People Powered Checkout Lines at Sainsbury Supermarkets
Submitted by Shawn on Monday, 15 June 2009One Comment
Sainsbury supermarket in Gloucester, UK has installed ‘Kinetic Road Plates’. These plates produce 30 kW of energy an hour. This will power the store’s checkouts.
According to Sainsbury this is how the plates work:
- Vehicles drive over the road plates placed in the road surface of the car park
- Plates are rounded so that it does not matter which direction you travel over the ramp
- The vehicle drives over the plates which are pushed down by the weight of the vehicle
- This creates rocking motions under the road surface that turn generators
- The generators create energy which is captured, redirected back to the store, and used as power for the checkouts
The store is also harvesting rainwater to flush toilets and solar panels to heat the water during the summer.
Popularity: 20% [?]
The unit “30 kW of energy an hour” is bunk. A watt is a spot, instantaneous power reading, not a measurement of energy. Energy of course is measured in kilowatt-hours (kWh).
It clearly means 30 kW average power. If you prefer to read it as 30 kWh an hour, that would still represent an average power level of 30 kW.
This power level is hard to believe. Suppose that they had two plates, and that a vehicle was actually driving over them and inputting power on average, 5% of the time per plate, i.e. 10 % of the time overall. To generate 30 kW on average, that would mean that each motor car had to input 300 kW (nearly 400 horsepower – as much as a very expensive supercar running flat-out !) as it drove over the device. That completely fails the common sense test – a motor car pootling around a supermarket car park is probably only using 5 horsepower (3 kW) if that, from its engine. If you drop the road underneath the back of the supercar to such a degree that the driver of the supercar would need to be pushing on the accelerator hard enough to get 400 horsepower from the engine (nearly full power for a smaller car), to accelerate up the hill that has just been created, the car would certainly stall and roll back as the driver couldn’t possibly react fast enough, even if a gear change wasn’t needed. It would also come as a nasty surprise and possibly injure some people.
Also the scheme clearly cannot be viewed as green. Petrol engines are not particularly efficient, and moreover if rather incidentally, the fuel is very heavily taxed. Making motorists use more petrol driving up artificial dynamically-created slopes is very un-green indeed. It’s not like these are instead of any other kind of speed bump, as Sainsbury’s stores never have speed bumps – they’re not popular.
Also, returning to the 30 kW figure, if there were 20 tills and it was just enough to power them, that would imply an average power consumption per till of 1.5 kW. Even allowing for the power needed to drive one or sometimes two intermittent belts per till, I’d estimate 100 watts or so per till, unless Sainsbury’s tills have some dreadful design fault.
So, 0 out of 10 for technical literacy, and 0 out of 10 for credibility.