English Market Produces Energy With Kinetic Plates 404
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."
useful energy is not free (Score:5, Insightful)
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 (Score:5, Interesting)
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.
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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.
Re:useful energy is not free (Score:5, Interesting)
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 (Score:5, Informative)
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.
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So if I drive a hybrid, they're stealing my energy? Those bastards!
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Kinetic energy is actually half m * v^2 - but it has nothing to do with this. You don't need to strike the plates quickly; the motion downward can in principle be arbitrarily slow, just as if you wind a crank you don't necessarily have to wind quickly.
The energy that can be generated (or I should say captured) by the plate is limited by the energy lost by the car. The car loses potential energy, which as dna_(c)(tm)(r) says is m*g*h.
The only reason kinetic energy would play a role is if we consider the forc
Re:useful energy is not free (Score:5, Informative)
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Unless this whole exercise is done when vehicles break (speed bumpers?) then it is just a tax on those driving there.
Wow, that's one hell of a speed bump if it breaks cars. I'd sue if a speed bump broke my car!
Re:useful energy is not free (Score:5, Insightful)
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 (Score:5, Informative)
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 [guardian.co.uk] 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 (Score:4, Insightful)
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Maybe it's piezo-electric.
Re:useful energy is not free (Score:5, Funny)
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.
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Just to be informative, the average curb weight of US cars is 3,239 lbs, or 1,469 kilograms. So not quite two short tons (although you might make it with four average mid-westerners and their groceries on board), and definitely nowhere near two metric tons.
Re:useful energy is not free (Score:4, Funny)
Re:useful energy is not free (Score:5, Informative)
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.
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Re:useful energy is not free (Score:5, Insightful)
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.
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The only energy they can reclaim is that from going up the speed bump and that may be regained when the car goes down the other side of the speed bump (ie: car goes faster as it's downhill). It depends on the normal driving patterns of people (do they hit the brakes at the top of a speedbump?) and the efficiency of that downward energy reclamation.
Re:useful energy is not free (Score:4, Interesting)
They can get energy from the downward motion of the plate on the speedbump as the car drives over the top of it. The car is now a little lower, so that's energy it can't reclaim. This energy would be offset a little by the springs required to push the plate back up again.
They might also be able to gain energy by absorbing some of the forward motion of the car when it hits the speedbump. That would be more in keeping with the usual purpose of speedbumps. Now all we'd need is a speedbump that could smoothly absorb & convert most of the excess forward velocity of the car (in excess of the speed limit, that is), then we could install them in residential suburbs everywhere and power all the streetlights with them.
Hmmm (Score:2)
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They claim "The system, pioneered for Sainsbury's by Peter Hughes of Highway Energy Systems, does not affect the car or fuel efficiency", which is impossible if this system is capturing any energy at all.
Only true if your car has 100% efficient regenerative braking. The system is designed to be used in places where the driver will be breaking, and will apply an extra retardation force on the vehicle. In most cases, this will reduce the wear on the break pads by a very small amount, not steal any energy.
For example, the supermarket nearest to my father has a car park elevated to about the height of a second story building. At the bottom of the exit ramp there are traffic lights. When you drive out, yo
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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.
Where the hell would you get all those thimbles?
Re:useful energy is not free (Score:4, Funny)
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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.
Plenty of supermarkets ask customers to drive at a low speed in their car parks, and use speed bumps to encourage this.
How is this any different?
If you were going to slow the car down anyway, what does it matter if you get some additional use out of the kinetic energy the car loses?
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Nobody seems to have pointed out yet that Sainsbury's also sell fuel, so it's a win for them all round. The execs must have been pissing themselves laughing, "Hey, we've got this idea that we can pass off as 'Green Energy', and will mean our customers will be buying more petrol from our stores! Muaahahaha! Stick another swan on the fire!"
Re:useful energy is not free (Score:5, Informative)
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 (Score:4, Insightful)
Well maybe they can integrate it into the bazillion speed humps then. The energy may not be "free" but I certainly think all the arguments I've read on this article are ridiculous. The energy "Stolen" from drivers would be negligible, most of the energy would be coming from that wonderful thing called gravity!
How can energy come from gravity, other than building a one way system when things up high (say asteroids) and moved to somewhere low (say Sydney) and the potential energy recovered in the process.
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So your point is that it doesn't cost you much energy. My counterpoint is that then it doesn't provide them much energy -- unless energy out > energy in.
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...which can be used to do work. Otherwise you better hurry up and let the people over at the hover dam know their master plan isn't working.
This scheme is obviously sapping energy from your car, but if it could be done in a place where you want to remove energy from your car (i.e. when you're braking) it could be a net positive. That said - I don't think this is ever going to pan out.
