Examining Major Sources Of Renewable Energy Engineering Essay

Published: Last Edited:

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Oil, Natural Gas, Coal, Uranium, are major sources of energy in 20th century, but all the resources will be consumed during the course of human development, possibly in the next few decades. Renewable sources of energy can solve the energy demand of the growing population of the earth. Many countries now are focusing more on developing technology for generating renewable energy. Most renewable energy sources are also environment friendly; they will reduce carbon emission and help preventing global warming process, and allow economies to reduce their dependencies on politically turbulent nations. From 2007 to 2008, the market for the top three renewable - wind, solar, and bio-fuels - grew from $75.8 billion to $115.9 billion, and the opportunity.

Only 7% of world energy demand is generated by renewable source of energy. This is very low compare to the potential of generating renewable source of energy. Hydroelectric, Wind energy, solar energy, Geothermal and Bio-fuel are some major source of renewable energy. Bio-fuel and Hydroelectric are two major contributor in renewable source of energy, but the potential of generating energy from Wind, Solar and Geothermal is more graters then all other existing source of energy.

Major sources of Renewable energy:

Wind Energy: Wind is caused by different parts of the earth heating at different rates to different temperatures, creating pressure and leading air molecules to move from areas of higher pressure to areas of lower pressure. As long as the sun shines, the wind will blow. It would appear that wind is the ultimate source of energy, but, like all other renewable, it faces some issues. Not every region has winds that are the right speed year-round; Wind parks can also "overproduce" on windy days, creating more electricity than needed by the utilities grid, though there are massive batteries being developed to store some of this excess energy for periods when the wind is weaker than needed. Wind turbines have the lowest installation costs of any of the renewable, and with large wind installations taking advantage of economies of scale to reach lows of $800 per kilowatt installed.

Geothermal energy: Geothermal energy uses hot water deep within the earth's crust to spin turbines and produce power 24 hours a day, seven days a week. It produces few carbon emissions and can re-inject used water back into the earth to be used again, making it fully sustainable. Not every part of the planet has geothermal resources; usually, they can be found in regions where there is volcanic activity, or where two tectonic plates meet. This is why places like Indonesia and the Philippines, which are situated on the Pacific "Ring of Fire", or California, with its myriad fault lines and hot springs, are such strong markets for geothermal technology.

Solar Energy: The appeal of solar power is obvious. It is a virtually limitless resource. It's free of greenhouse gas emissions, widely thought to contribute to global climate change. Once installed, solar systems can function for 25 or more years with little maintenance or oversight. Solar comes with limitations, however, with poor cost-efficiency being the most notable. Solar is weather dependent and intermittent, requiring storage or back-up systems to supplement during times of weak generation. More importantly, thanks to fast-rising silicon prices, solar systems average $8,000 per kilowatt installed - extremely expensive even in comparison to other renewable. Still, the solar market has exploded over the past year, with electricity generated from solar systems increasing from 2.5 GW in 2006 to 3.8 GW in 2007.

Solar Technologies

Solar Energy is already the "energy source of choice" in many circumstances where power is required, but the user does not have the option of connecting to a local electricity grid. This market segment is providing the economic platform from which a self-sustaining, commercially driven, high technology industry is emerging. The next economic challenge for the Solar Energy Industry is penetration of markets, where the user has the option to connect to the electricity grid. In these circumstances, it's often said that solar energy at 20-40c/kWh is two to three times as expensive as residential rates. So why, in the light of this, have an increasing number of Utilities, whether Government Owned or Private Corporations, expressed interest in including solar energy in their portfolio as we start the 21st century? It may surprise you that it is based on sound economic principles. Over the last two decades, the trend of solar energy prices has been consistently downwards, driven by continuous advances in PV technology and manufacturing economies of scale. Investment in solar energy today is set against an economic backdrop of an industry that will approach break-even costs with other grid connected energy sources at the end of this decade.

With 427 Megawatts of global incremental solar capacity installed capacity last year, solar energy is still a tiny fraction of the world primary energy market. However, its reduction in unit costs has yielded growth rates and market share gains that suggest solar energy have the potential to become a mainstream energy source in the foreseeable future, as part of a growing Renewable Energy sector. 

