Green Supermarket Makes Electricity from Passing Cars

JUN 17

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"With so many cars passing by a supermarket, I think this system works ..."

Written by Philip Proefrock on 17/06/09

We have been paying attention to the development of piezoelectric materials for electrical generation for quite a while. Using passing vehicles or even pedestrian motion and creating electricity is an idea that is being explored on a number of fronts.

And now, the first practical installation of this kind is in place at a supermarket in Gloucester, England, where "kinetic road plates" are being used to produce 30 kW/hrs of electricity per year (previously we reported this as 30 kW per hour, using the stat from the press release, but universal agreement is that is both impossible and nonsensical). The company's press release describes the process as a more physical process (plates are pushed down by passing cars to create rocking motions that turn generators) than a piezoelectrical one, but the broader concept of using transient motion to generate electricity is the same.

Of course, the store gets a much greater green energy benefit from customers who drive to the store, rather than those who walk or bike. The kinetic plates are only one of a number of sustainable building features of the new store. The building also has other features including utilization of natural light, rainwater harvesting, solar hot water, and a 50% reduction in electricity use compared to similar sized stores built before 2006.

via: Guardian

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Parking lots..
written by hyperspaced, June 17, 2009

I think parking lots thermal energy exploitation is the way to go. Ever stepped on a parking lot on summer bare-footed?

...
written by Bob Wallace, June 17, 2009

Can anyone flesh this idea out a bit?

Is energy being "stolen" from drivers? If all roads were to be built using these devices would gas mileage fall or is there simply wasted energy being harvested?

...
written by BBM, June 17, 2009

Can anyone tell me what "30 kW of electricity every hour means"?

net loss?
written by jay, June 17, 2009

Wouldn't the energy that the car loses to the plate have to be made up for by burning more gas? So the store get electricity, but at the expense of higher vehicle emissions.

The only way I can see this providing a benefit is if they're placed where cars will only be slowing down (i.e. approaching a stop sign).

JR
written by JR, June 17, 2009

it would waste just as much energy from the car as say driving over a speed bump, or driving over one of those pieces of plate steel used for construction purposes... negligible to the driver

-3

Negligible to the driver, but not to the environment
written by jello5929, June 17, 2009

This is stealing energy from the car to create electricity.

I can't think of a worse solution from a CO2 per watt perspective.

Now if somehow you could show that this energy is being shifted from brake pad heat to electricity, then maybe it's ok. But very likely this is just greenwash bull.

I call dodgy math.
written by Tom, June 18, 2009

The Guardian itself refers to kWh /hour (i.e. a kW on average). 30 kW is very large, and highly doubtful (*much* more likely, it was misquoted, and the actual figure was 30 kWh over the course of a year, which isn't really all that much, given the likely capital investment). To get an average 30 kW, one hundred 3,000 kg cars (for a total weight of 3,000,000 N) must push the "kinetic plates" an average distance of 1 cm every second (3,000,000 N * 0.01 m = 30,000 W = 30 kW). To get to the easier target of 30 kWh/year, 360,000 cars of the same weight would have to move the plate 1 cm a piece over the course of a year (that's 1,000 cars a day as opposed to 360,000 cars an hour). Compounding matters, of course are the inevitable thermal inefficiencies, which in the hypothetical have been assumed away.

Net Loss
written by Barney Sperlin, June 19, 2009

Yes, this is a net loss to the evironment. As energy is stolen from the car's motion (and would have to be made up via accelerator use) that energy isn't even harvested 100% by the store as thermal inefficiencies in the harvesting mechanism will reduce the input. Thus the store gets (steals?) less than the cars lose, so things are worse overall. The other ideas that the store uses sound alright, though.

RE: Net Loss
written by looselycoupled, June 19, 2009

Yes, this is a net loss to the evironment. As energy is stolen from the car's motion (and would have to be made up via accelerator use)

From a pure physics point of view you are probably correct, but you are not taking into consideration the other variables here.
These plates barely move and will probably create a negligible change in velocity to the cars driving over, and so there won't BE any increase in acceleration, particularly if these are placed in areas where cars are decelerating anyways, like near speedbumps or entry/exit points of a parking lot.

It would be interesting to see someone do a comprehensive review of these systems with all the different variables considered. Just running the math is insufficient because it doesn't account for the behavior of the vehicles.

Mistake
written by looselycoupled, June 19, 2009

Oh and one more thing:

where "kinetic road plates" are being used to produce 30 kW/hrs of electricity per year

Hank, I'm no scientist, but shouldn't that energy figure be 30 "kW-hrs" aka "kilowatts times hours" not "kilowatts divided by hours"

How much electricity to make and install?
written by Carl Hage, June 19, 2009

That's about $3.00/year of electricity-- way less than changing a light bulb, or replacing a desktop with a laptop, etc. It would seem to me that more energy than this in manufacturing, transporting, and installing these road plates would be consumed than would be returned over it's life.