On a somewhat related note, a while ago there was some work being done on placing a piezo insert into soldiers boots, and
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...which can be used to do work.
Of course. I'm merely pointing out that the energy comes from the car, nowhere else... "most of the energy would be coming from that wonderful thing called gravity" is just plain wrong.
This scheme is obviously sapping energy from your car, but if it could be done in a place where you want to remove energy from your car (i.e. when you're braking) it could be a net positive.
We already do that. It's called "hybrids", and they put the energy back where it belongs: back in the vehicle of the person who bought the gas. Once everyone's driving a hybrid, your fancy device to remove the energy from a braking car will no longer be productive. A hybrid braking on it would impart very little energy to it
Re:useful energy is not free (Score:5, Insightful)
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You said "push down the plate". And the end of the plate the car has to climb up the distance that it was pushed down. That climb will require a very small amount of gas in the engine, enough to create enough energy to climb out, plus friction losses and the inherint losses in the car engine. My guess is that this system will waste about double the energy a good thermal station would use to generate the same amount of electricity.
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Since this method converts potential energy into kinetic energy (the car pushing down), this means your car will be moving from a higher position to a lower position, losing it's potential energy.
Since your car has to drive out of the 'pit' it was lowered into, when the plate came down, your car has to expend the energy necessary to climb back out of that 'pit'.
So your car is directly providing the energy to power this plate system.
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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.
If the energy doesn't come from the car, where does it come from? You can't say it comes from gravity, that makes no sense. In order for gravity to do work, the object in question (the car) has to fall through some distance (work = force x displacement). In order to fall, it must have been lifted. How was it lifted? By the engine
Re:useful energy is not free (Score:4, Insightful)
So it'd be the same as dropping a giant stone on the plate? Free perpetual energy? No? Then where is the energy coming from? Remember those pesky laws that keep perpetual motion machine from working?
The energy doesn't come from gravity but rather from the potential energy of the car via gravity. The car has to gain that energy from the kinetic energy of it's engine somehow since nothing is free.
Let's say the plate is 1cm above the ground with no car on it. The car's engine exert extra energy to raise the car onto that 1cm plate. The plate then falls and takes that energy from the car by dropping it back to it's previous height. Had the plate not been there the car would not have used the gas needed to generate the energy to raise it 1cm against gravity.
Sort of sad how little physics is taught in school nowadays that people actually believe energy can come from essentially nowhere.
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Although I agree with you and all posters above, from what I get from the article this is just (an expensive ?) way to /create/ energy in an extremely inefficient way.
That said, I do wonder if it wouldn't be possible to somehow harvest some "free" energy from such a system, assuming the car-park is BELOW GROUND.
=> assuming the car-park is located below ground, the car will need to drive down a ramp anyway
=> if we replace that ramp with a series of 'steps' that are "pushed up" by an internal spring-sys
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I agree, it all comes down to how people brake and how much of the energy would have been wasted for braking anyway.
On the other hand hybrid and electric cars have regenerative braking so they even reclaim that energy. Given that they're becoming rather popular there may soon be very few places such a system has any real overall advantage.
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*sigh* Like I said before, it's not driving over the surface that generates the energy. It's changing you height compared to your previous surface. The plate is above ground level, regular pavement isn't. Going onto the plate costs extra energy that going down smooth pavement doesn't.
Even if there's a natural upward slope you still lose energy since there's no down slope that usually lets you regain the energy it cost your car to go up the first slope.
Re:useful energy is not free (Score:5, Insightful)
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.
Great (Score:2, Flamebait)
So when you drive in, it drains your battery to power their market. How the fuck is this 'green'?
If I had an electric car (Score:5, Funny)
lame? vampiring other people oil? (Score:2, Insightful)
is that energy extracted from the cars? then is not magically created, but just a inefficient way to suck energy from other people use of oil.
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Are those plates causing more oil to be consumed than would happen otherwise? Then it is not being magically wasted, but just a reasonable way of getting more energy out of the same use of oil.
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There is no magic involved. They deliberately create a piece of bad road to steal energy.
Of course this is a very small effect like a 'salami slice' financial scam, but it's still a scam.
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is that energy extracted from the cars? then is not magically created, but just a inefficient way to suck energy from other people use of oil.
It sounds to me (IANAPhysicist) like the energy is already being wasted, this is just using it. It harvests energy by pressing down on the plates, wouldn't the car driving over a strip of pavement use the same energy, except it wouldn't be reharvested at all?
Maybe not vampiring so much as collecting dropped change?
Maybe there's more friction moving over these plates though. In which case I'd say most of the drivers probably waste more energy driving around looking for parking spaces than they've lost to t
One Word. (Score:2)
Greenwash
it reminds me (Score:4, Interesting)
Supermarket, doofus (Score:4, Funny)
England market produces green energy ... Sainsburyâ(TM)s market of England has installed âkinetic energyâ(TM) plates in the parking lot of itâ(TM)s store in Gloucester.
