LAZAR's SOLAR ENERGY GUIDE

Environmental concerns, desire for energy independence as well as government mandates and incentives drive increasing interest in solar power. There is plenty information on this subject scattered throughout the web. It is just not always easy to quickly find what you are looking for among the numerous web sites. This site is designed as an online reference guide for anyone looking for practical information on the sunlight uses in your home. 		Solar picture
Photo courtesy of NASA Gateway to Astronaut Photography of Earth

FACTS ABOUT THE SUN AND ITS RADIATED ENERGY



The word "solar" originated from the Latin "solaris," which means "of the sun." Technically speaking, the sun is a star, which is a body of hot gases that emits radiation from thermonuclear reactions.

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All bodies with temperatures above absolute zero radiate certain energy in the form of electromagnetic waves whose amount depends on the body's temperature. As the temperature rises this thermal radiation rapidly goes up: according to Stefan-Boltzmann law the electromagnetic radiation per unit surface area is proportional to the fourth power of the absolute temperature. The scientists estimate that the temperature at the sun's radiative surface is about 5500°C (9900°F) and the total amount of power radiated in all directions called solar luminosity, is 3.84x1026 watts, which is about 63,000 kW per square meter of sun's surface. According to science, this power is produced at the core of the sun by nuclear fusion. Its intensity per unit area drops with the squared distance. Our planet intercepts only a small fraction of the sun's radiated power, determined by the Earth cross section area and the Earth-Sun distance. For more information see calculation of the energy that reaches the Earth).
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HOW IS SOLAR ENERGY USED



In a broad sense, sunlight along with gravitation, geothermal energy and tides, is the fundamental physical source for most forms of renewable energy, which we can practically utilize. For example, the sun's heat causes temperature differences between various areas, which produce winds whose power can be used in a home wind generator. Sunlight's heat also causes evaporation of water, which then falls on high elevations and flows down to the sea. Its streams can be used in hydroelectric turbines. However, the terms "solar energy uses" usually refers to the applications in which the sun's radiation is converted directly to usable products. Currently the resulting products of sunlight conversion systems fall into three basic categories: electricity, fuels, and heat. The first major application of photovoltaic technology was launched in US in 1958 with powering orbital satellites. Today this technology is utilized in both large-scale and small-scale applications. Examples of solar applications and uses in the world are central power stations, space installations, private home systems, outdoor lights, and portable consumer electronic devices. In residential homes sunlight can be used today for heating water and swimming pools and for generating electricity in prime power off-grid or on-grid backup generators.

HOW DOES SOLAR POWER WORK



Electromagnetic radiation in general interacts with matter in different ways in different parts of its spectrum: it can be reflected, absorbed or transmitted. When electromagnetic waves strike an object they can cause various effects, such as excitation of the molecules, excitation and ejection of electrons, and oscillation of charge carriers in the object. As the result, a portion of the radiated photons can convert to heat, electricity or chemical energy. A solar system that uses this energy can be active or passive. In active systems, the sun's radiation is converted or transported by various controlled electrical or mechanical equipment. For examples, photovoltaic (PV) based devices and solar power plants can actively generate electricity from sunlight. In PV systems, the electromagnetic radiation is transferred to electricity in the form of DC voltage by using PV cells. This voltage can then be transformed by solid-state SMPS power electronics devices to required voltages, such as a conventional household AC voltage. In the power plants, the heat from the solar thermal collectors heats a fluid, which produces steam that turns the blades of a turbine of an electric generator. A concentrating solar power system could also store captured sun rays energy as heat in a thermal medium (such as heating water or dry rocks) for later use. Today's photonic technology also allows to convert the electromagnetic radiation into chemical energy through a chemical reaction (such as photoelectrolysis that dissociates water into hydrogen and oxygen). Active solar hot water systems utilize pipes and pumps or fans to transport heated water.

In the passive designs, the sun's radiation is converted to thermal energy, which is then transported passively by natural convection without use of external energy. It can be used to heat, for example, water and buildings.


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