DESERT HOT SPRINGS, Calif.  Solar power, with its promise of emissions-free renewable energy, boasts a growing number of fans. Some of them, it turns out, are thieves.

Just ask Glenda Hoffman, whose fury has not abated since 16 solar panels vanished from her roof in this sun-baked town in three separate burglaries in May, sometimes as she slept. She is ready if the criminals turn up again.

“I have a shotgun right next to the bed and a .22 under my pillow,” Ms. Hoffman said.

Police departments in California  the biggest market for solar power, with more than 33,000 installations  are seeing a rash of such burglaries, though nobody compiles overall statistics.

Investigators do not believe the thieves are acting out of concern for their carbon footprints. Rather, authorities assume that many panels make their way to unwitting homeowners, sometimes via the Internet.