Alternative Energy Sources

Since the inception of electrical power in the 19th century the world has become increasingly centered around it. For many years the only reasonable way to obtain electrical power was through the burning of fossil fuels. Now as we head into the 21st century it is becoming apparent by nearly everyone around the world that electrical power from fossil fuels is not environmentally sustainable and becoming less and less economically stable every year. Thus around the world people from many different countries are coming up with many different ideas on sustainable ways to create the electrical power that our society has become so dependent on. While there are countless ways of solving the problem, the three most prominent involve converting energy from the wind, water, and sun into electrical energy. Each uses very different ideas, and while in the future they may be furiously competing with one another for the right to supply power, right now they all serve the common goal of weaning us off fossil fuels.

Wind Power
Due to the earth’s uneven distribution of heat from the sun, there is differential heating in parts of the world resulting from the sun’s varying radiation rate between days and nights and also the different tendencies of surfaces to absorb and reflect heat. For example, polar areas receive less sunlight than regions near the equator. As the warmer air rises and the pressure increases towards the surface of the earth, the denser cool air attempts to replace it and subsequently, wind results. Nearly 2% of the Sun’s energy received on Earth is transformed into wind energy (Baird, 315) [1]. Since wind is in motion, it has kinetic energy available to be transferred to useful forms such as mechanical and electrical energy. Wind power has historically been used for propelling sailboats, grinding grain, and sawing. In the past, wind power converted to mechanical energy was utilized for pumping water in rural locations.
Environmentally, there is much controversy in the world regarding greenhouse emissions primarily caused by coal burning fossil fuels. Since wind is a natural process that consumes no fuel and emits zero pollutants, it has recently become an increasingly popular alternative method for generating electricity.

Wind Power as Electrical Energy
Wind electric turbines are the major form for harnessing the wind’s kinetic energy for practical use as electricity. There are two types of wind turbines, the more popular horizontal-axis and the vertical-axis.

Wind Turbine
Wind Turbine

Turbine subsystems include:

  • a rotor, or blades, which convert the wind's energy into rotational shaft energy;
  • a nacelle (enclosure) containing a drive train, usually including a gearbox and a generator;
  • a tower, to support the rotor and drive train; and
  • electronic equipment such as controls, electrical cables, ground support equipment, and interconnection equipment.

The wind is used to spin the rotor of the turbine, which then drives the shaft of the attached generator to produce electricity. The wind turbine is highly dependent on the wind speed, which is indicated by the fact that the energy contained in wind is a function of the cube of its speed. For example, a location with 12-mph winds has more than 70% energy than a site with 10-mph average winds (WWEA, 2005) [2] Most regions of the U.S. receive electricity from utilities that come together to generate and distribute electricity. The utilities are “power pools” that gather electricity from many different forms including wind plants, hydro plants and coal-burning power plants. The utilities then distribute the electricity to thousands of users. More specifically, the electricity from a wind plant is easily absorbed by the power pools and can thus contribute to the generation of electricity. According to a recent study done by the World Wind Energy Association, wind power has the potential to provide 10% of the world’s electricity supply, meeting the needs of 500 millions households (WWEA) [2]

Wind farms, a group of wind turbines that are interconnected through a medium voltage power collected system, are the major use for generating electricity. The wind farms are connected to a higher voltage transmission system called a power transmission network, which in a sense serves as hub and distribution center for electricity (FEMP, 2002). [3] The location of wind farms is strategic because it encompasses numerous considerations. Good wind speeds, available transmission lines, an assessment of how significant the energy being produced will be, the cost of land used to support and maintain the turbines, and also the environmental impacts are all aspects that must be considered. Europe leads the world with the most offshore wind turbines. Denmark was the first country to install and implement wind farms. Today 20% of Denmark’s electricity comes from wind power, which is more than any other country (Sharman, 2005). [4]

Capacity Factor
One important method in determining the productivity of wind power turbines is the capacity factor, which is measured as the actual amount of power produced over time divided by the power that would have been produced if the wind turbine operated at 100% output (WWEA, 2005 [2]. This percentage can be compared to the capacity factor of other methods for generating electricity. Since wind is not a steady factor, it does not operate at its maximum potential. Most wind turbines have a capacity factor of 25-40%, but can be higher in the windier months. Since a conventional utility power plant uses fuel, its capacity factor is 40-80%. An explanation for this increase is that while the capacity factor for a fuel power plant is primarily based on its cost, the capacity factor of the wind turbine is dependable on the economic turbine design. For example, the capacity factor of a wind turbine would be higher if a large rotor and small generator were used, yet very little electricity would be generated (WWEA, 2005) [2]. This proves that the capacity factor should not be the only measure of comparison considered when evaluating the different forms of electricity generation.

