Solar power is contagious: Installing panels often means your neighbors will too

Solar power only generates about 0.4 percent of America's electricity. But it's expanding at a staggering rate, with a new rooftop system installed every four minutes. There are lots of reasons for that, from lower costs to federal subsidies to innovative financing schemes.

But here's another unexpected factor: Solar power appears to be contagious. Yes, contagious. If you install solar photovoltaic panels on your roof, that greatly increases the odds that your neighbors will, in turn, install their own panels.

That's the upshot of a fascinating 2014 paper in The...