South Korea seeks cleaner energy sources

Posted on April 5, 2008 by Rashid Faridi

SEOUL: South Korea plans to break ground for the world’s biggest solar power plant on Thursday as it tries to diversify its power sources and use cleaner energy.

The $170 million plant, along with the world’s largest tidal power plant that is already under construction off the country’s west coast, is part of an aggressive effort to seek new and renewable energy sources at a time when global concern about reducing the emission of heat-trapping greenhouse gases is rising.

The nation is attempting to increase its use of renewable energy from its current 2.28 percent to 10 percent by 2020.

The solar plant, being built in Shinan, near the southwestern tip of South Korea, is scheduled to be completed by late 2008. It will feature 109,000 rectangular solar modules that will cover a seaside plot the size of 80 football fields, engineers said Wednesday. The modules tilt on a sun-tracking system to generate up to 20 megawatts of electricity.

“The plant will produce more than 27,000 megawatt-hours of environmentally friendly electricity a year,” said Kim Ji Hun, president of the Korean subsidiary of SunTechnics, the German solar power company that will build the plant on a turnkey contract. “This will be enough to supply 6,000 to 7,000 households, and saves 20,000 tons of carbon dioxide a year, or the amount of carbon dioxide 23,000 cars emit a year.”

Electricity from a solar power plant costs seven times as much as electricity generated by nuclear or fossil-fuel power plants in South Korea, said Lee Gil Jae, president of Dongyang Engineering & Construction, which will operate the plant.

But with its emission of greenhouse gases increasing faster than in most other developed countries, South Korea agreed to subsidize the solar power plant as part of a program to encourage clean energy industries. In 2006 alone, the government spent 410 billion won, or $444 million, on that program.

SunTechnics is one of the alternative-energy companies that hope to capitalize on the cleanup of Asia’s polluted skies. China recently pledged to make renewable energy account for 15 percent of the country’s total energy supply by 2020 and to spend $200 billion on that effort.

“We are further expanding our market positions in the most important growth regions in Asia,” said Stefan Müller, Asia-Pacific head of SunTechnics. “By 2008, we will have more than quadrupled our sales in Asia-Pacific.”

Like China, South Korea is aggressively exploring offshore gas reserves and new and renewable energy. The country spent $66.7 billion on importing energy in 2005, or 22.1 percent of its total import bill, making its economy vulnerable to high oil prices.

South Korea aims to reduce its dependency on oil to 35 percent of its energy needs by 2030, a drop from 44 percent in 2005.

Last week, the city of Incheon, west of Seoul, said it would build the world’s biggest tidal energy plant by 2014. The plan calls for connecting four islands with a 7.8-kilometer, or 4.8-mile, barrier and installing dozens of turbines that will harness the energy of powerful tidal waves.

The $1.9 billion plant will have a capacity of 812 megawatts, exceeding that of the 240-megawatt La Rance project in France, currently the world’s largest operating tidal plant. It will also surpass the 254-megawatt Sihwa tidal energy project under construction on the west coast of South Korea. When it is ready in 2009, the Sihwa plant will be the world’s largest.

Increased concerns about global warming and air pollution have added urgency to efforts to reduce dependence on fossil fuels.

Last week, the Intergovernmental Panel on Climate Change, the top global body studying climate change, urged the world’s established and emerging powers to make major moves away from their current primary energy sources.

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Solar Energy — Energy from the Sun

Posted on April 5, 2008 by Rashid Faridi

ENERGY FROM THE SUN

The sun has produced energy for billions of years.  Solar energy is the sun’s rays (solar radiation) that reach the earth.

Solar energy can be converted into other forms of energy, such as heat and electricity.  In the 1830s, the British astronomer John Herschel used a solar thermal collector box (a device that absorbs sunlight to collect heat) to cook food during an expedition to Africa. Today, people use the sun’s energy for lots of things.

