NUS Breakthrough: Harvesting Electricity from Rain-Like Water Droplets 🌧️

Researchers at the National University of Singapore (NUS) have achieved a groundbreaking feat in renewable energy technology by developing a simple yet highly efficient system to generate electricity from rain-like water droplets. Led by Associate Professor Siowling Soh from the Department of Chemical and Biomolecular Engineering, the team published their findings in ACS Central Science on April 16, 2025, demonstrating a plug flow mechanism that converts gravitational energy from falling water into usable electrical power. This innovation addresses longstanding limitations in water-based energy harvesting, where previous methods struggled with low efficiency due to the nanoscale constraints of the electric double layer.

The device utilizes everyday materials like fluorinated ethylene propylene (FEP) tubes and metallic needles, making it scalable and cost-effective. In experiments, a single 2-millimeter diameter tube produced 440 microWatts of power, equivalent to a power density of approximately 100 watts per square meter when scaled. With just four such tubes, the setup powered 12 light-emitting diodes (LEDs) continuously for over 20 seconds, showcasing practical viability even at droplet speeds slower than natural rainfall.

This development positions NUS at the forefront of sustainable energy research within Singapore's higher education landscape, aligning with national priorities for innovation in resource-limited environments. Singapore, with its tropical climate averaging over 2,300 millimeters of annual rainfall, stands to benefit immensely from technologies that turn frequent downpours into a reliable power source.

Understanding the Plug Flow Mechanism Step-by-Step 🔬

The core of this NUS innovation lies in the plug flow pattern, a discontinuous flow where short columns or 'plugs' of water alternate with air pockets inside a narrow tube. Unlike continuous streaming current methods limited by the Debye length—a measure of the electric double layer thickness, typically around 1 micrometer in pure water—this approach achieves macroscale efficiency by leveraging unique interfacial chemistry.

• Step 1: Gravity-Driven Droplet Formation - Water from an elevated tower (0.75 to 1.65 meters high) exits through a horizontal stainless-steel needle (gauge 18), forming rain-sized droplets.
• Step 2: Collision and Plug Initiation - Droplets collide head-on with the top of a vertical FEP tube (2 mm inner diameter, 32 cm long), mixing air to create segmented plugs.
• Step 3: Charge Separation at Trailing Edge - As each plug moves downward, at its receding meniscus, H⁺ ions migrate into the bulk water (positive charge), while OH⁻ ions adsorb onto the tube's surface (negative charge).
• Step 4: Counterflow Charge Transport - Positive charge flows down with water; negative charge travels upstream along the moist surface.
• Step 5: Electricity Harvesting - Wires collect positive current at the bottom cup (P1, 61 GΩ resistor) and negative at the top needle (P2, 41 GΩ), generating sustained voltage.

This process yields over 10% energy conversion efficiency—up to 10.4% under optimal conditions—outperforming prior droplet generators by five orders of magnitude compared to continuous flow. The system's robustness is evident in its performance across deionized water, tap water, saline solutions (0.1-10 mM NaCl), and temperatures from 4°C to 50°C, with stability over 7 days of continuous operation.

Spotlight on the NUS Research Team and Leadership

At the helm is Associate Professor Siowling Soh, a distinguished chemical engineer at NUS whose prior work includes gravitational energy harvesting from water interfaces. Soh's team comprises talented early-career researchers: Chi Kit Ao, Yajuan Sun, Yan Jie Neriah Tan, Yan Jiang, Zhenxing Zhang, and Chengyu Zhang, all from NUS's Department of Chemical and Biomolecular Engineering. Their collaborative effort, funded by Singapore's Ministry of Education (grants like R-279-000-408-112) and National Research Foundation (NRF), exemplifies the interdisciplinary prowess of Singapore's higher education institutions.

Soh notes, "Water that falls through a vertical tube generates a substantial amount of electricity by using a specific pattern of water flow: plug flow. This plug flow pattern could allow rain energy to be harvested for generating clean and renewable electricity." This quote underscores the team's vision for practical deployment. NUS's emphasis on such high-impact research attracts top global talent, fostering a vibrant ecosystem for PhD students and postdocs in sustainable technologies.

