Collecting solar energy works on several different principles, including color absorption. Additionally, wet items hold energy longer than dry ones. For this activity from the University of Northern Iowa, the students learn that darker colors absorb energy faster than lighter ones.
Place four, similarly sized trays on a table. Fill each tray with a different type of material: dry light sand, dry dark dirt, wet light sand and wet dark dirt. Place a light at the same distance from each tray -- about 20 cm or 7 13/16 inches. Stick a thermometer in each tray of sand. Watch the changes in the thermometer over time. Turn the lights out after 30 minutes and continue to measure the thermometers. Discuss why the dark dry dirt heats up the quickest and why the dark wet dirt takes the longest to cool.
Concentrated solar energy is very strong. To illustrate this, build a solar energy oven, like the following one from the Cool Room.
Cover the entire inside of an unwaxed paper cup with black construction paper, then place an apple slice inside the cup. The weight of the apple holds the paper in place. Tightly wrap the cup with plastic wrap. Tape aluminum foil to the top of a sheet of white paper, covering it completely. Wrap the apple cup with the sheet of white paper, so that it creates a cone around the cup, with the foil to the inside.
Stand the entire "oven" in a coffee can filled with crumpled paper and place in a sunny spot. After an hour or so, the sun's energy will bake the apple.
Sometimes, a simple discussion on why solar power is important makes an educational activity. Instead of a classroom lecture, walk around the playground at the school and talk to the kids about all of the different inventions in solar energy. Ask them what they think solar energy could do for the planet. Let them create ideas as outlandish as they wish; for example, space ships running on solar energy, or a solar energy swing that doesn't require the swinger to push against the ground.
With the students, set up solar panels next to the classroom windows, or on a reserved part of the lawn. Attach certain classroom machines (such as a pencil sharpener or clock) to these solar panels. Explain the importance of renewable resources in today's world.