Floating Water Generators Turn Rainfall into Renewable Energy

The demand for energy is rising fast. In 2024, this world recorded a 4.3% jump in electricity demand. This was a much bigger increase than the 2.5% spike recorded in the year prior, which was close to the average pace of electricity demand growth between 2010 and 2023.

This growth is primarily driven by the massive growth in data centres due to the explosion of AI adoption and electric vehicles, with industrial expansion and increased use of air conditioning also contributing significantly.

While fossil fuels made up more than half (almost 60%) of electricity generation last year, with coal remaining the largest source in the world, the power mix is actually evolving. According to the IEA, for the first time ever, power generation from renewables and nuclear power accounted for two-fifths of total global generation in 2024. 

Renewables, in particular, were responsible for one-third of the world’s electricity production. Among renewable sources, hydropower leads with a 14% share of total electricity generation, followed by wind at 8%, solar PV at 7%, and bioenergy and waste at just 3%.

While a major development towards clean energy, renewables’ contribution to global energy production is still low. So, to further help accelerate this shift to renewable energy sources, researchers have been creating new technologies for energy conversion to meet the increasing demands for daily electrical energy consumption. 

Systems that collect energy directly from the environment, in particular, can help increase the use of renewable energy sources.

Hydrovoltaics: Turning Rain and Water Cycles into Electricity

Water is a critical element of life. Not only does it make up a large part of our body, but it also makes up a large part of the Earth. Covering 70% of our planet, water is the most abundant resource, and it contains a significant amount of energy in various forms, much of which remains largely underutilized.

One of the ways this energy is utilized is through hydropower, which involves using the natural flow of moving water to generate electricity.

Another powerful way to harvest energy from the water’s natural cycle is through hydrovoltaic technology. Unlike traditional technologies, which harvest water’s kinetic energy, hydrovoltaic tech generates electricity from the direct interaction of an electrode material with water. 

The hydrovoltaic technology actually allows the development of low-cost and high-efficiency systems that can directly convert thermal energy into electrical energy through the interaction of water with nanomaterials such as graphene, carbon nanotubes, carbon nanoparticles, and conductive polymers.

The energy that is converted here is generated by the drip, flow, fluctuation, condensation, or evaporation, and considerably increases the output power. Research states¹ that using only 1% of the available energy in the world’s water at a mere 1% efficiency through hydrovoltaic technology can help us meet 1/3 of the world’s energy needs.

As such, devices based on this developing technology are crucial to satisfy the demand of the power-hungry world using renewable energy sources.

This has led to extensive research into droplet energy generators, a type of hydrovoltaic technology that converts the mechanical energy of water droplets like raindrops into electricity. But limitations in current technology haven’t allowed it to efficiently convert the energy contained in water into electrical energy.

For instance, a traditional droplet energy generator based on the triboelectric effect, which generates an electric charge when two different materials come into contact and then separate, can produce electricity when a droplet strikes a surface. However, the interfacial effect limits the number of charges generated on the surface, resulting in relatively low energy conversion efficiency.

So, a team of researchers has developed a novel “water-integrated droplet electricity generator” that produces high output while floating on surfaces, offering a glimpse at the next generation of lightweight, high-efficiency devices. According to the study:

“We anticipate this work will open up a new avenue of harnessing water-like natural materials to construct hydrovoltaic devices and advance land-free large-scale applications.”

But before we dive into this research, let’s first take a look at what has been happening in this space.

State of the Art in Droplet Electricity Generators (DEGs)

Moving water droplets like raindrops are widespread and carry a considerable amount of kinetic energy, which shows promise for sustainable electricity generation. To harvest the kinetic energy of water droplets, researchers have been focusing their efforts on DEGs.

Droplet-based electricity generator (DEG) is a powerful technology and has shown promise as an efficient way to harvest energy from the natural environment. 

