/diy/ - Do It Yourself

>>1843451
>regardless of what the current into the buck converter is, assuming favorable conditions, the buck converter will supply up to the same power that the solar panel is producing
Yes, as long as it's in the operating range of the converter.
>Any insight as to what might be happening? Is this normal for a buck converter to sag that much? How might I go about stiffening the output?
You should expect around 2 % voltage variation on the output. You have more than 9%, so it seems to me like voltage from the solar panel drops too much which limits your power output. If you want to get full 7 W out of your panel you'll need a maximum power point tracker. Such devices vary the effective load of the solar cell such that maximum power is transferred. Your buck converter (when load is constant) is some resistance that determines power point of your solar cell, which can be shown on characteristic as red line. You can see that input resistance of buck converter determines your power point (intersection). When you use MPPT that circuit changes its input resistance to force panel in maximum power point. Try measuring output voltage of your cell with load (power bank) attached.