Written by Anxo Rodríguez Martínez, Marta Castro Lopez and Nuria Barros (Gradiant)
Every time you walk, your weight strikes the ground, and part of that energy dissipates as a vibration nobody captures. Every time your body produces heat, that heat escapes into the air without anyone collecting it. Every time a Wi-Fi router transmits a signal, much of that electromagnetic energy spreads across the room without anything picking it up.
We are constantly surrounded by small amounts of unused energy. Most of it disappears unnoticed, simply because there has never been a need (or no practical way) to recover it.
Energy harvesting starts with a fairly simple question: what if that wasted energy could be captured and turned into useful electrical power?
What is energy harvesting?
At its core, energy harvesting is the process of capturing energy that is already present in the environment, or that would otherwise be wasted, and converting it into useful electrical power. The energy may come from vibration, heat, motion, light, electromagnetic waves, or many other sources.
Energy harvesting can take place at very different scales. Wind farms or solar plants are designed to generate enormous amounts of electricity, meant to power entire cities. However, the term is often associated with collecting very small amounts of energy, typically microwatts or milliwatts, from sources that are already there (vibration, heat, motion, electromagnetic waves), with the goal of powering equally small devices: sensors, watches, medical implants, electronic tags.
The idea is not to replace the power grid, but to remove the need for a battery (or for replacing one) in places where that’s expensive, inconvenient, or simply impossible.
Energy harvesting technologies
The ways of capturing that lost energy vary greatly depending on where it comes from. Some materials, for instance, generate a small electric charge the moment they are mechanically deformed (the so-called piezoelectric effect1), and that simple principle has already been installed in experimental flooring at train stations or nightclubs, capable of producing electricity every time someone steps on it, and even in some stretches of road, where an attempt is made to harvest part of the vibration left behind by traffic. The amounts are modest, but enough to power, for example, a nearby light signal.
Something similar happens with heat2. When there’s a temperature difference between two points of a material, a small electric current is generated thanks to the Seebeck effect3, and that phenomenon is what lets some wristwatches run indefinitely without batteries, drawing on the difference between the body’s own heat and the ambient temperature. On a larger scale, there are industrial sensors that feed off the residual heat of pipes or machinery, without needing any external wiring.
Motion offers yet another route. The swing of an arm while walking is already used to wind certain mechanical watches and activity trackers, and that same idea is now being explored for implantable medical devices: if the heartbeat itself could power part of a pacemaker, it would remove one of its biggest drawbacks, having to undergo surgery just to replace the battery every few years.
Even the air around us, filled with radio signals (Wi-Fi, mobile networks, radio, television), carries energy, however minuscule the amounts. There are devices capable of capturing part of that ambient energy and turning it into enough current to power RFID tags or passive sensors, with no battery and no direct connection to any source.
And then there’s light, probably the best-known form of harvesting of all, even though it’s rarely thought of in those terms: a solar panel is, at bottom, nothing more than a device that harvests light energy and converts it into electricity.
It’s a good reminder that the concept of energy harvesting4, however novel it may sound, has been among us for decades in its most widespread form.
Why energy harvesting matters more and more
All of these technologies share the same underlying drive: the proliferation of small sensors and devices that need power in places where a battery is a problem. The rise of the internet of things means potentially deploying billions of sensors (in buildings, on roads, along production lines, even on the body), and the idea of having to swap batteries one by one is simply unworkable at that scale. Predictive industrial maintenance, smart buildings, structural monitoring of bridges or tunnels, implantable medical devices: all of these fields share the same underlying problem, and energy harvesting is one of the most promising answers being explored to solve it.
Photonic energy harvesting: the light traveling inside a chip
Everything above describes energy lost at our own scale: footsteps, body heat, radio waves in a room. But the exact same problem exists on a vastly smaller scale, inside photonic circuits themselves: chips through which light travels instead of electricity, and where, just as with footsteps or heat, much of that light is lost along the way without anything making use of it.
That’s precisely the ground we work in at BLOSSOM: exploring how to apply this same harvesting logic, but inside a miniature photonic circuit, where the source is no longer motion or heat but the light itself circulating through the chip. By recovering and reusing part of the optical energy that would otherwise be lost, we aim to open new possibilities for self-powered or energy-aware integrated devices. The underlying idea is the same one we’ve seen throughout this whole journey: almost no energy is ever truly lost, it’s just waiting for someone to find a way to collect it.
References
- Wakshume, D. G., & Płaczek, M. Ł. (2024). Optimizing Piezoelectric Energy Harvesting from Mechanical Vibration for Electrical Efficiency: A Comprehensive Review. Electronics, 13(5), 987.
- Safaei, B., Erdem, S., Kolamroudi, M. K., & Arman, S. (2024). State-of-the-art review of energy harvesting applications by using thermoelectric generators. Mechanics of Advanced Materials and Structures, 31(22), 5605–5637.
- Shi & Liu, “Energy Harvesters and Self-Powered Sensors for Smart Electronics” (Micromachines, 2024).
- Naifar et al., “Energy Harvesting Technologies and Applications for the Internet of Things and Wireless Sensor Networks” (Sensors, 2024)
