Energy harvesting is an option that is advancing in capability, opening new IoT options.
One of the logistical impediments to some applications for the IoT is supplying the thing with power. For many installations, line power is impractical and battery power comes with a need for periodic battery replacement that may be difficult or impractical to ensure. Energy harvesting is an option that is incrementally advancing in capability, opening new IoT options.
There are three elements that must come together for energy harvesting to be practical. The first, of course, is for the IoT device itself to have low power requirements. This requirement has two parts: the power needed for the processor and the power needed for the wireless communications link from the device to a server or hub. It will be a wireless link; if the application had allowed for a wired connection, the power could have been supplied over that connection. The third required element is supplying enough harvested energy to meet the device’s power needs.
The first element – low powered processing – has a long history of technical progress. There are many microcontrollers now available that operate with extremely low power demands, especially if they spend most of their time “sleeping” and can activate to perform their task quickly.
The element of low-power communications is where recent innovations are occurring. An example is the Monarch LTE-M/NB-IoT chip from Sequans, which provides a low-power combination of processor and radio. The company recently paired its chip with an e-peas AEM10941 IC solar energy harvesting module to provide a demonstration system that can be powered by the overhead lighting of an indoor installation as well as by solar power when outdoors. The e-peas device captures, stores, and regulates the energy from a photocell, providing the energy in bursts to the Sequans device. This allows the combination to power a sensor mix to gather environmental data and periodically report it to a server without needing any batteries.
There has also been innovation in the field of harvested energy generation. Switch manufacturer ZF has recently introduced a compact mechanical switch for windows and doorways that will generate a burst of energy whenever the door or window opens or closes (Figure 1). The device uses the switch movement to briefly power an electromagnetic induction generator. The energy generated is enough for a small processor and radio combination to send several telegrams using the EnOcean 3.0 protocol to a smart home hub, reporting the door or window activity.
Figure 1 Snapping this switch generates a burst of energy via electromagnetic induction, enough to power a small wireless transmitter for a telegram burst. Source: ZF
These examples demonstrate two of the key approaches that energy harvesting applications might use. In the first example, the energy is continuously being gathered and stored until there is enough to complete the desired task. To operate without batteries, capacitive energy storage is used. In the second example, the energy is generated by the very event the system is intended to sense. It converts the energy of motion into electrical energy and uses it immediately. The fact that the energy is available is what signals the event’s occurrence.
Energy harvesting technology is still not to the point that an IoT system can receive continuous power and connectivity, although incremental progress is still being made. But for applications where periodic or event-driven communications are sufficient, the approach offers an opportunity to do without batteries for an essentially indefinite installed lifetime.
This article was originally published on EDN.
Rich Quinnell is a retired engineer and writer, and former Editor-in-Chief at EDN.