Ambient light, thermal gradients, vibration/motion or electromagnetic radiation can be harvested to power electronic devices. EnerChips enable high-efficiency Energy Harvesting (EH) designs that convert the relatively low levels of energy into an amount that can provide the power for an electronic system. The diagram below shows the major components of an autonomous wireless sensor which are the EH transducer, Energy Processing, Sensor, Microcontroller and the Wireless Radio. There are 3 key areas in the Energy Processing stage that must be addressed for successful EH implementations: Energy Conversion, Energy Storage, and Power Management.
Energy Harvesting Hybrid for Battery Extension
There are cases where there is not enough ambient energy to power a device and a larger battery must be used. However, energy harvesting can be used to significantly extend the life of the battery. Cymbet EH solutions (especially solar) can be combined with primary or rechargeable batteries to extend their life. Click here for the EVAL-10 Solar Eval Kit Data Sheet that describes battery extension.
Energy Harvesting Design Background
An Energy Harvesting power management system must be capable of capturing, converting, storing and delivering energy in a form that can be used to provide the power needed by the system it serves. A typical Energy Harvesting system starts with an energy collector or transducer device and depends on the type of energy one is trying to convert. These are typically solar or photovoltaic cells for light energy, piezoelectric for pressure, kinetic for movement, inductive for rotational or motion, thermoelectric for heat or temperature differential, and electromagnetic.
The energy collected from these transducers must be converted to a form that can be stored for later use. In remote sensor systems or portable device applications that use Energy Harvesting a small rechargeable battery or storage capacitor is often employed to store the collected energy the system needs for operation. The drawbacks to each of these storage methods are numerous in that even rechargeable batteries wear out after a few hundred charge/discharge cycles and need to be replaced and super caps while they eventually change their characteristics, will self discharge rapidly, as much as 20% per day, causing much of the converted energy to be wasted. A more robust and permanent solution is to use an EnerChip solid state battery as the energy storage element in the system to eliminate the need for replacement since it can support in excess of 5000 cycles and has a minimal self-discharge of less than 3% per month.
The final stage of the system conditions to stored energy to suit the requirements of the system. This could be as simple as a regulator and level shifter to a complex power control circuit that intelligently manages the power distribution to the system based on power needs and system operation.