Solar Energy
About 47 percent of the energy that the sun releases to the earth actually reachesthe ground. About a third is reflected directly back into space by the atmosphere. Thetime in which solar energy is available, is also the time we least need it least - daytime. Because the sun's energy cannot be stored for use another time, we need to convert thesuns energy into an energy that can be stored. One possible method of storing solar energy is by heating water that can beinsulated. The water is heated by passing it through hollow panels. Black-coated stealplates are used because dark colors absorb heat more efficiently. However, this method only supplies enough energy for activities such as washingand bathing. The solar panels generate "low grade" heat, that is, they generate lowtemperatures for the amount of heat needed in a day. In order to generate "high grade"heat, intense enough to convert water into high-pressure steam which can then be used toturn electric generators there must be another method. The concentrated beams of sunlight are collected in a device called a solar furnace,which acts on the same principles as a large magnifying glass. The solar furnace takes the
Every atom has the same numberof electrons as there are protons, so, on the whole, it is electrically neutral. Some recombine after a lifetime of theorder of one millisecond, neutralizing their charges and giving up energy in the form ofheat. The opposite action also takes place, holes fromacceptor atoms in the p-region crossing into the n-region, combining with electrons andproducing positively-charged impurity atoms [Book 4]. Siliconso doped is called "n-type" [Book 5]. In the simplest model of the atom, electrons orbit a central nucleus,composed of protons and neutrons. This reverse field plays avital part in the functioning of the device. Solar energy generators are very clean, little waste is emitted from the generatorsinto the environment. On the other hand, boron, with a valence of 3, is anacceptor, leaving so-called "holes" in the lattice, which act like positive charges and renderthe silicon "p-type"[Book 5]. The net result of these movements is the disappearance of conduction electronsand holes from the vicinity of the junction and the establishment there of a reverse electricfield, which is positive on the n-side and negative on the p-side. Photon energy is inversely proportional to wavelength. Holes, like electrons, will remove under the influence of an applied voltage but, asthe mechanism of their movement is valence electron substitution from atom to atom, theyare less mobile than the free conduction electrons [Book 2]. Thehighly energetic photons in the ultra-violet and blue part of the spectrum are absorbedvery near the surface, while the less energetic longer wave photons in the red and infraredare absorbed deeper in the crystal and further from the junction [Book 4]. Solar cells today are mostly made of silicon, one of the most common elements onEarth.
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Acceptance Essays
