Humans have long harnessed wind and water power, stretching from early windmills to riverside watermills built to grind grain. Both traditional applications relied on kinetic energy and both survive to this day—though modern mills and turbines now harvest electrons rather than milling cereals. Solar photovoltaics arrived later, bypassing turbines altogether by using photosensitive cells to convert solar radiation directly into electricity. Hydrovoltaic energy belongs to this same turbine-free chapter.

We all know steam can drive massive turbines, but water also contains ions and charged particles at a molecular scale. Until recently, however, this natural energy source lacked effective technical mechanisms for direct, continuous harvesting.

The breakthrough lies in nanometre-scale interactions between fluids and structured surfaces designed to capture these fluidic ions. This is precisely the kind of device developed by researchers at the École Polytechnique Fédérale de Lausanne (EPFL), building on the raindrop-powered technology we covered recently.

Hydrovoltaic energy utilizes nanoscale materials to harvest electricity directly from fluid motion and evaporation. Unlike traditional hydropower, which harnesses falling water to drive mechanical turbines, this technology operates at the molecular level—tapping into the electrical currents that occur naturally when liquids pass over microscopic surfaces.

The underlying physics relies on the interaction between water ions—charged particles—and a solid surface. When the liquid enters a microscopic channel, ions of the opposite charge accumulate on the channel wall, forming an electric double layer (EDL).

As evaporation or capillary action drives the liquid forward through the channel, it drags these mobile ions along with it. This movement disrupts the electrical equilibrium, spontaneously generating a current and a potential difference. 

Since evaporation occurs spontaneously under normal ambient conditions, this technology opens the door to completely decentralized energy harvesting—even if, as we shall see, it comes with its own caveats.

To date, the Achilles’ heel of experimental hydrovoltaic devices has been their inability to maintain continuous electrical generation. Most prior prototypes relied on intermittent wetting and drying cycles. Without these cycles, salt accumulation or charge saturation within the channel quickly neutralized the electrokinetic effect, cutting off the current.

To overcome this limitation, a research team led by Professor Giulia Tagliabue at EPFL’s Laboratory of Nanoscience for Energy Technology (LNET) designed a nanodevice capable of producing electricity under steady-state conditions.

The EPFL chip operates via capillary action, mirroring the way trees draw water from their roots to their leaves. The device integrates a hexagonal network of silicon nanopillars. The microscopic spaces between these pillars form nanoscale channels that leverage capillary forces to draw fluid passively, eliminating the need for mechanical pumps. 

To prevent this, the scientists coated the interior of the nanopillars with an invisible, high-density insulating material (a dielectric oxide). This layer acts as a stabilizer, maintaining a surface charge density so high that running water cannot neutralize it. Furthermore, heat and light do more than just accelerate evaporation; they actively regulate ion movement and electron flow within the silicon, boosting power generation.

The design strikes a perfect balance: water flows seamlessly while carrying the maximum possible load of charged particles, allowing the chip to deliver a steady, uninterrupted current.

Operating entirely on nanoscale flows, the system can be woven directly into printed circuits or environmental microsensors. By harnessing natural water evaporation to run completely autonomously, it paves the way for battery-free edge computing and remote monitoring networks.

Admittedly, much like triboelectricity, hydrovoltaic energy isn’t about to light up cities or keep massive data centres running anytime soon. However, it may well prove vital for supplying power to the millions of small, low-consumption sensors used to monitor ecosystems or remote infrastructure in hard-to-reach areas.

Sources:

• EPFL