Fluttering flags could be used to generate enough electricity to power the sensors of our future smart cities.
Researchers at the University of Manchester have developed a hi-tech flag-like device that can simultaneously generate electricity from both wind and solar sources. The development, published last week in the journal Applied Energy, was specifically designed with a “deploy-and-forget” philosophy – allowing the flags to go about their long-term work with little maintenance or monitoring required.
The flags employ two materials currently sailing at the forefront of solar and green energy design: piezoelectric strips and flexible photovoltaic cells. The former allows for the generation of electricity via kinetic motion, while the latter provides a flexible and extremely thin alternative to traditional solar panels. Both of these materials are robust enough to function continuously with little need for replacement or repair.
The team discovered that the repetitive side-to-side movement of flags – known as Limit-Cycle Oscillations – makes them ideal for generating power from the deformation of piezoelectric strips. Meanwhile, the solar component allows the flags to continue to be useful, even in non-windy conditions. Dr Andrea Cioncolini, co-author of the study, explained:
- “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 flags were tested under a variety of conditions to examine their effectiveness as sources of electricity, including during calm winds as well as storms and gales. Additionally, advanced high speed photography and object tracking with advanced data-analysis allowed the researchers to accurately assess the movement of the flags and make additional efficiency adjustments.
On average, the flags are able to consistently generate around 3-4 milliwatts – a milliwatt equaling one-thousandth of a regular watt. Although this amount is not sufficient to meaningfully power large electrical appliances, it is ideal to support low power sensors and electronics. As such, the flags could become instrumental in powering sensors designed to read information in urban environments, such as those covering pollution, traffic or noise levels. Such sensors form the backbone of emerging smart city concepts, and the University of Manchester’s flags could be a practical, and non-invasive, means of powering such devices.
Additionally, their ability to generate electricity consistently with little human input or maintenance, also makes them useful for remote land and sea locations for which it would not be feasible to develop main grid electrical connections.
Ultimately, the team hopes to develop the concept further with the aim of boosting output to allow for the recharging of mobile electronic devices.