What atrocious writing. Sainsbury's [wikipedia.org] is a supermarket.
Re:Supermarket, doofus (Score:5, Funny)
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The summary is actually better than the article. Did the Slashdot editor actually do some work or did the Examiner editor trash the writer's work? (Story was submitted by the writer.)
Punctuation got borked in the original quote, trying again:
Sainsbury's market of England has installed 'kinetic energy' plates in the parking lot of it's store in Gloucester.
This is so stupid it hurts (Score:3, Insightful)
it's not green (Score:3, Insightful)
TFA calls it a "green energy project". The type of people who think this is green energy are the complete f-ing morons that side track the rest of us from real viable energy advancements.
Further more, the TFA claims this will "lower the energy consumption of the market". At the inefficiency of this (which is already limited to being no more efficient than a car is itself), it will actually increase the energy consumption of the market.
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it will actually increase the energy consumption of the market.
But it will lower their electricity bill. And isn't that the most important thing?
Mmm?
Not energy generation, but still fine (Score:2)
Since people usually slow down anyway when they enter a parking lot, it makes more sense to convert the kinetic energy into something useful than have everybody just brake and convert it into heat.
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Let's pave a road with that! (Score:2)
Hey if you pave a stretch of road with that, make the energy harvested available from a rail along the road and connect the engines of electric cars to that rail, do you get cars that can travel forever without spending any energy? OMG GREEN HOLY GRAIL!!
Also, pre-emptive 'whoosh' sound for anyone who wouldn't get it.
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Isn't this just theft? (Score:2)
I mean if this is "free" energy, why not pave the streets with them?
Energy isn't free (Score:2)
Basically to generate 30KWH of power requires about 41HP. In this case, the power would come from the car pressing down on the plate, but the car must then use additional power to climb off of the plate. Cars are far less efficient at generating power than a dedicated power plant (ICE is at best around 24% efficient not counting losses due to the drive train, a power plant is typically over 40% efficient).
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Careful there, you're mixing energy (kWh) and power (hp).
30kWh is approximately 40.2hp *during an hour*
Granted, TFA and TFS didn't realize either that mentioning an energy without a time span is basically useless.
A nuke can produce 30kWh (in 50ms), so can my bicycle (in a month).
As mentioned in other posts, to produce 30kWh with 10% efficiency, they "just" need to steal 30l of oil during an unspecified amount of time.
Stupid technology + stupid submitters = Welcome to Slashdot!
Put plates at the bottom of an exit ramp (Score:5, Interesting)
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: (Score:3, Interesting)
Agreed. Sainburys seems to care about looking green, rather than being green. At their Kingston store the large Sainsburys sign has a smallish wind turbine and a solar panel attached to it. Trouble is the wind turbine is positioned between buildings, so it never gets a clear airflow,
Green if it's for parking (Score:2)
Then again, this is Slashdot, so someone's going to point out that people may not park right the first time, or that they may be driving across parking spaces to get to the other side instead of on the designated driving lanes, etc...I guess I'll shut up now.
Not to bitch and moan but,... (Score:2)
There's no such thing as free energy. It probably will cost cars extra to drive over the plates. That is, the 30 kWh come from fossil fuel. Way to go!
This reminds me a story used in Superman (Score:2)
This reminds me a story where the guy stole fractions of cents from each Bank Account. Nobody noticed !
Who is going to stop going to that market because of this highly imperceptible extra charge ? In this perspective it is ingenious. But can you imagine cities going this route in low speed limit zones ? Where will it stop ?
Energy saving wise, it is no good, gas motor would use that energy more efficiently, there is always a lost when you transfer one form of energy to another.
As for the guy who stole fracti
Energy vs Power (Score:2)
30 kWh is something, but how long does it take to collect that? 30 kWh for each car hardly succeeds!
It could be calculated for each year, maybe..
Anyway kWh is a measure of amount of energy, not power. If the plates power would be 30 kW, it would take one hour to collect 30 kWh. But 30 kW is way more than the car normally uses.
Just converting kinetic energy into electrical (Score:4, Insightful)
Probably 2/3 of the comments so far seem to think this is some kind of perpetual motion machine con. Those people should be embarrassed.
It's not. It's simple. It's just slowing cars by converting kinetic energy into electrical, instead of dissipating it as heat in the brakes or converting it to potential energy like a speed bump.
There was a discussion a while back, I think here on Slashdot, about a device that used a revolving door to generate energy. It prompted exactly the same comments. What these people didn't seem to realize is, revolving doors have brakes, and that device replaces the brakes. Same damn thing.
