Environmental Science

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Environmental Science

• Solar Energy Lecture Notes

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Solar Energy is RENEWABLE

• Renewable vs. Nonrenewable Energy Resources
• DEMO

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Solar Energy can be used 3 ways

• Solar Heating
• Solar Heating ? Electricity
• Solar Radiation ? Electricity

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Solar Hot Water

• 1890 solar water heaters used in sunny states
  like California, Arizona, and Florida
• Artificial gas made from coal was available, but
  cost 10X the price we pay for natural gas today
• 1920 1,000s of solar water heaters had been
  sold. BUT large deposits of oil/natural gas
  were discovered in U. S.
• Solar water systems were replaced with heaters
  burning these cheaper fossil fuels.

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Solar collector for heating water
A home in California in 1906
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• Today, solar water heaters are making a comeback
  (more than ½ million in California alone!).
• Heat water for homes/businesses and swimming
  pools (see picture)
• Panels on roof contain water pipes. Sun hits the
  panels and pipes.
• Warmed water is then used in a pool

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Solar Thermal Electricity

• Solar energy ? electricity
• Some solar power plants (see picture from Mojave
  Desert) use curved mirror called PARABOLIC TROUGH
  to focus sunlight on a pipe running down center
  of mirror.
• Mirror focuses sunlight onto the pipe, causing
  the water to boil and produce steam. Steam can
  then be used to turn a turbine to make
  electricity.
• These rows of solar mirrors arranged in "solar
  thermal power plants. They make electricity for
  more than 350,000 homes.

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Solar Thermal Electricity

• PROBLEM Works only when sun is shining. On
  cloudy days/at night, the power plants can't make
  electricity.
• Some solar plants, use "hybrid" technology?
  During day they use sun. At night/cloudy days
  they burn natural gas to boil water to
  generate electricity.

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SOLAR THERMAL ELECTRICITY
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• Another form of solar power (heat) to make
  electricity
• (Central Tower Power Plant) ?
• Sunlight is reflected off 1,800 mirrors
  (HELIOSTATS) circling the tall tower.
• Fluid (liquid sodium) is heated by sun's rays.
  The fluid is used to boil water ?make steam ?
  turn a turbine and generator
• This experimental power plant is called Solar II.
  It was built in California's desert.
• Scientists say larger central tower power plants
  can make electricity for 100,000 to 200,000
  homes.

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Solar Cells or Photovoltaic Energy

• Sunlight converted directly to electricity using
  solar cells
• Solar cells also called photovoltaic cells (PV
  cells) and can be found on many small appliances,
  like calculators, and even on spacecraft
• First developed in 1950s for U.S. space
  satellites.
• Made of silicon, special type of melted sand
• Sunlight strikes solar cells and electrons (red
  circles) are knocked loose. They move toward
  treated front surface (dark blue color). When the
  two surfaces are joined by a wire, a current of
  electricity occurs between negative and positive
  sides.
• Solar cells ? PV module ? Array.
• Some arrays are set on special tracking devices
  to follow sunlight all day long.

Photovoltaic Energy Video
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• Electrical energy from solar cells can be used
  for lights/appliances
• Solar energy can be stored in batteries to light
  roadside billboards at night
• Energy can be stored in a battery for emergency
  roadside telephones where no phone wires are
  around
• Some experimental cars also use PV cells. They
  convert sunlight directly into energy to power
  electric motors on the car.
• Solar cells are used in satellites in outer
  space. Here's a picture of solar panels extending
  out from a satellite.

Rooftop PV Modules