New Study Finds Solar Panels Are "Contagious"

When I lived in Minneapolis, it was the law that a homeowner had twenty-four hours to remove graffiti or the city would do it for him and send a bill for the service.  The reason being that things like graffiti and litter only encourage more graffiti and litter - not to mention real crime.  Now there's a study out that shows how homeowners adding solar panels encourages other homeowners to add solar panels.  It makes sense.  I can easily see a neighbor asking about the newly-installed photovoltaic panels and then wanting to do the same once he learns how much he'll save.

From Good:

Are you more likely to install solar panels if your neighbor has them? A new study (PDF) out of Stanford says that you are. More specifically, it finds that for every 1 percent increase in the number of installations in a particular zip code, the time until the next adoption of solar decreases by 1 percent. Or, as Vote Solar's Adam Browning put it: Solar is contagious!
So just how quickly can solar power spread as this snowball effect gets rolling? John Farrell of the Institute for Local Self-Reliance's New Rules Project projects the trends forward:

If you start with a neighborhood with 25 solar installations, where it was 100 days between the 24th and 25th installation, this peer pressure effect will reduce the time between installations to just 10 days by the 250th [photovoltaic] project.

Here's what the effect looks like:

Of course, this process can take a pretty long time to actually unfold. In the example above, in a hypothetical zip code starting with one solar installation, it takes 15 years for the gap between installations to come down to 10 days.
What neither Browning or Farrell got into was what, exactly, caused solar power's contagiousness. Is it peer pressure? Infrastructure and training? Marketing density?
I dug into the study a bit, and it turns out it's a little bit of everything. One predictable factor is social caché. Call it Keeping up with the Joneses. Homeowners see others putting up solar panels, and they want to projecting the same "green image." Another is information transfer. It gets easier to find out about solar panels if there are people in your zip code who have them. Neighbors talk to neighbors, explaining the benefits of rooftop solar, and demystifying the installation process. Likewise, once local contractors are familiar and comfortable with the systems, they can serve more customers, and talk to other contractors. Finally, companies like SolarCity are taking a hyperlocal approach to marketing and sales. It benefits the company to have a lot of projects in one area, so they'll target a city or town, blast through, and move on.
All of this evidence points to the fact that the best possible way you can get more people to adopt solar energy is to put panels on your own home first.