Whys Guys: Sun’s energy

The Morning Show


U of I Professor Mats Selen joins us for Whys Guys Wednesday to learn about the sun’s energy. 

  • The sun is much bigger than the earth. If the sun was the size of a person then the earth would be the size of a fingernail and would be the length of a football field away. [show “sun.jpg”]
  • The temperature of the outside of the sun in about 10,000 F. The sun produces a lot of power – so much it keeps us warm even though it’s almost 100 million miles away from us.


Energy from the sun hitting the earth:


  • Even though the earth is so far away from the sun, the power from the sun at that great distance is 1370 Watts per square meter.
  • The fraction of this energy that reaches the ground depends on where you live and how cloudy it is and the time of year, but it can be up around 1000 Watts per square meter.


Getting energy from the sunlight using solar panels:


  • A solar panel can convert about 15-20% of this energy to electricity. A good solar panel in central Illinois will generate a peak power of about 200 Watts per square meter.
  • Solar panels last a long time and can produce power for many decades.
  • If you have a lot of solar panels you can generate a lot of electricity. The UIUC solar farms contains over 18,000 panels and can generate about 5 million Watts. [show “solar farm.png”]
  • You can think of a solar panel as an LED running in reverse. Future shows will have more details about how solar panels work.


Energy balance:


  • The Earth absorbs a lot of solar energy. If this was all that happened, the earth would get hotter and hotter.
  • Lucky for us, the earth also radiates energy back into space. Radiation of energy happens whenever an object is warmer than its surroundings. This is called “blackbody radiation”. [I will do a demo to show this]
  • The average temperature of the earth is a delicate balance between absorbing the suns energy, radiating away this absorbed energy, and the greenhouse effect of the atmosphere which raises the equilibrium temperature by about 33 degrees compared to what it would be without the greenhouse effect.
  • We will talk more about this in future shows.

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