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January 30, 2009

Feb 3rd a $10 Laptop and Future Energy Harvesting Convergence

A $10 laptop (Rs 500) prototype, with 2 GB RAM capacity, would be on display in Tirupati, India on February 3 when the Indian National Mission on Education through Information and Communication Technology is launched.

According to some unofficial reports the laptop will feature 2GB of memory, WiFi, fixed Ethernet, expandable memory, and consume just 2 watts of power. India could be swimming in cheap silicon within the next 6 months if the project can keep to schedule.

Energy Harvesting from humans is currently a separate development.


The Bionic Energy Harvester can produce enough power from a one-minute walk to juice a cell phone for 30 minutes. The Knee Generator can generate 7 watts. Over three times more than the $10 laptop will need. At more than three pounds, the generator, called the Bionic Energy Harvester, is cumbersome. But thanks to lighter gears and a framework made of lightweight materials such as carbon fiber, the latest model, which is expected in the next year or so, should weigh closer to one pound. A microcomputer will replace a standalone computer that is wired to the unit in the current prototype.


One knee brace-wearing subject generated 54 watts of power by running in place.

The Energy Harvester will cost a lot more than the $10 laptop. However, the price for energy harvesters and low power devices will converge for interesting applications.

The $10 laptop has come out of the drawing board stage due to work put in by students of Vellore Institute of Technology, scientists in Indian Institute of Science, Bangalore, IIT-Madras and involvement of PSUs like Semiconductor Complex. “At this stage, the price is working out to be $20 but with mass production it is bound to come down,” R P Agarwal, secretary, higher education said.

Apart from questioning the technology of $100 laptops, the main reason for HRD ministry's resistance to Negroponte's One Laptop Per Child (OLPC) project was the high and the hidden cost that worked out to be $200.

The mission launch would also see demonstration of e-classroom, virtual laboratory and a better 'Sakshat' portal that was launched more than two years ago.






Larry Rome of the University of Pennsylvania has created the Lightning Pack, a backpack that captures energy from the natural up-and-down movement of your hips. As you walk, a bag bounces on a spring, which connects through gears to an electrical generator. Wires carry the electricity to your batteries or gadgets. The output is impressive: 20 watts, enough for nearly all portable devices, Rome says. But the bag is impractical for most people because it needs to weigh 80 pounds to generate 20 watts. (The heavier the load, the more mass that oscillates up and down, and the greater the kinetic energy potential.) The U.S. Marine Corps, however, is interested and has commissioned a pack for soldiers.


Power From Radio Waves

An Intel research team set up a system that collected enough energy from a TV signal transmitter around 4km away to power a tiny electronic desktop meteorology gadget. They sampled some of the 960 KW of effective radiation power put out by a TV transmitter set on channel 48. Their set-up managed to harvest some 60 microwatts of power, which was enough to create 0.7 volts across an 8 kilo-ohm load: essentially just about enough juice to drive the little weather station and its LCD screen.

And that's the slightly creepy part. All that wireless power was there already. The TV transmission radio waves streaming past us all, pretty much all the time, contain that much energy. And that's not to mention the sea of FM radio transmissions, Wi-Fi signals, GSM signals from cellphones and towers, Bluetooth headsets...


FURTHER READING
IEEE : Energy Harvesting From Human and Machine Motion for Wireless Electronic Devices [30 pages]

The bending of the knee during walking is identified as one of the more promising opportunities to harvest energy from the body, because the leg muscles work against the motion of the leg for part of the gait cycle (while the leg is falling), during which time energy is turned into wasted heat. The authors estimate that up to 50 W could be harvested this way with little impact on the gait, although a large device would be required with well separated attachment points.

Determining the available power from a specific implementation of an inertial microgenerator powered by human walking motion. Acceleration data were collected from human male subjects walking on a treadmill and fed into a time-domain model of the generator in order to determine the available power. For a proof mass of 1 g and an available internal displacement of 5 mm, power outputs as high as 200 W were calculated; this would appear to assume ideal harvester performance.


2004 thesis project on energy harvesting



Apollo 13 had about 40 amp-hours in battery power after their explosion.

Batteries are rated using a term called ampere-hours. If you start with a 40 amp-hour re-entry battery, and then turn on a piece of equipment that uses 1 amp-hour, and it takes 8 hours to finish the re-entry and splashdown, you have only 32 amp-hours left to power everything else. The Knee generator would have been able to supply that power.

Conversion - Watt, Amp and Volt

Watt
A measurement of total power. It is amperes multiplied by volts. 120 volt @ 1 amp = 12 volts @ 10 amps.

Ampere or Amp
An Ampere or an Amp is a unit of measurement for an electrical current. One amp is the amount of current produced by an electromotive force of one volt acting through the resistance of one ohm. Named for the French physicist Andre Marie Ampere. The abbreviation for Amp is A but its mathematical symbol is "I". Small currents are measured in milli-Amps or thousandths of an Amp.

Amp Hour or Ampere-Hour
A unit of measurement of a battery's electrical storage capacity. Current multiplied by time in hours equals ampere-hours. One amp hour is equal to a current of one ampere flowing for one hour. Also, 1 amp hour is equal to 1,000 mAh

Convert Watt to Amp
You can also convert Wh to Ah by rebalancing the early equation to the one shown below.

amp = watt / volt
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