Scientists have created energy-harvesting flags that generate electricity using wind and solar power, an advance that could boost the use of remote ‘deploy and forget’ sensors.

The energy-harvesting flags have been developed using flexible piezoelectric strips that generate power through movement, and flexible photovoltaic cells.

The study, conducted by researchers Manchester University, is claimed to be the most advanced of its kind to date and the first to simultaneously harvest wind and solar energies using inverted flags. The research has been published in Applied Energy.

As well as remote sensors, the energy harvesting flags are capable of powering small-scale portable electronics which can be used for environmental sensing. The aim of the study is to allow cheap and sustainable energy harvesting solutions which can be deployed and left to generate energy with little or no need for maintenance. This “deploy-and-forget” strategy is the anticipated model that so-called smart cities will adopt when using remote sensors.

Jorge Silva-Leon, from Manchester’s School of Mechanical, Aerospace & Civil Engineering and lead author of the study, said: “Under the action of the wind, the flags we built bend from side to side in a repetitive fashion, also known as Limit-Cycle Oscillations. This makes them perfectly suited for uniform power generation from the deformation of piezoelectric materials. Simultaneously, the solar panels bring a double benefit: they act as a destabilising mass which triggers the onset of flapping motions at lower wind speeds, and of course are able to generate electricity from the ambient light.

Dr Andrea Cioncolini, co-author of the study, added: “Wind and solar energies typically have intermittencies that tend to compensate each other. The sun does not usually shine during stormy conditions, whereas calm days with little wind are usually associated with shiny sun. This makes wind and solar energies particularly well suited for simultaneous harvesting, with a view at compensating their intermittency.”

The team used and developed fast video-imaging and object tracking with advanced data-analysis to prove their flags worked.

The developed harvesters were tested in wind speeds varying from 0m/s (calm) to about 26m/s (storm/whole gale) and 1.8kLux constant light exposure, simulating a range of environmental conditions. Under these operation conditions, total power outputs of up to 3-4mW were generated.

Dr Mostafa Nabawy, co-author of the study, said: “Our piezo/solar inverted flags were capable of generating sufficient power for a range of low power sensors and electronics that operate in the micro-Watt to milli-Watt power range within a number of potential practical applications in avionics, land and sea remote locations, and smart cities. We hope to develop the concept further in order to support more power-demanding applications such as an eco-energy generating charging-station for mobile devices.”

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