I purchased a Renogy 165(?) W panel a couple of years ago and have not used my generator since (even in Winter); It's a portable panel, so I have to re-direct it a couple of times per day to make sure it's receiving direct sunlight.
What really surprised me was that I was camping for 3 days in overcast skies and the panel was keeping the batteries above 12.6 V (but only just). I did switch the fridge off at night to preserve as much energy as possible. On the 4th day the sun came out and battery voltage went up to 13.7.
I was quite impressed with the solar panel and it's ability to produce electricity even when there is no sunshine.