Solar School Activity Sheet

 

Olympic Solar Energy (1)

 

Introduction

The Olympic Games come to Sydney in the year 2000, and solar energy will play a big part both during and after the events have been held. Solar energy will be used to power the competitor's Olympic Village, and to heat the water of the Village's homes.

 

In this activity, you will learn the principles of solar thermal heating by building a solar concentrator that concentrates sunlight in order to generate enough heat to cook a hot dog.

 

Background
Four months before the start of the Sydney Games, Olympic officials will stand with a magnifying lens in the ancient temple of Zeus in Olympia, Greece, the site of the first Olympic Games 2,772 years ago. They will focus the rays of the sun on to dry grass. The grass will catch fire, and from that "Mother Flame" the Olympic torch will be lit, just as it was by the original Olympians.

 

As the lighting of the Olympic flame shows, the solar energy that strikes the earth is tremendous, despite travelling nearly 150 million kilometres across space to get here. The total annual energy consumption in Australia is only about 0.02% of the solar energy falling on this country each year.

 

People harness solar energy in many different ways, but the most common methods use solar collectors to heat water and photovoltaic cells to convert sunlight directly into electricity.

 

Photovoltaic cells, thin wafers usually made of silicon crystals, were first used in 1958 to power satellites in space. Now the cells are used for everything from running lighting systems to powering water pumps.

 

When photons (the tiny, individual packets of light energy that come from the sun) strike a cell, some are absorbed and transfer their energy to an electron in an atom. The electron, gaining energy from the photon, breaks free of its atom. The cells are made so that one layer of each cell is more highly charged than the other layer. The negative charges move toward the positive ones. The moving charges are an electric current, or electricity. This type of current production is called the photovoltaic effect.

 

At the 2000 Olympics in Sydney, more than 8000 photovoltaic panels covering over 6000 square metres will provide 650 kilowatts of electricity to power the Olympic Village.

 

Hot water for the village will also be supplied by solar thermal heating systems. Such systems work by aiming large, black metal solar collectors at the sun. Black and other dark colours absorb more sunlight than light colours. Solar energy makes the collectors very hot, much like the surface of a black road on a bright, sunny day. Water passing through the collectors is heated naturally and then can be used in the village houses.

Solar thermal heaters typically reduce water heating costs by about 50 percent. Many solar heaters also use natural gas heating as a backup for cloudy days when the sun isn't shining.

 

Introductory Activity

Build a small "greenhouse" out of a plastic, cardboard, or wood box that has a clear cover on the top (glass or clear plastic). Put the tip of a thermometer in a container of black dirt inside the greenhouse, then place the house in the sun or under a floodlight. Check the temperature every 15 minutes to see how much hotter it is inside the greenhouse. Open the top or sides of the box and see what effect that has.

 

Questions

Why does heat build up inside of a greenhouse? Can you maintain a constant temperature below the maximum temperature by opening and closing holes, or vents, in your greenhouse?

 

Main Activity

Harness the energy from the sun to power a parabolic oven.

Solar thermal collectors work because they not only gather solar energy, but concentrate it in a small space. In this activity, you'll build a solar oven that, by concentrating sunlight, will gather so much heat you can cook a hot dog.

 

Materials

  1. Cut two sections out of the piece of cardboard to form the ends of a parabolic cooking trough. Cut each piece so it has a straight edge that is 26cm long. At the middle of this edge (13cm from each end), measure a point 11cm back onto the cardboard and make a mark. Draw an arc from one corner of your straight edge, through the point, then down to the other corner. Cut along the arc and you should end up with two pieces of cardboard that look roughly like half circles.

    2.  

  2. Cut a piece of poster cardboard so that it is 30cm by 36cm. Cut a piece of aluminium foil the same size and glue it, shiny side up, to the poster board.

    3.  

  3. Curve the poster board around the two end pieces, with the aluminium foil facing in, and tape it in place.

    4.  

  4. Cut the top and front side off of your cardboard box and slide the back of your trough a couple of inches into the box. Secure the trough to the box by putting a bolt through each side of the trough and the sides of the box. Make sure the bolts are toward the rear of the trough. Fasten the two bolts with the nuts. The trough should be able to tilt up and down.

    5.  

  5. Straighten out the coat hanger and push it through the trough, from one side to the other, so it sits like a spit for cooking. It should sit about two inches back from the open front of the trough.
  6. Put a hot dog lengthwise on the coat hanger and point the trough at the sun.

 

Questions

  1. How long does it take the hot dog to get warm?
  2. Does the hot dog get warm at the same rate along its length?
  3. Does it cook faster if you move the coat hanger a little deeper into the trough? Try to explain your results.
  4. Does the hot dog cook when the sun goes behind a cloud? Try to explain your results.

    5.  

  5. What other machines could you build that would use the sun's energy?
  6. What can the sun's energy do around your house?

  7. What are the advantages of producing energy directly from the sun instead of burning coal or natural gas?
  8. Photovoltaic cells, solar thermal heaters, and other solar systems have been around for a couple of decades. Why weren't they more widely used?

 

 

Extension

Draw plans that would maximise sunlight energy in your house without using photovoltaic cells.