People Power: Capturing The Body's Energy For Work On and Off Earth

Can we harvest the unused energy that a human body essentially wastes (mainly it eventually radiates away as heat)?
The human body is on average of 15% fats, capable of producing 11,000 watt hours
When the average Joe eats his daily bread, he takes 3,300 watt hours. The charge rate is about 7kW. Broken into usable terms, waiting to be harvested are :

Activities energy (watts)
walking with heels 67w
sleeping 81w
soldier standing at ease 128w
walking person 163w
briskly walking person 407w
from a long distance runner 1048w
sprinter 1630w

Some of the most promising mechanisms for passively converting human body functions into electricity are:

1. Piezoelectric devices: Piezoelectric substances, like some ceramics, also generate electrical energy from mechanical strain but without the need for voltage to be applied. This well-understood material is the core of "heel strike" devices that generate electricity from walking. "Generating 1-2 watts per shoe is not out of the question. A major issue that remains is the durability of these devices," Dr. Robert J. Nowak, program manager for energy harvesting at Darpa, wrote to SPACE.com. Great for soldiers, bad for astronauts: "giant steps are what you take, walking on the moon."

2. Urine-based fuel cell: Yes, you can turn pee into power and not just by turning a turbine after a few beers. First subject urea to enzymatic hydrolysis to make carbon dioxide and ammonia, and then oxidize the ammonia to nitrogen and water. But the center notes that "one problem with the system is the need for alkaline conditions that may require transport of sodium hydroxide, a hazardous compound. Also, to achieve power generation in the range of 0.5 - 1W, a system to concentrate the breakdown products of urea, such as reverse osmosis, will be necessary." But for astronauts and soldiers on the run, "one attractive feature of this fuel cell concept is the production of water as a by-product of the system."

3. Thermoelectric materials: These materials convert body heat into electricity by using combinations of materials (metals or today, new ceramics) that are poor thermal conductors and good electrical conductors. When two of them at different temperatures come into contact, electrons migrate, charging a battery or creating usable current through something called the Seebeck Effect. The trouble is that you need great temperature differences to get significant energy, and "on Earth most places are pretty close to body temperature," notes Dr. Henry Brandhurst, director of the center. And what about in the cold depths of space? For the inner solar system at least, photovoltaic panels seem like a better bet, he says

4. Electromagnetic generator: Large muscular groups (especially legs) can generate electricity by simple motions against gravity and small direct current permanent magnet motors. But the center cautions, "there is little or no efforts within the scientific community to design efficient small generators of the type needed for harvesting of human energy."

Source : from space.com

Ridha Razak