--The sun produces a tremendous amount of energy, but only a small portion of it is radiated to the Earth, because most of it dissipates into outer space.

--Direct solar energy works best when the sun is most intense.

--Solar radiation varies in intensity depending on:

*Latitude: Areas at lower latitudes (closer to the Equator) receive more solar radiation annually than do latitudes closer to the North and South Poles.

*Season: Since the sun is directly overhead in the summer and lower on the horizon in winter, more solar radiation is received in the summer than during the winter.

*Time of day: Solar radiation is more intense in the afternoon when the sun is high in the sky than at dawn or dusk when it is low in the sky.

*Degree of cloud cover: Clouds absorb some of the sun's energy, thereby reducing its intensity.

How can we heat buildings and water using solar energy?

The sun's energy is directed by mirrors onto a fluid-filled pipe. The heated fluid is sent to a turbine-generator to generate electricity. (http://www.psa.es/project/tower/maindoc.html)

These are wafers or thin films of crystalline silicon that are treated with certain metals in such a way that they generate electricity when solar energy is absorbed. Photovoltaic solar cells are also used in things like watches and calculators, and were primarily developed for the space program, to power satellites.

*Advantages: They generate electricity with no pollution and minimal maintenance. They can be used on any scale, small to large.

*Disadvantages: They are not very efficient at converting solar energy to electricity. PV cells are also very expensive to produce. The number of solar panels needed for large-scale use requires a great deal of land.

  http://www.eren.doe.gov/femp/greenfed/3.0/3_1_energy_conservation.htm

            http://www.eren.doe.gov/pv/whyuse.html

Photovoltaic electricity can be used to split water in a process called electrolysis. This produces hydrogen gas, which represents a chemical form of solar energy. When burned in the presence of oxygen, it produces usable energy and water. Hydrogen can be transported by pipelines to users. This process is similar to gas burning in an internal combustion engine. (6)

A solar pond is a pond of water used to collect the sun's energy. The pond must be dug one to several meters deep and lined with black plastic or painted black at the bottom. It is then filled with very salty water, and then fresh water is added. Sunlight heats the black bottom and the temperature rises to between 90 and 100 degrees Celsius. The heat becomes trapped because the salt is heavier than the fresh water that is on top and can't rise. The water is then pumped to a boiler, which is then heated further to produce steam, which drives a turbine to create energy. (http://www.schwaben.de/home/kepi/solar5.htm)

In biomass energy, wood, fast-growing plant and algal crops, crop wastes, and animal wastes are used as fuel. In homes, biomass can be used for space heating or for cooking. Commercial-Industrial uses include space heating, hot water heating, and electricity generation. (http://solstice.crest.org/renewables/re-kiosk/biomass/index.shtml)

The things mentioned above are burned directly to obtain energy.

It can be converted to liquid fuels such as methanol (methyl alcohol) and ethanol (ethyl alcohol). This can then be used in internal combustion engines.

Animal wastes can be converted into biogas. Biogas is usually composed of a mixture of gases and can be stored and transported easily like natural gas. It is produced from plant matter of one form or another.

In India and China, biogas digesters are used. A biogas digester is a vat that uses bacteria to break down household wastes, including sewage. The gas produced by the bacteria is burned as a fuel.

 http://www.nrel.gov/research/industrial_tech/biomass.html

Wind energy is formed when the radiant energy of the sun is transformed into mechanical energy.

Where is wind energy most profitable?

*Advantages: It produces no waste or emissions of sulfur dioxide, carbon dioxide, or nitrogen oxides. Also, combining wind farms with cattle grazing (like in Altamont, CA) is a very productive and profitable use of land.

*Disadvantages: Wind machines detract from the beauty of the landscape. They are also noisy (like the howling of the wind over cables) because of the passing of the wind over the blade structure. Also, there are safety issues. People working in, living in, or passing through a wind farm area can be hurt in the event of the toppling of the tower or another part. Wind machines can also damage birds. Many birds are killed from flying into the blades of the windmills. The construction of wind farms in offshore ocean waters may be major migration routes for birds. Also, the noise of the turbine and its actual or potential effects on nearby breeding or resting birds. (4,10) http://www.awea.org/news/news990107.html

Hydropower is the energy of falling or flowing water used to make electricity. Currently hydropower produces approximately 53 percent of the world's electricity, making it the form of solar energy in greatest use.

The sun's energy drives the hydrologic cycle, which encompasses evaporation from land and water, transpiration from plants, precipitation, and drainage and runoff. As water flows from higher elevations back to sea level, we can harness its energy.

The potential energy of water held back by a dam is converted to kinetic energy as the water falls down a penstock, where it turns turbines to generate electricity.

A dam raises the water level, increasing the potential energy of the water. A dam is also used to create a water reserve to compensate for changes in river flow or power demand.

*Disadvantages: Building a dam changes the natural flow of a river. It also causes water to back up, flooding large areas of land and forming a reservoir. This destroys plant and animal habitats. In arid regions, the creation of a reservoir behind a dam results in greater evaporation of water because the reservoir has a larger surface area in contact with the air than the stream or river did. This creates serious water loss and an increase in the salinity of the remaining water. Dams also destroy farmlands, displace people, are expensive to build, and have a limited life span of 50 to 200 years. This is because over time, the reservoir fills in with silt until it cannot hold enough water to generate electricity.

Three Gorges Dam, is located on the Yangtze River in China, the third largest river in the world.

Ocean thermal energy conversion is the generation of electricity from ocean temperature gradients (the differences in temperature at various ocean depths).

Warm surface water is pumped into the power plant, where it heats a liquid, such as ammonia, to the boiling point (-33 degrees C, very low). The ammonia steam then drives a turbine to generate electricity as ammonia is cooled by the very cold water from the depths of the ocean.

