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27 FEB 2014: REPORT
In a Host of Small Sources,
Scientists See Energy Windfall
The emerging field of “energy scavenging” is drawing on a wide array of untapped energy sources — including radio waves, vibrations created by moving objects, and waste heat from computers or car exhaust systems — to generate electricity and boost efficiency.
by cheryl katz
Computers feasting on their own exhaust heat. Super-efficient solar panels snaring lost thermal energy and recycling it into electricity. Personal electronics powered by stray microwaves or vibration-capturing clothing. Cellphones charged with a user’s footsteps. These and more innovations may be possible with free, green energy that is now going to waste.
Ubiquitous sources like radio waves, vibration and pressure created by moving objects, heat radiating from machines and even our bodies — all have the potential to produce usable electric power. Until
recently, ambient energy was largely squandered because of a lack of ways to efficiently exploit it. Now, advances in materials and engineering are providing tools to harvest this abundant resource and transform it into cheap, clean electricity.
“This power is simply available and it’s not doing anything right now, so it’s truly being wasted,” said Steven Cummer, a Duke University electrical and computer engineering professor working on harvesting ambient electromagnetic radiation to power electronic devices. “And as people think of useful things to do with it, then you’re doing those things with available power instead of requiring new power.”
This up-and-coming technology, some experts say, can save energy, liberate portable electronics from the grid, and all but do away with disposable batteries. Although it won’t begin to replace solar and wind for generating utility-scale electricity, energy harvesting can serve as a multiplier for these and other sustainable resources, boosting productivity by feeding escaped power back into the system, expanding the range of sunlight that can be harnessed, and powering controls that keep
This up-and-coming technology could all but do away with disposable batteries.
equipment functioning at its peak. If obstacles of size and efficiency are overcome, repurposed ambient power can be an important contribution to the renewable energy supply.
The concept isn’t new — in a sense all energy drawn from the environment is “harvested.” Nor is there a standard definition for the emerging technology known as energy harvesting or energy scavenging, but it primarily involves collecting low-power electromagnetic, thermal, mechanical, or light energy and converting it to electric current.
Exploiting free, ambient energy is “an interesting idea and you’re going to see more applications of it,” said Jonathan Koomey, research fellow at Stanford University’s Steyer-Taylor Center for Energy Policy and Finance. But the technology has a long way to go, he said. Constraints on space and the amount of energy that can be gleaned in many settings now limit its use to small, fairly low-power devices. “It’s not this magic bullet,” Koomey said.
Still, in today’s power-hungry world, energy scavenging can help ensure that no watt goes to waste.
“Your computer, hot asphalt, there’s a million things that are fairly hot but not really viable for standard thermoelectrics,” said Harry Radousky, a physicist at Lawrence Livermore National Laboratory in Northern California and co-developer of a nanoscale harvester for low-temperature heat, such as exhaust from appliances. In contrast to high-temperature, waste-heat capture systems — in which sources like flue gas provide a steep heat gradient for thermoelectric generators — the small heat differences between low-temperature sources and their surroundings are much harder to convert into electricity. But new low-temperature thermal harvesting technology could turn these overlooked resources into working power.
For instance, Radousky said, “we park our cars in hot parking lots all over the U.S. in the summer, so in principle we could charge batteries in electronic devices, [and] run coolers to keep food cold” with heat from the pavement. Other prospects for reaping low-temperature thermal power include light bulbs, hot ovens, and plastic seats inside cars baking in the sun. “My rule of thumb is that if it is too hot to touch, it’s a candidate source,” he said. “So we were looking for things that could harvest that low
“Our motto is ‘No wires, no batteries, no limits,’” says one expert.
quality of heat … where a small amount of energy can get you a long way.”
As energy harvesters become increasingly efficient and cost-effective, a growing number of products such as light switches, thermostats, gas detectors, and avalanche alarms are going off-grid and battery-free.
“Our motto is ‘No wires, no batteries, no limits,’” said Graham Martin, chairman of EnOcean Alliance, a California-based consortium of companies promoting a wireless standard for automated building controls that run on scavenged power.
Regulating building heat, cooling, and lights with devices like room occupancy sensors can cut energy use by as much as 40 percent, Martin said. EnOcean Alliance reports that more than 250,000 buildings worldwide contain its energy-scavenging devices, like wireless, battery-free controls with tiny, integrated photovoltaic cells that harvest energy from room lights, or vibrations that agitate a pressure-sensitive material, releasing electrons. Martin estimates that EnOcean devices have saved 50 million batteries, and predicts that 3 billion switches, sensors, thermostats, transmitters, and other low-powered, self-contained gadgets will be in use within five years.
