An Engineer in Wonderland: Alice on the road to Damascus – Am I wrong to doubt power floors?
A couple of years ago the BBC carried a report that the “34,000 commuters who pass through Victoria underground station at rush hour, for example, could theoretically generate enough energy to power 6,500 LED light fittings.”
Being generous, allowing a fitting to be a single 5mm LED taking 70mW, that is 445W.
I use Victoria underground station, and although I haven’t timed it, I suspect I spend about three minutes walking in it (and many more standing around on its platforms) each time I use it, so if that is true of everyone, there will be 34,000 x 3/60 or 1,700 people in it at any on time.
So 445W between 1,700 moving people is 0.26W each.
Hmm, not too bad so far.
Will anyone notice this?
Well, Mr Google from many sources tells me a person walking consumes just over 260kcal (1.1MJ) per hour which I make about 300W.
He also reveals that power output is about 20 per cent of calories burned in humans, so walking across Victoria Tube Station or any other flat surface involves delivering 60W of mechanical power.
So I doubt’s 0.26W would be noticed, and I am going to take a flyer and assume that 1W would be fine, and 5W a bit of a drag.
Having guestimated this lot, I am even less sceptical, and am starting to believe in floor power – providing there is some way to get the Watts out.
How might this be done?
Having had a look at the website of a consultancy called The Facility, and then thinking about it and coming up with another answer, I reckon moulded flooring with thin walled cells on a 20mm pitch would probably do the trick.
Each squashy cell can pump fluid from a common low-pressure manifold to a common high pressure manifold.
A bit of work with a tape measure tells me my ground pressure is about 500g/cm2 – 7psi, which may be sort of constant as foot size is going to be a bit proportional to person size – although I feel a cube law battling against a square law here.
So with slightly narrower cells and a bit of structure above each to concentrate the weight, a usable 20psi should be possible, which could be developed across the manifolds at a flow rate depending on the number of people.
One big turbine – no microturbines here The Facility – and allowing for 75 per cent loss in the tubes and other works – conceivably enough to light all those LEDs.
The punters don’t get a sprung dance floor, but neither are they virtually squelching through a bog – and it is now a healthy ‘low impact’ floor.
OK – lots of potential leaks – but a one piece moulding would help, with non-generating edge zones to allow space for individual moulded mats to be butted together and connected.
It all starts to sound possible.
(Picture – markhillary, under Creative Commons Attribution Licence)