Solar Energy  Elmhurst College
 Chemistry Department
   Virtual ChemBook


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Energy from the Sun

Introduction:
 
Incoming energy (Insolation) from the sun is mostly in the form of ultraviolet, visible, and infrared energy. There are also cosmic rays.
A portion of the energy is reflected (Shortwave reflectance) back into space before reaching the earth's surface. The majority of the energy (Shortwave absorption) is used in the planet's heat cycle, evaporation of water to run the water - weather cycle, wind, and waves. Only a small fraction of the energy is actually utilized for photosynthesis in plants.
 
An important fact to remember for future discussions is that much of the energy is changed in form to infrared radiation (Long wave Terrestrial Emission) which is eventually radiated back into space.
 
The Greenhouse Effect Energy stored in the atmosphere is calculated by computing how much radiation is on average produced by the surface temperature (using a conversion method called the black body model) and then subtracting the amount that leaves the atmosphere (i.e. the outgoing long wave radiation). The difference is the Greenhouse Effect Energy being retained in the atmosphere measured in watts per meter squared. Percent Greenhouse Effect (March) - Shows the Greenhouse Effect as a percent of possible energy that is stored in the atmosphere compared to the total outgoing energy produced by the earth as a black body.


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Electromagnetic Spectrum:
 
The electromagnetic spectrum is important to understand as a number of environmental issues depend on it.
 
Electromagnetic energy is in the form of waves, with the different types characterized by the energy associated and the wavelength. For example gamma rays are very high energy, but with short wavelength. Radio waves are low in energy, but long in wavelength. Visible light is somewhere in the middle, all of the other waves are invisible to the human eye, but may be measured with various instruments.
 
Environmental Effects of Electromagnetic Radiation:
 Cosmic rays, gamma rays, and X-rays are important to understanding nuclear radiation. The energies are very high and will break bonds in molecules and ionize atoms and molecules.
 Ultraviolet radiation is important in understanding the formation and function of the ozone layer in the protection from skin cancer. The energy of UV radiation is sufficient to break bonds in some molecules.
 Infrared radiation is important to understanding the Greenhouse Effect and global warming. The energy is much lower and is only able to vibrate and bend atoms involving bonds of molecules.
 Microwaves are used for cooking because the energy is quite low but sufficient to cause the rotation of water molecules. This eventually causes the remaining molecules in the food to heat up.