Solar Poster

Highlights

• Two types of collection systems
  • Active - Uses other energy sources to increase effectiveness of the pannels. These systems include solar cells, solar heating, and solar heating.
    • Line focus: USes a trough or lines of mirrors to focus into a long line. This system is used in California.
    • Point focus: Uses a dish to "move" the light onto a central point where a collection center is.
    • Non-focusing: Has the benefit of being aboe to use diffuse solar radiation that can not be focused.
  • Passive - Requires no outside energy souces. It uses already existing architectural structers to maximize collection.

Power

• The most common way of collecting solar power is through the use of Photovoltaic Cells (PV). These are semiconductors.
  • Because of the high cost in production of these cells, they haven't been widely used until recently. A common place to find these are in solar powered calculators and at roadside assistant emergency phones. A third place that they are widely used is in powering satellites. The average retail cost between 1995 and 2005 was between $4 and $7.50 a watt. In 2004 the production of these cells jumped by 60%. This trend was expected to continue through 2005, but limited supplies of silicon have hampered production.
  • On a clear day at the equator the solar radiaton is approximately 1000 W/m². 1 square meter of a 10% efficient PV can continuously power a 100 W light bulb.
  • The most common and efficient material is Silicon, which can be produced in three manners.
    • Single crystal or monocrystaline wafers. Most commercial cells of this type have an efficiency on the order of 14-20 %. Because of the need to cut these from a cylindrical ingot they produce a lot of refined silicon waste and are expensive.
    • Poly or multi crystalline: these are cheaper to produce than single crystal, but have a lower efficiency. To make up for that, they can cover larger areas.
    • Ribbon silicon: “formed by drawing flat thin films from molten silicon and has a multicrystalline structure”. They have little silicon waste, especially compared to single crystal. Typically these are least efficient.
      • http://science.nasa.gov/headlines/y2002/solarcells.htm

Environmental Impact

• The manufacturing of solar panels is environmentally expensive. It requires a high amount of water, are energy expensive, and use toxic chemicals.
• In the past 10 years, there has been research into reducing the environmental impact of manufacturing silicon for both PV and other products.
  • Photovoltaic grade silicon is lower than Semiconductor grade and so, it may be possible for the refinement of cast off silicon from Semiconductor wafer production for use in solar panels.
    • If a reliable method of collecting and refining this waste silicon can be found, there is enough silicon to produce about twice as many PV cells as were required in 1998.
  • In 1998, there was intiation of an experiment into chlorine-free or reused chlorine production of PV grade silicon. This new process takes about 15-30 kWh per kg of silicon produces, as opposed to the 250 kWh per kg required for Semiconductor grade. Each watt of solar panel requires about 20 g of silicon.

Comparison of Power Plants

Background

• The original passive solar systems date back to the ancient greeks and romans who used solar energy to heat buildings by having south facing windows.
• Brief History of Solar Power
  • 1839 - Photoelectric effect was first observed
  • 1916 - Photoelectric effect proven through experiments run by Robert Millikan
  • 1918 - Jan Czochralski produces a method to grow single-crystal silicon.
  • 1950's - Bell Labs produces solar cells for space activity.
  • 1963 - Sharp Corporation produces a viable PV module of silicon solar cells

More Information

• • http://www.nrel.gov/highperformancepv/
  • http://en.wikipedia.org/wiki/Solar_power
  • http://en.wikipedia.org/wiki/Timeline_of_solar_cells - history of PV cells
  • http://www.uccs.edu/~energy/courses/160lectures/solhist.htm
  • http://www.nrel.gov/ncpv/pdfs/tsuo.pdf
    • Environmentally Benign Silicon Production