Pros and Cons
Some critics of wind power argue that the intermittency of wind makes it uncontrollably variable and will cause an increase in cost for its regulation. This would require backup facilities using traditional resources to remain constantly on-call (Baird, 320) [1]. In response to this complaint is that excess wind energy can be stored mechanically by pumping water to elevated storage facilities or in batteries and then used when needed to produce electricity. Another argument against wind power is that the motion of blades produces a constant noise and on shore wind farms are a form of visual pollution (Baird, 320) [1]. A counter to this is that studies show the noise level of wind turbines is comparable to traffic and areas distant from dense populations can be used to store and maintain wind turbines. Critics of wind power argue that wind turbine construction requires habitat clearing and the construction of roads. The windmills also have the potential of killing birds and bats. In response, those in favor of wind power have argued the results of studies showing that the number of birds killed by turbines are minimal compared to the number of birds being killed by cars or cats (Baird, 320) [1]. A brief summary regarding the downfalls of wind, solar, and hydroelectric power can be found here.

Future for Wind Power
In summary, there is a great potential for wind energy to supply the world with a significant portion of electricity. Its advantages include very few greenhouse gases being emitted along with zero waste products. The price for new wind power supplies is comparable to the costs of newly constructed coal and nuclear power plants (Baird, 321) [1]. Some concerns of wind power is its intermittent nature and unresolved problems of efficient energy storage.
Nevertheless, the use of wind power is growing substantially. By 2010, the World Wind Energy Association expects a net growth rate of 21% per year worldwide (WWEA, 2005) [2]. The U.S. has increased its use of wind turbines especially in the Great Plains states of Texas, Kansas, and North Dakota. By 2008, the wind will generate enough electricity for the U.S. to power over 1% (4.5 million households), which is a huge increase from 0.1% in 1999 (WWEA, 2005) [2].

Hydroelectric Power

Hydroelectric energy is one of the major renewable alternative energy sources along with solar, wind, and geothermal. The main idea behind hydroelectric power is to harnesses the flow of water to generate electricity via small or large scale facilities. Small-scale facilities are more common to build because they use the flow of a river to generate small amounts of electricity. Larger-scale facilities, such as the Hoover Dam, require waterfalls or more commonly dams, but also generates larger amounts of energy. [1]

How large scale dams work:
Many large scale hydroelectric power plants consist most noticeable of a dam build on a river to crate a reservoir behind it. The water from the reservoir flows through a channel in the dam containing a turbine, causing the turbine to spin and generate electricity. The greater the difference in height between the water intake and water outlet increases the amount of electricity generated because of the higher water flow rate. Hydroelectric Dams also have gates at the intake point to help control water intake. Overflow shoots are also built into the dams to help control flooding and water levels within the reservoir.

Pros and Cons:
Like other energy sources hydroelectric energy power has both advantages and disadvantages. Advantages to hydroelectric power include most chiefly the infinite source of energy that can be achieved by water. Hydroelectric dams produce energy in great quantity and at low costs. Both large and small scale dams can be used all over the world. The reservoirs created by the dams create new areas for water sports and activities, as well as help flooding.
With the advantages of hydroelectric power come some significant disadvantages that must be considered when looking to build a new plant. One of the major cons against hydroelectric plants comes from its environmental impact. Hydroelectric power plants cause flooding upstream of the dam which leads to displacement of people living in the area. Newly formed reservoirs also have the potential to create large amounts of carbon dioxide and methane due to the decaying plant and animal matter in an anaerobic environment [7]. With out the construction of fish ladders, dams can disturb the migration of fish, like salmon, to spawning grounds upstream. New power plants are also expensive to build and geological locations must be taken into consideration which causes favorable locations for new hydroelectric dams to be limited. Finally, even with the intake gates controlling water flow, if a rivers water flow rate decreases due to a drought, so will the amount of energy produced. Compared to other energy sources hydroelectric power is clean, it does not release CO2, it does not create radioactive waste like nuclear power plants, and it is a more predictable source of energy than wind or solar based electricity.

