Hybrid Solar Panels Generates Electricity From Raindrops

With solar power generation, a lack of sunlight during the day is always a bad sign. Dark clouds and rain reduce the electrical current being milked from the panels, meaning less power goes into the home, battery, or grid. But a team of Spanish researchers have figured out a way to embrace the rain instead of considering it an enemy.

Scientists from the Nanotechnology on Surfaces and Plasma lab at ICMS have developed a hybrid solar panel that runs as a regular photovoltaic power plant and can generate 110 volts from a single raindrop when it pours. They achieved this feat using a thin, teflon-like film that is only 100 nanometers thick, which was applied to a perovskite solar cell.

The film operates using the triboelectric effect, where raindrops falling on the surface slide across it and create friction, forming a charge difference. A single droplet might leave behind a positive ion while the film’s surface is negatively charged, creating a potential difference that can be harvested and converted into electricity.

Why Use Perovskite?

Halide perovskites are considered the next frontier in solar cell manufacturing because they are cheaper to make than their silicon counterparts and have relatively high power conversion efficiency figures. The only problem is that they are very delicate. Exposure to heat, extremely bright light, or moisture causes them to crystallize. Moisture exposure in particular crystallizes this perovskite into a yellowish lead iodide sludge that is unusable in extracting electricity from sunlight. So rain to perovskite panels is like a death blow, but these Spanish researchers managed to cheat death in an innovative way.

Killing Three Birds With One Stone Using an Energy Harvesting Shield

This ICMS research team layered the thin 100nm protective fluorinated polymer film onto the halide perovskite solar cell by growing it directly on the surface using the PECVD (Plasma Enhanced Chemical Vapour Deposition) process. This film deposition occurs at room temperature and is solvent-free, so it does not cause any harm to the highly sensitive perovskite layer underneath.

Once in place, this layer handles three tasks. It:

1. Waterproofs the perovskite solar cells by forming a hydrophobic shield above them that bumps the water contact angle to 110°, effectively doubling their water resistance.

2. Increases the light transparency to over 90% while reducing reflection, which helps the solar cells underneath to absorb more sunlight.

3. Forms a D-TENG (Drop Triboelectric Nanogenerator) that harvests electric potential from the friction caused by raindrops sliding on the surface.

Research Outcome

With this design, the team demonstrated the D-TENG fluorinated polymer film was capable of generating 110V open circuit voltage when a single drop of water hit the surface. The power density is relatively low for this setup because it only produced around 4 milliwatts per square centimeter, but this is enough to keep low-power electronics on and humming without needing an auxiliary battery power source.

To make it more practical, the research team developed a prototype with a customized boost converter to step up the voltage. When exposed to sunlight, this solar panel was able to power an array of red LEDs, and on exposure to falling drops of water to simulate rainfall, the D-TENG film was able to turn on an array of green LEDs, flashing it intermittently when every drop hit the surface.

Since the durability of the perovskite cells was also being tested here, the shielded perovskite solar cells proved to be relatively more reliable, retaining 50% of their initial power conversion efficiency after 10 days of exposure to high levels of heat and humidity. The biggest enemy for these halide perovskite semiconductor materials is water, so the team also did a torture test to measure the effectiveness of the film’s waterproofing. This test involved dipping a hybrid solar panel (shielded) and an unshielded panel in water. The former continued to generate power for over 15 minutes while the latter crystallized immediately.

Practical Commercial Applications of Hybrid Solar Panels

From the outcome, it is clear that the D-TENG film is not power-dense enough to handle functions like charging batteries, running home appliances, or sending power to the grid. So this hybrid technology is not ripe enough to replace the conventional silicon panels on roofs and solar farms. However, it is feasible in the IoT industry, where millions of sensors and actuators are deployed in the field, across cities, and other areas in large scale. Managing these devices can be hectic, sometimes almost impossible, especially if they are battery powered and need battery replacements every few months or years.

In most cases, these devices feature tiny solar panels with small, rechargeable onboard batteries. These batteries degrade over time, so they only connect and send data to the IoT network when the sun is out. If it rains, they go out, even if it is during the day. Even if the batteries are in good condition, prolonged bad weather can drain them, making the devices go into sleep mode when the available power is not enough to run the electronics inside.

By harvesting the kinetic impact from rain drops, hybrid solar panels flip the script, enabling continuous data collection in the IoT network even if rain persists. If the onboard batteries are fully degraded, the D-TENG film ensures more device uptime to collect data before a replacement is scheduled.

Fernando Nunez, the lead researcher in this project, stated that these panels are also feasible in smart cities when it comes to powering autonomous auxiliary lighting and signages, as well as in distributed energy structures scattered in remote, isolated, or inaccessible areas, such as in marine environments.

This research was published by researchers from the Nanotechnology on Surfaces and Plasma Laboratory at the Institute of Materials Science of Seville (ICMS) led by Fernando Núñez-Gálvez and is published in Nano Energy titled “Water-resistant hybrid perovskite solar cell - drop triboelectric energy harvester”.