Can I connect different voltage solar cells in series?

I have read that connecting different voltage solar cells in parallel could be an issue, but what if I want to connect them in series?

I have a larger panel of 21-24V, 15W and a controller with 2 solar panel inputs. I do not have enough space to put up another large panel, so I was thinking about putting a 13,5V and 4x2V cells in series.
Is this doable and a good idea? Any down sides to connecting them like this?

Thanks for your feedback & ideas in advance!

I've been doing it for a while with random solar yard light solar panels, I don't have the technology required to test them (the patience mostly) But it seems to work alright.
suhajdab (author)  TheWelfareWarrior8 years ago
Thanks! I will go ahead then!
It would ruin the efficiency of the larger solar cell, i guess.
I don't Know whether its do-able. But, you could try!
suhajdab (author)  Smokedasphalt8 years ago
Luckily my controller has 3 solar connections (+ + -) allowing me to connect 2 panels separately. So I guess all lights are green :) Thanks for the input!