Shocking News: Rotten Wood Floors Can Generate Electricity

Who can forget those Treehugger-incorrect, energy-sucking electric disco floors? Soon, we might have a new kind of electric floor made of wood that generates its own electricity when you walk on it, thanks to the piezoelectric effect.

Piezoelectricity is generated when certain materials are subjected to mechanical stress; we have shown piezoelectric tiles where people walking or jumping on them produces power and makes them light up, but they were all complex mechanical devices. It has long been known that the cellulose in wood is piezoelectric, but the output is negligible. However, now a team led by Ingo Burgert of the Wood Materials Science, Institute for Building Materials ETH Zurich has figured out how to crank the juice out of wood

The researchers explain in Science Advances that the piezoelectric effect in wood comes from the crystalline cellulose, but the effect is small because the wood is solid and prevents the crystals from being compressed. But anyone who has ever stepped on rotten wood knows that it is soft and squishy, because fungi eat the lignin, the structural material in wood. So the researchers treated balsa wood with white rot fungus, and found the sweet spot at 10 weeks, with 45% weight loss in the already very light balsa wood.

"The decayed wood (45% weight loss) shows a high mechanical compressibility along the tangential direction and can recover to the original state after release of the stress, in sharp contrast to the rigid native wood. To further evaluate the mechanical properties of balsa wood before and after fungal treatment, we carried out multiple compression measurements."

They found that the squishy wood could be pressed hundreds of times and still be mechanically stable. They then set up a motor to press the wood, and a meter to measure the electric output, which was 58 times as high on the decayed wood as it was with the native wood. "The growing voltage was ascribed to the increasing mechanical compressibility of decayed wood, which is linked to the increase in weight loss." 

The output still wasn't very high, only 8.4 volts with a current of 13.3 nanoamperes (nA, a billionth of an ampere) but the wood blocks are teensy, 5/8-inch square by 1/2-inch high. However, they can be wired together like batteries (which is why batteries are called piles in Britain, a pile of separate cells) to increase the output. The researchers hooked nine of them together and covered them with a thin veneer, and hooked them up to an LED. Voila: a self-powered disco floor, or in this experiment, a tiny home. "On the basis of our fundamental study, we envision the possibility to make large-scale wood floorings, allowing the production of electricity from human activities, such as in ballrooms."

The researchers note that there are many chemicals such as sodium hydroxide, that could have been used instead of fungus, that might have been faster. "However, these merits of chemical delignification approaches are outweighed by the fundamental advantage of our fungi-based method: that is, to be fully sustainable and environment friendly."

However, these biological processes like rotting don't happen evenly, which could cause issues. When asked about this, Burgert Ingo told Treehugger:

"We did not make a specific study on the uniformity yet, but our colleagues, who contributed the fungi treatment have great expertise in bioengineering wood with fungi. Similar concepts have been used for instance to improve the acoustic properties of violins."

Balsa wood does not come from endangered trees, and there are balsa plantations in Ecuador. One can imagine real benefits in an engineered wood flooring that's made without chemicals; as the study authors conclude,

"Decayed wood blocks connected in parallel or series to produce larger elements could generate higher current or voltage and be used to run low-power electronics, indicating the feasibility of application in future buildings. This study opens new possibilities to use renewable and sustainably processed materials for the design of future buildings with higher energy efficiency thanks to the ability to produce their own electricity through various indoor human activities."

Another benefit of having half an inch of squishy balsawood underfoot is that there would probably be tremendous sound attenuation benefits. When asked about this, Burgert Ingo told Treehugger:

"Indeed, an effect of sound reduction, particular footfall noise would be a very nice “side effect” of the treatment, but we have not investigated this yet. So far, our focus has been on enhancing piezoelectricity of wood by a fully green process. After this first step, work on upscaling and application-related optimization studies need to follow."

We look forward to this upscaling, and to power-generating all-natural engineered wood floors, coming to a living room or a discotheque near you.

Hat tip to Adam Vaughan in New Scientist.