This is the same phenomenon where covering just one cell in your panel will bring the power output to about half, and cover two cells or more, and your lucky to light an led. I wouldn't sell your 50 watt panel. You could just give it to me
, if not, hook it up on your house, and have it float charge some 12v batteries. Maybe have some halogens wired up to it. If your willing to do this, you can buy another 50 watt panel, wire them up in parallel and you should be set. I have done this many times with my small panels.
-Andrew