Window farms use cascading containers of plants hanging in windows to grow crops year-round. Have eighth-grade students build a window farm in the classroom and compare plant growth with sunlight warming and lighting one group of plants, a second farm using reflected sunlight and a third group using grow lights. Construct the first group as a standard window farm hanging in nets with a small aquarium pump to circulate the hydroponics solution to the plants. Construct a second window farm with a cardboard frame painted black behind the garden to reflect heat, solar blanket-covered sides to reflect sun on the plants and a plastic covering surrounding the garden to maintain a humid atmosphere. Construct the third farm group using standard grow lights to warm and light the plants. Compare growth of plants over a four-week period to determine which produces the best growing conditions.
Surgical instruments heated to 170-degrees Fahrenheit for one hour in a dry environment sterilizes them. Construct one solar cooker without newspaper insulation spray-painted flat black and a second one with the insulation. Place both cookers on rolling platforms you can move to track the sun. Place a thermometer in the box on the heating surface and chart the temperature every 10 minutes for one hour. Have eighth-grade students monitor the conditions and determine if either method would produce consistent temperatures high enough and consistent enough for medical personnel to autoclave surgical instruments in the field.
Water heated to 150 degrees Fahrenheit for 15 to 20 minutes will kill bacteria and render water safe to drink. Have the eighth graders experiment with different designs of solar water purification systems and determine which system works most effectively using recycled materials such as empty soda bottles, metal coffee cans, boxes, aluminum foil and newspaper. Discuss the feasibility of the most effective system in third-world countries and in the United States. Specifically, while the recycled materials may be readily available in the United States, discuss how available are they in other parts of the world.
The U.S. Department of Energy distributes plans for building a cardboard solar heater you can install in windows with a southern exposure. Have eighth-grade students work with two rooms with such windows. Install the solar heater in one room and blackout curtains in the second room. Close any heater vents in the rooms and place a thermometer in each room. Record the temperatures for both rooms at two-hour intervals over the course of three winter days. Determine which system works most effectively for warming the room.