CHAMPAIGN, Ill. - The U.S. Army Engineer Research and Development Center (ERDC) recently invented a field-portable system that can potentially supply power to forward operating bases by capturing the energy in low-speed winds. Called the “Flutter Mallard,” the technology is under development at ERDC’s Construction Engineering Research Laboratory (CERL).
Reliable, sustainable and net zero energy use is a top priority for both the Army’s installations and FOBs. The Flutter Mallard approach is to harvest the low energy portion of the wind that is otherwise too weak to be usable for conventional wind turbines of the type used worldwide. Typically these wind turbines are large, tall structures found in large groupings (“wind farms”) capable of generating many kilowatts of “green power.” However, they will not operate efficiently (or not at all) if the wind is too weak, typically for speeds less than about 4 meters per second. Further, they are not feasible structures for FOBs because they present a large, vulnerable target and would pose a severe logistic burden for deployment.
CERL’s researchers found inspiration for the Flutter Mallard from an unusual source. They observed that common venetian blinds, fluttering in the gentle breeze of an open window, could become a prime mover for low wind speed energy capture. Based on this concept, they replaced the rigid blind with an articulated flexible membrane capable of deforming and storing elastic energy in real time. They then affixed to the membrane a pick-up coil and magnet that can convert the vibrating membrane energy into an electrical current. This electrical energy requires power conditioning to compensate for the variability in wind speed, and presented a significant challenge.
The team’s solution was to capture the fluctuating electrical energy along with that from similar generating strips and perform rectification, so that the resulting direct current power can then be stored in a super-capacitor. The super capacitor represents a new class of electrical energy storage devices that can store very high energy densities. The CERL team developed one such device as an outgrowth of their research, which resulted in a patent application.
To determine the quality and availability of low-speed wind resources, the research team continuously measured the near-ground wind velocity at the CERL campus in Champaign, Ill. around the clock (24/7) from late February to mid-July 2012. During this time they amassed more than 400 million data points of wind velocity and confirmed that during evening hours, 70 percent of the average wind speed available was less than or equal to 3 meters per second, with only 46.4 percent available during daylight hours. These results suggest that, for climates similar to those in Illinois, any means of capturing the 70 percent nighttime availability could greatly help supplement a FOB’s low-energy requirements.
To get some measure of the energy available using the prototype Flutter Mallard, CERL compared the active wind capture area (about 0.65 square meters) required of a typical small wind turbine to that of the combined equivalent areas of several Flutter Mallards operating at low wind velocities ( less than or equal to about 3 meters per second). The Flutter Mallard generated about 3 watts of power verses the equivalent of nearly zero watts for an under powered turbine at these low wind speeds. As the research continues to progress, the team’s vision is to replace the vibrating membranes with a highly elastic membrane made out of flexible photovoltaic solar cells. Doing so will capture and store additional available solar energy during the day, which will complement the harvested wind energy. This research effort is part of an ongoing ERDC Center Directed Research project.