Harvesting wasted energy is like world peace. Both sound obvious, ridiculous and enticing at the same time. One of them, however, is just a dream.
And yet, the potential for significant harvesting is just real enough for business and government to invest at least modest sums in its development.
“Energy-harvesting is all about efficiency,” said John Langley, president and CEO of Ambient Micro, a small Half Moon Bay, Calif., firm researching energy-harvesting products. Using energy that you create but throw away means the energy that is used goes farther.
The potential is tantalizing. A car wastes gobs of energy, for example, most notably as engine heat and the heat of exhaust gases. If it runs out of gas and you have to push it, you waste energy as heat, too (and choice four-letter words). Drive off with a newly filled tank and some of the car’s energy is wasted as vibrations in the road.
And that’s a miniscule sliver of what’s out there to be harvested. That’s because doing any work wastes energy. Among the many kinds of potentially useful energy waste:
- Kinetic energy
- Corrosion (in which metal corrosion becomes fuel for a sensor that monitors corrosion)
Some interesting and sometimes counterintuitive applications are in the works or even on the market. One firm makes a sensor powered by the energy of sitting in a chair. Gluteus-maximus-derived pressure charges a sensor tied into a building’s environmental controls. Another company is using waste heat to create mini-tornadoes that drive turbines. Others covet waste energy created near, on or even inside the human body.
Langley’s Ambient is one of many players in the market, including industry luminaries like Linear Technology Inc. and Perpetuum Ltd. Both sell products that mostly power small wireless sensors that require little energy.
It’s still a tough slog for everyone, though.
“We get no respect as an industry,” said Langley. Advocates are held in the same esteem as were proponents of more-aerodynamic car designs until the oil crunch of the 1970s.
Part of the problem is that the amount of wasted energy that can be harvested today is typically very small and varies widely from application to application. Generally, energy harvesting can produce microwatts of energy. A microwatt is one-millionth of a watt. A 100-watt light bulb creates 100 million times more energy than 1 microwatt.
As it turns out, it takes a lot of efficiency to get respect. Among other activities, Ambient has looked at ways to extend the flights of unmanned aircraft by exploiting the temperature difference between the plane’s engine and the air surrounding the craft.
“So, you have a plane that can fly for five days” before refueling, he said. “Using the waste heat, we can make it a five-and-a-half-day plane. That’s not really that attractive to builders, given all the other problems they are trying to solve.”
That obviously hasn’t stopped entrepreneurs from mining for gold in those tiny hills. A handful of microwatts might be nothing to most engineers, but electronics are becoming more efficient themselves. That means that sensors and wireless transmitters require less power.
Chinese researchers are working with microwatt electronics to monitor the corrosion of metal rebar used to strengthen concrete. Corrosion is an electro-chemical reaction, making a highway, bridge or office floor batteries for power-sipping measurement and transmitting devices. Their weakening would power a warning.
One of Langley’s projects would place heat-powered sensors in the belly of unmanned aircraft to watch for pooling fuel and hydraulic oil, which can turn composite parts to mush.
The same technology can be used on cars, too. Lighter and stronger though they may be, they can break down when exposed to some chemicals.
“You would want some warning that a spring mount on your car was delaminating,” or peeling apart, he said.
And if that warning arrives compliments of engine heat, all the better.