In the previous video I used a small solar panel, but I found it really hard to find a cheap way of securing it to the letterbox.
So I picked up this one from Jaycar. It had everything reliably water-proofed.
You could probably pick one up cheaper, but make sure it’s a 6V version as the DFrobot charger can’t handle anything over that.
Under my studio lights it was generating an open-circuit voltage of around 9v, whilst the loaded voltage dropped down to around 2.6v. Nice. Note the open-circuit voltage of this panel can hit around 10v, so you have to be careful when connecting up.
The other end of the cable I trimmed and tinned so I could screw into the DFrobot LiPo solar charger and allow me to remove either the panel or ESP8266 box for maintenance.
Before connecting up make sure you black out the panel, because the open-circuit voltage could potentially damage the LiPo charger. The voltage levels were all in spec and predictable. Chucking a battery on and checking the voltage. Yup everything seems to be working, and the solar cell will charge the LiPo when there’s enough photons hitting it.