In this blog series so far, we have considered the energy consumption of motors measured in hundreds of kW and Power-over-Ethernet (PoE) for sensors and actuators at a more modest 100W. Energy harvesting is at the other end of the spectrum where power is in the µW range.
Where is energy harvesting useful?
The Industrial Internet of Things (IIoT) puts intelligence in sensors and actuators to better control and monitor manufacturing processes - efficiency and productivity gains result. At a minimum, this intelligence needs some data processing and storage.
A typical temperature monitoring sensor; will have a microcontroller, memory, and an interface for communications. Routing Ethernet cables or other wired communication systems, such as ones based on RS432 serial connections, may be inconvenient to the IIoT node, so wireless communication is often employed.
The IIoT node needs some power to operate, which poses additional challenges– batteries run down and take time and labour to replace. At the same time, DC from a mains adapter or PoE will only work if there is a convenient mains source.
Harvesting local energy of some type to provide a power source is the right solution – if the energy demands are low. A prime example would be ultra-low-power microcontrollers and WLAN modules that only take power in infrequent bursts, as data is accumulated and transmitted in packets at set intervals.
What type of energy can we harvest?
There are four primary sources of harvested energy:
- Mechanical vibration
The voltage and current characteristics are different in each case. All require a level of power conversion for the end-load supply rail. The energy sources are also generally of an intermittent nature. Hence, a rechargeable battery or supercapacitor is often employed to ensure supply and deal with the peak power demands.
A photovoltaic panel is perhaps the most familiar 'free' energy source, but for IIoT, illumination inside buildings is typically low – producing