Solar Poster

Highlights Two types of collection systems are used for collecting solar radiation, active and passive. The passive version, which also has the longest history, uses existing architectural structures to maximize collection, such as large windows on the eastern side of a building. The active variation uses other sources of energy to increase the effectiveness of the panels. These systems include solar cells and solar heating. With in the active variation there are subcategories. Focusing systems generally use mirrors to concentration the energy. Line focusing uses a trough or lines of mirrors to focus the light into a long line. Point focusing uses a dish to ‘move’ the light onto a central point where a collection center is.

Power

• The most common way of collecting solar power is through the use of semiconductor Photovoltaic Cells (PV). Because of the high cost in production of these cells, they haven't been widely used until recently. Common places to find these are in solar powered calculators, at roadside assistant emergency phones, and in powering satellites. The average retail cost between 1995 and 2005 was between $4 and $7.50 per 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 radiation is approximately 1000 W/m². One 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 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. Production requires a high amount of water, is 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 initiation 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

Cost Element	Nuclear	Coal	Solar
Fuel($/Mw-hr)	5.0	11.0	X
O & M - Labor & Materials ($/Mw-hr)	6.0	5.0	X
Regulatory Fees ($/Mw-hr)	1.0	0.1	X
Projected Life (years)	X	X	20-25
Construction period (years)	5	4	X

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
  • http://www.eere.energy.gov/solar/csp.html
    • Concentrating Solar Energy
  • http://www.nucleartourist.com/basics/costs.htm
    • Comparison of Nuclear and Coal Costs