16 July 2009

Harvesting energy for flight

Dye-sensitized solar cells (DSSCs) will be the energy source of the future powering Air Force unmanned aerial vehicles (UAVs) because they are an optimum energy harvesting source that should allow for longer flight times without refueling.

These airborne solar cells consist of a flexible film and a thin glass coating with transparent conductive electrodes, said Lead Researcher Dr. Minoru Taya of the University of Washington’s Multidisciplinary University Research Initiative project team. He found DSSCs made from organic materials, which use dyes and moth-eye film, are able to catch photons and convert them into synthesized electrons that can harvest high photon energy.

A few years ago, the team mounted dye-sensitized solar cells on the wings of a toy airplane. The propeller gained power, but the plane was not able to become airborne because the glass based solar cells they used were too heavy. Upon experimentation, they decided to use film battery technology, which allowed the plane to fly.

“These kinds of solar cells have more specific power convergence efficiency, very clean energy and easy scalability to a larger skin area of the craft, as well as, low-temperature processing, which leads to lower costs overall,” Taya said.

The team is currently working on DSSCs with higher power convergence efficiency using bio-inspired dyes, which go on the wings of the UAV.

“Any airborne energy harvester must satisfy additional requirements, like weight and durability in airborne environments. If those are met, then there may even be longer UAV flight times,” Taya said.

Engineers are now researching the challenges of DSSCs’ technology and are seeking to learn how durable they are and how well their technology may integrate with other Air Force vehicles. The team is also trying to determine how to build the solar cells in the wing surface of the aircraft and how to store energy harvested from them.

The team should overcome some of the challenges within the next two years, Taya said. “In order to make the DSSCs’ solar energy harvester transferable to the wings of an UAV, additional engineering tasks remain, which may require another project to be funded for five additional years,” Taya said.

In the end, the team hopes to reach their goal of developing large, flexible DSSCs with higher energy conversion efficiency. Generally, solar cells that are larger have decreased efficiency. Therefore, the team is using a metal grid, which has high surface resistance and can accelerate electron transport for larger-sized flexible DSSCs while maintaining high efficiency.

For related information, go to www.isa.org/manufacturing_automation.