English Market Produces Energy With Kinetic Plates

Johnathan Martinez writes "Sainsbury's market in England has installed 'kinetic energy' plates in the parking lot of its store in Gloucester. The plates are an experiment with a newer energy producing technology. The plates create as much as 30 kWh of energy as cars drive over them. The weight of the cars puts pressure on the plates creating kinetic energy to run a generator. The current is used to power the store and will lower the energy consumption of the market."

Comments

useful energy is not free

[seanadams.com]

This is just an gas powered electric generator, the likes of which rube goldberg would be proud of. You'd be better off siphoning a thimble of fuel from each car, selling it, and using the proceeds to buy electricity from the utility.

Re:useful energy is not free

[fractoid]

Not to mention that's a crap ton of energy per car:

The plates create as much as 30 kWh of energy as cars drive over them.

30 kWh is 108 MJ. Say your car weighs 2 tons, well that's 18.1 kN of force it exerts on the ground. So your car would have to push one of these plates down a total of 5.9 kilometers to generate that much energy. Assuming that the plate only moves an inch, that's 238 thousand car/plate crossings to generate the quoted energy.

Re:useful energy is not free

[MichaelSmith]

This is just an gas powered electric generator, the likes of which rube goldberg would be proud of. You'd be better off siphoning a thimble of fuel from each car, selling it, and using the proceeds to buy electricity from the utility.

True but if you are going to build speed humps and waste energy that way, this may make sense.

Re:useful energy is not free

[MichaelSmith]

You are not stealing any energy from the car at all. This argument is ludicrous. It is using the force of gravity to push down the plates.

The car has to climb on to the plate. It uses energy to do that.

Re:useful energy is not free

[Kickboy12]

Another Point: You ever driven in a parking lot? Count the number of speed bumps you go over. I wonder how "fuel" the stores are "stealing" from you by making you drive slow over these bumps. Replace those with plates. Might actually get some energy while making people drive slower at the same time. What a concept!

Re:useful energy is not free

[carou]

Perhaps they only install these at the entrances to the car park, where you expect everybody to be slowing down - the excess kinetic energy might as well be siphoned off somewhere useful rather than being wasted as heat in the brakes.

However, I agree with your analysis that the numbers, as presented, make no sense (and the picture with illustrates the article is only a few mm thick, so 238,000 crossings is probably a rather conservative estimate). Another article on the topic says "The kinetic road plates are expected to produce 30 kWh of green energy every hour" (so that would just be 30kW, then) but I can guarantee you that a supermarket is not going to get a quarter of a million visitors in an hour (or to put that another way, more than 60 every second).

It's all just meaningless posturing, and it takes attention away from anything which might actually be useful. Any journalist reporting this as a green initiative ought to be ashamed of themselves.

Re:useful energy is not free

[terminal.dk]

If you put the plates on a downhill ramp, then the car need to move vertically anyway.
So instead of having to use the brakes to convert energy into waste heat, they can convert it into electricity.

A Parking house with multiple levels would be perfect if there are different lanes up and down. Or other descending roads.

We have e=m*v^2 - So the faster the plate can be pressed down, the more enery we will get, but there will also be some impact force. So the number can be much lower.

Re:useful energy is not free

[umghhh]

There is no magic there - energy comes from somewhere. Unless this whole exercise is done when vehicles break (speed bumpers?) then it is just a tax on those driving there. It may be small but it does not mean it is not there.

Re:useful energy is not free

[dna_(c)(tm)(r)]

If you put the plates on a downhill ramp, then the car need to move vertically anyway. So instead of having to use the brakes to convert energy into waste heat, they can convert it into electricity.

Then it would be more efficient to build a conveyor belt or a lift for descending cars only... But still more efficient is to cut of fuel - all modern cars do that - AND use some regeneration - some more expensive/advanced cars do that already.

BTW, e=m*v^2 has nothing to do with it, that's just the kinetic energy stored in a moving body, it can be converted to potential energy and back, as in a pendulum. What you are looking for is force x distance: F*s (or mass x gravitational constant x vertical distance: m*g*h)

The original idea is silly from a thermodynamic point of view, but bright from ecological theatre point of view, I think.

Re:useful energy is not free

[Viol8]

You're wasting your time trying to explain this I'm afraid. Some people are so utterly clueless when it comes to basic physics that it would be funny if it wasn't such a sad reminder of the state of schooling these days.

Re:useful energy is not free

[siloko]

Say your car weighs 2 tons

Say that as loud as you want sunshine but the average car weight over here (Europe) is 1175 Kg, compared to 2000 Kg in the US. Of course this only adds weight to your argument . . .

