In Februari 2019 I designed revision 2.

I changed following specifications

• use cheap ($0.50) 1F 2.7V supercapacitor from Aliexpress or ebay
• make a slot in the PCB to embed the supercapacitor
• use a cheap  ($0.40) solar panel form Aliexpress, make two solder holes in the PCB 
• few holes for hanging or mounting the board
• different PCB color
• PCB with rounded edges
• simplify schematic, remove the configuration resistors from revision 1 and use only the 1.8V output, use only one LED
• remove the LED series capacitor

What I've learned from revision 2 PCB

• the USB connector has sharp corners
• the 2x 0.5V/44mA Ixys solar cells  are cool but very expensive and low power when compared to the 1V/80mA solar panel from Aliexpress
• the cheap 1F/2.7V supercapacitors from Aliexpress work just fine
• the cheap chinese solar panel is just $0.40 in qty 10 and works fine
• the large slot for the super capacitor is still too large
• the PCB is still large and heavy

I also wanted to experiment with waterproofing because it must be wearable. The boards were poured over with super clear epoxy resin.

The epoxy was pretty thin. In the beginning it made a nice layer but after 6 hours most of the epoxy dripped off the board. It does not have same thickness everywhere. The epoxy does not fill the holes around the supercapacitor because it is too thin. The epoxy layer on the surface mount solar cells is actually ugly