It makes use of falling water droplets to generate electricity. Typically, it consists of two triboelectric layers and a pair of electrodes, where charges are separated as a water droplet impacts the surface and then slides off. 

The low cost, simple structure, and high power density of DEGs have made them popular among researchers to harvest kinetic energy from environmental water sources. 

However, its broad application is obstructed by the complex structure and low output power density. Their application being limited to land-based use also makes them impractical for lakes, rivers, and oceans.

Other challenges with DEGs include significant performance degradation over time in integrated systems, material durability issues, and the high spatial footprint required for large-scale applications.

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So, research is ongoing with a focus on improving efficiency through better designs, using natural water as part of the structure, or optimizing materials, with recent innovations creating lightweight, cost-effective, and even floating devices. 

A few years ago, a team of researchers from the City University of Hong Kong (CityU) developed² a DEG with a field-effect transistor (FET)-like structure that achieved high energy-conversion efficiency. Its instantaneous power density was much higher, about thousands of times higher, than its counterparts without an FET-like structure. 

Their work had two key factors; one was the team’s finding that when continuous water droplets impinge on the surface of polytetrafluoroethylene (PTFE), a dielectric material with a quasi-permanent electric charge, the surface charges produced accumulate and gradually reach saturation. This helped the team overcome the previously encountered low charge density by providing a new way to accumulate and store high-density surface charges.

The other factor was their design, whose key feature was a unique set of structures similar to a FET. The device is made up of an aluminum electrode and a PTFE/ITO electrode, which involves an indium tin oxide (ITO) electrode with a film of PTFE deposited on it. When a droplet strikes the PTFE/ITO surface and spreads across it, it bridges both electrodes, turning the system into a closed-loop electric circuit.

The design allowed a high density of surface charges to be collected on the PTFE. And when the spreading water connects the two electrodes, stored charges on the PTFE are fully released to produce an electric current.

While CityU’s design focused on boosting charge accumulation, another team from the Chinese Academy of Sciences simplified the DEG’s architecture to make it more scalable.

The team of Chinese researchers proposed³ a DEG with a simple open structure to fully utilize the self-capacitance effect of the upper electrode to promote its wider application.

The thing is, it is difficult to continuously provide energy for the electrical equipment by a single or several DEGs. 

As the team noted, when harvesting large-scale raindrop energy in sloping buildings like sheds, a simple method is to connect all DEGs in parallel to supply power to the load, like a bulb. So, with reference to the cell structure of a solar panel and by making full use of the upper electrode’s self-capacitance effect, they introduced SCE-DEG with a simple open structure, which is primarily made of an upper and lower electrode, PTFE film, and load. 

The electrodes here don’t need to connect to each other, but high instantaneous output power can still be obtained by the upper electrode’s self-capacitance effect, making the structure much simpler and more convenient for large-scale popularization.

When tested, it could produce 212 mW output power by a 61 μL water droplet and can direct light to 100 commercial LEDs.

Most recently, researchers from KTH Royal Institute of Technology, Sweden, tailored the bottom electrodes of DEG⁴ to make their area comparable to the spread area of the impinging water droplets, which doubled the average output power of individual cells.

The team also fabricated large-scale (30-cell) arrays that achieved about 2.5 times higher power than state-of-the-art arrays. Furthermore, they integrated a large-scale (400-cell) micro-supercapacitor (MSC) array to store the electricity generated by the 30-cell generator array at 21.8% efficiency, without using any power management chip.

This integration creates a self-charging power system (SCPS) with an output power of 81.2 μW. 

After the 30-cell DEG array charges the 400-cell MSC array for only 30 seconds, the integrated SCPS can supply an LED to work continuously for 60 seconds, “suggesting the promise of the strategy to integrate large-scale DEG arrays with large-scale ultrafast MSC arrays to build SCPSs for high-efficiency energy harvesting from natural water towards practical applications.”

