Harvesting Energy
There’s power everywhere—if only we knew how to harness it
Our world offers vast amounts of clean, constantly replenished energy from such sources as the sun, wind, tides, even the motion of human feet in train stations. Yet, to fuel our economy and heat and cool our homes, we keep delving underground for sources of latent energy that pollute when we burn them and will someday run out.
How smart is that?
Of course, our problems in harvesting ambient energy don’t stem solely from a lack of smarts. We still lack the technologies to skim off and store more than small amounts of the energy that nature and our own civilization expend in such abundance. With coal, oil, and natural gas, nature has solved the problem of energy capture and storage for us.
Energy harvesting dates back millennia to the windmill and waterwheel, direct ancestors of today’s wind turbines and hydroelectric dams. Recently scientists have redoubled efforts to find ways to siphon energy that has long been free for the taking, if only we could figure out how to do it.
PEOPLE POWER
Harvesting energy from your body
In the future, pacemakers and other implantable medical devices may be powered by the oxidation of blood sugars inside biofuel cells that contain bioengineered enzymes.
In 2007, two MIT students came up with the concept of a “crowd farm” that would convert the mechanical energy of footsteps into electrical energy. The public space selected for the project would house a sub-flooring of blocks that depress slightly beneath footsteps, generating power through the dynamo principle.
Researchers elsewhere envision devices that harvest energy from piezoelectric pads in shoes or tiny wires imprinted on clothes.
FUTURE GADGETS
Large-scale dreams, small-scale uses
Efforts to harvest ambient energy for large-scale commercial or military use have so far fallen short. They do, however, show promise as alternative means of powering hand-held and other low-energy electronics.
Solar cells power satellites and some earthbound watches and telephones. Other small devices scavenge energy from radio transmitters. A thermocouple—a junction between metals that produces a voltage through temperature difference—can tap body heat to power a finger heart-rate meter used in sports training.
A device resembling a knee brace taps the biomechanical energy of walking to generate enough power to charge several cell phones, although its inventor, Max Donelan, intends a therapeutic use—using a sound limb to generate power for a prosthesis.
Piezoelectric (pronounced “pie-ee-zo”) crystals generate voltage from mechanical stress. Using piezo technology, the U.S. Defense Department has sought to harvest enough energy from leg and arm motion, shoe impact, and blood pressure to power wearable sensors. Piezoelectric harvesters have been used to power wristwatches, a wireless doorbell, and a TV remote control.
