Work, work, work

System Administrator Saturday 03 of April, 2010
It's all come down to work and what is becoming our favorite measure of work, the Joule. Work is defined as force times distance or how much energy it takes to move a object a certain distance1 . It has units of Newton*Meters or Joules. We define volt as the amount of work it takes to move a charge through an electric field. Thus, 1 Volt = 1 Joule/Coulomb2 . Power is defined as the rate of work of over time3 . Power has units of Watts or Joules per second.

I did not think much about this until I got this nifty little energy harvester module. A look at last months electric bill showed that we average about 17 kWH per day. That's 61.2 Million Joules! This does not include the gas furnace that consumes 809.8 Million Joules on average per day. Yikes. My energy harvester module comes in two version: Model EH300 at 4.6 milliJoules and EH300A at 30 mJ. There are like nine orders of magnitude between my daily electricity consumption and the storage capability of my energy harvesting module. That's a factor of a billion!

I looked at the battery in my cell phone which is rated at 820 mAh or 3 WH. This translates to 10.9 kiloJoules. 5 orders of magnitude more than my energy harvester. D'oh. This seems to indicate that designing nanostructures to harvest meaningful amounts of energy will be challenging and the electronics associated with such systems will need to be rethought to use far far less energy than they do today. To see more about the modules, check out my Electronics blog Energy harvesting modules.

Work Diagram

1 Physics by Halliday & Resnick, ©1978, p117.
2 Physics by Halliday & Resnick, ©1978, p622.
3 Physics by Halliday & Resnick, ©1978, p127.