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."
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:leeching energy from cars (Score:5, Informative)
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: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: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.
Re:useful energy is not free (Score:2, Informative)
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)
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.
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.
Re:useful energy is not free (Score:3, Informative)
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:3, Informative)
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, you need to keep your foot on the clutch and a little on brake. The clutch is fully depressed, so there is no energy going from the engine to the wheels (or vice versa). The brakes are partially engaged, so there is energy being turned from kinetic energy into heat. Add this system on the slope, and you can turn some of it into electrical energy instead.
The situation is different if your car has regenerative breaking, but the efficiency of most forms of regenerative breaking is proportional to the speed of the vehicle, while this system has no such limitation.
Re:Cars waste 95% of gasoline energy when cruising (Score:3, Informative)
That's the only problem data that I can see in my little experiment.
Re:useful energy is not free (Score:3, Informative)
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 force acting downward to derive from not just the weight of the car, but a component of its momentum - i.e., the car is going downhill and is being slowed down by *hitting* the plate, rather than smoothly riding over it.