Saturday, August 16, 2014

Give me Strength! And Energy




Question1:Could this sweat-powered tattoo power our gadgets?

Answer: No


Question2:Could coffee shop chatter charge our phones?


Answer: No



For 2 mornings in succession I have been subjected to what I can only describe is further what I call

/Energy Ignorance/

I did work in the UK Power Generation Industry for some years and one of my take away nuggets is that many people have no idea how much energy they use per day, or the magnitude of energy differences used by their technology, nor how much energy the different power generation sources such as Solar, Wave, Wind, Coal, Nuclear actually produce.

So back to the first article

http://www.gizmodo.co.uk/2014/08/this-temporary-tattoo-is-actually-a-battery-thats-powered-by-your-sweat/

and 

http://www.shinyshiny.tv/2014/08/sweat-powered-tattoo-power-gadgets.html

by Kelsey Campbell-Dollaghan

The article does say the electricity produced is about 70 microwatts per square centimetre of skin,  which probably already lost most of the prospective audience.

With that as an exercise to the reader, and given the basic fact that 1 Watt is 1 Joule per second.   Then how many Joules of Energy or Watts of Power do the following require or produce:

  1. A serious cyclist, sprinting on a straight road
  2. You Apple iPad or equivalent tablet, switched on and connected to Wifi
  3. An 80Kg man or woman performing a 10Km run
  4. Realisable energy from burning 1Kg Petrol in a car engine
  5. 30 minutes of a Cooker Oven being on at 200 deg C to make a modest dinner 
  6. A dishwasher on a 90 minute, 50 degree C cycle
  7. A one metre square solar panel in direct sunlight
  8. The end to end Energy production cost of a one metre square solar panel including shipping, and recycling
  9. The power produced by a 300 BHP car engine
  10. The time in seconds to boil 100ml cup of water from room temperature at 20 degrees C using the Sweat Powered Tatoo.

I am just going to answer question 10.  It is for you to solve 1 -9.

70 microwatts is 70 x 10 -6 watts

100ml of water is 0.1 litres and 100 grams

The specific heat of water, which is 4.186 Joule/gram per degree C.

So therefore the energy in Joules to heat 100 grams of water thru 1 degree = 4.186 * 100 = 418.6 Joules

So to raise by (100 - 20) = 80 degrees == 418.6 * 80 = 33488 Joules


1 Watt is 1  Joule per Second

so 70 x 10 -6 * <answer.seconds> = 33488

Time =  478, 400, 000  seconds

=  5537 days == 15 years

So based on the Sweat Technology it would take 15 years to boil 1, small cup of Water, say for a cup of coffee.

In summary: The next time somebody tells you that there is a revolutionary way to solve the worlds energy problems, please make a few calculations before applauding.