[Image above] Wind turbines at dusk. Credit: Ana & Michal; Flickr CC BY 2.0
Wind energy is the fastest-growing source of electricity in the world, and harnessing it is one of the cleanest, most sustainable ways to generate power. That’s because wind power doesn’t produce any of the toxic and heat-trapping emissions that contribute to global warming (aside from the embodied energy and emissions associated with manufacturing).
According to the Department of Energy, wind generation in the U.S. tripled in the past six years and now accounts for nearly 5% of the country’s total electricity across 39 states. But rather than focusing on slow-wind technology at lower altitudes, engineers are making wind turbines taller to unlock the wind power potential exclusive to higher altitudes.
Last year, we reported on engineers at Iowa State University who were working on making wind turbines stronger and taller thanks to high-strength concrete technology they call “Hexcrete” and a $1-million investment from the DOE. The Department awarded the team—lead by Sri Sritharan, professor of civil, construction, and environmental engineering at Iowa State—an 18-month grant to improve its Hexcrete concept developed during earlier work at reinforcing concrete towers.
After almost a year of research and development, Sritharan and his team put those taller concrete wind turbine towers to the test.
In Iowa State University’s Structural Engineering Research Laboratory, “hydraulic equipment in two civil engineering labs recently pushed and pulled at test sections of a new kind of wind turbine tower, simulating the heavy, twisting loads that towers have to withstand,” according to an Iowa State University news release.
As part of the testing, an actuator “rocked a 12-foot-high and 6.5-foot-wide test section with 100,000 pounds of force every 1.25 seconds. The test section’s two panels and two columns only moved a tenth of an inch, but the movement was visible—especially the swaying of the long wires attached to 65 strain and displacement sensors,” the release explains.
Unlike standard 80-meter steel wind turbine towers planted throughout the Iowa countryside, these precast concrete columns and panels are easily transportable and made from high-strength, ultra-high-performance concrete. The columns and panels are “tied together by cables to form hexagon-shaped cells that can be stacked vertically to form towers as tall as 140 meters,” according to the release.
University of Minnesota’s MAST Laboratory also conducted tests, focusing on operational and extreme wind turbine tower loads on a full-scale cross section of a tower—an assembly that was “16 feet 7 inches high, 8 feet in diameter and included six panels and six columns tied together with prestressing cables,” according to the release.
Engineers took data to see if the assembled tower pieces would hold up under pressure and if the load would be transferred efficiently from piece to piece, acting as a single unit. After almost 200,000 load cycles, the fatigue test indicated no damage.
Sritharan says in the release that the tower cross section had “no trouble resisting the loads and preliminary data analysis confirms that observation.”
“It’s fair to say these tests were a success,” Sritharan says. “I think we’ve made great progress in validating a new concept of using prefabricated concrete for taller wind turbine towers.”
Iowa State University engineers think their Hexcrete technology could revolutionize production of wind energy for many reasons, including portability and relatively easy assembly compared to steel towers, to help reduce production and transportation costs.
But a major benefit is these bad boys can be built taller than standard 80-meter steel towers—and that means better access to faster, steadier winds that only exist at altitudes above 100 meters. Watch the short video below to see the team’s simulation of how a 120 meter-tall tower might be constructed.
“Now our goal is to build a full tower in the field,” Sritharan says. “Our intent is to identify partners who can work with us on a prototype tower. We’ll also work to develop a commercialization plan.”
Sritharan’s team will host technical and commercialization workshops next year to help further their research efforts. Check out the project website to learn more.
Credit: Sri Sritharan; YouTube