Solar energy can be converted to thermal (or heat) energy and used to:

  • Heat water – for use in homes, buildings, or swimming pools.
  • Heat spaces – inside greenhouses, homes, and other buildings.

Solar energy can be converted to electricity in two ways:

  • Photovoltaic (PV devices) or “solar cells” – change sunlight directly into electricity. PV systems are often used in remote locations that are not connected to the electric grid.  They are also used to power watches, calculators, and lighted road signs.
  • Solar Power Plants –  indirectly generate electricity when the heat from solar thermal collectors is used to heat a fluid which produces steam that is used to power generator. Out of the 15 known solar electric generating units operating in the United States at the end of 2006, 10 of these are in California, and 5 in Arizona. No statistics are being collected on solar plants that produce less than 1 megawatt of electricity, so there may be smaller solar plants in a number of other states.

The major disadvantages of solar energy are:

  • The amount of sunlight that arrives at the earth’s surface is not constant. It depends on location, time of day, time of year, and weather conditions.
  • Because the sun doesn’t deliver that much energy to any one place at any one time, a large surface area is required to collect the energy at a useful rate.

PHOTOVOLTAIC ENERGY

Photovoltaic energy is the conversion of sunlight into electricity. A photovoltaic cell, commonly called a solar cell or PV, is the technology used to convert solar energy directly into electrical power. A photovoltaic cell is a nonmechanical device usually made from silicon alloys.

Image of how a photovoltaic cell works.Sunlight is composed of photons, or particles of solar energy.  These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum.  When photons strike a photovoltaic cell, they may be reflected, pass right through, or be absorbed.  Only the absorbed photons provide energy to generate electricity.  When enough sunlight (energy) is absorbed by the material (a semiconductor), electrons are dislodged from the material’s atoms.  Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to free electrons, so the electrons naturally migrate to the surface.

When the electrons leave their position, holes are formed.  When many electrons, each carrying a negative charge, travel toward the front surface of the cell, the resulting imbalance of charge between the cell’s front and back surfaces creates a voltage potential like the negative and positive terminals of a battery.  When the two surfaces are connected through an external load, electricity flows.
The photovoltaic cell is the basic building block of a photovoltaic system.  Individual cells can vary in size from about 1 centimeter (1/2 inch) to about 10 centimeter (4 inches) across.  However, one cell only produces 1 or 2 watts, which isn’t enough power for most applications.  To increase power output, cells are electrically connected into a packaged weather-tight module.  Modules can be further connected to form an array.  The term array refers to the entire generating plant, whether it is made up of one or several thousand modules.  The number of modules connected together in an array depends on the amount of power output needed.

The performance of a photovoltaic array is dependent upon sunlight.  Climate conditions (e.g., clouds, fog) have a significant effect on the amount of solar energy received by a photovoltaic array and, in turn, its performance.  Most current technology photovoltaic modules are about 10 percent efficient in converting sunlight. Further research is being conducted to raise this efficiency to 20 percent.

The photovoltaic cell was discovered in 1954 by Bell Telephone researchers examining the sensitivity of a properly prepared silicon wafer to sunlight.  Beginning in the late 1950s, photovoltaic cells were used to power U.S. space satellites (learn more about the history of photovaltaic cells).  The success of PV in space generated commercial applications for this technology.  The simplest photovoltaic systems power many of the small calculators and wrist watches used everyday.  More complicated systems provide electricity to pump water, power communications equipment, and even provide electricity to our homes.

Some advantages of photovoltaic systems are:

  1. Conversion from sunlight to electricity is direct, so that bulky mechanical generator systems are unnecessary.
  2. PV arrays can  be installed quickly and in any size required or allowed.
  3. The environmental impact is minimal, requiring no water for system cooling and generating no by-products.

Photovoltaic cells, like batteries, generate direct current (DC) which is generally used for small loads (electronic equipment).  When DC from photovoltaic cells is used for commercial applications or sold to electric utilities using the electric grid, it must be converted to alternating current (AC) using inverters, solid state devices that convert DC power to AC.

