Following my previous post I revised my circuit to measure the short-circuit current generated by my small panel. I will not take twin measurements of voltage and current.
First in full sunlight I measured an open-circuit voltage of 6.5 V and a short-circuit current of almost 105 mA on a 50 ohm load. That's more than 500 mWpk, free.
Once my circuit has been adjusted to allow reading a 5 V maximum value, I measured two consecutive sunny days.
On the second day the panel was moved a bit further out in the balcony so that it would reach full input exposition at 10:00 (red line). March 10th was a bit more cloudy than 9th.
I will continue to take readings every minute until the partial eclipse that will take place in 10 days. The plan is to keep the whole setup stable until then.