4. Wind energy

Wind energy is the indirect form of solar energy which is always being replenished by the sun [4]. The energy conversion occurs when electrical power or electricity is generated using the abundant natural resource wind. A wind turbine is an energy conversion device that changes the wind's kinetic energy into electrical energy. The operation of wind turbines makes use of the turning of two or three propeller-like blades around a rotor by wind. The rotor is attached to the main shaft, Modeling and Simulation of a 10 kW Wind Energy in the Coastal Area of Southern Nigeria… DOI: http://dx.doi.org/10.5772/intechopen.85064

which turns a generator to create electricity [5]. The quantitative measurement of accessible wind energy at any point is called the wind power density (WPD). It is calculated as available mean power per square meter of area swept by a turbine with SI unit of watt per square meter. This indicates how much extractable energy on site.

Wind turbines are fabricated in two axis types (vertical and horizontal) and in a wide variety. The smallest types of wind turbines are used as a means of charging battery units used for generation of back-up power. Larger turbines are used to generate power for domestic use. Wind power can be classified as:


#### 4.1 Wind energy in Nigeria

capacity to power entire countries. With wind energy however, developing offshore wind turbines fit for tackling the substantially higher wind speeds accessible offshore while avoiding the issues of horizon and noise pollution is the way to go. In Ogoja community of southern Nigeria, the average wind speed is seen in this research to be good enough for a horizontal axis wind turbine using a Squirrel Cage Induction Generator due to its seeming advantages as detailed in later sections.

Natural gas is being used in gas turbines as a means of power generation in most countries, majority of which are in Africa. The effects of these fuels in the atmosphere led to the need for green energy, a clean and sustainable alternate source of energy generation. Different countries are facing devastating effects from the climate change, stormy rain, hurricane, great flood, etc., leading to different countries conducting research in renewable energy sources which will produce power without damaging the environment. Wind energy is abundant on the Earth and has a low or no impact in environmental pollution. The energy is generated naturally from wind; hence fuel needed for wind turbines is free and occurs every day. This study shows a wind energy system modeled and runs at various wind speeds,

The aim of the project is to design with the aid of mathematical modeling a wind energy conversion system that will produce energy at varying speed and test results

• Model a wind energy conversion system by using mathematical equations.

• Simulate the system design using MATLAB SIMULINK Software, version

• Simulate the aerodynamic, mechanical and electrical component design.

Wind energy is the indirect form of solar energy which is always being replenished by the sun [4]. The energy conversion occurs when electrical power or electricity is generated using the abundant natural resource wind. A wind turbine is an energy conversion device that changes the wind's kinetic energy into electrical energy. The operation of wind turbines makes use of the turning of two or three propeller-like blades around a rotor by wind. The rotor is attached to the main shaft,

Modern offshore wind energy systems are now faced with expectations of generating highly efficient, network frequency electricity in an autonomous and programmed manner and for 20 or more years consistently and continuously with little or no maintenance requirements in some of the harshest environments in the world. This constitutes the challenges encountered by wind energy engineers

similar to wind speeds found in some parts of the world.

using simulations. The following are the objectives:

• Test to see the effects of varying wind speeds.

3. Aim and objectives of study

R2017a.

4. Wind energy

46

today [2].

2. Problem statement

Wind Solar Hybrid Renewable Energy System

Wind energy is of course, one of the cheapest renewable sources per unit of energy produced, as well its technologies is one of the fastest rising technologies in energy generation industry across the world, yet not so much in Nigeria and Sub-Saharan Africa. It has been suggested that a network of land based 2.5 MW wind turbines can generate over 40 times the current electricity consumption in the world [5]. In Nigeria, renewable energy sources have been restricted to solar energy this is because wind energy is not considered viable due to low wind speeds in most parts of the country. Wind speed is generally considered moderate in the south with the exception of coastal areas and offshore. On the other hand, in the hilly regions of the north, it is strongest [6].

An analysis of wind energy potential in Kano State, Nigeria was done by [7], based on wind data taken for 21 years at a height of 10 m. The data was statistically tested using Weibull probability density function. Results showed an expected average wind speed ranging from 6.5 to 9 m/s, good enough to drive a wind conversion system with wind power estimations as high as 12 MWh/m<sup>2</sup> . Five practical wind turbines where also analyzed with the data, giving positive results and economic viability of wind power in Kano State. Refs. [8, 9] noted the viability of renewable energy in Nigeria, the advantages and challenges and as well stated that the high cost of power supply and carbon emission reduction could be realized with the use of renewable sources energy.