Historically, PV has been used at remote sites to provide electricity.  In the future PV arrays may be located at sites that are also connected to the electric grid enhancing the reliability of the distribution system.

SOLAR THERMAL HEAT

Solar thermal(heat) energy is often used for heating swimming pools, heating water used in homes, and space heating of buildings. Solar space heating systems can be classified as passive or active.

Passive space heating is what happens to your car on a hot summer day. In buildings, the air is circulated past a solar heat surface(s) and through the building by convection (i.e. less dense warm air tends to rise while more dense cooler air moves downward) . No mechanical equipment is needed for passive solar heating.

Image of a house with solar cells on the roof.Active heating systems require a collector to absorb and collect solar radiation.   Fans or pumps are used to circulate the heated air or heat absorbing fluid.  Active systems often include some type of energy storage system.

Solar collectors can be either nonconcentrating or concentrating.

1) Nonconcentrating collectors – have a collector area (i.e. the area that intercepts the solar radiation) that is the same as the absorber area (i.e., the area absorbing the radiation). Flat-plate collectors are the most common and are used when temperatures below about 200o degrees F are sufficient, such as for space heating.

2) Concentrating collectors – where the area intercepting the solar radiation is greater, sometimes hundreds of times greater, than the absorber area.

SOLAR THERMAL POWER PLANTS

Solar thermal power plants use the sun’s rays to heat a fluid, from which heat transfer systems may be used to produce steam. The steam, in turn, is converted into mechanical energy in a turbine and into electricity from a conventional generator coupled to the turbine.   Solar thermal power generation works essentially the same as generation from fossil fuels except that instead of using steam produced from the combustion of fossil fuels, the steam is produced by the heat collected from sunlight. Solar thermal technologies use concentrator systems due to the high temperatures needed to heat the  fluid.  The three main types of solar-thermal power systems are:

SOLAR ENERGY AND THE ENVIRONMENT

Solar energy is free, and its supplies are unlimited. Using solar energy produces no air or water pollution but does have some indirect impacts on the environment. For example, manufacturing the photovoltaic cells used to convert sunlight into electricity, consumes silicon and produces some waste products. In addition, large solar thermal farms can also harm desert ecosystems if not properly managed.

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Mountain Building Models

Posted on April 5, 2008 by Rashid Faridi

In the past 1.1 billion years the eastern seaboard of North America has experienced four major mountain building events, the Grenville, Taconic, Acadian, and Alleghenian. Virginia has a good record of each of these. But do these mountain building events include the modern Appalachian mountains? In a word, No.
For many people a mountain is just some place that has an elevation significantly higher than the surrounding area. The Appalachian “mountains”, for example, or the Blue Ridge “mountain.” You know they are mountains if you have ever tried to climb them; it takes a lot of time and effort, and the view at the end is worth it.
But when we speak of mountains here we speak of them geologically, and that is often not the same thing as the everyday term “mountain.” The modern Appalachian mountains, for example, are not “mountains” in a plate tectonic sense. That is, they have not been created by dynamic forces currently thrusting the land upward. The Appalachian mountains are in fact more complex than that. The rocks that make up the mountains are the fragmented, eroded remains of at least four ancient mountains that were huge compared to the present ones (anywhere from 5 to 10 times taller). And the structures in the rocks that give the Appalachian mountains their distinctive valley and ridge shapes and sizes are ancient structures created in a former mountain 300 million years old, and long since dead and gone.
Instead the modern Appalachian mountains are the result of a gentle, almost passive uplift, followed by erosion that has removed the soft rock in the valleys, and left the hard, resistant rocks at the ridges. It is the last few subdued breaths before the whole region goes to sleep.
So, when we talk about “mountains” in the geologic history we are talking about something different, something more dynamic and powerful than the modern Appalachian mountains. “Real” mountains. But there are so many kinds of mountains in the world today, mountains that are dynamic and powerful. We need some system, some models, for understanding the different kinds of mountains so that we can distinguish them in the history.

