A rooftop wind turbine at the University of Stuttgart (Stuttgart, Germany) has been equipped with natural fiber-reinforced blades, made with Biotex Flax fibers supplied by Composites Evolution (Chesterfield, U.K.). Designed and manufactured by a team formed by the SWE (Endowed Chair of Wind Energy) at the University, the blades were conceived in 2011, to replace the blades on the school’s existing 1-kW rooftop turbine. Reportedly, the SWE team found that the Biotex Flax reinforcement’s “twistless technology” results in a high degree of fiber alignment and, thus (based on tests against other materials in a variety of matrices), yielded the desired performance characteristics. The finished blades incorporate Biotex Flax 2x2 twill (400 g/m2) in the outer half shell with Biotex Flax unidirectional (275 g/m2) used in the blade’s spar and root. Shells, spar and root were hand-layed. Shells were vacuum-bagged and cored in separate female molds, then joined using RIM 235 epoxy adhesive, supplied by Momentive Specialty Chemicals (Columbus, N.Y.).
Three blades were performance tested on the rooftop turbine, and further testing will gauge their performance against blades of other materials. A fourth blade was embedded with strain gauges, and the team will compare the results to data derived from tests on standard carbon and glass blades. A finished blade was on display on the Composites Evolution stand at the JEC Europe 2014 trade show.
Standard Biotex reinforcements also include jute, commingled flax/polylactic acid (PLA) and commingled flax/polypropylene (PP). Other forms are available on request, in formats that include yarns, fabrics (woven and noncrimp) and preconsolidated sheets.