Sainsbury's nicking petrol off customers?

adouglasmhor

Lemonade_Pockets wrote: »

. Therefore the only bit that is doing the work is the gravational element in the middle.

Yes and it is doing the work of converting the kinetic energy of your car (made from your fuel expenditure), into the kinetic energy of the gravitational drop, it is not producing energy from nowhere. So what exactly is the point of you posts?

MRab2

Lemonade_Pockets wrote: »

So in a effort to articulate my point better. The energy expended before and after the pad would of either been expended anyway or is very negligible. Therefore the only bit that is doing the work is the gravational element in the middle.

Negligible multiplied by a million cars isn't neglibile anymore, but that's not important right now.

The device is converting kinetic energy from your car into electricity. Can we agree on that?

To be green a significant majority of the cars passing over it would have to be a braking (whats size of majority is dependent on the efficiency of the pad, which I don't know know, but could take an educated guess). For every car that stops on it, or accelerates through it (as might happen if the pumps are busy), then several cars MUST brake as they pass over it. If not then the device as actually causing more pollution, though Sainsburys saves money wither way

prowla

Lemonade_Pockets wrote: »

I'm not disputing whether the car will use any extra energy up going over one of these things. Although it would be negligible to anynormal human being, unless you put chocks in your springs and pump your tyres up to 50psi, tape over all the panel gaps on your car to save money as well! What i'm saying is that the energy used by the car is not powering this pad, the two energy equations are not related.

Absolutely they are related; the energy that moves the pad comes from the car; the energy that moves the car comes from the petrol.
To say otherwise is to say that the pads would generate energy without the car being there.
And you acknowledge that the car would use extra energy to go over one of the things; that is the energy that the car gives to the unit.

hundredk wrote: »

This is not free because you would only be freewheeling as a result of the car having momentum and that momentum is from using fuel to gain speed in the first place.

Sorry, I meant free as in if you had previously been freewheeling to get there anyway and it was just before where you would stop, so putting the device in the way just meant you had to use the brakes marginally less than before.

freebie-fan-jen wrote: »

surely if you waste petrol going up this monster ramp you can save energy by rolling off it again?? therefore it wouldnt make a difference at all!!

silly thread lol x

Unfortunately car engines are very inefficient (that's why they get hot - all of that heat is energy wasted), so the cost of going up is not outweighed by the free ride down the other side.

MRab2 wrote: »

You're missing the point. The effect on an individual motorist will be high on zero. Certainly not enough to be noticeable, but since Sainsburys is using this to bolster their green credentials you need to look at the overall effect.

It's hardly a green idea if in order to save themselves 1000kwh off their electricity bill they're *stealing* 2000kwh from motorists.

Just so - unless it is in a place where the energy would simply be wasted (eg. going down an incline where you have to brake anyway), they will be recovering less energy in total than the total expended by all of the cars. In our Sainsburys fuel station, the pumps are on an uphill slope, so you would have to rev your car to go over the device.

pault123

Would you use up more kinetic energy opening the door to the petrol station to pay for the fuel or going over the bump - in terms of KJ?

Or if its an automatic door you would have to slow your pace down while it opens and then speed up again. Would an automatic door be better than a manual door then for kinectic energy consumption?

How much % of my weetabix would I waste having to negate my way through the automatic door?

Am I getting more bang for buck from my weetabix on a manual door on the offchance someone could hold it open for me?

Would weetabix in my fuel tank be a better alternative to save money on petrol and not have to go over the Eco bump in the first place?

mikey72

I love these arguements, MSE forum paying Sainsburys electric bill, but it's ok as it's only a little bit each.
If we asume, for the same of the aurguement, they are taking energy from cars, from the picture it's not near the pumps, but I agree you can see them in the background. I've never coasted into a petrol station after making a turn. I slow for the turn, then accelerate down the road. Sainsburys are quoted as being green and saving energy, by using petrol, to reduce their bills. My car runs at about 70% efficiency at best. It would make more sense to give them a fiver a year to pay their bill directly, as the power station is much more efficient than my vechicle, at generating electricty.
On the other hand, if the people claiming it's not using petrol are right, lets have them in highstreets, motorway sliproads, traffic lights everywhere, and the energy crisis will be over.

AHAR

mikey72 wrote: »

My car runs at about 70% efficiency at best.

70%!? What are you driving?
A quick bit of searching around suggests ~20% is typical.

Bongedone

A power station is also a lot lower than that 70% figure.

mikey72

AHAR wrote: »

70%!? What are you driving?
A quick bit of searching around suggests ~20% is typical.

Yes, either a typo, or I'm rocket propelled.

Money_Grabber13579

mikey72 wrote: »

I love these arguements, MSE forum paying Sainsburys electric bill, but it's ok as it's only a little bit each.
If we asume, for the same of the aurguement, they are taking energy from cars, from the picture it's not near the pumps, but I agree you can see them in the background. I've never coasted into a petrol station after making a turn. I slow for the turn, then accelerate down the road. Sainsburys are quoted as being green and saving energy, by using petrol, to reduce their bills. My car runs at about 70% efficiency at best. It would make more sense to give them a fiver a year to pay their bill directly, as the power station is much more efficient than my vechicle, at generating electricty.
On the other hand, if the people claiming it's not using petrol are right, lets have them in highstreets, motorway sliproads, traffic lights everywhere, and the energy crisis will be over.

Yep but the problem with that is that they'd only work provided you had to slow down anyway. For normal driving conditions, they would be very inefficient.

mikey72

That's been my point all along - it's a very inefficient way to make electricity from fossil fuel, then dressed up as a green solution by their pr to make it an even worse concept.