Floating W-DEG: A Lightweight, Cost-Effective Path to Rain-Powered Energy

Now, researchers from the Nanjing University of Aeronautics and Astronautics have developed a new solution, a floating DEG that uses natural water as a key part of its structure, thus providing a lightweight, affordable, and eco-friendly pathway to renewable energy production.

Instead of having a dielectric film sitting on a rigid base with a metal electrode underneath, the new design has the water acting as both the supporting base and the conductive electrode. This approach, top electrode-dielectric-water architecture, cuts down both the material weight and cost by 87% and 50%, respectively, compared to older models, while maintaining a similar level of electrical output and demonstrating great durability in different working environments. 

Published in National Science Review⁵, the study details the ‘nature-integrated’ design route that has led to the development of a novel water-integrated floating DEG (W-DEG) that leverages the electrical and structural functions of water.  

The way it works is, when raindrops, a fresh water source carrying unused energy, land on the floating dielectric surface, a film of fluorinated ethylene propylene (FEP) responds immediately. Being chemically inert, the thin FEP film resists extreme temperature variation, corrosion, and growth of algae and bacteria.

As the droplet spreads, it creates a stream of ions, causing a transfer of charge between the upper region and lower region, generating a very small amount of electricity. The surface resets when the droplet bounces.

The natural properties of the water here provide the mechanical stability that’s required to absorb the impact and let the droplets spread efficiently, without bending or breaking. 

These natural properties include strong surface tension and incompressibility. Water is considered nearly incompressible, which means it doesn’t compress much under pressure. Meanwhile, the strong cohesion between water molecules, caused by hydrogen bonds, creates strong surface tension.

Ions within the water, meanwhile, serve as charge carriers, which allows it to act as a reliable electrode. 

Together, these features enable the floating generator to generate peak voltages of about 250 volts per droplet, on par with the performance of traditional rigid designs that make use of metal.

The design is also durable, with tests showing that the generator maintained performance across varying conditions, including different salt concentrations (up to 500 millimolar sodium chloride), temperatures, and even exposure to outdoor lake water with biofouling —a considerable issue for marine devices.

While many energy devices degrade in harsh environments, the floating generator continues to operate stably because of the water-based structure’s resilience and the dielectric layer’s chemical inertness.

When tested in highly saline water, the generator maintained its functionality after a week of deployment. And if any debris gets deposited on it, simple cleaning returns it to maximum performance.

To further increase the stability of their device, the team exploited the high surface tension of water to design drainage holes that allow water to pass downward in only one direction. So, by using gravity and surface tension, the team can mitigate the build-up of contaminants and keep it clean, thus creating a self-regulating system for removing any excess droplets. This way, water accumulation is avoided, which could otherwise reduce output.

Yet another key aspect of the floating W-DEG is scalability. With a size of 0.3 square meters, the researchers showcased a much larger droplet generator than previously reported ones. With each of these generators producing ~250 volts per droplet, they can power 50 LEDs simultaneously.

Furthermore, the system was also able to charge capacitors to useful voltages in a matter of minutes. The team piloted 10 W-DEG devices and produced simulated rainfall using 120 mock rainfall droppers, then charged the capacitor to three volts, demonstrating its potential to power wireless sensors and small electronics. 

With further development, these systems could be used to harvest renewable electricity from lakes, reservoirs, or coastal regions without occupying valuable land resources.

“By letting water itself play both structural and electrical roles, we’ve unlocked a new strategy for droplet electricity generation that is lightweight, cost-effective, and scalable,” said the study’s co-author, Professor Wanlin Guo. “This opens the door to land-free hydrovoltaic systems that can complement other renewable technologies like solar and wind.”

In regions that experience frequent rainfall, the floating droplet electricity generator could provide a distributed energy solution that powers off-grid applications or supplements local grids. 

