The use of solar energy is not new and in fact, development of solar energy dates back more than 100 years, to the middle of the industrial revolution. Following is a brief overview of solar energy history and applications.

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A Century of Solar Power

The use of solar energy is not new. In fact, development of solar energy dates back more than 100 years, to the middle of the industrial revolution. Several pioneering solar power plants were constructed to produce steam from the heat of the sun, which was used to drive the machinery of the time. At the same time, Henri Becquerel discovered the photovoltaic effect; that is, the production of electricity directly from the sun. Becquerel's research was investigated and extended by, among others, Werner Siemens. Photovoltaic power remained a curiosity for many years, since it was very inefficient at turning sunlight into electricity. Early photovoltaic applications were geared more towards sensing and measuring light (such as a camera's light meter) than towards producing power. With the advent of the transistor and accompanying semiconductor technology, however, the efficiency of photovoltaic power increased dramatically. Photovoltaic power became more practical. Over the years, many companies, including Siemens Solar, have worked to increase the efficiency of photovoltaic power. Today, commonly available solar panels are 12% efficient, which is four times greater than only a few years ago. Today, solar power is still used in two primary forms: thermal solar, where the heat of the sun is used to heat water or another working fluid, which drives turbines or other machinery to create electricity; and photovoltaic, where electricity is produced directly from the sun with no moving parts. Siemens Solar manufactures photovoltaic panels which produce electricity directly from the sun.
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Solar Technology Today

Photovoltaic power can be produced in many ways, with widely varying efficiency and costs. They can be divided into two basic groupings: discrete cell technology and integrated thin film technology.
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Discrete Cell Technology

Single-crystal silicon

Sliced from single-crystal boules of grown silicon, these wafers/cells are now cut as thin as 200 microns. Research cells have reached nearly 24-percent efficiency, with commercial modules of single-crystal cells exceeding 15-percent.

Multicrystalline silicon

Sliced from blocks of cast silicon, these wafers/cells are both less expensive to manufacture and less efficient than single-crystal silicon cells. Research cells approach 18-percent efficiency, and commercial modules approach 14-percent efficiency. Edge-defined film-fed growth ribbons Nearly single-crystal silicon ribbons grown from a crucible of molten silicon, drawn by capillary action between the faces of a graphite die.

Dendritic web

A film of single-crystal silicon pulled from a crucible of molten silicon, like a soap bubble, between two crystal dendrites. Gallium Arsenide (GaAs) A III-V semiconductor material from which high-efficiency photovoltaic cells are made, often used in concentrator systems and space power systems. Research cell efficiencies greater than 25 percent under 1-sun conditions, and nearly 28 percent under concentrated sunlight. Multijunction cells based on GaAs and related III-V alloys have exceeded 30-percent efficiency.
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Integrated Thin Film Technology

Copper Indium Diselenide (CuInSe2), or CIS

A thin-film polycrystalline material, which has reached a research efficiency of 17.7 percent, delivers the highest completed module efficiency for full sized power modules, reaching over 11 percent. Amorphous Silicon (a-Si) Used mostly in consumer products for solar watches and calculators, a-Si technology is also used in building-integrated systems, replacing tinted glass with semi-transparent modules. The primary issue with a-Si technology remains the low efficiency and associated greater requirement for space and higher array installed cost and weight.

Cadmium Telluride (CdTe)

A thin-film polycrystalline material, deposited by electrodeposition, spraying, and high-rate evaporation. Small laboratory devices approach 16-percent efficiency, with commercial-sized modules (7200-cm2) measured at 8.34-percent (NREL-measured total-area) efficiency and production modules at approximately 7 percent.
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Advantages of Photovoltaic Power

Photovoltaic solar power is one of the most promising renewable energy sources in the world. Compared to nonrenewable sources such as coal, gas, oil, and nuclear, the advantages are clear: it's totally non-polluting, has no moving parts to break down, and does not require much maintenance. A very important characteristic of photovoltaic power generation is that it does not require a large scale installation to operate, as different from conventional power generation stations. Power generators can be installed in a DISTRIBUTED fashion, on each house or business or school, using area that is already developed, and allowing individual users to generate their own power, quietly and safely.

Rooftop power can be added as more homes or businesses are added to a community, thereby allowing power generation to keep in step with growing needs without having to overbuild generation capacity as is often the case with conventional large scale power systems But even when photovoltaic power is compared to other renewable energy sources such as wind power, water power, and even solar thermal power, there are some obvious advantages. First, wind and water power rely on turbines to turn generators to produce electricity. Turbines and generators have moving parts that can break down, that require maintenance, and are noisy. Even solar thermal energy needs a turbine or other mechanical device to change the heat energy of the sun into mechanical energy for a generator to produce electric power. Photovoltaic power, by contrast, is generated directly from the sun. PV systems have no moving parts, require virtually no maintenance, and have cells that last for decades.
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Uses of Solar

How practical is solar for home and mobile home/marine use? These days, it's pretty practical, especially for remote homes. Until solar power came along, people who wanted to live in remote areas frequently had to pay large fees to have a power cable run to their house. Now, a remote home can be virtually self-sufficient with solar power. Even in areas where power lines are nearby, solar may be a viable alternative to being connected to a power company. An average home has more than enough roof area to produce enough solar electricity to supply all of its power needs. With an inverter, which converts direct current (DC) power from the solar cells to alternating current (AC), which is what most home appliances run on, a solar home can look and operate very much like a home that is connected to a power line. For recreational vehicles, solar power provides the freedom to go to more remote locations, without relying on a plug-in power source or a noisy electric generator. Systems for RVs can be small for charging batteries only or large enough to power the entire vehicle for a period of time. Similarly, boats can use solar power for many of their power needs, rather than a generator or engine.
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Solar PV Power in Industry

Some of the most important applications of solar energy are nearly invisible. Telecommunications, oil companies, and highway safety equipment all rely on solar power for dependable, constant power, far from any power lines.

Call Boxes: look at any California roadside call box, and you'll see a solar panel. California standardized on the use of solar power and cellular phones to eliminate the need for any buried cable connections to these phones. Given the sometimes literally life-saving nature of these call boxes, dependability is a must.

Roadside signs: solar power is used for many lighted highway signs, eliminating the need for diesel generators. Telecommunications installations: when you need a microwave repeater on a remote mountaintop, the last thing you want to do is run a power line up to it. For reliable power, many communications repeaters in remote areas use solar. The Solar Future Siemens Solar alone has shipped over 130 megawatts of modules since its inception, and the use of solar power is projected to grow at 10-15% per year from now until the year 2010. This is over three to five times the rate of growth of the Gross National Product of the United States!

Given this growth, solar power will be a much larger part of our lives in 2010 than it is today. Homes could incorporate solar power at the time that they are built, dramatically reducing both the cost of buying solar power and the cost of utility bills. New communications technology may make living in remote areas a practical reality given the availability of solar power. Mobile uses will undoubtedly increase. And industrial applications will continue to enjoy the versatility of solar power.
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