Dear EarthTalk: What's the deal nowadays with aerosol spray cans? I thought that the ozone-depleting chemicals used in them were eliminated back in the 1970s. Is this true? If so, what is now used as a propellant? Are aerosols still bad for the ozone layer? -- Sheila, Abilene, TX
Dear EarthTalk: I am considering solar panels for my roof to provide heat for my hot water and possibly to do more than that. Are there some kinds of solar panels that are better than others? How do I find a knowledgeable installer? --Elise, Watertown, MA
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.