While the market for energy-harvesting devices is currently “not massive,” it is growing steadily, said Harry Zervos, senior technology analyst with the consulting firm IDTechEx. Some of the biggest uses at present include vibration-driven equipment monitors on oil rigs and other remote settings,
The greatest benefits may lie in cutting waste and boosting output from existing electricity sources.
and car tire pressure sensors running on mechanical energy from the wheels. The technology is now at a tipping point with advances in efficiency, reliability, and affordability, according to Zervos, who expects revenues to hit roughly $4 billion in a decade or so.
Future applications could range from powering a car’s electrical systems with heat captured from the tailpipe, which University of Houston physicist Zhifeng Ren estimates would increase mileage by 5 percent, to a film that can be attached to human skin, converting a person’s movements into energy for portable devices.
Energy harvesting’s greatest benefits, however, may lie in cutting waste and amping up output from existing sustainable electricity resources.
Self-powered wind turbine monitors, for instance, could warn of problems in time to keep turbines from going off-line. And capturing lost heat would significantly boost solar production. Mahmoud Hussein, an assistant professor of aerospace engineering sciences at the University of Colorado Boulder, has come up with a process that could convert heat to electricity much more efficiently: topping thermoelectric material with nano-sized pillars to slow escaping heat vibrations called phonons. The pillars stem heat loss by interacting with, rather than impeding, the phonons, leaving the electric current undiminished, a significant gain over existing thermoelectric materials.
Improved thermoelectric technology can help recoup energy lost by photovoltaic cells that utilize only part of the light spectrum while the rest escapes as heat, Hussein explains. Harnessing waste heat “adds to the field of harvesting energy from the sun,” Hussein said.
Engineers and entrepreneurs are also coming up with a host of other ingenious ways to put ambient energy to work.
At the Lawrence Berkeley National Laboratory on the University of California, Berkeley campus, bioengineer Seung-Wuk Lee is harvesting energy produced by a virus. Genetically engineered to contain a protein that generates electricity when squeezed, the virus infects bacteria and makes them create “zillions of copies,” Lee said. The result is layers of piezoelectric biopolymer with strong positive charges on the inside and
One possible application is biomedical devices powered by motions from the body’s organs.
negative charges on the outside that transform pressure into power.
“Piezo means press,” Lee explained, “so when we mechanically press, we break the symmetry and induce their electric potential.” He demonstrates, tapping a super-thin, fingertip-sized biopolymer sandwich. A few inches away, a small display lights up, spelling out “Virus.”
This so-called Bacteriophage Power Generator can produce enough electric current to power LEDs, but the output would need to be increased a thousand-fold to illuminate a light bulb. Lee and colleagues are now working on boosting that performance.
Another possible application is biomedical devices powered by motions from the body’s organs — especially useful for implants like pacemakers now driven by batteries that must be surgically changed. “We can convert
small energy from our heartbeat,” Lee said. “The potential is endless.”
At the University of California, Los Angeles’ Henry Samueli School of Engineering and Applied Science, Professor Kang Wang and colleagues are developing a way topower appliances and electronics with their own excess heat. The process channels heat given off by a working computer, for example, into spin waves able to power and speed up the machine at the same time.
Reprocessing waste heat can save electricity used not just in powering up computers, but also in cooling them down. Such savings would be especially significant at large server farms, where Wang says the dissipation of power is “an enormous drain on energy.”
Lawrence Livermore’s Radousky and partner Morris Wang, meanwhile, combined two technologies to wrest energy from low-temperature sources. Their hybrid harvester contains a phase-change material that deforms when heated and stresses a piezoelectric surface, producing current. Although the output is less than a volt, it could be deployed in arrays of miniscule sensors and processors known as MEMS (microelectromechanical systems), currently used as autonomous controls in cars, airplanes, imaging systems, and numerous other applications, Radousky said.
“The basic idea is to create energy which is used locally, rather than needing to be transmitted,” he said.
But don’t plan on getting rid of that tangle of chargers and power cords just yet. Satiating sophisticated portable electronics like cell phones with
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ambient radio waves sounds great, but unless you’re standing next to a transmitter, pulling in enough signal requires an antenna larger than the phone, according to Koomey. And even that can only power a very basic model, he said. “Your iPhone is not going to get charged.” Alternatives are in the works: Researchers at Georgia Tech have developed cell phone-powering shoe inserts, and a company called Sole Power plans to market footwear late this year that charges your phone while you walk. Both, however, need “many steps” — on the order of a 10-mile hike — to get the job done.