Sometimes I even crack myself up.

Re:useful energy is not free

[Peet42]

The numbers are bullshit, but so are all these suggestions that the plates are magically causing MORE gas/battery power to be wasted than would happen otherwise.

Add together the energy required to lift the weight of the car up onto each plate, then back up from the level of the plate to street level after the plate has sunk down - you'll find it's more than the car would have used traveling the same distance on the level. They're effectively making each customer pay a levy to use their checkouts, yet making themselves look "greener" by shrouding it in misdirection.

Re:useful energy is not free

[Fzz]

The company that makes this system has some videos that explain how it works.

From their FAQ:

Q1. Doesn't the ramp just steal pennies from our petrol tanks?

A1. The ramp is designed to be situated in parts of the roadway where vehicles are having to slow down, for example on downhill gradients, when approaching traffic lights or roundabouts as well as replacing sleeping policemen and traditional traffic calming measures. In the these situations, the kinetic energy of the car is being dissipated into heat (i.e. through the braking system) anyway; the ramp at this point scavenges a degree of kinetic energy as the car passes over it, but this is far less than is lost through other mechanisms.

Seems to me like it probably works if it's deployed in the right place. So the idea seems OK.

But what about the numbers? The website claims it can generate 5-10kW. Looks like at least one of the plates moves about three inches (7.5cm). So, lets use their numbers:

10kWh = 36MJ. Taking your 18.1kN force from your 2 ton car, that requires a distance of about 2km. 2km / 7.5cm = 26700 crossings in that hour. Thats 7 per second. No, still doesn't add up.

Best you could reasonably hope for is a car every two seconds. That would give a distance of 7.5cm * 1800 = 135m in an hour. Your 2-tonne car falling 135m would generate 2.4MJ in an hour, so that's about 670W average. And that's assuming 100% efficiency. Likely this thing can power a streetlight or two.

But is it cost effective? Lets say it operates at that rate for 10 hours a day (pretty optimistic for a car park, but maybe on a busy road). 670W gives 6.7kWh per day, or 2400kWh per year. Electricity costs maybe 7p/kWh, so that's GBP171 (or $270). No, this doesn't seem cost effective anywhere where you can get mains electricity.

If I had an electric car

[MichaelSmith]

...I could put these in my driveway, use it to charge the car and never have to buy energy again!

Re:leeching energy from cars

[jginspace]

It's not leeching. The cars are slowed down at the point at which the cars should be slowing down anyway - they're coming into the car park. The 'kinetic energy' device helps where the vehicle's brakes would normally be doing all the work. Bin the TFA, see this insightful article from yesterday's Guardian.

Re:leeching energy from cars

[nadaou]

rationalized leeching is still leeching. Perhaps you own a hybrid with regenerative brakes?

Put plates at the bottom of an exit ramp

[SomethingOrOther]

For those who are rightly saying this energy isn't free...
If the plates are positioned at the bottom of a downhill exit ramp, they will aid drivers braking, prividing kinetic energy without "stealing" drivers fuel. Somehow, I doubt this is where they will be positioned though :-)

(Incidentally... a similar idea was to build tram / light-rail stations on the top of small hills. Thus gravity assists the train in braking and accelerating away from teh station)

Oh and Sainsburys is a British Supermarket, not an English Market..... Big difference !

Re:Supermarket, doofus

[BigZee]

Quiet true. And it also doesn't have a parking lot either, it has a car park.

Cars waste 95% of gasoline energy when cruising

[slashbart]

I once measured my cars efficiency (an old Renault 5).
I drove 100 kph (28m/s) on a flat freeway, with no wind, and set the gears in neutral. It took the car about 30 seconds to slow down to 90kph (25m/s). The car weighs about 900kg.
So we have E0=0.5*m*v*v = 353kJ and E1=281kJ. The car lost 717kJ in 30 seconds or 2.4kW
So it takes just 2.4kW to keep a small car cruising at 100kph on a freeway. The stated gas consumption of that car is about 1 liter/18 km at 90 kph so 1.3 ml/second of gasoline. Gasoline has ca 32MJ/l energy content, so 1.3ml/s is equivalent to 44kW.
The system efficiency of a car cruising on a flat freeway is about 5%!
Do the experiment yourself and see what numbers you come up with. It's also a really good highschool experiment.

Re:No such thing as free lunch...

[BeardsmoreA]

No. But afterwards, if you didn't give the engine any gas during the process, it would be moving slower. As lots of people have tried to point out, this might be desirable (see speed bumps). If the driver is just going to accelerate back to speed however, you have gained nothing.