To test whether the small IXYS solar panel would provide sufficient power, we ran the power supply for a week. The load was a simple diode with 330 Ohm resistor, taking 5mA at 3.3V Vcc. The results suggest that the supply is ample, especially because the average power consumption of the detector will be much less (< 1 mA).
In the final design, we may still want to go for a more advanced solution. This solar energy harvester solution has been adopted by Decagon for its next generation weather stations and would work nicely here as well. The voltage regulator, lp2950, was chosen for its efficiency but sometimes gives off higher voltages than 3.3V, up to 4.5V, while operatiing withing the specified current range. Any suggestions as to why would be very welcome.