Mountain Building Models
What we are interested in are mountains that result from plate tectonic processes. It is not easy to provide a clean classification here since the processes over lap. But we can look at mountain building from two perspectives, the energy source driving it (heat vs mechanical), and the relationship to plate tectonics (divergent, convergent, and transform boundaries, and within plates). The table below illustrates some of the processes and how they overlap, although we do not attempt to be complete about this.

 

It is important to recognize that all mountain building ultimately comes from heat, but we are not interested in the ultimate cause, but the immediate cause of the mountain. And, very commonly, more than one of these mechanisms may operate at the same place, either at the same time, or sequentially.

Energy Source Mountain Building: Heat vs Mechanical Energy
First, is mountain building resulting primarily from heat. The uplift comes because heat from inside the earth heats the overlying lithosphere, causing it to expand, lifting and swelling the surface upward. Often associated with this are volcanos that accumulate even higher on top of the swollen earth. These processes include hot spot and subduction volcanos. Hot spot volcanos are discussed in the rifting model. Subduction volcanos are generated along subduction zones at convergent plate boundaries; they are cordilleran mountains, discussed below.
Second, is mechanical mountain building; that is, tension (pulling apart) and compression (squeezing together). The relief (differences in elevation) come primarily because different blocks of earth move relative to each other, either falling or rising vertically, or one block being shoved (thrust) horizontally over another.

Plate Boundary Mountain Building
Mountain building is associated with all three kinds of plate boundaries, divergent, convergent, and transform. We only deal with divergent and convergent plate boundaries.
On a dynamic earth things change fast, or easily transform from one thing into another. For example, the Wilson cycle explains that events begin with divergent plate boundaries (tension producing rifting), but end in convergent plate boundaries (compression leading to collision).
It is this dynamic we want to capture in the classification below. Below we discuss only the mountain types written in red in the table above, although clicking on any mountain type will take you to a fuller discussion of it somewhere.

PLATE BOUNDARY MOUNTAIN CLASSIFICATIONS

Divergent Plate Boundaries: Continental Rift Zones
New divergent plate boundaries are created at continental rifting centers by tension (pulling apart). In the rifting model this mechanism is explored in more detail. Here we just look at the principles of tensional mountain building.
Tensional mountain building is almost always of the block faulted type (horsts and graben). Any condition that pulls the earth apart can cause this faulting. For this to occur something must create the tension, must pull the earth apart. There are circumstances where the tensional stresses operate horizontally, parallel to the earth’s surface (for example at transform plate boundaries), but many times the tension occurs because the earth is lifted upward from below by heat, such as at a hot spot. Lifting the earth upward is something like blowing up a balloon; the surface stretches.
When the earth stretches the brittle rocks crack into blocks, and a gap opens as the earth spreads apart. Into the gap a block of the earth slides down because of gravity. The graben is the down faulted block, and as it goes down a valley is formed (drawing to right). The blocks on either side of the valley that do not slide down are the horst mountains. This process occurs in tens of thousands of tiny steps, each creating a small gap, the sum total of which stretches the earth apart many kilometers.
This type of faulting is called “normal.” Note that the faults form a dipping surface, an inclined plane, and that the graben block slides down that plane. It is “normal” for things to slide down inclined planes under gravity; thus normal fault (if the block moves up the inclided fault plane it is a “reverse fault”). These faults can be quite large as the picture illustrates. The picture is of the East African rift west of Nairobi, Kenya. The “mountains” are horst blocks, and the valley is the graben.
It is possible, of course, for the horst block to move up, but most of the time it does not matter; only relative motion is observed. Relatively if one block goes up the other must have gone down, and vice versa.

