Energy Harvesting in the age of an Internet of Things

6 ways you will power your smart city

Segments of our cities are being infused with technology capable of scavenging energy from the environment, and then using that harnessed power to drive low power communication and sensor technologies. Traffic patterns, pollution monitoring, parking space availability, and utility usage will soon become accessible to citizens in real-time with the combination of embedded sensors and wireless communication being distributed throughout our neighborhoods.

These ‘talking’ cities are being driven by:

  1. Increased efficiency from energy harvesting technologies.
  2. Low powered and improved SoC (system-on-a-chip) development.
  3. Creation of power-savvy protocols and software (Think 6LoWPAN and micro OS’s like Contiki and TinyOS).
  4. The ability to Internet enable devices which were previously considered too resource constrained.


Overview: Energy Harvesting

The ideal minimal Internet of Things device is small, able to reliably transmit information, and operates on its own with little maintenance throughout its lifetime. One of the main barrier’s to making these IoT devices a reality has been the difficulty of locating adequate power sources without encumbering the size of the device or requiring frequent battery replacements.

Energy harvesting from naturally occurring sources like solar, wind and vibrations are leading the way as an option to power these devices but at the same time our good friends down at the lab have been looking at alternatives to get things rolling. Their latest answer? You.

Below are 6 examples of how energy captured from you and your daily activities can help gather previously inaccessible information about your environment and jump start an era of truly networked cities

1- Walking the streets (Energy output: 1 square generates up to 2.1 watts)

Every time you step on one of these power tiles, renewable energy is generated from your footsteps. The harvesting process, called Piezoelectricity, is generated from specifically applied materials such as crystals, polymers, and ceramics. Without the force of a human step, the atomic structure of the material is in equilibrium and produces no net electric charge. However, when the force of your weight is applied to these materials an electric gradient is created producing a voltage that can be harnessed and potentially used to power street lighting or an embedded sensor.

Notable companies in the space: Pavegen & Powerleap

2- Parking your car

If parking itself wasn’t fun enough already, these state of the art sensors are taking it to a whole new level. Embedded in the pavement these devices are triggered by a disturbance in the magnetic field from your car pulling into a space. This interaction is registered and sent in simple messages from sensor to sensor until making its way to a gateway (a small box sitting on top of a streetlamp or in a traffic signal). The end result is the latest parking information on your smart phone saving you that 3rd trip around the block, and at the same time providing the local government with more efficient ways to manage and price its infrastructure.

Notable company in the space: Streetline

3- Stepping in your shoes (Estimated to be between 7- 67w possible but practically around 1w could be captured)

If cardiovascular health is not enough of a reason to walk to work, new harvesting technology is making the journey even more productive. InStepNano Power, headed by UW Madison professor Tom Krupenkin, has developed a system called ‘human gait energy scavenging’ to capitalize on the energy that is produced by a human step. Though most of us are not likely to run to our next meeting, the professor’s research has identified that, "While sprinting, a person can produce as much as a kilowatt of power."

The device is installed in the bottom of your shoe and is capable of capturing watts of electrical power that can then be saved and reused instead of being lost forever in your sneaker. The harvester functions via the interaction of thousands of liquid microdroplets on a ‘nanostructured substrate’. Once this energy is stored, the system can also act as an intermediate transceiver between a mobile device and a wireless network. A more detailed FAQ on the product can be read here.

4- Wearing your clothes (Possible energy output: uW)

Dr Steve Beeby and his team at the University’s School of Electronics and Computer Science have been developing an energy harvesting film that can be screened directly onto any piece of clothing or textile. This innovative film will use a combination of printing processes and active-printed inks to create garments that are able to capture energy as you move.

This technology could potentially be applied to more diverse materials beyond clothing as well. We are constantly in contact with textile surfaces throughout the day (your car seat, couch, and all of those office hall carpets). Our accessibility to such a high volume of surface coverage combined with this technology is a energy system worthy of some investment.

5- Shaking that thing (Energy output: 5-12 W)

Biomechanical harvesting focuses on capturing the energy offered by the bending of your body parts (your knee has the most power potential). Your muscles work against the motion of the leg at the point during your stride when your leg begins falling back towards the ground. Energy normally dissipates during the braking process of your movement, but with bio-mechanical technology, the braking process can instead drive a generator (similar to how braking generates power while decelerating a hybrid car). With a device on each leg, a user walking at a comfortable speed can generate an average of 12 watts of electricity using the latest devices.

Notable company in the space: BionicPower

6- From the sky (Current possible energy output: 5uW)

Taking this harvesting potential to a whole new level, another possible method being developed is technology that can pull energy out of the air from radio frequency transmissions. Using a “wide band” receiver capable of soaking in signals sent between government regulated frequencies such as radio and TV towers, the Wi-Fi in your house, and the phone in your pocket, new devices can create usable energy from these frequencies after being converted into DC voltage. Researches haven’t yet been able to glean enough power out of this process to make it really worthwhile, (currently up to 5 milliwatts), but its exciting to think that an Internet of Things could potentially power another piece of itself.

