Charging Bankruptcy and the Case for Energy Harvesting

Posted on June 20, 2013

How many phones, tablets, laptops, and eReaders do you plug in before bed? Two, five, ten? Each night, we perform a carefully choreographed routine of plugging in tiny connectors after searching through couches and bags to find phones and devices. Failure to perform this dance has dire consequences. It could mean a day of crouching near outlets to juice-up dying devices or even worse, the dreaded no-battery shutoff.

The problem is even worse for the early adopter crowd whose collection of Fitbits, Pebble watches, Google Glasses, and extra laptops can easily total more than ten devices that need charging at least once per week. We are approaching charging bankruptcy.

Almost every day we hear of a new battery-powered device with fantastic promises like activity tracking for dogs but at some point will we simply be unable to handle yet another device in our life? Even though we may desperately want Google Monocle, the thought of charging yet another device every night may cause us to abandon the purchase. The charging problem has already become an important impediment to the nascent hardware renaissance. What would happen in a world in which there are 20, 50 or even hundreds of connected personal sensors and actuators that need power1? We can’t continue to plug in each device, so we must find alternatives.

One piece of technology that has been receiving recent attention is wireless charging or inductive charging. Inductive wireless chargers promise to cut the final wire and free us from the pain of wired charging. While wireless chargers are indeed a significant improvement, they really only solve the ‘final inch’ problem. That is, users will still need to perform the interruptive and time-consuming tasks of (1) remembering to charge each device and (2) finding the devices and bringing them to the induction charger. With current technology like that from WiTricity or PowerMat devices need to be brought within several millimeters of the charger. While this might be a step in the right direction, this technology certainly won’t help us move from having three battery-powered devices to 20 or 100 devices unless we end up building induction coils into every chair, table, and wall in our homes and offices.

To realize a world in which a hundred tiny discrete devices work for us 24 hours a day we need a new approach. We can’t assume that humans will remember where all their devices are located or remember to periodically charge them. Nor can we assume devices will always be placed within inches of a battery or inductive charger. Devices must be become power self-sufficient.

That means that either devices must come from the factory with enough energy to last the lifetime of the device or they must dynamically harvest enough energy from the surrounding environment. Both approaches are still far from being widely available or utilized. Wider adoption will require new ways of looking at power and energy consumption. For example, we often focus on the power consumption of computation rather than the power consumption of communication. This is crucial considering that the latter can be five orders of magnitude greater than the former. Professor Prabal Dutta, an expert in ultra-low power systems wrote that

“For the same chunk of energy a mote [wireless sensor] could perform 100,000 operations on its CPU but only transmit one bit of information to the outside world.”

Developing the technology that supports the construction of self-sustaining systems that do useful work power on 100 or 1000 times less power will require advances in ultra low-power material science, ultra low-power electronic devices, ultra low-power communications, and updated tooling that makes energy consumption a fine-grained metric that is tracked and optimized at all levels of hardware and software. An example of this evolution is the energy-centric toolchain provided by Energy Micro that can track per-function realtime energy consumption in a processor.

I am personally fascinated by the concept of completely self-sufficient systems powered by energy harvested from the environment. We already build multi-million dollar satellite platforms that last decades and are powered only by the sun. I believe that simple versions of similar technology that is designed to be completely self-sufficient for years and available for a few dollars could radically transform homes, offices, and the lives of rural communities around the world. This is exciting. We know the problem, we have many of the pieces of a solution, and now we just need to start putting them together.

1 Not everyone agrees this will be a problem. One could argue that most of the sensors and actuators we’ll ever need can be easily and effectively integrated into our existing phones and tablets. There may never be a need for a world in which we have 20 or more personal devices. For example, why buy a separate Fitbit when we could just reuse the accelerometers in our existing mobile phones?