Hardware engineer Jasper Sikken recently designed the Tiny Solar Energy Module (TSEM), a one-inch square solar energy PCB for charging Li-ion batteries to power small hardware such as BLE or LoRa sensors.
According to Sikken’s description, “It is unique because it is an easy to manufacture tiny module that other hackers can drop into their PCB design or breadboard.” It seems like it would be a good fit for IoT projects such as remote monitoring or perhaps automating plant nurseries that depend on certain light conditions for optimal growth.
The TSEM board is outfitted with a pair of IXYS KXOB22–12X1F-ND monocrystalline solar cells capable of harvesting 0.55mAh (@ 23uA) per-day on average, with an output of 0.5V/44mA for each cell. It also features an AEM10941 IC that offers an ultra-low power startup and draws most of its power directly from the solar cells through MPPT power point tracking every 5-seconds. For continuous or backup power, the board allows for a 3.7V Li-ion battery.
As far as how much energy the board is capable of harvesting indoors, that depends on how much ambient light there is. Indoor light is roughly 1/100th of outdoor light, which translates to 10W/m2. Sikken estimates that at that power, solar cell open voltage is 0.458Vwith Vmp at 0.36V per cell. Considering there is a pair of solar cells, the boost will work at 0.72V input voltage. Sikken states that if more power is required, you can connect an external solar panel via the board’s terminals.