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Directory:CEA/Leti-Minatec:Energy from Rain
Harvesting Rain Power Via Piezoelectric Landing Pads
Scientists from CEA/Leti-Minatec in France have developed a system that recovers the vibration energy from raindrops falling on a piezoelectric structure. The system works with raindrops ranging in diameter from 1 to 5 mm. Simulations show that it's possible to recover up to 12 milliwatts from one of the larger "downpour" drops.
The recoverable energy depends directly on the size of the piezoelectric membrane, the size of raindrops, and their frequency.
- "Our work could be considered as a good alternative to power systems in raining outdoor environments where solar energy is difficult to exploit." -- Thomas Jager
One square meter of such a mechanism, situated in a continental climate region in France is calculated to produce one Watt-hour of electricity per year from the rain that falls there. At that miniscule rate, it's hard to imagine that this technology could ever be made cost effective enough to be plausible in any real-world application.
Would it work? Yes. Would it ever be practical? Probably not. In fact, one could probably argue that this technology could win as the most innefficient use of resources for harvesting free energy available from the environment.
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How it Works
To capture the raindrops’ mechanical energy, the scientists used a PVDF (polyvinylidene fluoride) polymer, a piezoelectric material that converts mechanical energy into electrical energy. When a raindrop impacts the 25-micrometer-thick PVDF, the polymer starts to vibrate. Electrodes embedded in the PVDF are used to recover the electrical charges generated by the vibrations.
The research group has experimented with raindrops of different sizes, falling heights, and speeds. They found that slow falling raindrops generate the most energy because raindrops falling at high speeds often lose some energy due to splash. By using a micropump to generate and test the properties of raindrops, the researchers demonstrated that, for low drop heights, the electrical energy is proportional to the square of the drop’s mechanical energy, while voltage and mechanical energy are directly proportional.
The largest raindrops caused the largest vibrations on the PVDF, and therefore generated the greatest amount of electrical energy. The researchers demonstrated that their system could generate 1 microwatt of continuous power as a worst-case scenario, while simulations showed that a single large raindrop might generate up to 12 milliwatts of power.
“The corresponding instantaneous converted power starts from a few µW up to 10 mW for a converter area of a several square centimeters. An interesting figure to keep in mind could also be the available rain power per year in common France regions with a continental climate: almost 1 Wh per square meter per year.?
In the future, the scientists plan to develop a method to store the electrical power to provide a steady current for practical use.
An R&D institute in Grenoble, France
- Thomas Jager
- Romain Guigon
- Jean-Jacques Chaillout
- Ghislain Despesse
- “Harvesting raindrop energy: theory? and “Harvesting raindrop energy: experimental study.? Guigon, Romain, Chaillout, Jean-Jacques, Jager, Thomas, and Despesse Ghislain. Smart Materials and Structures; 17 (2008) 015038-9.
In the News
- It's Raining Energy. Hallelujah! - Researchers have developed a technique that harvests energy from rain showers and converts it into electricity. The technology could work in industrial air conditioning systems, where water condenses and drops like rain. (Discovery; Feb. 7, 2008)
- Rain Power: Harvesting Energy from the Sky - Scientists from CEA/Leti-Minatec in France have developed a system that recovers the vibration energy from raindrops falling on a piezoelectric structure. The system works with raindrops ranging in diameter from 1 to 5 mm. Simulations show that it's possible to recover up to 12 milliwatts from one of the larger "downpour" drops. (PhysOrg; January 22, 2008)
See Discussion page.