i.e. the link of the offshore wind farms to a grid. Generally, wind farm can be connected to AC grid via a high voltage alternative current (HVAC) or a high voltage direct current (HVDC) connection. However, for distance at least 50km far from the AC network[16], many technical problem such as charging current and reduction in the transmitted power make the deployment of HVDC in power transmission for long distance more efficient than HVAC [14] Furthermore, HVDC connection have two main technologies, voltage soured converter (VSC) using IGBTs and line commutated converter (LCC) [15] in addition ,”New types of generators (asynchronous generators, doubly fed induction generators and fully converted synchronous generators) are going to be used and, therewith, replace the classical turbo and salient pole generators”[13]. These generators are have an effect on the power system stability. Moreover , their control is different from the former generator. However, the HVDC link and the generator types and it’s control will be discussed in details in the next chapter.

1.6 the motivation and the plan of this project :

It seems to be that a large offshore wind farm is the best solution for meeting governments renewable energy targets. However, the coordination of the HVDC link and the wind farm a has attracted a lot of attention in the last few years. The aims of this project is to design a HVDC link and a wind farm by using MATLAB simulink software . Due to the complexity of modeling the HVDC link and a wind farm by using complete models of the switching devices, a non switching model of HVDC link using a pharos solution will be considered. This will be done in five stages. In the first stage, the HVDC link with suitable control at wind farm said will be constructed and demonstrated . in the second stage, the HVDC link with suitable control at grid said will be constructed and demonstrated . the both HVDC link in pervious stages will be combining and their action will be demonstrated in the third stage. in the fourth stage, the complete HVDC link will be attached to a phasor model of wind farm in order to demonstrate the operation of the system under different circumstances . in the last stage, a CIGRE 12 bus bench mark model will be constructed in order to demonstrate the system operation under both normal and fault conditions.