Snip a piece of copper flashing approximately 5 inches square. Lay it on an electric stove burner and turn the temperature up as far as possible. As the copper heats, colors will swirl across its surface before it turns completely black. Let it bake for another 30 minutes after it turns black; this helps separate the oxidized copper from the charred layers.
Turn off the burner and let the copper cool as the burner cools. Charred, black pieces of the copper's outer layer will flake and pop off as it cools. This is a good thing; it reveals the cuprous oxide underneath. Let the copper cool for another half hour, and do not scrape or rinse it off. You may rinse the oxidized layer away.
Detach the sides of a clear CD case, setting one aside. Snip a U-shape of fresh copper flashing 5 inches wide and 6 inches tall with two 90-degree angles at the bottom. Squeeze a thick bead of silicone caulk onto one side of the U-shape, centering it on the copper. Press the U-shape, caulk side down, onto your CD case window. Smooth the U-shape with your thumbs, sealing up gaps while making sure the U-shape and the plastic don't touch.
Squeeze a second bead of silicone onto the front of your U-shape. Press the baked copper sheet down onto the caulk, once again pressing to seal gaps. There should be a pocket between your copper U-shape and the baked copper; wide edges of the U-shape should be located inside this pocket. Seal up the outside edges of your copper plates with more caulk.
Attach an alligator-clip wire to the left corner of the baked copper and one to the right corner of the copper U-shape. Make three more solar cells just like this one.
Bend a piece of 2-foot by 4-foot cardboard in half, propping it up like an easel. Glue your four solar cells to the cardboard with dots of silicone on the baked copper. Press them into place in two rows of two, spacing them about 2 inches apart.
Clip the left wire on the lower right cell to the shiny copper on the cell to the left and the right wire to the baked copper on the upper right cell. Clip the left wire on the lower left cell to the shiny copper on the cell above it. Clip the right wire on the upper left cell to the baked copper on the cell to the right.
Mix 2 tablespoons of salt into approximately 4 cups of water. Fill the pocket in each of your cells with water. Prop the assembly outside a south-facing window and slip the remaining loose wires under the window sash. You can connect them to a solar battery, generator or other electrical unit to produce a small amount of electricity.