Convergent Plate Boundaries: Subduction Zones
Convergent plate boundaries exist when two plates move toward each other. Convergence begins when oceanic lithosphere decouples, that is, breaks at some place and descends into the mantle along a subduction zone. It is always oceanic crust that decouples and descends. Continental crust is too light to subduct.
Subduction zones can form anywhere in an ocean basin, and face any direction. Also, more than one subduction may be active in an ocean basin at the same time. Thus a complex sequence of mountain buildings are possible, and are not unusual.
Convergent mountain building is also complex in its mechanisms, since although convergence is compressive, mountains may be either heat driven, or mechanically driven, or a combination of them. But even in the heat driven examples, it is compression that is ultimately generating the heat so we have to understand the relationships and processes operating. A simple classification is possible, however, and is shown in the illustration below. Mountains result from either subduction or collision.

Subduction Orogeny
Two kinds of subduction orogenies exist, those within ocean basins (island arc type), and those that descend under continents (cordilleran type). The island arc type orogeny is illustrated by the islands of Japan, and the Aleutian islands. Here uplift is mostly heat driven as magma rises off of the subduction zone. In addition, the volcano itself builds a mountain on top of the swelling.
The cordilleran type mountain building is illustrated by the Andes mountains, or the Cascades. Here also, heat swells the continent upward, and then volcanos build even higher on top of that.
Both of these subduction orogenic types have numerous processes, and generate a wide diversity of rocks and structures. For full details and explanations see the Wilson Cycle, Stages E and G.

Collision Orogeny
The second class of convergent plate orogenies are collision orogenies. We recognize two types, continent-island arc type, and continent-continent type. In both cases an ocean basin descends completely down a subduction zone until it disappears completely. These are called “remnant ocean basins” (ROB) since they are only a remnant of their former selves. The two floating blocks on either side of the remnant ocean then have no choice but to collide. The floating blocks may be island arcs, or microcontinents, or continents, or some combination of these.
In the cross sections above the continent-island arc collision has not taken place yet, but is imminent. The continent-continent collision has occurred and the one continent overridden the other. In both cases the subduction zone acts as a ramp, and one block will slide up over the other. The overriding block is a hinterland; the overridden block the foreland.
Observe, that it is not possible to get collision orogenies without at least one of the floating blocks having a subduction orogeny first (island arc or cordilleran type); it is the only way an ocean basin can close.
As with the subduction orogenies, collision orogenies produce a wide diversity of rocks and structures. For the details see the Wilson Cycle, Stages F and H.
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Mountains

Posted on April 4, 2008 by Rashid Faridi

A mountain can be defined as an area of land that rises abruptly from the surrounding region. A mountain range is a succession of many closely spaced mountains covering a particular region of the Earth. Mountain belts consist of several mountain ranges that run roughly parallel to each other. The North American Cordillera, the Himalayas, the Alps, and the Appalachians are all examples of mountain belts that are composed of numerous mountain ranges.

Some mountains are volcanic in origin forming where rising magma breaks through the Earth’s surface. Volcanic mountains tend to have sporadic distributions within a mountain range (Mounts St. Helens, Rainier, and Baker) or can occur alone because of a localized hot spot (Hawaiian Islands). Most mountains were created from tectonic forces that elevate, fold, and fault rock materials. Tectonic mountains can occur as a single range (the Urals) or as a belt of several mountain ranges (North American Cordillera). Figures 1 and 2 show the location of some of the major mountain systems found on the Earth’s surface. These major mountain systems include the North American Cordillera, Andes, Alps, Urals, Appalachians, Himalaya, Caledonian Belt, and the Tasman Belt.

