It’s not uncommon for friends, family, and neighbors to ask sustainability scientist Ryan Cornell about his home’s solar power. And he loves most of the questions. It’s a chance to talk about a subject he enjoys, while encouraging people to think about adding solar to their own homes. Most questions are pretty straightforward: How much energy does it produce? Does it produce enough electricity to power your cars? What happens when it is cloudy?

The fact that it is possible to power an entire house and two cars with today’s technology seems to intrigue most people. It also inevitably leads to another question. The question that drives Cornell a little bit crazy: When will the roof pay for itself?

"It is a completely valid question," says Cornell, "and while there are problems with the question itself, I still understand why someone wants to know. The problem with the question is that it is a gross oversimplification."

Read the article in Slate to see what Cornell says about fossil fuels, human health and peer pressure.