WASHINGTON, D.C. — In many places, wind power is getting to be a big deal. Already by last year, some 4.7 percent of all U.S. electricity came from wind turbines. Farms of these wind-power devices are spreading across the planet. And some are becoming true giants. The largest are taller than 60-story skyscrapers. Just one can produce enough electricity to power more than 1,500 homes.
But some researchers are bucking this trend. They’ve chosen to go small for uses that are also tiny. For instance, a small-scale windmill might be all that’s needed to run a single sensor that will only gather some type of data once every few minutes, if that often.
Such low-cost generators could be particularly useful in remote spots, where it would be too expensive and troublesome to run power lines. Or they might replace batteries that would run down and then need frequent recharging or replacement.
And professional researchers are not the only ones trying to develop these devices. Two of this year’s Broadcom MASTERS finalists are also working to harness wind power for these tiny needs.
MASTERS stands for Math, Applied Science, Technology and Engineering for Rising Stars. The Broadcom MASTERS competition brings together 30 middle-school students each fall. The program was created by Society for Science & the Public, which publishes Science News for Students. Broadcom Foundation sponsors it. Part of the competition is based on research the students entered the year before in a science fair.
Harnessing the wind
There are many sorts of sensors that can operate on low power, explains Heath Hofmann. He’s an electrical engineer at the University of Michigan in Ann Arbor. That’s especially true for sensors that operate only infrequently, he notes. “Scientists are still trying to figure out all the possible uses there might be for such sensors,” he says.
Some researchers have used low-power sensors to monitor wildlife or environmental conditions on the seafloor. Others use such sensors to monitor the vibrations of bridges as traffic passes across them. Changes in those vibrations over time, he notes, could signal that parts of the bridge have worrisome cracks that are growing in size. Still other engineers have proposed using remote sensors to scout signs of corrosion in energy pipelines.
Before anyone can rely on such sensors, however, they’ll need a power source such as the tiny systems being developed by this year’s Broadcom MASTERS contestants.
To create his, Akhilesh Balasingam, 13, of San Jose, Calif., used a piezoelectric material. When such materials flex, electrons inside them move to generate an electric current. (The “piezo-” prefix comes from the Greek word piezein. It means “to squeeze” or “to press.”)
The teen glued a strip of the material roughly 2 centimeters (about an inch) long to a flexible strip of brass. Then, he stuck a tough plastic weight onto the end of the metal strip. Finally, he hung that strip from the underside of a board so that the weight could swing back and forth like a pendulum whenever the wind blew. That motion caused the piezoelectric material to bend and flex. This created a small amount of electric current.
Engineers use large wind tunnels to analyze the airflow around models of devices, such as airplanes and rockets. Akhilesh built a small wind tunnel that was powered by a household fan (the same type people use to cool off in hot weather). To make sure the airflow was straight and not swirling, he had the wind blow through a filter made from drinking straws. The long paths through the straws helped straighten the flow so there would be no turbulence.
Finding the right mix of materials to produce the most power required some tinkering. For instance, the teen applied different amounts of electrical resistance to his device to test its power output. (The more light emitting diodes, or LEDs, he hooked up to the device, the more resistance the circuit had.) Finally, Akhilesh varied the size and shape of the weight attached to the end of the metal strip. Some were shaped like small boxes. Others were shaped like a solid triangle.
The device could produce power at winds speeds as low as 1 meter per second (or about 2.2 miles per hour). The best design produced between 600 and 700 microwatts of power. That sounds like a very small amount. And it is. The small bulb in a nightlight can consume more than 5,000 times as much power as Akhilesh’s device produces. But some sensors require only 100 microwatts of power, the teen points out. So his device could power thousands of those. A device such as his might be used to power sensors that measure moisture levels in forest soils. Or it might run sensors that track those bridge vibrations caused by traffic, he suggests.
A roadside breeze
Rachel Pizzolato, 12, of Metairie, La., designed a system that would work even when no winds blow. It’s powered by traffic.
As a vehicle passes, it kicks up dust — and a good bit of wind. Big trucks can create enough wind to almost knock someone down. Such breezes could be a ready source of electrical power, particularly in places where traffic is nearly nonstop, she notes.
The trick, though, is capturing that energy. Although roadside wind is plentiful, Rachel’s first design didn’t work. She started out by mounting a bicycle wheel on a small pole horizontally (giving it the same orientation as a bike laying on its side). Then, she attached eight large flaps of cardboard to the rim of the wheel, sticking out so that the wind could spin them. To test her device, Rachel had her dad drive by.
Yet the wheel didn’t spin.
So Rachel scouted for the problem. She soon realized that the flaps on one side of the wheel captured the wind just as effectively as those on the other side. Because those forces canceled each other out, the wheel remained motionless. No rotation equals no power from her mini windmill.
So Rachel changed the orientation of those flaps. Instead of having them stick straight out from the rim, she bent them so that they all projected from the rim at a 30-degree angle. (Think of a clock. If a line pointing directly outward from the rim is pointing toward 12, the flap would be pointing toward 11 o’clock.) Now the flaps on the left side were pointed slightly into the wind. Those on the right side pointed slightly away from the wind.
That difference now allowed the wheel to spin easily when the breeze from a passing car blew past it. And as the windmill spun, a small device mounted on the windmill’s pole turned the motion into electricity. (Such devices are called generators, because they use the relative motions of magnets to generate electricity.)
To test her windmill, Rachel set it next to the road and had her dad drive the family car past it. Her dad got up to speed and then set the cruise control. In this way, he could be sure that the car maintained the same speed each time it passed her device.]
