while looking for. a solution, have you contacted the manufacturer of that collector? Send them the picture and ask what they recommend. It obvious to me that it is something on the surface causing surface tension and hence the drops. The manufacturer should be aware of that problem and might already have either a replacement for that unit or a viable solution.
In the meantime, you could get some Rain-X and carefully wipe the surface to break that tension, and see if that works, but I definitely would write the company as well. You don't want to have to be going out to put something every week on that collector.