Amount of captured solar energy depends critically on orientation of collector with respect to the angle of the Sun.

• Under optimum conditions, one can achieve fluxes as high as 1000 Watts per sq. meter

  In the Winter, for a location at 40 degrees latitude, the sun is lower in the sky and the average flux received is about 300 Watts per sq. meter

  A typical household Winter energy use is around 2000 KWHs per month or roughly 70 KWH per day. This is equivalent to about 72 hours of incident sunshine on your rooftop or roughly 9 days per month of steady sunshine (which most locations won't receive).

  But, at the moment solar collectors are only about 10% efficient so the true yield of 1000 square feet of collecting area is only about 22 KWH under 8 hours of sunshine in the Winter. This represents 1/3 of the typical daily Winter energy usage and it assumes the sun shines on the rooftop for 8 hours that day.

  Another example calculation for Solar Energy which shows that relative inefficiency can be compensated for with collecting area.

  

  Solar Energy: Conduction and Heat Transfer
  

  How Solar Energy is Used:

  • Direct conversion into electricity --> Photovoltaics
  • Fixing of atmospheric Carbon into the biomass --> photosynthesis
  • Converting into heat energy for space heating, driving heat engines, etc

  The Key to efficient use of solar energy lies in efficient modes of heat transfer. There are three possible modes:

  • Conduction
  • Convection
  • Radiation

  

  Thermal Conduction:
  • heat energy flows from regions of high temperature to low temperature
  • wide variation among different materials --> depends on the density of free electrons in the material

    Thermal Conductivity of some Materials:

    • Silver 4.2
    • Copper 3.9
    • Gold 2.9
    • Aluminum 2.0
    • Steel 0.5
    • Concrete 0.02
    • Brick 0.01
    • Wood 0.001
    • Air 0.0002

  So Clearly metals are required for efficient heat transfer.

  Heat flow through a wall:

  

  Next Page

  ___________________________________________________________________

  The Electronic Universe Project

  e-mail: nuts@moo.uoregon.edu