Considering the fact that efficient pv panels need less than 4% of their lifetime output for production (if in service 25 years (most panels last up to 40 years)), that must have been the late 70s or so.

You were probably remembering that 2010 study talking about the rapidly growing solar industry as a whole becoming net producers of energy, e.g. current industry energy input is now lower than current running PV output (http://news.stanford.edu/news/2013/april/pv-net-energy-04021...). But that doesn't say much about net energy production per panel over the panel's lifetime, e.g. if the PV industry would disappear this very moment, existing PV installations would still produce energy for decades.

Good point. Q. Would the amount of energy generated by a solar/wind system outstrip energy used to maintain?