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dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Sun Dec 18, 05 4:35 pm Post subject:

Milo -
I hope you noted my positive suggestions towards the energy cost of traffic lights.
These ramps are a daft solution to an essentially non-existant problem, and are likely born out of a lack of understanding of the basic physics/science/engineering.
These things would be an expenditure of quite a lot of money, specifically in order to increase petrol/diesel consumption.
Bad idea.
If you really want to see the promoter's website, its linked at the right hand side of the BBC page https://www.hughesresearch.co.uk/

If we can get beyond the concept that *all* energy used for personal transportation is wasted, and assume the journey is needed, the driver reasonably skilled, the car appropriately sized and well maintained, etc...
We eventually get to the point when we can say that the only time that energy is really and truly being *wasted* is when the vehicle's kinetic (movement, proportional to the speed squared) energy is dumped as heat energy during braking.
{Incidentally, this leads to the realisation that much of the skill of (fuel) economical driving is to *minimise* the use of the brakes, by thinking ahead to avoid unneccessary acceleration and pre-emptively lifting off early instead of braking hard and late.}
Causing traffic to slow down suddenly (dumping kinetic energy to brake heat) is bad for fuel consumption. And pollution. Hence enlightened traffic management is about keeping the vehicles movng steadily (not braking and accelerating) and maintaining a safe and appropriate speed.

However, as TD notes, there are other ways to absorb the kinetic energy and slow the vehicle, rather than simply dumping it as frictional heat.
Today, you can buy "hybrid" cars from Honda and Toyota that slow the vehicle by 'engaging a dynamo to charge a battery'. When the car accelerates away, the battery-stored energy drives an electric motor to return the energy to the form of kinetic (movement) energy.
That is a simplification of how these hybrids work. But its broadly true.
Other systems have been tried, including using hydraulic chargers/motors and storing the energy in a spinning flywheel.
I think that the electric ones are the only ones that have made it to the point of going on sale.
The problem that TD notes is that this extra kit (motors/chargers and batteries or their alternatives) adds to the weight of the vehicle (batteries are not light) which tends to make it more thirsty on fuel, and carries additional resource costs.
{Side note - a hybrid engine permits the vehicle to be more efiicient, but it doesn't per se make it an efficient vehicle...}

One technical problem with today's hybrids is that today's batteries cannot be fully charged really, really quickly - like during a few seconds of braking. So some, but nowhere near all, of the braking energy wastage can be avoided, and only some of the energy can be reused.
In the near future, I expect Nanotechnology batteries (prototypes already demonstrated) to be able to absorb much more of the braking energy, because their Nanotech design permits much faster charging.

Milo

Joined: 16 May 2005
Posts: 342
Location: Oop North-ish.

Posted: Mon Dec 19, 05 1:28 am Post subject:

I hope you noted my positive suggestions towards the energy cost of traffic lights.

Yes.

These things would be an expenditure of quite a lot of money, specifically in order to increase petrol/diesel consumption. Bad idea.

You've lost me, (it's not difficult!), but you're surely not saying that these ramps might be put in place in order to increase fuel consumption.

If you really want to see the promoter's website, its linked at the right hand side of the BBC page https://www.hughesresearch.co.uk/

Course I do, but it won't open at present.

the only time that energy is really and truly being *wasted* is when the vehicle's kinetic (movement, proportional to the speed squared) energy is dumped as heat energy during braking.

{Incidentally, this leads to the realisation that much of the skill of (fuel) economical driving is to *minimise* the use of the brakes, by thinking ahead to avoid unneccessary acceleration and pre-emptively lifting off early instead of braking hard and late.}

Indeed, and so with adequate warning one can take ones foot off the accelerator and without braking reach the right speed for driving over the ramps.

Causing traffic to slow down suddenly (dumping kinetic energy to brake heat) is bad for fuel consumption. And pollution. Hence enlightened traffic management is about keeping the vehicles movng steadily (not braking and accelerating) and maintaining a safe and appropriate speed.

No probs with that. And I take your points about the hybrids, but can't (yet) see their relevance to the ramps.

Treacodactyl
Downsizer Moderator

Joined: 28 Oct 2004
Posts: 25795
Location: Jumping on the bandwagon of opportunism

Posted: Mon Dec 19, 05 7:11 am Post subject:

Milo wrote:

Indeed, and so with adequate warning one can take ones foot off the accelerator and without braking reach the right speed for driving over the ramps.

No. You should never tackle a ramp at speed so a good driver would slow and then *drive* over them. You also seem to forget that there is likely to be a stationary car infront due to the concept of queues at traffic lights.

I mentioned hybrid cars as an example of a *better* way to harness excess braking energy.

dougal

Joined: 15 Jan 2005
Posts: 7184
Location: South Kent

Posted: Mon Dec 19, 05 12:08 pm Post subject:

dougal wrote:

These things would be an expenditure of quite a lot of money, specifically in order to increase petrol/diesel consumption. Bad idea.

milo wrote:

You've lost me, (it's not difficult!), but you're surely not saying that these ramps might be put in place in order to increase fuel consumption.

The ramp takes energy from the car.
The car's energy comes from petrol/diesel.

