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
AEMLION is sold on Tindie for $24.90
AEMSUCA is sold on Tndie for $24.90