LTC3130 minimum on time solar power supercapacitor

www.analog.com/.../3130f.pdf

My project is basically the same as the first example on page 30 of the datasheet here. It has PV solar panel input with MPPT and RUN pin control and outputs to supercapacitors, in my case a series of 5 of them. But the output voltage of 15V is a bit too much. Sometimes it can give ~14V, sometimes not.

How can I calculate a reliable output voltage? Especially considering I might only have a trickle of current as power at the input. Maybe I can tweak the inductor or other parts to squeeze out more?

In some of my practice implementations, I've seen the "ambitious" design work great. The PV gives ~4v and it slowly charges up the supercaps even in low power times at the end of the day, like dusk. Other times I connect it to a power supply at 5.5v and it doesn't charge the supercapacitors at all, the output is stuck at ~3v.