Backing Off Batteries as Our Default IoT Device Power Source

What you’ll learn:

• What are the issues with using batteries to power billions of small-scale devices?
• Why these issues are such a big deal.
• What are the alternative solutions?

Batteries have been a reliable source of power for many decades in electronic devices where wired power isn’t feasible, or, at the least, inconvenient. Coin-cell batteries have played a significant role in the recent deployment of vast numbers of wireless IoT transmitters, switches, and sensors. Experts predict a future of “trillion-sensor networks” but these types of simple connected devices are already all around us, and many if not most are powered by batteries.

This scale is built on batteries’ utility as a simple, portable power source. However, it elevates some significant downsides for electronics designers who batteries bring with them, including power-delivery style, replacement-related challenges, and a considerable amount of waste. Each of these are worth addressing individually. Collectively, they represent the real need to explore different solutions for small-scale wireless device power, especially if we’re going to have so many.

Power Supply and Draw Clash

Batteries are essentially a chemistry device built to be most efficient at low currents—the lower the draw, the less “damage” to the battery’s internal chemistry, and the longer the battery will live. While wireless electronic devices like transmitters, switches, and sensors operate at low average currents, they don’t necessarily draw at low currents during peak operation. And because they don’t need to always be awake, the average current is low.

Such devices experience short spikes of immediate activity followed by long periods of complete inactivity. During the current spikes, batteries operate well above the average currents that were used to benchmark these devices. During the periods of inactivity, some of the power that’s stored in batteries is just wasted away because of small leakage currents.

Both extremes are less efficient than if the battery could operate at its average current. This mismatch between the power draws of these types of devices and the optimally efficient power-delivery style of batteries results in hindered device performance and faster battery depletion than anticipated (and advertised). These types of “pulse power applications” could be powered more efficiently if they could use energy off a capacitor as it was collected, with no need for continuous storage.

What Happens When Batteries Run Out

Though impressive strides have been made in extending batteries’ lifespans and developing rechargeable battery chemistries, batteries dying will always be their default downside. A battery dying presents a number of complications, starting most obviously with the fact that the device it’s powering will stop working. That can have dire consequences.

Consider a water leak detector for example, which is designed to send an alert when it detects a particular condition. These critical warning devices are often placed in areas such as under sinks, washing machines, or toilets, or in basements that are damp and dark. Wired power is no good in these spots, so batteries are a logical power choice.

Over time, owners will grow accustomed to thinking, “no alert, no leak.” But once the batteries die, that correlation will break. Leaks will occur without an alert and only get worse from there, leaving homeowners vulnerable to mold and other property damage.

Some environments, like industrial settings, avoid these issues with proactive maintenance by requiring regular battery inspection and/or replacement by technicians. However, this constant need is remarkably costly, time-consuming, and tedious for everyone involved. Power consumption can be particularly difficult to manage in industrial environments, too, as data-monitoring IoT devices may be placed in locations that are difficult to access.

In addition, because batteries have this need for replacement or recharge, designers of small-scale electronics must include user access in the devices. This makes the products less secure from dust or moisture ingress, which is a big issue because they’re frequently deployed in either high-touch applications (industrial switches, car key fobs, etc.) or inclement conditions (water leak sensor, etc.).

We Discard 3 Billion Batteries a Year

Not only do batteries provide power in a way that clashes with small-scale wireless device draw, they’re also expensive and difficult to replace and design for. And—you guessed it—they’re dreadful for the environment.

Environmental groups have reported that Americans dispose of more than 3 billion batteries annually, causing 180,000 tons of hazardous waste. EnABLES, an EU-funded energy research project, claims that nearly 80 million batteries powering IoT devices will be discarded every day by 2025 if no alternatives arise.

That number is even greater according to Mike Hayes, head of ICT for energy efficiency at the Tyndall National Institute in Ireland. He projects that “in the trillion-sensor world predicted for 2025, we are going to be throwing over 100 million batteries everyday into landfills” unless we find a longer-lifespan solution.

A Sustainable, Scalable Alternative

We’ll never do away with batteries entirely because they remain the best option in too many applications. Still, for the coming trillions of wireless connected devices in every area of our lives, continuing to rely on batteries seems economically inefficient and environmentally unsustainable. Harvesting energy from the device’s direct surroundings offers an interesting alternative.

The availability of energy depends on our ability to capture it through technology, as demonstrated by solar panels, wind turbines, and hydroelectric dams. At the small-scale device level, the sun, wind, or water require too much infrastructure to provide enough power at the low target costs and small sizes required. However, in a subset of sensor applications, we can rely on something else: motion.

Advances in electromagnetism, microelectronics, power-conversion circuitry, and nano- and pico-power technology have unlocked the potential for many of these countless small-scale devices to be powered by their very triggering condition. Examples include a water leak sensor whose alert is powered by the arrival of water; a fire door sensor whose alert is triggered when doors are opened and closed; a car key fob whose transmission is powered by the force of your thumb press; or an industrial switch whose action is powered by the switch being flipped.

This kinetic-energy-harvesting process involves electromagnetic induction, where a kinetic force such as pressing a button moves a small magnet through a metal coil. As a result, an electromagnetic charge is produced in accordance with Faraday's Law. This charge can power various actions, such as transmitting data.

The quality, reliability, and functionality of the data transmission depends on the magnitude of the electromagnetic charge. Until recently, though, kinetic-energy-harvesting technology could not capture the charge efficiently enough to power these devices, nor were devices able to start up on such low voltage. Things have changed and kinetic-energy harvesting is now a viable alternative to batteries for many sensor applications.

With kinetic energy harvested onto a capacitor and used directly by the devices, the power draw/delivery clash suffered by batteries may be addressed. These components don’t require regular recharging or replacement as they rely on energy from their surroundings, not in storage, addressing all relevant longevity, logistics, and device design issues. Moreover, they have a lifespan that can last for millions of activations, eliminating all of the disastrous waste of battery disposal.

We have a long way to go before batteries are phased out from our IoT devices. However, if we want to speed up deployment, we need to strip out the things holding back device performance, design, and sustainability. That means saying goodbye to energy from batteries wherever possible and instead sourcing it from motion coming from the devices’ own surroundings.