The author didn't do a very good job interpreting these statistics. The conditions that would exist when someone would choose to invest in solar panels exclude

The author didn't do a very good job interpreting these statistics. The conditions that would exist when someone would choose to invest in solar panels exclude a large fraction of homes; solar panels are a recent enough addition for most that homes which have been allowed to fall into disrepair are excluded. They further exclude homes that don't have a view, homes that are part of a multi-unit bloc, and, in some cases, duplexes.