The advancement in technology which led to industrialization over the last century has resulted in geometric increase in population. Breakthrough in the field of medicine and other technologies subsequently improved fertility, rise in life expectancy and rise in standard of living. The baby boom era saw an unprecedented rise in population from 2.1 billion to over 6.5 billion and the population is expected to rise to about 9 billion people by year 2050 (United nations,2006).
This increase in population has led to increase in demand for energy. This has resulted in the burning of more fossil fuels which has raised lots of concerns. The first concern being the question of sustainability due to fossil fuel being non-renewable and the second being the issue of global warming.
With population set to be on the rise, demand for electricity and other energy sources is bound to increase, more cars begin to ply our roads as more people need to move from one place to the other. These means the rate at which we consume fossil fuel increases as well. This increases the fear of running out of fossil fuel someday questions the sustainability of fossil fuel.
The bye products of combusting fossil fuel has also been having derogatory effects on our environment. The release of Carbon monoxide into the atmosphere has contributed to the increase in greenhouse gases. This has resulted in an increase in the average temperature of the earth surface and subsequently contributed to the climate change we are experiencing.
Renewable energy sources has been identified as the solution to these problems. Renewable energy sources include solar energy, wind energy, biomass, geothermal energy, hydroelectric power among others. All these sources are renewable and at no risk of running out. Also, unlike fossil fuel, they are environmentally friendly as they contribute little or nothing to the greenhouse gases. According to the U.S. Energy Information and Administration, Renewable energy accounted for 12.7 percent of the total primary energy production in 2017. About 77.6 percent came from fossil fuel (2018).
However, renewable energies have various limitations which affects their contribution to energy production. Among these limitations are technological limitations, economic limitations and environmental limitations. In this paper, the limitations of Wind energy will be discussed and probable solutions will be proposed.
Wind energy is the kinetic energy due to airflow. This airflow is a result of the uneven heating of the earth’s surface by the sun. The difference in the rate causes the movement of air, as the hot air rises and the cold air goes opposite way in other to reach an equilibrium. The energy in the wind is harnessed by using a Wind Turbine which captures the kinetic energy in the wind. The kinetic energy in the wind causes the blades of the turbine to rotate here by creating a mechanical energy which turns a shaft connected to a gear box. Depending on the gearbox configuration, the speed of rotation of the shaft is multiplied by a factor of 100 or more which in turn drives a generator that produces electricity.
Since the Energy crises in 1973, Wind energy has been identified as one of the economically viable renewable energy. Countries like Denmark, Sweden, China, and USA among others have invested heavily in the technology that converts wind energy to electrical energy. This has reduced the cost of per Kw hour of electricity generated by wind by about 80%. However, electricity from wind energy is still more costly than energy generated by fossil fuel. This is due to the high cost of setting up a wind farm as well as running cost. Wind turbines have potential for high efficiency , low operating costs , zero carbon dioxide emission and it only takes the wind turbine about 25 percent of its age to break even and produce the energy that goes into producing, operating and recycling the it (Rose mary P.J, 2014). There are a few things that can be done to reduce the cost of per KW of electricity generated from wind energy. We can improve the technology to produce more electricity at the same cost or reduced cost by trying to eliminate exergy destruction in the system. We can also make policies that help to reduce the running cost of wind turbines. Policies such as reduced tax and incentives for investing in wind turbines.
ECONOMICS OF WIND ENERGY
The cost of wind energy per KW hour depends on lots of factors ranging from wind speed, location, type of wind turbine. A study done by Raghed showed that the cost of electricity generated in wind power mainly depends on capital and investment cost, operation and maintenance cost and fuel cost. A closer look into the cost of electricity per KW hour in wind energy shows that the cost depends on other things such as the economic depreciation of the capital equipment, interest paid on initial loans, taxes, government incentives and tax credits, electricity bills while on standby, wind speed among others (Ragheb, 2017). This factors vary from location to location. The cost of leasing land for wind farms in the Middle West is less than the cost of leasing the same land mass in the north east coast or in southern states like Texas or California. However the wind speed is more favorable in the Midwestern states than the North east coast and the aforementioned southern states. Other factors that contribute to the cost of wind energy per KW hour is the type of turbine. Different turbines have different efficiencies at different wind speeds. The height of the hub and the diameter of the wind turbines also play a key role in the output of the wind turbine (Rose, 2014). Due to all these factors, it is difficult to specifically pinpoint a particular cost for wind energy as these factors vary from one location to another but one fact that has been ascertained is that the cost of electricity generated per KW hour from wind energy is more than that generated from fossil fuels hereby making it less competitive in the market.
However, there are various policies that has been implemented to offset some of these costs, hence making wind energy more profitable for investors. Federal policies like the Production Tax Credit (PTC), Renewable Energy Production Incentive (REPI), and Modified Accelerated Cost-Recovery System (MACRS) among others have been initiated over the years. This has resulted in increase in the installed capacity of the wind power. It was recorded that the installed capacity grew by about 35% in 2005 when the PTC was reinstated after the PTC expired in 2004 (Ragheb, 2017). The policies discussed above has encouraged investors to invest in renewable energy but there has not really being a federal move to reduce dependency on cheaper fossil fuel. Elisabeth Rosenthal in an article for the New York Times in 2010 wrote that If the United States is to catch up to countries like Portugal, the United States must overcome obstacles like a fragmented, outdated energy grid poorly suited to renewable energy, a historic reliance on plentiful and cheap supplies of fossil fuels, especially coal, powerful oil and coal industries that often oppose incentives for renewable development and an energy policy that is influenced by individual states. The federal government must improve the energy grids to be more renewable energy friendly to reduce the cost of transporting the energy. The federal government should also reduce the incentives on electricity from fossil fuel and allocate more of the funds to renewable energy.
EXERGY ANALYSIS OF WIND TURBINE
Exergy is the useful energy in a system. It is the energy available for useful work. It can be referred to as the dollars in a generating plant as it is the energy available for sale. Although the wind power energy has been ascertained to have high efficiency potentials, the wind turbine can only harvest a small portion of the kinetic energy in the wind. To increase the quantity of energy resources harvested from the wind, a set of turbines which forms a wind farm are strategically located on a field. The set of turbines are connected to a grid to transport the energy to distribution centers. The performance of the wind farm depends on wind speed, wake effects which depends on the spacing between the turbines as well as the topography of the field. In other to maximize the efficiency of the wind farm hereby optimizing power production, the turbines must be positioned at a distance from each other. This distance must be sufficient for the wake effects to diminish and the wind to recover from the energy harvested from it by the turbine ahead of it (Hui, 2015).
For individual wind turbines, the exergy efficiency is a measure of how well the stream exergy of the wind is converted into useful turbine work output which is converted to electricity or used to do work. (ozgener and ozgener, 2006, Reynaga et al, 2017). The input exergy of a wind turbine is dependent on the mass of air causing the blades to rotate. Exergy depends on the dead state and the only difference between the wind at a point and dead state is the velocity it possesses when it is not in dead state. This velocity gives it its kinetic energy which can be converted to useful work by the wind turbine. Irrespective of the temperature and pressure, the energy input of the wind turbine is dependent on the velocity of the wind (Ozgener and Ozgener, 2006). The maximum amount of power available to the wind turbine is equal to the product of the mass flow rate of the air and the specific exergy of the air. The output exergy is equal to the exergy available at the inverter. The exergy destruction is the difference between the output exergy and the input exergy. Sources of exergy destruction in the wind turbine includes heat, friction and noise. And these losses occur during the mechanical (shaft speed multiplication and braking) and electrical (generators) activities of the wind turbine.
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