Three key elements in a solar cell form the basis of their manufacturing technology. The first is the semiconductor, which absorbs light and converts it into electron-hole pairs. The second is the semiconductor junction, which separates the photo-generated carriers (electrons and holes), and the third is the contacts on the front and back of the cell that allow the current to flow to the external circuit.  The two main categories of technology are defined by the choice of the semiconductor: either crystalline silicon in a wafer form or thin films of other materials.

Crystalline silicon:

Crystalline silicon (c-Si) has been used as the light-absorbing semiconductor in most solar cells, even though it is a relatively poor absorber of light and requires a considerable thickness (several hundred microns) of material. Nevertheless, it has proved convenient because it yields stable solar cells with good efficiencies and uses process technology developed from the huge knowledge base of the microelectronics industry.

Two types of crystalline silicon are used in the industry. The first is mono-crystalline, produced by slicing wafers (up to 150mm diameter and 350 microns thick) from a high-purity single crystal boule. The second is multi-crystalline silicon, made by sawing a cast block of silicon first into bars and then wafers. The main trend in crystalline silicon cell manufacture is toward multi-crystalline technology. For both mono- and multi-crystalline Si, a semiconductor homo-junction is formed by diffusing phosphorus (an n-type dopant) into the top surface of the boron doped (p-type) Si wafer. Screen-printed contacts are applied to the front and rear of the cell, with the front contact pattern specially designed to allow maximum light exposure of the Si material with minimum electrical (resistive) losses in the cell.

The most efficient production cells use mono-crystalline c-Si with laser grooved, buried grid contacts for maximum light absorption and current collection. Some companies are product ionizing technologies that by-pass some of the inefficiencies of the crystal growth/casting and wafer sawing route. One route is to grow a ribbon of silicon, either as a plain two-dimensional strip or as an octagonal column, by pulling it from a silicon melt. Another is to melt silicon powder on a cheap conducting substrate. These processes may bring with them other issues of lower growth/pulling rates and poorer uniformity and surface roughness. 

Each c-Si cell generates about 0.5V, so 36 cells are usually soldered together in series to produce a module with an output to charge a 12V battery. The cells are hermetically sealed under toughened, high transmission glass to produce highly reliable, weather resistant modules that may be warranted for up to 25 years. 

Thin film solar cells:

The high cost of crystalline silicon wafers (they make up 40-50% of the cost of a finished module) has led the industry to look at cheaper materials to make solar cells. The selected materials are all strong light absorbers and only need to be about 1micron thick, so materials costs are significantly reduced. The most common materials are amorphous silicon (a-Si, still silicon, but in a different

form), or the polycrystalline materials: cadmium telluride (CdTe) and copper indium (gallium) diselenide (CIS or CIGS). 

Each of these three is amenable to large area deposition (on to substrates of about 1 meter dimensions) and hence high volume manufacturing. The thin film semiconductor layers are deposited on to either coated glass or stainless steel sheet. The semiconductor junctions are formed in different ways, either as a p-i-n device in amorphous silicon, or as a hetero-junction (e.g. with a thin cadmium sulphide layer) for CdTe and CIS. A transparent conducting oxide layer (such as tin oxide) forms the front electrical contact of the cell, and a metal layer forms the rear contact. Thin film technologies are all complex. They have taken at least twenty years, supported in some cases by major corporations, to get from the stage of promising research (about 8% efficiency at 1cm2 scale) to the first manufacturing plants producing early product. 

Amorphous silicon is the most well developed of the thin film technologies. In its simplest form, the cell structure has a single sequence of p-i-n layers. Such cells suffer from significant degradation in their power output (in the range 15-35%) when exposed to the sun. The mechanism of degradation is called the Staebler-Wronski Effect, after its discoverers. Better stability requires the use of a thinner layer in order to increase the electric field strength across the material. However, this reduces light absorption and hence cell efficiency.

This has led the industry to develop tandem and even triple layer devices that contain p-i-n cells stacked one on top of the other. In the cell at the base of the structure, the a-Si is sometimes alloyed with germanium to reduce its band gap and further improve light absorption. All this added complexity has a downside though; the processes are more complex and process yields are likely to be lower. In order to build up a practically useful voltage from thin film cells, their manufacture usually includes a laser scribing sequence that enables the front and back of adjacent cells to be directly interconnected in series, with no need for further solder connection between cells.

