Solar Energy Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Solar energy comes from the sun in the form of electromagnetic radiation. This energy generated by the sun exceeds any known form of energy generated by man. The amount of incoming radiation, known as the solar constant (because it is almost invariable), measured by satellite at Earth orbit, is 1370 watts per square meter.

The sun radiates like all other hot bodies. When the sun’s radiation reaches the Earth, it contains wavelengths ranging from invisible ultraviolet, which can cause skin sunburn and eye damage (0.2 to 0.38 micrometers), through the visible rainbow colors (0.38 to 0.75 micrometers) and up to invisible infrared, which we sense as heat (0.75 to 2.5 micrometers). Only low levels of ultraviolet and infrared rays reach the Earth’s surface since they are strongly absorbed by the Earth’s atmosphere.

It is believed that the sun generates energy by the nuclear process called proton-proton fusion in which four hydrogen protons are fused into a single helium alpha particle under conditions of extremely high temperature and pressure that exist within the sun’s core. This process releases energy that we know as solar energy, along with two positive electrons and two neutrinos. The sun, as the main source of energy on Earth, delivers light and heat essential to the existence of life. Sunlight drives photosynthesis, an important biochemical process, in which plants, algae, and some bacteria convert solar energy into chemical energy. During photosynthesis, plants produce oxygen and nutrients while absorbing carbon dioxide, thus making Earth a vital, living, and breathing planet. Fossil fuels in the form of coal, oil, and natural gas also come from such plants. Warmth from the sun is essential to keep the water on Earth in its liquid state-hence, without the sun, the Earth would be an icy planet.

Solar energy is the driving force for most environmental processes on the Earth’s surface and in the atmosphere. The Earth is heated by sunlight, and to maintain steady temperature it gives energy away to space, thus the Earth begins to radiate. The receiving and giving of heat is made possible by the flow of air, which influences spatial variation of temperature and pressure, thereby creating wind and moisture that determine weather and climate zones. The power of hurricanes is driven by the heating of water and subsequent heat release during condensation. In desert environments, wind power heaps sand into dunes. A portion of incoming solar radiation is reflected by clouds, scattered (making the sky appear blue and the clouds white or gray) and absorbed, e.g., ultraviolet radiation is almost completely blocked by the ozone (three-atom oxygen) layer.

According to Vien’s displacement law of physics, since the Earth is cooler than the sun, it must re-emit energy with longer wavelengths than the sun emits, with the peak at far infrared (10 micrometers). Earth’s re-emitted heat is absorbed by minor components of the atmosphere called greenhouse gases: carbon dioxide, water vapor, methane, nitrous oxide, and ozone, thus creating a blanketlike protection and keeping the ground warmer by about 33 degrees C than the Earth would otherwise be. Most scientists believe that this natural greenhouse effect has been enhanced by anthropogenic (human-caused) activities that contribute to global warming (the increase of average temperature on Earth). Carbon dioxide, a major greenhouse gas in the atmosphere, has increased significantly due to the burning of coal for electricity generation and heating, as a result of deforestation, and also in the form of emission of exhaust gases from vehicular engine combustion. Emission of gases from industrial processes, like perfluorocarbons, chlorofluorocarbons, halons, and agriculturally produced methane and nitrous oxide also contribute to global warming. Efforts are being made to limit their release into the atmosphere, but global warming is expected to continue since many of the greenhouse gases have a long lifetime in the atmosphere.

Ozone produced at high altitudes by the action of sunlight on ordinary two-atom oxygen is also a greenhouse gas, but importantly, it absorbs ultraviolet light and protects living beings from the damaging effects of ultraviolet light on genetic material. Recently concern has arisen due to the fact that gases escaping from refrigerators, air conditioners, and aerosols are broken up in the stratosphere by ultraviolet light, releasing chlorine that damages the ozone layer. These gases also persist in the atmosphere for many years. Because of the damage to the ozone layer, their use is being phased out.

Solar Power

Over the past several decades, techniques for harnessing solar energy have been developed as people realize the environmental costs and limited supply of fossil fuels. The most popular output has been the photovoltaic cell, a light-absorbing device that delivers electricity. An array of many photovoltaic cells becomes a solar battery, also called a solar panel. Solar batteries have been used where other power supplies are absent, such as in remote locations with no access to electricity grids and on spacecraft. Use of solar panels is being encouraged in developing countries of south Asia and Africa, where the supply of electricity from national grids is often unreliable or unavailable for long durations.

New generations of power plants use solar heat for generator rotation to produce electricity. There are three main systems that concentrate solar power to the levels needed for power generation. The parabolic-trough system concentrates heat through long curved mirrors tilted toward the sun and focuses sunlight on a pipe that runs down the center of the trough. This heats oil flowing through the pipe. The hot oil boils water in a conventional steam generator to produce electricity. The dish/engine system uses a mirrored dish, which collects heat onto a receiver transferring the heat to the fluid within the engine. The heat causes the fluid to expand against a piston or turbine to produce mechanical power. The mechanical power is then used to run a generator producing electricity. The power-tower system uses a large field of mirrors to concentrate sunlight onto the top of a tower, where a receiver is mounted. This heats molten salt flowing through the receiver. The salt’s heat is then used to generate electricity through a conventional steam generator. Molten salt retains heat efficiently, thus it can be stored for days before being converted into electricity, making it possible to produce electricity on cloudy days or after sunset.

Solar energy has simpler uses as well. Smaller thermal collectors consisting of a metal box with a mirror or focusing lens to collect heat are being used in solar cookers and ovens. On a sunny day it is possible to obtain temperatures of 150-200 degrees C in the solar cooker, enough to cook food or bake. Governments and humanitarian organizations around the world are encouraging people in rural areas without electricity to use solar cookers to help stop deforestation, since in many remote rural areas wood is the principal fuel.

Development of various methods of harnessing solar energy has also influenced modern architecture. Examples include sun-facing and roof-windows, movable awnings repositioned seasonally to create shadows in the summer and exposure to sunlight in the winter, thermal collectors for water heating, and photovoltaic solar panels on roofs. Solar collectors coupled with plastic optical fibers are used to send sunlight into the interior of buildings and to illuminate them.

The installation of solar panels is more expensive than the setting up of conventional electricity grids and the best locations for the conversion of solar power into electricity, such as deserts, are often far from places with high electricity demand. Also, during nights and cloudy days solar energy has to be stored. Additionally, DC to AC voltage converters are necessary to make photovoltaic solar panels compatible with electricity grid devices. On the other hand, the major advantage is that solar energy especially for electricity production is pollution free. With new technological developments making the conversion of energy more efficient, and legislation providing cheaper and easier access to unconventional energy sources, solar equipment is expected to become more affordable. For areas with a large number of cloud-free days, solar energy together with other forms of unconventional energy such as thermal and wind power holds great promise in alleviating dependence on fossil fuels and on foreign sources.

Bibliography:

T.J. Quinn, Frohlich, “Accurate Radiometers Should Measure the Output of the Sun,” Nature (v.401, 1999);
Michael E. Ritter, The Physical Environment: An Introduction to Physical Geography, www.uwsp.edu;
P. Stern, “From Stargazers to Starships,” National Aeronautic and Space Administration, www-spof.gsfc.nasa.gov.