*Disadvantages: Bringing massive quantities of cold water to the surface in a tropical area could be dangerous. Dissolved gases, cloudiness, nutrient levels, and salinity gradients (difference in salt concentrations), and temperature could be altered. This could have a profound impact on marine organisms.

http://bigisland.com/nelha/otec.html

Ocean waves are produced by winds, which are caused by the sun.

Geothermal energy is the heat contained in the Earth that can be recovered and put to useful work. It is sometimes considered renewable or very slowly renewable because it takes many years for natural processes to replace groundwater. It is actually a form of nuclear energy.

California's geothermal power plants produce about one-half of the world's geothermally generated electricity. The geothermal power plants produce enough electricity for about two million homes. http://geothermal.marin.org/pwrheat.html

Iceland is one area, because it has intense volcanic activity and numerous hot springs. Also, it is located on the mid-Atlantic ridge, a boundary between two continental plates. Geothermal energy is used to heat many of the homes in Iceland, and most of their fruits and vegetables are grown in geothermally heated greenhouses.

*Disadvantages: As water from the hot springs is removed, surrounding land may sink. Geothermal energy produces pollutants such as hydrogen sulfide and carbon dioxide. Another downfall is that it becomes non-renewable if the hot groundwater is tapped faster than it can be replaced from natural processes.

Tidal Energy

Tidal energy is caused by the change in water level between high and low tides.

How does tidal energy work?

As tides go in and out, energy can be captured by tidal power stations, which can be stretched over estuaries, beaches, deltas, or any other place affected by tides. When high tide comes in, water goes through a turbine to create electricity. Some water is caught by what is called a barrage. This water is captured when a gate is lowered from the barrage. When low tide comes, the gate is raised and the water flows out and transfers its energy through the turbines.

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Energy Conservation vs. Energy Efficiency

 

Energy Conservation

Energy conservation is moderating or eliminating wasteful or unnecessary energy-consuming activities.

There are many ways energy can be saved in homes. You can save energy by turning off appliances, TVs and radios that are not being used, and turning off the light when no one is in the room. Also by insulating walls and attics, the amount of energy it takes to heat or cool your home will be reduced. Recycling is also important because it takes a lot of energy to make things like newspapers, aluminum cans, and plastic bottles.

We can also save energy in our automobiles by making sure the tires are properly inflated and making sure it is tuned up (has clean air and oil filters, and is running right). This will reduce the amount of gasoline the automobile uses. Also, be sure not to overload your automobile. For every extra 100 pounds, you cut your mileage by one mile per gallon.

Energy Efficiency

Energy efficiency is using technology to accomplish a particular task with less energy.

An example of energy efficiency in reference to automobiles, would be coming up with more fuel-efficient cars.

 

*Advantages: They reduce air pollution and acid precipitation. They also cost less than the development of new sources or supplies of energy. They could also cut our carbon dioxide emissions by millions of tons each year, thereby slowing global climate change.

 

*How else can we conserve energy in our homes?*

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Solar Cooking

2. 

   Solar cooking uses the sun to cook food. It is practiced in most developing countries. A simple solar cooker can be made out of a box. Enclose the inside with aluminum foil, so when you point the box towards the sun it will become hot. You can increase the temperature of it by using mirrors instead of aluminum foil. This will decrease your cooking time.

   There are several other ways to construct solar cookers.

   In countries such as Africa, food had to be cooked using wood, which would eventually deplete the forests and destroy what might have been arable land. Also, the collection of wood consumes a lot of time, energy, and money. Now solar cooking is becoming more popular. It even reduces smoke and air pollution.

    http://www.windows.umich.edu/cgi-bin/tour_def/headline_universe/hunger.html

   http://home.earthlink.net/~drduggee/solar.htm

   *What are your thoughts on solar cooking? *

    

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     Bibliography

   1. Aldrich, Bob. (1999, June 15). Energy Quest. The Energy Story. <http://www.energy.ca.gov/education/renewableroad/index.html (1999, September 14).

   2. "Energy conversion" Encyclopedia Britannica Online. <http://www.search.eb.com/bol/topic?eu=108532&sctn+20&pm=1 (1999, September 7). START="3">

   FEMP. Energy and Conservation Issues. <http://www.eren.doe.gov/femp/greenfed/3.0/index.htm (1999, September 7).

   4. Heathcote, Isobel W. 1997. Case study 1: Denmark. p. 5-14. In Environmental Problem Solving, a Case Study Approach. McGraw Hill, Inc., New York.

   5. Lovins, Amory B. 1997. Soft Energy Paths: Toward a Durable Peace. p. 97-103. In Theodore D. Goldfarb's Sources: Notable Selections in Environmental Studies. Dushkin Publishing Group, Connecticuit.

   6. Raven, Berg, and Johnson. 1998. Renewable Energy and Conservation. p. 247-269. In Environment. Saunders College Publishing, New York.

   7. Schoch, Robert M. 1996. The Dangers of Conservation. p. 47-48. In Case Studies in Environmental Science. West Publishing Company, Minnesota.

   8. SOLSTICE. An Energy Guide for Pennsylvania Consumers. <http://solstice.crest.org/efficiency/state-guides/pdf-files/pennsylvania.pdf (1999, September 7).

   9. U.S. Department of Energy. (1998, December). Renewable Energy Annual 1998. <http://www.eia.doe.gov/cneaf/solar.renewables/rea_data/html/front-1.html - tabh1 (1999, September 7)

   10. Wasserman, Harvey. 1999. Inherit the wind. p.83-87. In John Allen's Environment 99/00. Dushkin/McGraw Hill Inc., Connecticut.
    

    This web page was created by Erin English eenglish@falcon.lhup.edu  (Senior Journalism Major)

   October 25, 1999