Piezoelectric elastic energy harvesting arrives

Dr Peter Harrop
Piezoelectric elastic energy harvesting arrives
Elastic piezoelectric generators are being developed with microwatts demonstrated and watts in prospect for large formats. For example, in 2015, Ricoh has announced that it has created a novel flexible material "Energy-Generating Rubber" that converts pressure and vibration into electric energy with high efficiency. Major piezoelectric materials are ceramics and polymers, but they have some deficits which inhibit acceptance in energy harvesting beyond gas lighters despite them being very successful as sensors and acoustic emitters. Fragility, weight, toxicity and cost come to mind for ceramic versions while polymeric ones have weak action.
Now a breakthrough. The "Energy-Generating Rubber" created by Ricoh is claimed to generate as high a level of electricity as ceramics while its appearance is a soft and flexible sheet. Since it overcomes the deficits of previous piezoelectric ceramics and polymers, it is expected to be applied to multiple areas combining the advantages of flexibility and high-output. Ricoh will commercialize the material for driving flexible sensors, for example. They see it a key to the Internet of Things and generation of substantial power in wide spaces.
The mechanism of the "Energy-Generating Rubber" is not the same as that of previous piezoelectric materials. Ricoh, in collaboration with Tokyo University of Science (Project leader: Associate professor Takahiro Yamamoto), launched mechanism analysis in molecular level using leading computational chemistry. The study results will expand the possibilities with the material.
Also newly announced in 2015, we have Professor Keon Jae Lee of the Department of Materials Science and Engineering at the Korea Advanced Institute of Science and Technology (KAIST) who has developed a hyper-stretchable elastic-composite energy harvesting device. He targets wearable/biomedical devices and electronic skins (e-skins) that should stretch to conform to arbitrarily curved surfaces and moving body parts such as joints, diaphragms and tendons. They must be able to withstand the repeated and prolonged mechanical stresses of stretching.
Researchers from KAIST and Seoul National University (SNU) have demonstrated a practicable high-performance and hyper-stretchable elastic-composite generator (SEG) using very long silver nanowire-based stretchable electrodes. Their stretchable piezoelectric generator can harvest mechanical energy to produce about four volts output with large elasticity (~250%) and durability over 104 cycles.

What next?

The Japanese and Korean advances in piezoelectric elastic harvesting have a competitor in the work by Fraunhofer IZM in Germany using capacitive elastic harvesting. Will someone now reinvent the other basket cases of energy harvesting? It could transform an industry with$100 billion success at the kilowatt level in vehicles, and on remote buildings, major success at mid-range power for everything from garden lights to road furniture, cranked flashlights and bicycle dynamos and modest success at low power with wireless sensors, piezoelectric gas lighters and the like. A major challenge remains the creation of a widely acceptable way of charging a mobile phone. Will the basketcase technologies offer something one day? For more see the new IDTechEx report, Energy Harvesting; Off-grid Renewable Power 2015-2025.
Top image: Hyper-stretchable elastic-composite generator. Source: KAIST