My tank has a similar positioning...It is acroos from a door with a window at the top and it gets about 3 hours of sunlight a day coming through it hitting the tank while the tank lights are off (about an hour in the morning and about 2 hours in the late afternoon). Initially I put a small blanket over the window part to stop the rays from coming in when I had an algae problem a few years ago. Since I have cleared up the algae problem, I recently folded back a corner of the blanket to allow one ray to hit a part of the front of the tank. As an experiment I planted a piece of rotala sp. mini that I got by accident in the path of the light just to see what would happen, and it took off. I have low light in my tank, and by all accounts, I don't think I should have been able to grow it. I moved it out of the way, and now I have a Water Onion in the path of that Sunlight, and it started growing almost immediately (much better than my 2nd onion plant that is not in the path of the light).
I do have a patch of algae on that one pane of glass where the sunlight hits, but it never gets too big that my bristlenose can't take care of it. By the look of your pic, your tank is getting a lot more sunlight than mine, but if you can control it, I think a little sunlight can be a great supplement to the light in your tank.