For those inspired by this work, opportunities abound in research jobs at NUS and other Singapore universities, where cutting-edge projects in energy and materials science are prioritized.

Impressive Performance Metrics and Comparisons

The NUS generator's metrics set new benchmarks. A single tube at 80 mL/min flow delivers 440 ± 13 μW, with power density ~100 W/m² for close-packed arrays. Efficiency remains above 90% of optimal across varied conditions, far surpassing streaming current devices (<1%) or electrostatic induction setups (0.1-1 W/m² average).

• Scalability: Power doubles with two tubes; four tubes light 12 LEDs continuously.
• Durability: Consistent output over 2 hours or 7 days.
• Versatility: Functions with natural rainwater equivalents, no purification needed.

Compared to earlier triboelectric nanogenerators (TENGs) from NUS dating back to 2017, this plug flow method eliminates pulsatile output, providing steady power ideal for sensors or low-energy devices.

Singapore's Unique Advantage: Rain as a Renewable Resource

Singapore receives about 2337 mm of rain annually, far exceeding many nations, yet lacks rivers for traditional hydro. This NUS technology could integrate into urban infrastructure like rooftops, gutters, or building facades, generating supplemental power for smart cities. In a pilot scenario, a 100 m² rooftop during heavy rain could yield meaningful kilowatt-hours, complementing solar amid cloudy skies.

This aligns with the Singapore Green Plan 2030, targeting net-zero emissions. NUS's role amplifies Singapore's higher education contribution to national sustainability goals, inspiring similar innovations at NTU and SUTD.

Prospective engineers might find fulfilling roles via higher ed jobs in green tech at Singapore universities.

Integration with RIE2030: Fueling Singapore's Research Engine

Singapore's Research, Innovation and Enterprise 2030 (RIE2030) plan, unveiled in December 2025 with S$37 billion funding, prioritizes energy sustainability and advanced manufacturing. Allocating S$8.9 billion to foundational research, including university scientist training, RIE2030 directly supports projects like Soh's.

NUS, a key beneficiary, leverages this for quantum, AI, and green tech hubs. Such investments have elevated NUS to global top-10 rankings, drawing international collaborations and boosting PhD enrollments in chemical engineering by 15% over five years.

Beyond Powering LEDs: Diverse Applications and Impacts

The generator excels in self-powered applications: driving chemical reactions (e.g., methylene blue decolorization, DPPH radical scavenging), surface modifications (changing PDMS wettability from 109° to 37°), and even electrostatic manipulation of liquids. In higher ed labs, it could power sensors for environmental monitoring without batteries.

• Urban energy: Rooftop arrays for IoT devices.
• Agriculture: Rain-harvesting for remote irrigation controls.
• Disaster relief: Portable power in flood-prone areas.

Stakeholders like policymakers view it as a complement to solar/wind, while industry eyes commercialization.

Challenges, Solutions, and Future Outlook

Challenges include optimizing for high-velocity rain and scaling arrays without clogging. Solutions involve durable coatings and modular designs. Future work may hybridize with solar cells for all-weather generation. NUS plans prototypes for real rooftops by 2027, potentially under NRF grants.

Timeline: Lab proof (2025) → Urban pilots (2026-28) → Commercial (2030+), syncing with Green Plan milestones.

Career Opportunities in Singapore Higher Ed Research

This breakthrough highlights booming demand for experts in electrokinetics and nanomaterials. NUS and peers offer lecturer jobs, research assistant positions, and postdocs. Singapore's higher ed ecosystem provides competitive salaries (S$80K-150K for mid-career) and work-life balance.

Check career advice or resume templates to join. Rate professors via Rate My Professor.

Global Perspectives and NUS's Leadership Role

While China and EU explore TENGs, NUS's macroscale plug flow leads in practicality. Comparisons show 2-3 orders higher density. Multi-perspective: Academics praise simplicity; skeptics note weather dependency—mitigated by hybrids.

Photo by Kamil Tatol on Unsplash

Conclusion: Powering Tomorrow's Sustainable Future

NUS's droplet electricity generator exemplifies how Singapore universities drive global innovation. As rain becomes a powerhouse, explore higher ed jobs, university jobs, research jobs, or higher ed career advice. Share insights in comments and visit Rate My Professor for faculty reviews.