'Pavement power' - The bad idea that never seems to die

We've said it before, but because “walk on this pavement for renewable energy” remains a recurrent news story, it's worth saying again.

You can't get a useful amount of energy that way: it's a gimmick.

The latest iteration comes from Las Vegas, which according to the Las Vegas Review-Journal is installing street lights from EnGoPlanet, complete with charging footpads.

EnGoPlanet says each footfall can generate between 4W and 8W, and because the Review-Journal isn't a tech publication, it's not asked how much battery charge you'll get out of that.

The Register is a tech publication and we can tell you the answer is "not much”.

If you're charging a battery, the spec that matters isn't watts – it's watt-hours (or, if you're trying to power a home, kilowatt-hours), and that's not a figure that EnGoPlanet provides for the footpads.

The Register asked for a watt-hour spec for the chargers, but didn't get a reply.

Let's imagine, however, that the street lights are rated at 10 watts, and have a daily duty cycle of 8 hours: you need 80 watt-hours of storage to get through eight hours of night.

How much might one footstep on the charger deliver?

If a footstep produces a “charge moment” of 100 milliseconds, it's quite a simple calculation – a maximum of 0.8 watt seconds per person passing by.

Divide that by 3,600 to turn seconds into hours – and you're down at 0.22 milliwatt-hours; and you'd need 360,000 steps to charge the battery enough to run the lamp overnight.

The busier parts of the Vegas strip could well clock up 360,000 steps a day. Or perhaps 3.6 million. Which would still leave pavement power well short of powering even a single block of Las Vegas Boulevard's lights.

As we said, it's not the fault of the Las Vegas Review-Journal – but other tech publications, who probably have access to both Microsoft Excel and Google Docs could have run the same calculation.

“Charge as you walk” is a gimmick, not a technology. ®