How Solar Cells Are Manufactured
Solar power is being touted as one of the solutions to the energy needs of a hungry world. This brings up the rather fundamental question of how solar cells are actually manufactured.
The vast majority of solar cells on the market these days are polysilicon. These are the cells you see in panel systems on homes and portable versions on boats and motorhomes. The panels are essentially a grouping of individual cells. A single cell does not produce much electricity, but a group does.
The first step in manufacturing a solar cell is preparation of the silicon. Most cells are created using silicon dioxide. It is first exposed to severe heat in a furnace, which reduces it to a purity of 99 percent. It then is put through another purification process that results in 99.5 percent purity, the grade needed to build cells.
Once the silicon is process, the next step is the crystallization of the silicon. The silicon is melted. During the melting, a material such as boron is added. The specific additive creates the electrical basis of the silicon. In solar cells, this is p-type or positive charged.
At this point, the silicon is in the form of ingots. These are then cut in very thin wafers using computer guided machinery. The depth of the wafers is typically 200 to 300 microns. The wafers are then cleaned and we move to the next step.
Now it is time to actually build the cells. The cells are immersed in a negative charge chemical in water. An anti-reflective layer is then added. This is what makes solar cells and panels look dark, often blue. Silver or aluminum conductors are then attached to the cells so electricity can be conducted out of the cells.
At this point, it is panel time. The cells are organized in rows on a sheet. They are then connected. A sheet of glass or plastic is placed over them for protection. The edges are then framed to create more protection. At this point, you have a solar panel system and are ready to go.
An individual solar cell is not particularly powerful. It will produce roughly half a volt. The problem is efficiency. Polysilicon only converts between 8 and 15 percent of the sunlight hitting it into electricity. As efficiency improves, panels should get smaller and cheaper.
Rick Chapo is with SolarCompanies.com - a directory of solar energy companies.
What is Time ?
Time is an abstract concept that we generally take for granted. Time passes in years, months, days, hours, minutes and seconds without much thought. However, humans have developed extremely complex ways of measuring time and maintaining accurate time references. From sundials to atomic clocks and NTP time servers, to maintain time on computer networks, people have strived to accurately measure time.
This article discusses the fundamental nature of time, how it is measured, by movement, and how it is related to the concept of space. It also describes the spin-offs from high technology time references and International time standards.
Time Measured By Movement
Humans relate and measure time with reference to movement. The hands of a clock moving around a clock-face describe hours, minutes and seconds. A year is described by the rotation of the Earth around the Sun. A month is described by the rotation of the moon around the Earth. A day is described by the rotation of the Earth itself. In fact space and time are closely intertwined.
Space and Time
Einstein's General Theory of Relativity suggests time is closely related to the concept of space. Both time and space began with the Big Bang and the creation of the Universe some 14 Billion years ago. At the instance of the Big Bang, all matter was tightly packed into a tremendously dense, infinitely small, hot state. The universe, suns, planets and all matter contained within them emerged from this infinitely small dot.
The Theory of Relativity suggests that the Universe will reach a maximum size and begin to collapse back to its original state. The universe will become denser and hotter and return to a state similar to that from which it started. However, some of the latest observations of space have shown that galaxies are moving away from us at an ever-increasing rate. This implies that the Universe will continually cool and expand.
Measuring Time
The study of time measurement is called Horology. During Human history a large variety of devices have been used to measure time. Sundials were among the earliest examples of time measurement devices. A sundial casts a shadow on a series of markings that indicate the current hour of the day. More commonly in use today are mechanical or electronic clocks. Mechanical clocks are generally regulated by the movement of a pendulum. Electronic clocks are based on the resonance, or movement, of a crystal oscillator.
Modern atomic clocks, based on frequency reference masers, can maintain accurate time measurement to an astonishing degree. Atomic clocks form the basis of the Global Positioning System (GPS), which can provide positioning information for any location on the planet. NTP time servers use the Network Time Protocol and GPS time to ensure time synchronisation of computers and computer networks across the globe.