Story continues below video.
Rachel’s dad drove by at speeds ranging from 24 to 56 kilometers per hour (or 15 to 35 miles per hour). Rachel then measured the highest voltage produced by the windmill during 100 trials. (Volts are a different measure of electricity than watts. Voltage measures the electrical potential between two points in a circuit. Watts considers the amount of electrical current passing between those points as well as the voltage.)
At a slow drive-by speed, the car got the windmill generating an average of 20 millivolts. High-speed tests caused the spinning windmill to generate roughly 77 millivolts. Again, these amounts seem small. But because many cars may pass a particular spot throughout a day, any power generated by such a windmill could add up to a substantial amount, Rachel notes.
The students have not yet designed a way to store the power generated by their devices. But Akhilesh says that should not be hard. A battery is one option. Better yet might be a device called a capacitor. It can store electrical energy and then release it again as needed, just as a battery would, he says. But batteries often lose their ability to hold a charge over time, the teen notes. They also need to be recycled or disposed of in special ways. Capacitors typically don’t have such problems, he points out.
These tiny devices also could send their energy into the power grid, Rachel says. And then these tiny windmills could help power anything from your refrigerator to a charger for your cell phone.
(for more about Power Words, click here)
angle The space (usually measured in degrees) between two intersecting lines or surfaces at or close to the point where they meet.
average (in science) A term for the arithmetic mean, which is the sum of a group of numbers that is then divided by the size of the group.
battery A device that can convert chemical energy into electrical energy.
Broadcom MASTERS Created and run by the Society for Science & the Public, Broadcom MASTERS (Math, Applied Science, Technology and Engineering Rising Stars) is the premier middle school science and engineering fair competition. Broadcom MASTERS International gives select middle school students from around the world a unique opportunity to attend the Intel International Science & Engineering Fair.
capacitor An electrical component used to store energy. Unlike batteries, which store energy chemically, capacitors store energy physically, in a form very much like static electricity.
circuit A network of that transmits electrical signals. In the body, nerve cells create circuits that relay electrical signals to the brain. In electronics, wires typically route those signals to activate some mechanical, computational or other function.
corrosion (v. to corrode) A chemical reaction in which metals react with gases or other materials in their environment and undergo a type of degradation. The rusting of iron, for instance, is one example of corrosion that is driven by exposure to moisture.
current (in electricity) The flow of electricity or the amount of electricity moving through some point over a particular period of time.
degree (in geometry) A unit of measurement for angles. Each degree equals one three-hundred-and-sixtieth of the circumference of a circle.
electrical engineer An engineer who designs, builds or analyzes electrical equipment.
electrical resistance The tendency of an electricity-conducting material to oppose the passage of a current through it. That resistance (usually measured in units known as ohms) will convert some of the electric energy into heat.
electric current A flow of charge, called electricity, usually from the movement of negatively charged particles, called electrons.
electricity A flow of charge, usually from the movement of negatively charged particles, called electrons.
electron A negatively charged particle, usually found orbiting the outer regions of an atom; also, the carrier of electricity within solids.
engineering The field of research that uses math and science to solve practical problems.
flex To bend without breaking. A material with this property is described as flexible.
generator A device used to convert mechanical energy into electrical energy.
grid (in electricity) The interconnected system of electricity lines that transport electrical power over long distances. In North America, this grid connects electrical generating stations and local communities throughout most of the continent.
light emitting diodes (LEDs) Electronic components that, as their name suggests, emit light when electricity flows through them. LEDs are very energy-efficient and often can be very bright. They have lately been replacing conventional lights in auto taillights and in some bulbs used for home lighting.
resistance (in physics) Something that keeps a physical material (such as a block of wood, flow of water or air) from moving freely, usually because it provides friction to impede its motion.
sensor A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly. (in biology) The structure that an organism uses to sense attributes of its environment, such as heat, winds, chemicals, moisture, trauma or an attack by predators.
Society for Science and the Public (or SSP) A nonprofit organization created in 1921 and based in Washington, D.C. Since its founding, SSP has been not only promoting public engagement in scientific research but also the public understanding of science. It created and continues to run three renowned science competitions: The Regeneron Science Talent Search (begun in 1942), the Intel International Science and Engineering Fair (initially launched in 1950) and Broadcom MASTERS (created in 2010). SSP also publishes award-winning journalism: in Science News (launched in 1922) and Science News for Students (created in 2003). Those magazines also host a series of blogs (including Eureka! Lab).
technology The application of scientific knowledge for practical purposes, especially in industry — or the devices, processes and systems that result from those efforts.
turbine A device with extended arm-like blades (often curved) to catch a moving fluid — anything from a gas or steam to water — and then convert the energy in that movement into rotary motion. Often that rotary motion will drive a system to generate electricity.
voltage A force associated with an electric current that is measured in units known as volts. Power companies use high-voltage to move electric power over long distances.
watt A measure of the rate of energy use, flux (or flow) or production. It is equivalent to one joule per second. It describes the rate of energy converted from one form to another — or moved — per unit of time. For instance, a kilowatt is 1,000 watts, and household energy use is typically measured and quantified in terms of kilowatt-hours, or the number of kilowatts used per hour.
wind tunnel A facility used to study the effects of air moving past solid objects, which often are scale models of real-size items such as airplanes and rockets. The objects typically are covered with sensors that measure aerodynamic forces like lift and drag. Also, sometimes engineers inject tiny streams of smoke into the wind tunnel so that airflow past the object is made visible.
wind turbine A wind-powered device — similar to the type used to mill grain (windmills) long ago — used to generate electricity.