Solar Basics

Solar Basics
Grade: A. Reason: ready, BUT problems with the print page (blank page)
Energy from the Sun
The sun has produced energy for billions of years. Solar energy is the sun’s rays (solar radiation) that reach the Earth. This energy can be converted into other forms of energy, such as heat and electricity.

Radiant energy from the sun has powered life on Earth for many millions of years.

Source: NASA
In the 1830s, the British astronomer John Herschel famously used a solar thermal collector box (a device that absorbs sunlight to collect heat) to cook food during an expedition to Africa. Today, people use the sun's energy for lots of things.

Solar Energy Can Be Used for Heat and Electricity
When converted to thermal (or heat) energy, solar energy can be used to:

Heat water — for use in homes, buildings, or swimming pools
Heat spaces — inside homes, greenhouses, and other buildings

Solar energy can be converted to electricity in two ways:

Photovoltaic (PV devices) or “solar cells” change sunlight directly into electricity. PV systems are often used in remote locations that are not connected to the electric grid. They are also used to power watches, calculators, and lighted road signs.
Concentrating Solar Power Plants generate electricity by using the heat from solar thermal collectors to heat a fluid which produces steam that is used to power the generator. Out of the 16 known concentrating solar power generating units operating in the United States at the end of 2007, 10 of these are in California, 5 in Arizona, and 1 in Nevada. No statistics are being collected on concentrating solar plants that produce less than 1 megawatt of electricity, so there may be smaller solar plants in a number of other States.

Two drawbacks of solar energy are:

The amount of sunlight that arrives at the Earth's surface is not constant. It depends on location, time of day, time of year, and weather conditions.
Because the sun doesn't deliver that much energy to any one place at any one time, a large surface area is required to collect the energy at a useful rate.
Offshore Solar
(From: http://www.eia.doe.gov/kids/energyfacts/sources/renewable/ocean.html)
Research is being done to place solar farms over the ocean. With oceans making up 70% of the Earth’s surface, there are opportunities to place solar farms near the coasts. Currently, solar energy is used on offshore platforms and to operate remotely located equipment at sea. Solar energy is a renewable energy source, is free, and does not pollute.

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Where Solar is Found
Grade: A. Reason: ready
Solar Energy Is Everywhere the Sun Shines

Click to enlarge »
Source: National Renewable Energy Laboratory, U.S. Department of Energy

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Source: National Renewable Energy Laboratory, U.S. Department of Energy
World Map of Solar Resources

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Source: United Nations Environment Programme (UNEP), NASA Surface meteorology and Solar Energy (SSE), 2008.
Solar energy is by far the Earth's most available energy source. Solar power is capable of providing many times the total current energy demand. But it is an intermittent energy source, meaning that it is not available at all times. However, it can be supplemented by thermal energy storage or another energy source, such as natural gas or hydropower.

California Has the World’s Biggest Solar Power Plant
Nine solar power plants, in three locations, in California's Mojave Desert comprise the Solar Energy Generating Systems (SEGS). SEGS VIII and IX (each 80 megawatts), located in Harper Lake, are, individually and collectively, the largest solar power generating plants in the world. SEGS plants are concentrating solar thermal plants.

Concentrating solar power technologies use mirrors to reflect and concentrate sunlight onto receivers that collect the solar energy and convert it to heat. This thermal energy can then be used to produce electricity via a steam turbine or heat engine driving a generator.

Europe Has Some Large Photovoltaic Power Plants
Another solar generating technology uses photovoltaic cells (PV) to convert sunlight directly into electricity. PV cells are made of semiconductors, such as crystalline silicon or various thin-film materials. Photovoltaics can provide tiny amounts of power for watches, large amounts for the electric grid, and everything in between.

Recently multi-megawatt photovoltaic plants have also been built. The Moura photovoltaic power station in Portugal and the Waldpolenz Solar Park in Germany, both completed in 2008, represent the trend toward larger photovoltaic power stations.

Solar Power Can Be Used Almost Anywhere at a Variety of Scales
Low-temperature solar collectors also absorb the sun's heat energy, but instead of making electricity, use the heat directly for hot water or space heating in homes, offices, and other buildings.

Even larger plants than exist today are proposed for construction in the coming years. Covering 4% of the world's desert area with photovoltaics could supply the equivalent of all of the world's electricity. The Gobi Desert alone could supply almost all of the world's total electricity demand.

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Solar Photovoltiac
Grade: B. Reason: Too technical for kids and diagram is confusing
Photovoltaic Cells Convert Sunlight into Electricity
A photovoltaic cell, commonly called a solar cell or PV, is the technology used to convert solar energy directly into electrical power. A photovoltaic cell is a nonmechanical device usually made from silicon alloys.

Photons Carry Solar Energy
Sunlight is composed of photons, or particles of solar energy. These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum.

When photons strike a photovoltaic cell, they may be reflected, pass right through, or be absorbed. Only the absorbed photons provide energy to generate electricity. When enough sunlight (energy) is absorbed by the material (a semiconductor), electrons are dislodged from the material's atoms. Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to free electrons, so the electrons naturally migrate to the surface.

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