Hmmm so you have no input or output capacitors in this regulator ?

Probably 10uF or so on the input for a nominal 80V panel circuit (allowing for 100V at low temperature).
Then I'll common the outputs of multiple buck circuits so output capacitance can be kept to a minimum.

 

Well I am sure you are aware of this but for the sake of clarity instantaneous input current in a switching device is drawn from it's input capacitor and the instantaneous load impedance/voltage is controlled by it's output capacitor. Given this the inductor current will rise merely according to vin-vo inductance and on time, especially when starting when vo is zero saturation is highly likely unless peak inductor current sensing is employed to prevent it, if the inductor saturates switch destruction follows.
I am afraid relying on PV panel power limits will not prevent this destructive process.
Unfortunately in a buck regulator the switch is high side and that is also the natural place to put the current sensing, there are some nice integrated solutions available for this problem, along with the complete controller.

EDIT 17/01 You do not mention the size of your system, a simple integrated buck controller is the MCP16301 and in the data sheet para 4.2.2 you can see it integrates peak current control. So if you use an integrated solution you may need no extra components/complexity to implement current sensing.

 

Well I am sure you are aware of this but for the sake of clarity instantaneous input current in a switching device is drawn from it's input capacitor and the instantaneous load impedance/voltage is controlled by it's output capacitor. Given this the inductor current will rise merely according to vin-vo inductance and on time, especially when starting when vo is zero saturation is highly likely unless peak inductor current sensing is employed to prevent it, if the inductor saturates switch destruction follows.
I am afraid relying on PV panel power limits will not prevent this destructive process.
Unfortunately in a buck regulator the switch is high side and that is also the natural place to put the current sensing, there are some nice integrated solutions available for this problem, along with the complete controller.

EDIT 17/01 You do not mention the size of your system, a simple integrated buck controller is the MCP16301 and in the data sheet para 4.2.2 you can see it integrates peak current control. So if you use an integrated solution you may need no extra components/complexity to implement current sensing.

It would be an iron powder inductor, so it would take a x5 increase in dc current to go from 95% to 25% of zero-current inductance, so it's not going to saturate unexpectedly.
The energy stored in 10uF/80V is only 32mJ = 32W for 1ms which is well within the dissipation capability of most MOSFETs, taking the worst case scenario of it all being dissipated in the MOSFET.
MCP16301 isn't going to be very useful for a nominal 80V DC input.