Efficiency? Dunno, they still keep my batteries charged. My system is pretty much set it and forget it. I don't look at the volts or amps coming in. The volts and amps in are always changing as altitude, season and clouds always interfere. I do take a quick glance as I step through the Trimetric to see if the batteries are getting back to 100% or not though. If the input looks too low or not getting back to 100%, I plug in the portable panels.