The photovoltaic MOSFET approach would work of course. Current is more than enough but regulation is compulsary at >13 V open circuit. The sampler diodes in reverse bias hardly allow any current through.
Raymond
Another possibility on the photovoltaic approach is Vishay's LH1262 photovoltaic MOSFET drivers. It has two photovoltaic generators in a DIP or SOIC package. You can get a minimum of 2.6uA each (3.4uA to 6.9uA typ, depending on drive current), with an open circuit voltage of about 13.5V.
Regulation would still be needed, obviously, probably by loading the output and controlling the drive current as in the referenced artcicle. Or maybe that's enough current for an ultra-low power regulator.
