Socially-desirable doesn't seem to be a technical term to me. I
think it simply refers to goods that give utility to every
individual in the system. So if you assume that every individual is
a rational agent, then in the absence of regulation, no one would
pay for the good because everyone is waiting for everyone else to
buy it for everyone to enjoy.
This will not apply to the solar panel example because a
corporation that buys the panels can exclude other corporations
from energy consumption. Counter-terrorism works because you can't
limit the consumption of safety to a select group of individuals in
your system.