Compared to a traditional droplet generator, which costs about 210 yuan (about $29.50) per square meter and weighs over four kilograms (about 8.818 pounds), the team’s floating version costs about 106 yuan (less than $15) and weighs only 0.5 kilograms (1.1 pounds).

Besides rainwater harvesting, the device can have other applications thanks to its functionality to float naturally on water surfaces. For instance, it can be deployed in diverse aquatic environments to power environmental monitoring systems like sensors that track pollution, water quality, or salinity. 

Its ‘nature-integrated design,’ where the naturally abundant material is used as a functional component, could also inspire new approaches in eco-based technologies.

But before the device can be deployed on a large scale, there are challenges that need to be addressed first. The varied size and velocity of actual raindrops means the performance of the device can be affected. Additionally, further engineering is required to ensure the robustness and durability of large dielectric films in dynamic outdoor conditions. 

Despite these challenges, the laboratory results have been promising, and the demonstration of an efficient, durable, and scalable prototype marks a key step toward practical applications of water-integrated floating DEG (W-DEG).

Investing in Water Harvesting Tech

Xylem (XYL -0.17%) is a global water technology company focusing on smart water management, involved in integrating sensors, monitoring, and water flow systems.

Its Water Infrastructure segment offers products like treatment equipment, water, wastewater, and storm water pumps and controls. The Applied Water segment covers products including pumps, valves, heat exchangers, and dispensing equipment, while its Measurement & Control Solutions (MCS) segment builds advanced solutions for intelligent use of critical resources, as well as analytical instrumentation for water testing. The Integrated Solutions & Services segment provides equipment systems for industries and municipalities.

Xylem also leverages AI to monitor water flow and detect leaks in real-time. This allows problems to be detected on time and then fixed quickly, saving water and lowering costs.

With a market cap of $36.8 billion, XYL is currently trading at $151.3, up 30.42% YTD. It has an EPS (TTM) of 3.89 and a P/E (TTM) of 38.93. The company pays a dividend yield of 1.06%.

For third-quarter 2025 results, Xylem reported “strong execution and demand” that resulted in a total revenue of $2.3 billion. Its net income was $227 million, or $0.93 per share, with margin declining 30 basis points to 10%, and adjusted net income of $333 million, or $1.37 per share.

Latest Xylem (XYL) Stock News and Developments

Conclusion

Earth’s life source, water, is a powerful form of renewable energy. One promising way to harness this potential is through hydrovoltaic technology. Researchers exploring how to convert the simple motion and interaction of water into usable electrical power have driven innovations in droplet-based electricity generation, which makes use of raindrops that fall naturally from the sky and are completely free.

The latest floating droplet generators point toward a future of renewable energy, where water-integrated, low-cost solutions can power sensors, remote systems, and even microgrids while remaining in harmony with nature.

References

1. Yin, J., Zhou, J., Fang, S. & Guo, W. Hydrovoltaic Energy on the Way. Joule 4, 1852–1855 (2020). https://doi.org/10.1016/j.joule.2020.07.015
2. Xu, W., Zheng, H., Liu, Y. et al. A droplet-based electricity generator with high instantaneous power density. Nature 578, 392–396 (2020). https://doi.org/10.1038/s41586-020-1985-6
3. Li, Z., Wang, X., Liu, Y., et al. A droplet-based electricity generator for large-scale applications. Cell Reports Physical Science 3, 100521 (2022). https://doi.org/10.1016/j.xcrp.2022.100521
4. Li, Z., Chen, S., Fu, Y. & Li, J. Efficiency optimization for large-scale droplet-based electricity generator arrays with integrated microsupercapacitor arrays. Nature Communications 16, 8530 (2025). https://doi.org/10.1038/s41467-025-64289-y
5. Deng, W., Wang, Z., Wang, J., Hu, T., Wang, X., Li, X., Yin, J. & Guo, W. Floating droplet electricity generator on water. Natl Sci Rev. 12, 11 (2025). https://doi.org/10.1093/nsr/nwaf318