Harvesting energy is extremely context-specific (see Starner & Paradiso, 2004). Mechanical rotors have powered wrist watches for hundreds of years, however, their efficiency is poor and they depend on a very specific type of movement (but see Vogel et al., 2012). Furthermore, implantable devices are associated with their own challenges depending on the organism. For example, wireless recharging is possible with humans whereas it takes a clever rigging of nests or resting areas to apply a similar approach in wild animals. Solar power is an interesting route of harvesting, with solar panels being placed underneath skin to power a device or charge a battery.

Below is a calculator to estimate power from implanted solar panels based on the fundamental work by Vogel et al. using solar panels to power a cardiac pacemaker. I have also added inputs to estimte the charge time for a small lithim polymer (LiPo) battery being charged at 5-volts.

See also:

• Power Management Using Photovoltaic Cells for Implantable Devices

• Subcutaneous Solar Energy Harvesting for Self-Powered Wireless Implantable Sensor Systems

• A Wireless Implantable Sensor Design With Subcutaneous Energy Harvesting for Long-Term IoT Healthcare Applications

• High‐efficiency photovoltaic modules on a chip for millimeter‐scale energy harvesting

• A Contemporary Survey on Energy Harvesting Techniques for Next Generation Implantable Bio-Medical Devices

• Skin Implantable Thin Membrane Solar Cell Battery