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