Dpurdy's List: Photovoltaic

• The PV effect was discovered in 1954, when scientists at Bell Telephone discovered that silicon (an element found in sand) created an electric charge when exposed to sunlight.

• Solar energy is free - it needs no fuel and produces   no waste or pollution.
• Handy for low-power uses such as solar powered   garden lights and battery chargers, or for helping your home energy   bills.
• Very expensive to build solar power stations, although   the cost is coming down as technology improves. In the meantime, solar   cells cost a great deal compared to the amount of electricity they'll   produce in their lifetime.
• Is it renewable?

  Solar   power is renewable.   The Sun will keep on shining anyway, so it makes sense to use it.

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• 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.
• Photovoltaic (PV devices) or “solar cells” change sunlight directly into electricity. Individual PV cells are grouped into panels and arrays of panels that can be used in a wide range of applications ranging from single small cells that charge calculator and watch batteries, to systems that power single homes, to large power plants covering many acres.
• Solar energy systems do not produce air pollutants or carbon-dioxide
• 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.

• 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.

• Weather Affects Photovoltaics

   

  The performance of a photovoltaic array is dependent upon sunlight. Climate conditions (such as clouds or fog) have a significant effect on the amount of solar energy received by a photovoltaic array and, in turn, its performance.

• History of the Photovoltaic Cell

   

  The first practical photovoltaic (PV) cell was developed in 1954 by Bell Telephone researchers examining the sensitivity of a properly prepared silicon wafer to sunlight. Beginning in the late 1950s, PV cells were used to power U.S. space satellites. PV cells were next widely used for small consumer electronics like calculators and watches and to provide electricity in remote or "off-grid" locations were there were no electric power lines. Technology advances and government financial incentives have helped to greatly expand PV use since the mid-1990s.
• Using solar energy produces no air or water pollution and no greenhouse gases, but does have some indirect impacts on the environment.

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• 200,000 homes in the U.S. use some type of photovoltaic solar technology-and   the market is expanding at a healthy 15% annually.
• PV modules covering 0.3% of the land in the U.S., equivalent to one fourth   of the area currently occupied by railroads, could provide all of the US's   electricity needs.

• Solar power is pollution free during use. Production end wastes and emissions are manageable using existing pollution controls.
• • In situations where connection to the electricity grid is difficult, costly, or impossible (such as island communities, areas not served by a power grid, illuminated roadside signs, and ocean-going vessels) harvesting solar power is often an economically competitive alternative to energy from traditional source
• Intermittency: It is not available at night and is reduced when there is cloud cover, decreasing the reliability of peak output performance or requiring a means of energy storage.
• Locations at high latitudes or with frequent substantial cloud cover offer reduced potential for solar power use.

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  Method	Cents/kW-h	Limitations and Externalities
  Wind Currently supplies approximately 1.4% of the global electricity demand. Wind is considered to be about 30% reliable.	4.0 - 6.0 Cents/kW-h	Wind is currently the only cost-effective alternative energy method, but has a number of problems. Wind farms are highly subject to lightning strikes, have high mechanical fatigue failure, are limited in size by hub stress, do not function well, if at all, under conditions of heavy rain, icing conditions or very cold climates, and are noisy and cannot be insulated for sound reduction due to their size and subsequent loss of wind velocity and power.
  Geothermal Currently supplies approximately 0.23% of the global electricity demand. Geothermal is considered 90-95% reliable.	4.5 - 30 Cents/kW-h	New low temperature conversion of heat to electricity is likely to make geothermal substantially more plausible (more shallow drilling possible) and less expensive. Generally, the bigger the plant, the less the cost and cost also depends upon the depth to be drilled and the temperature at the depth. The higher the temperature, the lower the cost per kwh. Cost may also be affect by where the drilling is to take place as concerns distance from the grid and another factor may be the permeability of the rock.
  Hydro Currently supplies around 19.9% of the global electricity demand. Hydro is considered to be 60% reliable.	5.1 - 11.3 Cents/kW-h	Hydro is currently the only source of renewable energy making substantive contributions to global energy demand. Hydro plants, however, can (obviously) only be built in a limited number of places, and can significantly damage aquatic ecosystems.
  Solar Currently supplies approximately 0.8% of the global electricity demand.	15 - 30 Cents/kW-h	Solar power has been expensive, but soon is expected to drop to as low as 3.5 cents/kW-h. Once the silicon shortage is remedied through alternative materials, a solar energy revolution is expected.
• Tide
  
  2 - 5 Cents/kW-h Blue Energy's tidal fence, engineered and ready for implementation, would provide a land bridge (road) while also generating electricity. Environmental impact is low. Tides are highly predictable.

• The   sun delivers about 7000 times more energy than we currently consume   globally. However, we cannot cover the whole surface of the Earth   with solar energy collectors. How much of this energy can we collect?   Will it be enough to replace fossil fuels?
• Our   global consumption of electricity in 2005 was 15,182 TWh/y (see   The   Little Green Handbook).   However, 9,541 TWh/y of electricity was produced by fossil fuels and   2,555 TWh/y by nuclear power, or the total 12,096 TWh/y. Assuming   the lowest solar potential and the lowest efficiency of solar cells   we can calculate that we could produce 35 times more electricity than   produced by fossil fuels and nuclear power. The additional advantage   is that solar power is clean and last practically forever.
• Even   if we used only 1% of unused land area we could produce nearly 4 times   more electricity than we produce using fossil fuels and nuclear power.

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• Solar energy, radiant light and heat from the sun

• t is expected to be completed by the end of 2012, and will sell its output to UniSource Energy Corp's Tucson Electric Power under a 20-year contract