Examples from around the world:

The Hoover Dam

The Hoover Dam in the United States is a well known landmark and one of the most well known hydroelectric plants in the U.S built on the Colorado River straddling the Arizona and Nevada border. Construction began on the Hoover Dam in 1931 and was completed in 1936. Today the Hoover damn consists of “fifteen 178,000 horsepower, one 100,000 horsepower, and one 86,000 horsepower” turbines that feed into “thirteen 130,000 kilowatt, two 127,000 kilowatt, one 61,500 kilowatt, and one 68,000 kilowatt generators” [5] that supply power to Arizona, Nevada, and parts of California. On average the Hoover dam puts out 4.2 billion kilowatt-hours of electricity annually. Lake Mead, which was formed due to the construction of the dam, is currently the world’s largest man made lake and supplies the surrounding area with water recreation. However, there have been changes to the aquatic life in the area and water intake ports must be kept clean of shellfish to maintain water intake levels.

Three Gorges Dam - China

The Three Gorges Dam in China is the world’s largest hydroelectric power plant consisting of 26 generators, but the completion of the dam did not come without conflict. Building the dam and the flooding that occurred caused 13 cities, 140 towns, and around 1,350 villages [6] to be destroyed, displacing over one million people with little compensation from the Chinese government. There are many environmental concerns as well concerning the dam. With so many settled areas being flooded many factories, mines, and waste dumps are being submerged which brings forth the concern of polluting the river water [6]. Despite the controversy, the Three Gorges Dam is estimated to put out 49 billion kilowatt-hours annually once it is fully operational, supplying China with ten percent of its power needs [10].

The Vajont Dam - Italy

The Vajont Dam in Italy is an example of what can happen when a dam is built in a geographically unfavorable area. In October of 1963 a heavy rains caused a massive landslide into the reservoir behind the Vajont Dam. The impact of the landslide with the water caused a huge ripple of water that toppled over the dam down into the Paive valley below destroying the towns of Longarone, Pirago, Rivalta, Villanova, and Fae. As many as two thousand people were killed in the surge of water and mud [11].

Solar Power
Nearly all sources of energy on this planet can trace their roots back to the sun. This massive star hits us with unfathomable amounts of energy each day, and many people simply ignore it. When it is not ignored it can be turned into the an abundant, accessible, and free power source, and thousands of people worldwide are working to do just that.

The sun's radiation has been used for very basic energy needs for thousands of years. Thousands of years before the “invention” of modern electricity, ancient civilizations were already augmenting their structures to get the maximum benefit from the sun. South facing buildings allowed extra sunlight to enter the building during the day, and heat absorbing materials caused some of that heat to be stored and slowly leak out during the night raising the average temperature. [12]

Types of Solar Power
The idea that sunlight can be converted into energy is again becoming a huge deal. Two major methods of harnessing solar energy have arisen to solve this problem, photovoltaics and solar thermal energy. Solar thermal energy uses the idea that sunlight is heat and can be concentrated and used to heat water, which can be used in a steam engine to produce power. Alternatively photovoltaics use the idea that sunlight can be used directly to create energy by simply exciting electrons on a photovoltaic cell. Both these methods have many positive effects as well as some drawbacks, but are also both being highly researched and utilized worldwide. Another method of using the earth's natural heating capacity is through the use of geothermal heat pumps (GHP), which take advantage of the steady heat temperature below the earth's surface and channels it to homes during the winter. Since the focus of this subject is solar power, geothermal energy will not be discussed. However, geothermal energy is discussed in greater detail here.

Photovoltaic Cells
Photovoltaic cells are the most direct way of converting light into energy. Some substances exhibit the property of absorbing photons and emitting electrons when exposed to light, this is known as the photoelectric effect. A semiconductor such as silicon sits in between a positive and negative conductor. As photons hit the silicon, the electrons are displaced and are immediately picked up by the conductors to create an electric current. The entire cell is also encased in an anti-reflective material in order to let less than 5% of the light that hit the cells to bounce off. This increases the chance of any given photon to loose an electron and thus increases the electrical yield produced. Most cells are also cased in a barrier, usually glass, to prevent damage from outside sources. [14]

