For the HackadayPrize 2018 I designed a Tiny Solar Energy Module. It is cool because it can harvest enough energy from indoor light to power simple BLE or LoRa applications. I am selling two boards on Tinde for $24.90. One stores it's energy into a Li-ion battery, EAMLION, and the other stores it into a pair of supercapacitors, AEMSUCA. The AEMSUCA is really cool because now you can make applications that runs forever from indoor light without a battery!

Tiny Solar Energy Module project on Hackaday.io
https://hackaday.io/project/159139-tiny-solar-energy-module-tsem

AEMLION project on Hackaday.io
https://hackaday.io/project/160376-solar-harvesting-into-li-ion-battery

AEMSUCA project on Hackaday.io 
https://hackaday.io/project/160470-solar-harvesting-into-supercapacitors

AEMLION is sold on Tindie  for $24.90
https://www.tindie.com/products/jaspersikken/solar-harvesting-into-li-ion-battery/

AEMSUCA is sold on Tndie for $24.90
https://www.tindie.com/products/jaspersikken/solar-harvesting-into-supercapacitors/