Notable Company: RCA Airnergy Charger

Honorable Mention Harvesting Methods:

Still in the works, there is potential to also generate energy for your devices by working out at the gym, capturing the motion in your arm to power a device on your wrist, exploiting differences in temperature between your body and the air around you, or even from energy taken from the shifting motion of a bag on your back.

Internet Enabled

Until recently, the use of the Internet Protocol (IP) and Wi-Fi on small sensor devices was not considered viable. But now, with the development of things like 6LoWPAN (IPv6 over Low power Wireless Personal Area Networks), uIPv6, IEEE 802.15.4, Contiki, and TinyOS combined with other new protocols/compression methods and increasingly efficient system-on-chip technology it is possible to start bringing even the smallest of devices online.

So what kind of applications can be created using this combination of small Internet enabled devices and energy harvesting?

These deeply embedded computers start making the invisible visible by presenting us (and other objects) with physical information - sensor readings and actions occurring at particular places and at particular times in the real-world. The capabilities and applications for these IoT devices will vary greatly depending on how often they need to communicate and their size, but their potential uses can be seen in the general categories below:

  • Structural monitoring of buildings and transporation systems
  • Monitoring pollution levels
  • Enabling alerts for environmental conditions like floods and fires
  • Tracking and controlling temperatures and utilities inside homes and offices


Though not yet implemented on a large scale, a data gathering system created from energy contributions from your daily activities and the backbone of wireless network connectivity seems to be an ideal combination of technologies leading us into a new era of networked cities.

Product Spotlight



“Radio frequency energy harvesting” might sound like snake oil — Free energy, pulled out of thin air? Yeah, right! — but the idea of using radio waves to transmit power has been around for more than a century and is finally coming into its own with the Internet of Things. Between Wi-Fi, Bluetooth, cell phones and myriad other wireless signals, there are plenty of ambient RF sources to draw from. And even though only small amounts of energy can be reclaimed this way, it doesn’t take much to keep a simple sensor or actuator running.

Freevolt Diagram

Freevolt, developed by Drayson Technologies, is an RF energy harvester designed with the IoT in mind. It’s essentially a broad-spectrum antenna that picks up all kinds of wireless signals and, instead of reading them for data, converts a bit of their energy into usable electricity.

According to the company’s promotional materials, an antenna about the size of a credit card can collect 100 microwatts of power in a typical home or office. That’s several orders of magnitude less than you’d need to run your smartphone, but it’s enough for low-power devices like embedded sensors that can subsist on a trickle of energy. As long as there are enough wireless signals available, a Freevolt device would never need to be plugged in or have its batteries changed.

Freevolt Product View

In a presentation last year at the Royal Institute, CEO Paul Drayson said the technology could be scaled up, with larger antennas embedded in billboards or walls to provide energy for e-ink displays or building infrastructure. But as a first step, the company is marketing an air pollution sensor, the CleanSpace Tag, to demonstrate Freevolt’s immediate applications in the IoT market. The gadget is about the size of a smartphone, connects over Bluetooth Low Energy to share sensor data, and uses Freevolt to maintain the charge of an internal battery with a usable lifespan of five years.

Learn more about Freevolt in the video below, or read the whitepaper about the technology.



AdaptivEnergy's Joule-Thief energy harvesting module with a size of 2.22" (56.5mm) x 1.38" (35.0mm) x 0.65" (16.5mm) and in the middle is their 1.73" (44 mm) x 2.00" (51 mm) x 1.65" (42 mm) Ground Transport Energyversion which operate on small vibrations (less than 0.040 grms) these have been combined with Gainspan products to demonstrate powering and sending temperature and light data through standard Wi-Fi access point and onto a web hosted application.

A typical lifetime for a current wireless sensor network is between 2 to 5 years and needs its power consumption to be below 100 microwatts in order to function. “For monitoring a pipeline, if you generate 100 microwatts, you can power a network of smart sensors that can talk forever with each other” says Arman Hajati a researcher at MIT talking about a similar system he was working on.


Besides AdaptiveEnergy and Gainspan other companies working on products in this arena include

Additional Resources

Image sources:
Header- Seattle Municipal Archives, Walking- Pavegen, Parking- Streetline, Shoes- InStepNanoPower, Clothing- Andy Vowles & littlekissme, Movement- BionicPower, WSN Mote- AdaptivEnergy, WiSe

*Disclaimer: not an EE. The electricity output amounts were pulled from a variety of sources so let me know if they are off

Interested in more? See our Smart City Infographic here: