I start charging my solar generator (70Mai 1000) early in the morning with a single BougeRV180w panel. When I first plug the panel into the generator I get about 20 watts with sun on the entire panel. An hour or so later, I go to check on the progress and see the generators display only showing 35 watts, but when I unplug and reinsert the panel into the generator it now shows 140 watts. Is this normal for a solar generator charging from a solar panel? Thank You.