 As before, thin film cells are laminated to produce a weather resistant and environmentally robust module. Although they are less efficient (production modules range from 5 to 8%), thin films are potentially cheaper than c-Si because of their lower materials costs and larger substrate size. However, some thin film materials have shown degradation of performance over time and stabilized efficiencies can be 15-35% lower than initial values. Many thin film technologies have demonstrated best cell efficiencies at research scale above 13%, and best prototype module efficiencies above 10%. The technology that is most successful in achieving low manufacturing costs in the long run is likely to be the one that can deliver the highest stable efficiencies (probably at least 10%) with the highest process yields.

Amorphous silicon is the most well-developed thin film technology to-date and has an interesting avenue of further development through the use of "microcrystalline" silicon which seeks to combine the stable high efficiencies of crystalline Si technology with the simpler and cheaper large area deposition technology of amorphous silicon. However, conventional c-Si manufacturing technology has continued its steady improvement year by year and its production costs are still falling too. The emerging thin films technologies are starting to make significant in-roads in to grid connect markets, particularly in Germany, but crystalline technologies still dominate the market. Thin films have long held a niche position in low power (<50W) and consumer electronics applications, and may offer particular design options for building integrated applications.

3rd Generation Technology:

Science and the industry have not yet achieved widespread application in photovoltaic cells, but solar concentration has been widely used in solar thermal electricity generation technology where the generated heat is used to power a turbine. Today, the 3rd generation approaches being investigated include Electrochemical PV cells, dye-sensitized titania solar cells, organic photovoltaic's, tandem cells, and materials that generate multiple electron-hole pairs.

Corporate Background

First Solar, Inc. is one of the largest publicly-held U.S. energy companies in the solar sector. It mainly into production of photovoltaic solar components using a thin film semiconductor process based on Cd-Te (Cadmium Telluride). The company works towards providing superior environmental benefits in addition to providing clean, sustainable energy. Presently it is the largest manufacturer of thin-film cells and world's second largest manufacturer of photovoltaic (PV) cell. By combining higher performance with low cost, First solar is providing truly sustainable energy solutions.

Corporate History

Glasstech Solar was founded by McMaster in 1984. McMaster envisioned the opportunity for low cost thin films made on a large scale. After trying amorphous silicon, he shifted to CdTe at the urging of Jim Nolan and founded Solar Cells inc. (SCI) in 1990. In February 1999, McMaster sold the company to True North Partners, an investment arm of the Walton family, owners of Wal-Mart. John T. Walton joined the Board of the new company, and Mike Ahearn of True North became the CEO of the newly minted First Solar. In its early years First Solar suffered setbacks, and initial module efficiencies were modest, about 7%. Commercial product became available in 2002. But production did not reach 25 MW until 2005. The company built an additional line in Perrysburg, Ohio, then four lines in Germany. In 2006 First Solar reached 75 MW of annual production and announced a further 16 lines in Malaysia. As of Q3 2009, First Solar is producing at over one Giga-watt annual rate. and in 2006 and 2007 was among the largest PV module manufacturers in the world. In 2009, First Solar invested in two additional production plants in Malaysia, consisting of four manufacturing lines each. This expansion is expected to increase First Solar's annual capacity by 424 megawatts (MW). Additionally, in the summer of 2009 First Solar announced plans to build its fourth production plant in France. Research and development takes place at the Ohio facility, and headquarters are in Tempe, Arizona.

Collaboration with Desertec:

To demonstrate the potential of photovoltaic (PV) solar technology to provide clean, sustainable energy on a vast scale by harnessing the desert sun, on March 2010, First Solar joined with Desertec. Another reason for which First Solar joined Desertec is to provide a significant portion of the electricity for the Middle East and Northern Africa as well as Europe by 2050 via a network of solar and wind energy sources. The manager of First Solar said, "We look forward to working with Desertec to demonstrate the potential of renewable energies - and PV in particular - to deliver clean, reliable power to the people of Africa and the Middle East as well as Europe," said Stephan Hansen, managing director of First Solar GmbH, the company's European sales and customer service unit for Europe, the Middle East and Africa. "The challenges of energy security and global warming demand bold solutions and Desertec certainly provides an ambitious vision".