Normal photovoltaic cells can only accept photons traveling at a certain wavelength. If the photons energy is not large enough it wont be able to release protons, in additions if the energy is too high the extra energy beyond that needed to free the electron is lost. This causes a huge loss in productivity in the cell, as a majority of the photons that enter the cell do not have the correct energy level to activate it. Newer multi-junction cells are using multiple semiconductors or and are capable of absorbing a wider spectrum of photons.[13]

One of the largest criticisms for photovoltaic cells is the energy payback time, or how long it would take to create enough energy to offset the massive amount of energy needed to create the cells. Some studies 10 years ago suggested that the payback time was as high as 11 years. With the assumption of a 30 year lifetime of the cell, there would only be less than 1:3 ratio between energy input and energy output. Recent studies suggest that the payback time may be as low as 1 year with the newest state of the art cells sporting a more impressive looking 1:30 ratio. [16] In time, photovoltaics may end up being more useful for large scale power, but currently the other form of solar power looks more promising.

Solar Thermal Power

Solar thermal power works simply by using the heat from sunlight to create electricity. Mirrors, formed to parabolas, reflect the light that hits them onto a concentrated point. This point where all the rays of light convene is usually a tube carrying a liquid that absorbs the heat. Two major types of these systems exist, one that operates at high temperatures, and on that operated at low temperatures. The low temperature variant simply cannot heat the liquid to high enough temperatures to create electricity, so instead the liquid, notably water, is simply used for hot water needs on a small scale. The more important high temperature modules use the heated liquid to create energy. The liquid is boiled to its gas state and then moving along a pipeline enters in a steam accumulator where the heat energy can be stored temporarily. Finally the gas is moved into a Stirling engine or steam engine where it can be converted into electricity.

A large scale solar power plant in Nevada, named Nevada Solar One, was opened in 2007 and uses a 400 acre solar thermal system to create 64 megawatts. This could supply over 15,000 houses annually if it was devoted to them. Instead it is sold to local power companies and portions of the electricity created by it are used to power many more homes in the state. [17] While largest in the world at its time of conception, newer and larger plants will be built around the world as the technology evolves and its use becomes more widespread. Arizona has plans to construct a plant larger than Nevada Solar One by 2013, creating over 50,000 homes worth of power. [18]

Alternative Fuel

One form of alternative fuel that is growing in popularity is biodiesel. This diesel alternatvie is produced from soybean, canola, palm, or even cooking oils. These oils are mixed with alcohols to create alkyl esters, which is biodiesel. Biodiesel is renewable, about to be created from used cooking oils, and has lower emissions than standard diesel.

[1] Baird, C.; Cann, M. Environmental Chemistry, 4th edition; W.H. Freeman and Company: New York, 2008.
[2] “Wind Industry Statistics.” American Wind Energy Association. (2005).
[3] “A Primer on Electric Utilities, Deregulation, and Restructuring of U.S. Electricity Markets.” United States Department of Energy Federal Management Program. (May. 2002).
[4] “Why Wind Power Works For Denmark.” Civil Engineering. (May. 2005).
[5] “Hydropower at Hoover Dam.” United States Bureau of Reclamation. (April 18, 2009).
[6] “Three Gorges Dam.” International Rivers. (April 20, 2009).

[7] “Hydroelectricity.” Wikipedia. (April 18, 2009).
[8] “Renewable energy sources in the United States.” National Atlas. (April 18, 2009).
[9] “Hydroelectric power: How it works.” United States Geological Survey. (April 18, 2009).

[10] “Three Gorges Dam Hydroelectric Power Plant.” Power Technology. (April 18, 2009).

[11] “Vajont Dam.” Wikipedia. (April 18, 2009

[12] "History of Solar" Southface.
[13] Knier, Gil. "How do Photovoltaics Work?" Nasa. (4/22/09)
[14] Aldous, Scott "How Solar Cells Work." How Stuff Works. (4-22-09)
[15] Jacoby, Mitch "Photovoltaic Cells: Power at a Price." Chemical and Engineering News. (4-22-09)
[16] Blaker's Andrew and Weber, Klaus. "The Energy Intensity of Photovoltaic Systems" [5] (4-22-09)
[17] "Largest Solar Thermal Plant Goes Online" The Chief Engineer. (visited 4-27-09)
[18] Markham, Derek. "Arizona to get Billion Dollar Solar Thermal Power Plant" Clean Technica. (4-27-09)