The Earth’s mountain ranges have various ages of formation. Parts of the Himalayas are relatively quite young. Mountain building in this region of the world began about 45 million years ago when the continental plates of India and Eurasia converged on each other. The Himalaya mountains are still actively being uplifted. The Appalachian belt is quite old. Mountain building in this region of the world started about 450 million years ago. Orogeny stopped in the Appalachians about 250 million years ago. The long passage of time without active uplift has allowed weathering and erosion to remove large amounts of bedrock from the Appalachians. These processes have also significantly lowered and rounded the peaks of the various mountains found in this belt. Mountain building episodes in the North American Cordillera have been occurring over a very long period of time and still continue today. Some sedimentary rocks in the Rocky Mountain range (located on the eastern edge of the North American Cordillera) date to over a billion years old).

Evolution of Mountains

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Geologists have developed a general model to explain how most mountain ranges form. This model suggests that mountain building involves three stages: (1) accumulation of sediments, (2) an orogenic period of rock deformation and crustal uplift, and (3) a period of crustal uplift caused by isostatic rebound and block-faulting. The later two stages of this model involve tectonic convergence of crustal plates which provides the compressional and tensional stresses that produce rock deformation, uplift, and faulting.

Mountain belts normally contain numerous layers of sedimentary and volcanic igneous rocks. These accumulations can be several kilometers in thickness. Most of these accumulations were originally deposited in a marine environment. The beds of the sedimentary rocks are composed of particles that came from nearby terrestrial landmasses. These particles were released from rocks by weathering and then transported by erosional forces to the edge of the terrestrial continental crust. Beyond the edge of the continents, these sediments are lithified to form shales, limestones, and sandstones that make up the continental shelves, slopes, and rise. Accumulations of volcanic rock develop along convergent boundaries where subduction is causing magma plumes to form plutons and volcanoes. The volcanoes are usually spatially organized in a line, called an island arc, that runs at right angles to the direction of crustal movement.

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In the orogenic stage of mountain building, the accumulated sediments become deformed by compressional forces from the collision of tectonic plates. This tectonic convergence can be of three types: arc-continent, ocean-continent or continent-continent. In an ocean-continent convergence, the collision of ocean and continental plates causes the accretion of marine sedimentary deposits to the edge of the continent. Arc-continent convergence occurs when an island arc collides with the edge of a continental plate. In this convergence, the ocean plate area between the arc and the continent is subducted into the asthenosphere and the volcanic rocks and sediments associated with the island arc become accreted to the margin of the continent over time. This type of collision may have been responsible for the creation of the Sierra Nevada mountains in California during the Mesozoic Era. The final type of convergence occurs when an ocean basin closes and two continental plates collide. Continent-continent convergence mountain building is responsible for the formation of the Himalayas, Ural, and Appalachian mountain systems.

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In all three types of tectonic convergence, layered rocks that were once located in the ocean basin are squeezed into a smaller and smaller area. This compression causes the once flat sedimentary beds to be folded and uplifted. When the compressional forces become greater than the rocks ability to deform, faulting occurs. Compressional forces typically result in reverse and overthrust faulting. Another consequence of the orogenic stage is regional metamorphism and the incursion of magma plumes, plutons, and volcanoes into the growing mountain range.

 Collision of Eurasian and Indian plates created the Himalayas. In this orogeny, compressional forces squished sedimentary deposits that existed between the converging continental plates and rocks at the margin of the Eurasian and Indian plates upward in elevation. These forces also created a number of overthrust faults. Folds and Faults are important in case of Himalayas.

At the end of plate convergence, mountain building enters its final stage. This stage is characterized by crustal uplift because of isostatic rebound and block-faulting (Figure 5). Isostatic rebound involves the vertical movement of continental crust that is floating in the plastic upper mantle. As erosion removes surface materials from mountains, the weight of the crust in this region becomes progressively less. With less weight, the continental crust makes an isostatic adjustment causing it to rise vertically (float higher) in the mantle. This process also causes tensional forces to exist in a horizontal direction breaking the continental crust into a number of blocks. Each block moves vertically to compensate for the tensional forces producing normal and graben faults.

Further Readings

Source:http://www.eoearth.org

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