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.
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