These things are well defined in the research community and they don't have any issues with this. The input energy is all the energy from the sun that is incide

These things are well defined in the research community and they don't have any issues with this. The input energy is all the energy from the sun that is incident on the panel. Efficiency is electrical power generated by the panel divided by the power from sun (~1000 W/m^2). For the NREL efficiency records, the measurements are all taken at the same temperature at the NREL facility. To find the max power of a device you just sweep the voltage applied to the device and measure the current output and determine which voltage produced the most power (P=V*I). Then operate your cell at that voltage.