Pavegen To Tap Pedestrians For Power In the UK

An anonymous reader writes "Several years ago Laurence Kembell-Cook unveiled Pavegen floor tiles, which capture kinetic energy from footsteps and convert it to electricity. Now after two years of product testing and picking up a slew of awards across the U.K., Pavegen has received its first commercial order — to light up the new Westfield Stratford City Shopping Centre."

Comments

Errors in article

[Zouden]

I was curious how much energy these things produce:

The Pavegen floor tiles flex a slight 5 millimeters when stepped on, capturing kinetic energy which is either stored in lithium polymer batteries beneath its surface or converted into 2.1 watts of electricity and distributed throughout surrounding lights.

It produces 2.1 watts for how long? 1 second? 100ms? I guess it could make some LEDs flash.
Also:

Kembell-Cook is now in the running to win the Shell LiveWIRE Young Entrepreneur of 2011 Award which would give him 10,000 lbs to use towards his invention.

Wow. Will his prize be in the form of a giant cartoon-style weight with "10,000 lbs" written on it? Perhaps they'll drop it on his house.

Re:Errors in article

[dutchd00d]

It produces 2.1 watts for how long? 1 second? 100ms?

For as long as you keep walking, I guess. As long as you produce a Joule each second, you're producing 1 Watt.

The potential energy in a gravitational field is m * g * h, so if you sink 5 mm with every step, you're producing 9.81 * 0.005 = 0.04905 Joule for every kg of body weight at each step. If you take p(ace) steps per second while walking, you're producing p * m * 0.04905 Joules per second, i.e. Watts, as long as you keep walking. So an 80 kg (~160 lbs) person who walks at 2 steps per second could theoretically (i.e. at 100% efficiency) produce 2 * 80 * 0.04905 = 7.8 Watts. So 2.1 Watts means a 30% efficiency. Doesn't seem unbelievable to me.

Waste of energy in manufacture

[eastlight_jim]

Some quick back of the envelope calculations: FTFA, each tile generates "2.1 W" per step. If we assume a typical step time of 500ms based a pace of 120 steps per minute this could be interpreted as about 1.05J captured per step.

The casing is made from stainless steel which required about 53 MJ/kg for production in 2004. If we assume a tile casing mass of 2kg that is 106 MJ required for the steel production alone.

The shopping centre may be open around 10 hours a day with perhaps 20 seconds between each step averaged over a typical day. This is 1800 steps per day at 1.05J per step giving a total of 1890 J captured per day. Assuming 100% efficiency and a never-closing shopping centre, this gives an energy breakeven for the steel alone of around 56000 days or 153 years.

I know that other factors are in play such as the potential to raise awareness of environmental issues but this is ridiculous. I noticed that the award that the guy is in the running for is sponsored by Shell and part of me suspects that they know that these things are crap but want to be seen to promote something like this which appeals to the public and appears "green".

Re:Laws of Thermodynamics...

[AI0867]

Actually, a softer (energy-absorbing) surface is more comfortable to walk on, provided it doesn't absorb excessive amounts.

The plastic tracks in stadiums are softer than asphalt, which again is softer than concrete. Guess which one people like to run on best?
Some athletes from poor countries practice on alphalt and find they run slower in a stadium. Concrete would be even faster, but it tends to wreck your knees unless you have good shoes, which, again, absorb energy.