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Off Grid Energy Independence
Posted on November 11, 2014 by  & 

Tiny renewable wind turbine for developing world

00002 miles per hour might remind you of a bad day on the interstate. But that's how fast some bamboo can grow: up to 35 inches every day — a world record. It's a grass that can, in a few months, grow as tall as a tree. And, as it grows on, say, a mountainside in China or Chile, it gets hammered by the wind. But it doesn't break. It flexes and resists, using the power of the sun to grow up and the power of the wind to grow strong.
"The wind makes the bamboo grow in different directions," says UVM professor of engineering Ting Tan, "which means that the plant's microstructure is adapted to wind."
"Inspired by the bamboo, we decided to adapt it," Tan says. Using bamboo as their primary building material, Tan and his colleague, professor of electrical engineering, Tian Xia, and a group of students, have built a hybrid energy harvester: it combines a small-scale wind turbine — built out of bamboo — with a solar panel. The whole device is about the size of a trashcan. "We capture the wind and the sun at the same time, just like the bamboo does," Tan says, "and put the energy into a battery."
Tan and his team see the device as a prototype — a first test — for a kind of energy collection that could be useful in parts of the developing world that have few resources and limited or no access to the traditional electrical grid.
"Most wind turbines now are huge," says Tian Xia. "We want to make this convenient for a family or a small community that could not afford an industrial wind turbine. We wanted to design this as a standalone, small-scale system. In portions of Africa and the developing world there are places that have no infrastructure, but they want to use electricity." With its blades and supports made from bamboo, key parts of the turbine should be able to be harvested from local land in many parts of the world, comparatively easy to repair, and renewable.
"You could use this turbine to charge a cell phone or run some lights," says Ting Tan. "This distributed system is not as efficient as a large system. But the advantage is that it can be used everywhere."
Before joining the faculty at UVM, Tan, an expert on the mechanical properties of materials, studied bamboo as a graduate student at Princeton. There, he was part of a team that helped build a bicycle out of bamboo that led to a bamboo-bike manufacturing company. Famed architect Simón Vélez describes bamboo as "vegetable steel" and has built buildings, including a church in Colombia, out of bamboo. Bamboo has a tensile strength that rivals steel, and bamboo products, especially composites that are combined with strong polymers, are becoming increasingly popular. But, "even though bamboo has been used in various applications," Tan notes, "its role in renewable energy infrastructure has not been well defined." He and his UVM team are on the leading edge of changing that.
Much of the work on the new turbine was completed last spring by a team of undergraduate students in the Student Experience in Engineering Design (SEED) program in the College of Engineering and Mathematical Sciences: class of 2014 graduates Hunter O'Folan, Justin Dao, Karl Johanson and Zachary Basch.
The students and professors studied the few other bamboo wind turbine designs they could find, but nothing seemed highly refined, so they set out to make their own. "We tested six or seven structures, but some didn't rotate," Tan says, "and this one gives the best RPMs," he says, slowing spinning the model he and the students built. The three helical blades, for catching the wind, have a handsome curving shape — guided by National Advisory Committee for Aeronautics airfoil designs. They have "a pitch angle of 60 degrees and twist angle of 80 degrees," Tan explains. The underlying polymer skeleton of the blades was produced in the UVM Fabrication Laboratory using a 3D printer.
As the vertical turbine spins, picking up speed, the bamboo blades undulate in a warm brown weave. At night, it makes a pleasing pattern with glowing LED lights that are embedded into the blades. Below the turbine, a group of additional LEDs shine down its mounting pole onto the ground, demonstrating how the team imagines this device could be deployed: as a standalone power source for a street light — whether in a sub-Saharan village or as arty installation on a Paris boulevard.
"Since it's both wind and solar powered, this microcontroller determines what source will be charging the battery depending on how much power we're getting from each source," says Justin Dao, pointing to a black box full of wires and circuits. Dao, part of the SEED team, graduated from UVM's Honors College with a degree in electrical engineering and is now a graduate student in the engineering program. "This microcontroller also determines if it's dark enough out to turns the lights on."
With funding from UVM's Clean Energy Fund, the team tested the turbine on the roof of the Votey Building earlier this year. "Yes, it spins beautifully," Tan says. He also says they have applied for a preliminary patent. In 2015, the team will move into the next, more rigorous testing phase: running the new turbine through detailed tests in a world-class wind tunnel in Williston, Vt., operated by SOH Wind Engineering.
In its habitats, bamboo works as a cantilevered beam, fixed to the earth. Responding to its swaying motion, bamboo's internal structure also naturally develops into what engineers call a "functionally graded material." This means that its fibers transition from inner to outer surfaces in a way that gives bamboo a remarkable combination of flexibility, resilience and strength. "Functionally graded materials are effective in reducing stress concentrations between different layers," Tan notes, "which are critical to the performance of many devices." For example, a bamboo wind turbine that would need to withstand the full onslaught of summer heat and winter freezing.
Tan credits his inspiration for the new device to participation in the UVM Sustainability Fellows Program. "I came up with this idea in those discussions with faculty from all over UVM. As I attended the program, I was thinking: because we're engineers we want to help people, and we can help people in a beautiful way."
And Tan's time as a post-doctoral researcher at the U.S. Department of Energy's Oak Ridge National Laboratory — working on next-generation ideas in energy production — makes him acutely aware that one of the biggest sustainability challenge in his team's new system is finding batteries that are longer lasting, more disposable and less toxic than the current generation. The protype they built uses a car battery. "Develop better future batteries," Tan says, "and we can definitely increase the lifetime of these systems."
"I see the need for a power system that is convenient, that is sustainable and that is beautiful," he says. "We are not building wind turbines; we are planting wind turbines."
Source and top image: University of Vermont
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