To Koomey, the greatest value of energy-harvesting is information: enabling small, self-contained sensors to provide data that can optimize power use and trim waste. “The way we operate the economy now, there’s all this inefficiency because we just don’t know, we’ve never been able to measure the inefficiency before,” Koomey said. “There’s huge efficiencies that can be wrung out of the system.”
As Zervos put it, “By using just microwatts, you can save kilowatts of energy that would have gone to waste.”
POSTED ON 27 FEB 2014
24 FEB 2014: ANALYSIS
Is Weird Winter Weather
Related to Climate Change?
Scientists are trying to understand if the unusual weather in the Northern Hemisphere this winter — from record heat in Alaska to unprecedented flooding in Britain — is linked to climate change. One thing seems clear: Shifts in the jet stream play a key role and could become even more disruptive as the world warms.
by fred pearce
This winter’s weather has been weird across much of the Northern Hemisphere. Record storms in Europe; record drought in California; record heat in parts of the Arctic, including Alaska and parts of Scandinavia; but record freezes too, as polar air blew south over Canada and the U.S., causing near-record ice cover on the Great Lakes, sending the mercury as low as minus 50 degrees Celsius in Minnesota, and bringing sharp chills to Texas.
Everyone is blaming the jet stream, which drives most weather in mid-latitudes. That would be a significant development. For what happens
to the jet stream in the coming decades looks likely to be the key link between the abstractions of climate change and real weather we all experience. So, is our recent strange weather a sign of things to come? Are we, as British opposition leader Ed Milliband put it this month while surveying a flooded nation, “sleepwalking to a climate crisis”?
The story gets tangled because trying to identify long-term trends amid the noise of daily weather is hard.
The U.K. Met Office, which keeps a global weather watch, said in a rushreport put out in mid-February that we are experiencing a “hemispheric pattern of severe weather,” and that the events are linked. The most extreme days of the U.S. cold event, for instance, coincided with some of the most intense storms over the U.K. And physically the connection is through the polar jet stream, which the report said showed a “persistent pattern of perturbations” — in other words, it ran wild.
The polar jet stream is a narrow stream of fast wind circling the globe from west to east at the top of the troposphere from 7 to 12 kilometers up, and usually between 50 and 70 degrees north. It forms where cold, dense air from the Arctic meets warmer and less dense air from mid-latitudes. At the
Climatologist Jennifer Francis links ‘this bizarre winter’ to changes in the jet stream caused by a warming Arctic.
boundary, winds rush in to equalize the pressure difference. The earth’s rotation diverts these winds to travel eastward.
As the jet roars around the world, it drags weather systems with it. Most of Europe’s weather rides in under the jet stream from the Atlantic, and most of the western U.S.’s weather comes from the Pacific in a similar manner.
This year, the jet has been unusually far north in the Pacific, bringing balmy weather to Alaska. But across the Atlantic it has been unusually far south, unusually persistent, and 30 percent faster than normal. It has sent more than 30 storms, many of them much larger and more intense than normal, crashing into the shores of Britain in the past three months. With the storms have come high winds and heavy rains almost every day, delivering amounts of precipitation unseen in records going back more than a century — and probably exceeding anything else in the last 250 years, according to the Met Office report.
At the annual meeting of the American Association for the Advancement of Science in Chicago this month, climatologist Jennifer Francis of Rutgers University linked “this bizarre winter” to climate change, and in particular to changes in the jet stream caused by a warming Arctic. “Weather patterns are changing,” she said. “We can expect more of the same.”
Francis notes that the Arctic has been warming faster than the rest of the planet in recent decades, driven by melting ice that replaced reflective white surfaces with dark, energy-absorbing ocean. That is expected to continue. While lower latitudes will also warm, the result will be to reduce the temperature gradient between polar and mid-latitude air that drives the jet. So, says Francis, we can expect the jet to slow. A slower jet is generally more meandering and inclined to get “stuck,” delivering unchanging weather.
There is one problem with this analysis as regards recent events, says Tim Woollings, who researches atmospheric dynamics at Oxford University in England. While the jet stream has indeed been “stuck” for the past two months, delivering cold weather to North America and storms across the Atlantic, it is not slow and meandering. Across the Atlantic at least, it has been fast and remarkably straight. “That is the exact opposite to the weak meandering jet of your hypothesis,” Woollings told Francis in an email exchange last week that both shared with Yale Environment 360.
