I changed the diode to a 1N4148 and it would not oscillate, adding a 1 meg resistor from Q2 Base to GND fixed it, at the expense of the leakage.

Replacing the diode with a bjt fixed this


Glad it helps

 

Replacing the diode with a bjt fixed this

Glad it helps

Wracking my brain to understand WHY the transistor fixes it???!!
Does it have a lower total Vf at low current levels?

 

About 20-years ago, a guy (Miller) started showing off some cool solar powered "robots" that he called "beam bots". The little solar panel charged until a trip point and a motor would move the toy across a desk a few centimeters and then, a few minutes later, it would repeat. Some moved, some spun, some clicked, etc. He was very creative. They all used the now extinct Panasonic 1381 voltage trigger. The best offset for that extinct part is rumored to be a microchip MCP 112 but I haven't tried it.

My kids made a windmill and a grasshopper. I think the windmill is still in a box around here somewhere. The grass hopper was made as a gift but really cool.

 

http://solarbotics.net/library/circuits/se_t1.html

This link has a number of relaxation oscillator circuits that perform this function.