Cut two sheets of copper approximately the size of the large burner on a stove. Wash the copper sheets thoroughly with soap and water to remove any oil. Sand the copper sheets to remove any copper sulfides or other corrosion.

Heat one copper sheet on the largest burner at the highest heat setting. Allow the sheet to turn completely black and continue heating it for another half-hour to build a thick coat of cupric oxide.

Turn off the burner and allow the sheet to cool for about 20 minutes by leaving it on the burner. Remove most of the cupric oxide by scrubbing gently, but don’t remove the red layer. Cut off the top of the plastic bottle and bend both sheets of copper carefully so that they fit inside the bottle without touching each other. The cupric-oxide layer should be facing away from the other copper sheet.

Attach one alligator clip lead to each copper sheet. Connect the positive terminal of the ammeter to the clean copper sheet and the negative terminal to the copper sheet with the cupric-oxide layer.

Stir 2 tbsp. of salt into a half-gallon of hot tap water until the salt is dissolved. Pour the salt water into the bottle without getting the clips wet and leave about an inch of the plates above the water. Place your solar cell in the sunlight and watch the current reading on the ammeter increase.