That certainly doesn’t prove Francis wrong. Woollings agrees that Francis’s prediction of a stuck meandering jet looks very like the situation in the Pacific this winter. But it does complicate claims that this winter’s
Britain’s Met Office says the real driver of recent climate patterns has been the jet stream over the Pacific Ocean.
extremes can be blamed on man-made climate change.
So what is going on? The Met Office came to the conclusion that the real driver of the action in recent months was not in the Arctic or the Atlantic, but far away in the western Pacific Ocean. The jet stream, remember, is a global wind, circling the earth. This winter, the jet stream over the Pacific has been deflected much further north than usual. This, according to the Met Office, is likely a consequence of some combination of heavy rains over Indonesia, warm Pacific waters, and unusual pressure systems.
The displaced Pacific leg of the jet stream dragged warm air up over Alaska. But, once east of the Rockies, it met the dense cold air of the Arctic and plunged south. A long way south — as far as Texas at times. This southward excursion of the jet brought freezing weather across much of the U.S. But it also brought that cold polar air into contact with warm southerly breezes. Thus the temperature gradient at the boundary between polar and non-polar air was exceptionally great. At times, says Francis, Arctic air was meeting tropical air as the polar jet coalesced with the sub-tropical jet, which forms where tropical air meets air from the north.
The scientists agree that this exceptional temperature difference dramatically speeded up the jet stream as it pushed out over the Atlantic on its unusually southerly trajectory. A fast jet stream is usually also a straight jet stream. And the southerly route allowed the surface air it pulled along to pick up unusual amounts of moisture evaporating from the warm waters of the Atlantic.
The result was that the jet slammed a long succession of intense storms into southern England, where they would normally hit Scotland or miss the U.K. altogether. The storms contained huge volumes of moisture. And, to add to the tumult, the fast winds across the Atlantic also whipped up big waves and tidal surges; so in places record flood flows coming down rivers met flood waters coming off the sea. Parts of Britain were submerged.
Where does this leave us on climate change? It is no great surprise that there is confusion. Weather is weather. It is always changeable, with a large
Scientists remain uncertain about how the major features of world’s weather will respond to global warming.
random element. Stuff happens. The Met Office notes that the winter’s weird weather has a range of causes besides the jet stream, including unusual upper atmosphere winds over the North Pole, and anomalies in the eastern Pacific that have delivered severe drought to California. There is, the Met Office says, no compelling evidence from this winter to suggest that there is a new emerging pattern.
But that doesn’t mean nothing is going on. Long-term trends are hard to spot, and natural variability is still generally dominant over the subtle changes in climate, or “average weather.”
Yet there are some instances where attribution is possible. For example, climate researchers have persuasively argued that a few intense heat waves — such as the one that killed 70,000 people in western Europe in 2003 — would have been highly unlikely without the added impetus of global warming. But for weather extremes other than rising temperatures, unambiguous attribution of even extreme events is very hard to make, whatever the suspicions that something is up.
Climate scientists remain very uncertain about how most of the major features of the world’s weather will respond to global warming. The climate will change, for sure, but exactly how is a tough call.
El Niño, the Asian and African monsoons, Atlantic hurricanes, the jet streams: The most recent report of the Intergovernmental Panel on Climate Change (IPCC), issued last October, puts a big question mark over the likely trends for all of them. And while Francis suggests the polar jet stream should slow as the Arctic warms, the IPCC noted that most climate models predict a faster polar jet.
Actual trends so far don’t tell us much. According to the Met Office, the number of storms crossing the Atlantic in a normal year is no higher today
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than 150 years ago. But Xiaolan Wang of Environment Canada, a government agency, last yearreported evidence that winter storms are becoming stronger over the North Atlantic. This may not have anything to do with the jet stream, however. These storms could just be picking up more moisture from an Atlantic that is now substantially warmer than in past decades.
Data from weather stations around the world reveal more extreme precipitation events — and more droughts, too. This is firmly in line with the predictions of climate models and is “what is expected from fundamental physics,” says the Met Office. A warmer atmosphere will contain more energy, and more moisture from evaporation, says Woollings. It already does. And, in general, more energy and moisture will mean wetter storms in many places.
Weird weather is definitely on the agenda, and the jet stream is very likely to be an important part of it. The nightmare scenario is that Francis will be proved right about the jet stream becoming more “stuck” in a particular trajectory, but that, as happened this winter, it will get stuck while traveling at express speed and bringing strong winds and heavy rain with it. The Met Office says the Francis scenario “raises the possibility that disruption of our usual weather patterns may be how climate change may manifest itself.” If so, that would indeed unleash the perfect storm.