World Time
The measurement of time is critical to the modern way of life. So much so that International Standards exist to coordinate time. The basis of world time is Coordinated Universal Time (UTC). World time is split into a series of longitudinal time zones. Time zones are generally one hour apart and their local time is referenced as an offset from UTC time.
Summary
Time is an abstract concept that is inextricably linked to the concept of space and the creation of the Universe. Humans have strived for millennia to maintain accurate time references. Modern technology allows us to maintain highly accurate time references. Atomic clock technology has resulted in the creation of the GPS system and NTP time servers. The world has created an internationally agreed measurement of time, UTC time.
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The author, Simon Davies, is a Product Author who specialises in the documentation of GPS NTP server and time server synchronisation solutions. Click here if you would like more information about NTP Server and Time Server solutions.
Developing A Quality Homeschooling Lesson Plan Does Not Have To Be Hard
For the novice homeschooling parent, one of the most intimidating steps in the whole process is the idea of developing a lesson plan that is both effective and manageable. Fortunately, this does not have to be hard. The important thing to remember is that your child should be the main focus and you should do what is in the best interest of the child. For those choosing to do it on their own, this article will briefly outline nine steps to developing a quality lesson plan.
Step 1 The first thing that you will have to consider, obviously, is what you will be teaching. This, in large part, should be based upon your state or local school standards. In addition, you will also need to be aware of what grade level you are developing the lesson plan for and record a reasonable time estimate for your lesson plan.
Step 2 You will need to develop clear and specific objectives for the lesson plan from the beginning. However, you must note that these objectives should not be activities used in the lesson plan. Instead, they should be the specific learning outcomes of those activities.
For example, if you wanted to teach your child how to add 1 + 3, your defined objective may be that "the student will learn to demonstrate how to add 1 + 3."
Your objectives should also be measurable. What this means is that you need to make sure that you will be able to tell specifically whether the defined objectives were met or not. Keep in mind that you can certainly have more than one objective for a lesson plan if you feel that this would be more beneficial.
Step 3 You should show, as early as possible in your lesson plan, what materials you are going to use. Be specific in this case so that you can make sure another teacher will have everything that they could possibly need in the event that you, the parent, choose not to teach yourself.
Step 4 It is highly suggested that you write out an anticipatory activity as a way to lead into the main lesson plan. This will help develop the student's interest in learning what you are getting ready to teach.
Step 5 At this point you need to write the step-by-step procedures that will be performed to reach each of the above-mentioned objectives. These don't have to involve every little thing that the teacher will say and do but, they should list the relevant actions that the teacher needs in order to perform them.
Step 6 After all of the outlined procedures have been completed, you may want to provide your students with time for independent practice. This step will help to reinforce the main concepts and lessons learned. In addition, it will help the students determine for themselves what additional information they may need to fully comprehend the material.
Step 7 Before you start moving to the assessment phase of your homeschooling lesson plan, you should be prepared to create some sort of closure for the lesson plan. A good idea for this part of the process is to return to your anticipatory set discussed earlier. It is at this point that your children can ask for additional information or clarification on the main lesson points. After having gone through the lesson, you can return to the introduction exercise and ask how things may have changed given what they have just learned.
Step 8 For this step, it is a good idea to include a "connection" section, which clearly shows how the lesson plan could be integrated with other subjects. This builds on step 7 and by putting a lot of work into it, you can really help to develop complete thematic units that help integrate related topics into many different subjects.
Step 9 In this step, you will want to write your assessment and evaluation. In reality, many lesson plans don't really need them. However, they are helpful and most of them should have some sort of evaluation as to whether or not the objectives were met.
The key to doing this is to make sure that the assessment specifically measures whether the objectives were reached or not. As a result of this step, there should be a direct correlation between the defined objectives and the evaluation assessments.
That's really all there is to creating a lesson plan! If you follow the steps as outlined here, you are on your way to writing a very thorough lesson plan that will be useful for you regardless of the subject that you may be teaching.
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David Dunlap is the founder of The Homeschooling Report, a daily blog designed to provide informative and relevant information for prospective and veteran homeschoolers alike. For more homeschooling information and resources, please visit http://homeschoolinginfoforyou.com/blog/
