Developers are increasingly able to access reference designs and off-the-shelf systems for IoT energy harvesting.
Replacing batteries can be a significant logistical problem as well as a significant operational cost with battery-powered IoT designs. Energy harvesting can allow designs that will operate without ever needing a battery change, but do require careful power management. Fortunately, IoT energy harvesting systems are becoming turnkey.
While low-power MCUs and radio devices have gone a long way toward reducing IoT device power needs, battery life for them still seem to top out at under five years and more typically achieve only one or two years. This limited lifetime can create a significant problem for users requiring a widespread deployment. Not only would users need to regularly keep track of their device’s battery status, they must then deploy service personnel to replace depleted batteries. If the deployment encompasses thousands of devices scattered across a wide geographic area, the labor cost of the replacement effort can become overwhelming, not to mention the additional battery costs. Even with a few hundred devices within a single building, the cost can be substantial.
There is thus a significant economic advantage to be had if the device can be designed to never require battery changes. Achieving this goal might involve ensuring access to line power or reducing the planned operating lifetime so that the device is replaced when the battery dies. A third alternative is to harvest energy from the device’s environment to regularly recharge the battery. As long as ambient energy is available, the device’s power is ensured.
There are many types of ambient energy that devices might harvest. Photoelectric energy is perhaps the most well-known, and there are now photocells available that can efficiently gather energy even from typical indoor artificial lighting. Harvesting of radio energy is also practical, forming the basis of most RFID systems. Vibrational energy is a third alternative, converting anything from the regular movements of active machinery to the random footfalls of pedestrian traffic.
A common challenge that designers face with virtually all forms of energy harvesting, however, is managing the collection and storage of that energy into the battery or supercapacitor that is powering the device. Most harvested-energy generators produce a trickle of energy at low voltages, whereas the IoT device typically requires bursts of energy at much higher voltages. This disparity requires careful design of power conversion and storage systems and can be a daunting challenge.
Fortunately, developers are increasingly able to access reference designs and even off-the-shelf systems that have already addressed that challenge. One recent example comes from Atmosic Technologies, a fabless semiconductor company that designs ultra-low power wireless devices and energy -harvesting systems. The company recently released a series of photovoltaic energy-harvesting reference designs that feature its low-power Bluetooth transceiver and energy-harvesting power management chips. These designs include a wireless keyboard, a remote-control device, and a combination sensor module with Bluetooth beacon.
Figure 1 Turnkey energy harvesting modules such as the Xidas VP3 are becoming increasing available, simplifying the design of IoT devices with essentially unlimited battery life. Source: Xidas IoT
For developers seeking something more off-the-shelf to power their “forever battery” IoT designs, the emerging startup Xidas recently released the VP3 Vibrating Perpetual Power Pad. This device captures energy from vibrations as small as 1g of acceleration, stores it, and provides up to 10 mW of direct power to the device it is powering. The VP3’s integrated EHM-UNIV-1 energy-harvesting power module can continuously charge the unit’s battery with the harvested energy and deliver bursts of up to 1A from that battery on demand with an output voltage configurable from 1.5 to 3.6V. The power module is also available separately as a surface-mount device capable of handling photovoltaic or thermoelectric energy sources, as well as electromechanical ones.
These examples are only the most recent in a growing number of products available to designers seeking to power their IoT designs from ambient energy. They resolve many of the challenges associated with the disparity between the power source and the power demand, easing the device designer’s task considerably. Energy harvesting was once an esoteric approach to avoiding the need to periodically change batteries. Now, however, the approach is becoming increasingly turnkey.
This article was originally published on EDN.
Rich Quinnell is a retired engineer and writer, and former Editor-in-Chief at EDN.