In another article on wind energy potential in selected south western states, the investigation surveyed wind energy capability often chosen sites in the south western region of Nigeria and carried out a cost benefit analysis at those sites. Wind speed data at 10 m height gotten from the Nigerian Meteorological Agency was utilized to classify the sites wind profiles for electricity generation. The result demonstrated that sites in Lagos and Oyo States were suited for generation at a substantial scale with average wind speeds. Enough power can be generated with several small turbines connected together. The result demonstrated that the region's wind profiles and qualities are reasonable enough for wind power generation. Average wind speeds from 1.9 to 5.3 m/s are predominant, while the most likely wind speed ranged between 1.9 and 6.2 m/s, with the maximum energy conveying speeds between 2.2 and 8.6 m/s across all the stations [7].

Ref. [10, 11] conducted a research and reported on the wind energy reserve in Nigeria at 10 m (or 40 m) height based on data analysis on 10 wind stations across the North West, North East, North Central, South East and South West geopolitical zones. The research showed some promise, with some sites having wind regime between 3.6 and 5.1 m/s, therefore confirming that Nigeria falls into the moderate wind regime according to the Beaufort scale. Along these lines it can be inferred that the sites are potential wind farm areas. This is because most wind turbines start generating electricity at wind speeds of around 3–4 m/s, known in wind generation as the cut in speed. The report also suggested that Nigerian shoreline areas from Lagos State through Ondo, Delta, Rivers, Bayelsa to Akwa-Ibom States also showed promising potentials for harvesting moderate wind energy throughout the year. Coastal regions constitute majority of oil and gas activities in the country, with these activities causing environmental degradation while some of these communities are also cut off from the electricity grid hence leading to a quest for alternate energy sources.

of enough energy to drive an electrical generator [14]. Most HAWTs are either two or three blades, but the number of blades has no limit, it depends solely on the designer. HAWT could also be classified as upwind and downwind turbine. In Ref. [15] it is stated that a gear system is used for stepping up the speed of the generator, although designs may likewise utilize an annular generator. Some designs operate at fixed speed, but variable speed turbines have better efficiency and employ a power converter to communicate with the transmission system. All turbines come with protective lineaments for damage limitation during turbulence. In such turbulence the system is also controlled by feathering the blades into the wind hence stalling

Modeling and Simulation of a 10 kW Wind Energy in the Coastal Area of Southern Nigeria…

The main rotor shaft of this type of turbines are arranged vertically, hence the name. The major advantage of this arrangement is the turbine does not need to follow the direction of the wind to exhibit high efficiency, which is advantageous in sites with highly variable wind directions. Also advantageous is its ability to be mounted on a building because it is much less steerable. The drivetrain and electrical machine can also be positioned close to the ground with the aid of a direct drive from the rotor arrangement to the ground-based gearbox, enhancing availability for repairs. Energy efficiency over time is still poor, a severe drawback. Key disadvantages also include the relatively low rotational speed with the consequence being increased torque with a proportional increase in cost of the drive train, reduced power coefficient, pulsating mechanical torque, and modeling difficulties for accurate wind flow studies leading

The conservation of mass demands that the measure of air in and out of a turbine must be equivalent. Consequently, Betz's Law defines maximum achievable wind power drawn by a wind turbine as 16/27 (59.3%) of the aggregate kinetic energy of the air entering the turbine. The best hypothetical power yield of a wind turbine is therefore 16/27 times the kinetic energy of the air entering the turbine

� <sup>ρ</sup> � <sup>v</sup><sup>3</sup> � <sup>A</sup> <sup>¼</sup> <sup>8</sup>

27

� <sup>ρ</sup> � <sup>v</sup><sup>3</sup> � <sup>A</sup> (1)

them, and brought to a halt with the aid of brakes (Figure 1).

to issues of rotors design analyses prior to fabrication [16].

6. Efficiency of the wind turbine system

<sup>P</sup> <sup>¼</sup> <sup>16</sup> 27 � 1 2

effective area (Figure 2).

49

5.2 Vertical axis wind turbine (VAWT)

Figure 1.

A horizontal axis wind turbines [30].

DOI: http://dx.doi.org/10.5772/intechopen.85064

#### 4.2 History of wind energy for wind farms

Arrays of large turbines, called wind farms, are utilized to generate power as a means of reducing fossil power generation in developed countries. By the start of the twentieth century in Denmark, there were already in subsistence some 2500 windmills used to drive mechanical loads like grinding mills and water pumps with an estimated total peak power in the region of 30 MW. By 1910 there were electric generators ranging in power from 5 to 25 kW driven by wind and in use in the United States. During World War I, windmill engineers in the United States were manufacturing 100,000 small-scale farm windmills yearly, mostly used as water pumps [12]. One of the very first modern design horizontal-axis wind generators was used in the Soviet Union by 1931. It was a 100 kW generator placed on a 30-m tall tower and connected to the Nation's 6.3 kV electricity distribution system. It was accounted for to have had a yearly capacity factor of about 32%, which shares close similarity to the efficiency exhibited by current wind machines [12]. As stated earlier, turbine blades can spin about a horizontal or a vertical axis, with horizontal axis rotation being older and more popular. They can also come with blades or be bladeless. Vertical axis wind turbines are not used as much because they produce less power [3].
