The energy payback time (EPBT) is the time an energy source needs to function before it has generated the energy that was required to manufacture and install said energy source in the first place. The Fraunhofer Institute produced some interesting graphs showing that the EPBT for solar panels is remarkable low, even less than a year for southern European locations. Encouraging is that the EPBT has come down considerably over the past years. Currently solar panels exist with a EPBT of 6 months. For an economic lifetime of 30 years, this implies an EROEI of 60, which is spectacular.
[fraunhofer.de] – Photovoltaics Report, November 2013 (pdf, 42p)