“Be kind, for everyone you meet is fighting a hard battle” - Often attributed to Plato but likely from Ian McLaren (pseudonym of Reverend John Watson)

Friday, November 29, 2013

Ack! ANOTHER "capture the energy of walking/driving" system

I really don't want to turn this blog into a debunking site but some things just must be said. Here I described a completely impractical system for "capturing energy from pedestrians." And now we find an article from Science Daily about Mexican entrepreneur Héctor Ricardo Macías Hernández, pictured at left, who's developed yet another system for capturing energy from passing traffic - vehicular or pedestrian.

It apparently consists of a traffic wearing surface that sits five centimeters above street or sidewalk level. Passing traffic squeezes a bellows, compressing air into a tank (the linked article says "...where it is compressed..." but I don't imagine that that's accurate) from which it is expanded into a turbine to generate electricity.

Think about it. Your engine (either that of your vehicle or of your metabolism) is squeezing air into a tank. This work will reduce your gas mileage (or use your food energy) as your vehicle or your feet do the work of compression. There is no free lunch here. I'm surprised to see it in Science Daily which, although it is sometimes prone to exaggeration, usually doesn't publish nonsense.

There are no figures given, either in the Science Daily article or the articles linked from there, so I don't know what kind of traffic would be claimed to generate what kind of power. But I do know that, whatever the amount generated, it would be more efficient to burn natural gas in a turbine. Both vehicular internal combustion engines and human metabolisms are inefficient and compressing air is a lossy process. I'd love to see figures for this but it's yet another candidate for my prospective Greenwashing Hall of Fame. Yes, I know that the term "greenwashing" is typically applied to deceptive ad campaigns but I think it's equally applicable to deceptive products.

Update: In thinking about it, I suppose that one could concoct a scenario wherein a developing country with few energy resources would rather have the "rich" who own cars spend some of their energy (i.e., gasoline or diesel) purchase on providing energy for township than purchase natural gas, oil, or coal and then charge the poor residents for the electricity or pay for the fuel with taxes. But even there, better a gasoline tax with the proceeds used to pay for more efficient energy generation.


Ed Davies said...

Won't make sense in reality but at least in principle it could for bits of roads where cars are all slowing down anyway - approaches to junctions and so on - giving the effect of regenerative braking for non-EVs.

Rob Ryan said...

It's a good point Ed. Though the driver wouldn't get the benefit, energy that would otherwise be wasted might be put to use. Good thinking, whether practical or not.

rab said...

Amazingly, this was also posted to ScienceDaly. Either the proponent does not understand energy (that it is conserved, and that a force does not constitute an energy source), or he is fine with siphoning other people's resources as long as it is too small for them to notice. One could call it energy embezzlement.

Rob Ryan said...

rab, yes, I was very surprised to see it in Science Daily with no mention of the point you brought up. You've hit the nail on the head as far as what's happening, though Ed Davies brings up the possibility of only using it where a driver would be wasting kinetic energy via friction between rotors and calipers or shoes and drums while slowing down.