Solar energy doesn't pollute, it's very safe, and there's lots of it

Part of the solution to global warming lies in finding alternative energy sources so that we don't burn so many fossil fuels and add too much carbon dioxide to the Earth's atmosphere. The sun is a source of both heat and light energy. People have used the sun for centuries to heat water. Today, there are solar farms that convert the sun's energy into electricity, and some people even have solar collectors as part of their homes.

A solar collector can consist of a shallow box with a clear glass or plastic top. Sunlight passes through the glass and heat is trapped inside the box, much like it is in a greenhouse. A dark plate at the back of the collector absorbs the heat. Air or water can be run over the plate and used to heat a home or produce hot water. The sun's energy can be successfully turned into small amounts of electricity using a "photovoltaic cell." The cell is usually made with silicon, a material which allows electricity to pass through it in one direction only. The sun's energy drives electrons from their normal places in the atoms that make up the silicon; that flow of electrons is electricity.

Photovoltaic cells are currently used to power things like calculators, signs and other electronic devices in remote areas; there are also some installations on buildings and in fields to produce electricity. However, the cells aren't practical yet for large-scale use. Silicon is expensive and the numerous cells required has to cover a lot of land, though research continues to improve the technology and bring costs down. Another problem with solar energy: it doesn't work when the sun isn't shining.

There are certain "basics" to efficiently capturing the sun's energy. A pie tin painted black absorbs more heat than an ordinary tin; the shiny surface on the ordinary tin reflects the sunlight away. A large pie tin heats water to a higher temperature than a smaller pie tin because the larger surface area collects more heat.

Experiment with collecting solar energy. But, never look directly at the sun because it can damage your eyes.

Start by filling a measuring cup with 200 ml of water. Take the temperature of the water and write it down.

Pour 100 ml of water into an ordinary, small pie tin and 100 ml of water into a small pie tin painted black. Carefully secure plastic wrap over each tin.

Put the pie tins in direct sunlight for about 20 minutes. Which pan do you think will heat the water to a higher temperature?

When the 20 minutes is up, carefully but quickly spill the water from each tin into separate measuring cups. Take the temperatures of the water in both cups. Subtract the initial water temperature from the final temperatures. Did the black tin heat the water to a higher temperature? How much higher? Why?

Now, fill a measuring cup with 200 ml of water. Take the temperature of the water and write it down. Pour 100 ml of water into a small pie tin painted black and 100 ml of water into a large pie tin painted black. Carefully secure plastic wrap over each tin.

Put the pie tins in direct sunlight for about 20 minutes. Which pan do you think will heat the water to a higher temperature?

When the 20 minutes is up, carefully but quickly spill the water from each tin into separate measuring cups. Take the temperatures of the water in both cups. Subtract the initial water temperature from the final temperatures. Did the large tin heat the water to a higher temperature than the small tin? How much higher? Why?

You can try changing some of the other variables, like the depth of the water or the presence of a plastic cover.