Sun Power

Class III

Solar Ovens!

• Types: Box, parabolic, forty fivers, trough, panel, integrated convective ovens (Mexico). 
• Examples: www.solarcooking.org
• Pros and cons: wind, burning, portability, need for accuracy, etc. 
• Energy Balance and temperature
• Effect of steam: latent heat of water = 970 Btu/lb
• Water pasteurization - only 150 degrees fahrenheit is required.
• Timing/Aspect ratio
• Effect of outside air temperature
• Cultural advantages: avoid travel for firewood, avoid deforestation. 
• Cultural barriers: round vs. square, inhibitions about using the sun's energy. 
• Books: Heavan's Flame (See www.homepower.com), etc. 
• Barbara Kerr, P.O. Box 576, Taylor, Arizona 85939 USA. 
• History: The first solar cooker we know of was invented by Horace de Saussure, a Swiss naturalist experimenting as early as 1767. Later developments by Herschel, etc. 
• Present: 
  • Solar Cookers International: Sponsors the solar cooking archive: http://solarcooking.org
  • Projects in many countries, early projects mostly failed, some later successes. 
  • 100,000 cookers in use in both India and China. 
  • The solar box cooker project in the Indian Himalaya, sponsored by the Indo-German Dhauladhar Project: earth and brick ovens double glazed with glass. An inner tin oven is fabricated from used ghee or oil containers. Husk from a rice sheller provides insulation around the tin oven. 
  • Recent major breakthrough by Solar Cookers International using the Bernard panel sun cooker.
• Making your own:
  • Glazing; tempered glass, low iron, avoid plexiglas. Double glass/low-e glass increases temperature
  • insulation: cardboard, aluminum foil (radiant reflector), feathers (down feathers are best), spun fiberglass, rockwool, cellulose, rice hulls, wool, straw, and crumpled newspaper.
  • angles and reflector strategies
  • inner surface: foil, Aluminum flashing. Reflective sides, black bottom. Black paint should be thoroughly cured, and never in contact with food (especially metallic paints).
• Using it: 
  • Wear sunglasses - retinal damage cannot be felt
  • Cure an oven first before using it
  • Some people report difficulty with odors from brocolli and similar vegatables
  • Watch out for burns with parabolic ovens.

Review of previous class:

• Algebra and units of ten: simple examples
• Basic Names and units
• Nominal Solar intensity ("irradiance") outside Earth's atmosphere: "Solar Constant" ~ 1367 w/m²
• Nominal Solar intensity ("irradiance") at Earth's Surface: "One Sun" = 1000 w/m²

New Material

• New Energy Units:

• Simple calculations
  • Calculate area needed to power US
  • Calculate area needed to power a house: several hundred square feet
  • Calculate area needed to power a car
  • Scale of human body usage