Do you really think the engineers who designed this device didn't think it through? This reminds me why it's never a good idea to discuss physics on Slashdot. I leave it to psychologists to explain why there are so many kneejerk contrarians.
Better uses of a good idea (Stairs)? (Score:2)
Shock Horror (Score:2)
Newsflash! Supermarket requires customers to pay for electricity that the supermarket uses!
Next you'll be telling me that shop assistant's wages are paid by a small portion of the money that we hand over at the till.
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Calling it "green" is wrong, true, but I fail to see why attempting to do some good with traffic that would still be going through there anyway is such a waste.
They aren't getting people to waste gas driving over these plates, people would be driving through that space ANYWAY, all they're doing is trying to harvest some energy from that traffic's passing. Its almost as ridiculous as all these people talking about "stealing" and "leeching" energy from petrol that would still be consumed ANYWAY. All that's ha
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All that's happening is some of the waste energy is being captured.
Its not waste energy if the original driving surface was smooth. This sounds like they have replaced a speed hump (which wastes energy) with a generator which recovers some of the energy wasted by the speed hump.
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The picture shows those plates as being... flat plates.
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Except they wouldn't have since energy has to come from somewhere and car's don't magically use it for no purpose. The energy they're using comes from raising the car's height (ie: potential energy due to gravity) to the height of the plate. Without the plate that energy would not have been used period as there'd have been no need to raise the car's height.
Had there been a natural downward slope present (say it was a speed bump, small hill, etc.) then the energy would have been partially reclaimed and conve
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Re:No such thing as free lunch... (Score:4, Insightful)
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Let's all point and laugh at the parent for his lack of understanding of physics and his lack of common sense.
Good. Now let's laugh at whoever modded him underrated.
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Man, did someone beat ya'll with the stupid stick today???
Allow me to ask you the same question. If there was any free energy to be made out of 'gravity' best believe it would be harnessed one way or another. Which is not. In this occurence the energy is wasted because the plates go down. The extra energy spent by the car is in going back up/going up in the first place.
Re:RTFA (Score:4, Informative)
Wait, so the plate drops down and it makes some power, how does your car get out of the now slight pot-hole? Why it has to drive forward, which (considering you are driveing up a very brief and very small hill) uses a tiny amount more fuel.
There is never, and WILL never be a free ride, all power comes from somewhere.
Re:leeching energy from cars (Score:5, Informative)
Re:leeching energy from cars (Score:4, Interesting)
rationalized leeching is still leeching. Perhaps you own a hybrid with regenerative brakes?
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Kudos for finding that link. TFA reads like a worthless press release.
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Bin the TFA
Is the bin next to the ATM machine?
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Are you alluding to RAS syndrome, perchance?
It's called PNS Syndrome in my neck of the woods, but yes.
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... unless the plates are only installed on the downramps, where they should be.
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Re:It's not generation (Score:4, Informative)
Technically, you're right. Practically, cars waste such vast amounts of energy that the energy drain for this thing (about equivalent to driving over a small bump) probably couldn't even be measured.
People don't understand just how much energy cars use, because car engines are typically measured in horsepower rather than in kilowatts. But it's the same quantity --- they're dimensionally equivalent. It's instructive to play with Google's units converter a bit: the Tata Nano, the world's cheapest car, has a crappy little engine producing 33 horsepower. That's 25 kilowatts, which is slightly more than the entire electrical supply to my house. A typical racecar produces about 400 kilowatts. A medium model wind turbine (with a 50m tower) produces about 600 kilowatts.
Cars waste 95% of gasoline energy when cruising (Score:5, Interesting)
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.
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That's the only problem data that I can see in my little experiment.
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So I don't see why I can't do what I did. I think it's completely valid.
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-Get to the top of the parking garage.
-Worker attaches giant bungee cord with peizoelectric transducers to rear bumper.
-Drive off edge.
-Bungee stops car just before ground, bungee cord stretches, peizoelectric transducer produces jolt of electricity.
-Driver gets charged for fun ride, car park gets some kilowatts.
-Profit.
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No, piracy is when you copy something without paying for it. This actually deprives someone of tangible goods, if in a tiny quantity. Don't fall for the "intellectual property" fallacy; there are analogues but it's not the same.
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Yeah, insignificant, by their own words...
They can't have it both ways, they can't claim they get a useful amount of power from it per car and at the same time say that amount is insignificant.
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Totally wrong.
The obtains energy from dropping heavy vehicles a very small distance, driving a plate as falling water drives a water wheel. Water is recycled to above the wheel by evaporation (solar power, of a sort), while the vehicles use engine power to climb back to their previous level.
This system steals a small amount of motor fuel from each passing vehicle.