IoT has benefited immeasurably from two concurrent trends: wireless technology and low-power electronics. Untethered, and able to run on progressively smaller batteries, connected devices in increasing number and variety are being deployed in more and more places. The IoT market is likely to grow faster and more expansive still, however, with the introduction of devices that can scavenge their own power.
Wireless connectivity has made it easier to use certain items in more places. Security cams have long been connected through wireline networks, but by making them wireless people have been able to install them in so many more places. The entire industry of asset tracking and the insights gathered during an object’s transit would not at all be possible without battery-powered wireless technology.
Some products, such as residential doorbell/camera combinations, might not ever be widely successful if they couldn’t be both wirelessly connected, and battery powered.
Battery usage
Batteries represent portable power, and as such have proven endlessly useful. Over decades, as many electronic products were miniaturised, they required progressively less power. Products that once may have needed several relatively large D cells were eventually able to work well on AAs or AAAs. Some of those can now operate for extended periods on coin batteries.
A great many of these products are constituents of the IoT: fitness trackers, smart speakers, location trackers, traffic monitoring systems, the aforementioned cameras and doorbells.
But batteries become depleted, and then they are disposed of – recycled or trashed.
Battery drawbacks
Roughly 5 billion dry cell batteries are sold in the U.S. every year, according to the Environmental Protection Agency (EPA), which is responsible for tracking solid waste and potential waste hazards. As many as 8 billion are sold in Europe every year, according to several sources. By inference, several billion dry cell batteries are disposed of every year.
Almost every type of battery includes materials that can be toxic, but it isn’t always easy or cheap to recycle batteries, and so recycling of batteries around the world is inconsistent at best. For example, only about half of discarded batteries in Europe are recycled, by one estimate. Current levels of waste and pollution are unsustainable.
And yet meanwhile the world is deploying more and more IoT devices. There were 14.4 billion IoT devices deployed through 2022, according to IoT Analytics, and the firm expects that number to double by 2027. Whether in a home or industrial setting, as these IoT devices scale their replacement costs and efforts are scaling as well! Some of the newest, most ambitious IoT applications propose to use vast arrays of sensors, to monitor large-scale endeavours ranging from agriculture to industrial automation.
Energy harvesting
These IoT devices are candidates for battery power, but it turns out that many might not need it. Some sensors need only the most miniscule trickles of power that the universe provides freely.
In such cases, energy harvesting is an attractive possibility. The basic concept is to capture energy from some natural phenomenon, in some cases, from multiple energy sources and convert it into electricity.
By definition, solar power and wind power qualify as energy harvesting. Both can scale up to megawatts, but for IoT devices at the distant edge of the network, the need can be measured in milliwatts and even microwatts, and that means many other physical phenomena can be considered.
Types of energy harvesting
To be sure, photovoltaics (PV) are an option for ultra-low power IoT devices. Classic PV cells, the same as those used in solar panels, remain an option, but there are alternative PV technologies being developed, including some based on manufactured compounds that mimic photosynthesis. Modern PV cells have greatly improved power density and can operate under both outdoor and indoor ambient light to recharge batteries or charge supercapacitor banks.
Small temperature differentials can be exploited by thermo-electric generators to capture microwatts from any number of sources that can include everything from industrial machinery to the human body. In some applications, the additionally present energy source of AC vibration can be harvested as well!
Piezoelectric materials generate energy when deformed. Applications where physical movement is nearly constant could benefit from harvesting energy in this manner, motor vehicles for example. Many leading smart home and smart building light switch manufactures are adding this piezo-kinetic energy harvesting to their line of moveable battery-less light switches.
Other energy harvesting technologies being used include new high tech-minded companies using electric and magnetic induction to harvest comparatively large fields of electricity to power sensors and radios in remote locations.
Ambient energy
Manufacturers of ultra-low power IoT devices looking to provide battery-less operation rely on energy harvesting technologies in part because there is no infrastructure for powering such devices.
But what if there were? What if there were something similar to cordless smartphone charging, such as Qi, but with a range of metres instead of just centimetres? The easy availability of tiny rectifying antennas (rectennas) has encouraged some to investigate the creation of standardised wireless power schemes.
There are several schemes being developed, usually depending on Sub 2.4GHz RF broadcast. At the moment, the closest devices to being commercialised are Industrial applications for factory automation machinery, warehouse equipment tracking, battery-less asset tags and electronic shelf labels, because these settings allow for the installation of RF energy transmitting gateways. Imagine the future of the smart home if every router and smart device gateway was also transmitting RF energy! The market could soon be flooded with very exciting longer lasting electric toothbrushes, key tags, keyboards, earphones, computer mice and more!
Looking ahead
The future of IoT cannot scale at the rate it is forecasted if it remains dependent on batteries. Many use-cases are still not realising their full wireless potential – experts in this space are continually improving IoT wireless stacks within alliances, but the fundamental power source needs revisiting.
Furthermore, as more and more companies and governments impose green incentives, the only path forward is to re-think the battery as we know it.
Tristan Cool is Industrial IoT Product Marketing Manager at Silicon Labs, leading the company’s exploration into alternative power solutions for the IoT.