Jim and Robyn Dahlin knew replacing the roof of their home in Greenbrae, Calif., would be expensive. But they hadn't planned to spend an extra $15,000 on solar panels. For that, they have their 8-year-old son, Luke, to thank.

After Luke acted in a school play about global warming, he went on a campaign to get his parents to install the panels. He routinely lectured his dad from the backseat of the minivan about how reducing their energy consumption could help save the planet.

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