The only way the ramp can take energy from the car *without* increasing fuel consumption is if the ramp ***substitutes*** for the car's brakes to slow the car.
The actual slowing down must be achieved ***by*** the ramp itself (NOT slowing down **for** the ramp).
**Any** other energy taken by the ramp is achieved at the direct cost of additional fuel consumption.
**Any** additional slowing beyond what the traffic would do without the ramp costs extra fuel.
**Any** slowing specifically *for* the ramp, wastes additional car fuel energy to the brakes, increasing the fuel consumption while generating no extra energy in the ramp - ie it reduces the efficiency of generation.

The ramp energy comes either as a *substitute* for brake heat or from extra fuel consumption.
There is no such thing as a "free lunch".

milo wrote:

I take your points about the hybrids, but can't (yet) see their relevance to the ramps.

The ramp claims to reclaim some of the energy 'wasted' on braking, but only at particular points on the road network.
'Hybrid' vehicles do reclaim some of the energy that would otherwise be 'wasted' on braking - every time they slow down, everywhere they go. And do it today.

I believe that the tiny amount of energy such a ramp might generate would be achieved at the expense of the wastage of lots of *additional* petrol/diesel.
As Treacodactyl noted, the Hybrid loses some of its extra efficiency by carrying around batteries and motor/generator. However, the practical results that such vehicles give show that its well worthwhile to transport the extra kit. They *do* achieve better mpg - they *are* more fuel efficient.

I strongly doubt that these ramps would generate much power - and lets talk kWh 24/365 rather than instantaneous kW rates as a vehicle crosses the ramp - and what little was generated would be at a cost of additional fuel consumption, making the power generation grotesquely inefficient.

jema
Downsizer Moderator

Joined: 28 Oct 2004
Posts: 28234
Location: escaped from Swindon

Posted: Mon Dec 19, 05 12:31 pm Post subject:

Coming in late here, minute I started reading this thread though I thought doh basic physics "conservation of energy" someones trying to get something for nothing and that simply does not work

I am trying hard to convince myself that the criteria so eloquently explained by Dougal that the ramp must substitute for when a car would be breaking, can be met in any real and significant way

I can think of some roundabout approaches on dual carriage ways where it might just work. But i'd need some serious convincing even there.

cab

Joined: 01 Nov 2004
Posts: 32429

Posted: Mon Dec 19, 05 12:47 pm Post subject:

Apologies for taking this all in a rather light hearted way, but I'm reminded of this article here:

https://www.sullivan-county.com/id3/thermodynamics.htm

This is basic thermodynamics. Unless the energy here is being gained by using the cars deceleration (so you'd put a device in a location where cars are slowing down anyway, and take a cut of that reduction in the cars momentum), and it doesn't loook like it really is, then this device is merely a way of using some of the cars fuel to power the lights.

If you're going to have traffic calming measures anyway (there's an oxymoron if ever there was one!) then by all means get some of the wasted energy out of them. But there's no such thing as a thermodynamic free lunch!

Milo

Joined: 16 May 2005
Posts: 342
Location: Oop North-ish.

Posted: Wed Dec 21, 05 12:44 am Post subject:

Never while posting on any topic on any forum anywhere have I felt so perplexed and apparently misunderstood (and been almost accused of being a crap driver), but I'm still of the opinion that a competent driver can, without braking, slow his vehicle to a speed suitable for driving over ramps (whatever they might be powering).

Locations abound where a reduction from 40 to 30 and back to 40, or from 30 to 20 and back to 30mph in an urban setting is entirely appropriate and I don't expect it matters greatly if the ramps are not located right alongside the equipment requiring the electrical power.

Treacodactyl
Downsizer Moderator

Joined: 28 Oct 2004
Posts: 25795
Location: Jumping on the bandwagon of opportunism

Posted: Wed Dec 21, 05 6:59 am Post subject:

Milo wrote:

Never while posting on any topic on any forum anywhere have I felt so perplexed and apparently misunderstood (and been almost accused of being a crap driver)

May I suggest it might have something to do with being too idealogical without thinking through the facts? When it was first pointed out that the laws of physics meant the energy would come from fuel you appeared to try and say the laws could be changed.

Going back to the ramps, I bet if you ask a driving instructor what you should do with a speed bump they would say slow right down and drive over it. I suppose you could train drivers to no do this on these new ramps but I doubt I would listen as what happens when they stop working? Either through a fault, debris lodge in them or a vandal wedging something in them? Hitting one at 40mph that stay up who knows what may happen.

Behemoth

Joined: 01 Dec 2004
Posts: 19023
Location: Leeds

Posted: Wed Dec 21, 05 9:47 am Post subject:

The only way I could see these wroking is in sequence like the 'speed cushions' we seem to have a lot around here. These you can drive over without discomfort if you 'hit' them at under 30mph and straight. Put a sequence of these in along a road and you limit the max speed to 30 without any braking. Any faster and you start to get jarred and enter a stop/start way of driving. However, I'm sure it would take some driver education to convince us that you shouldn't slow down when confronted with a metal ramp in the road.

sally_in_wales
Downsizer Moderator

Joined: 06 Mar 2005
Posts: 20809
Location: sunny wales

Posted: Wed Dec 21, 05 9:52 am Post subject:
I'm still disappointed that it doesnt seem to work When I read it I was under the impression it was the weight of the car passing over the splunger, rather than the forward momentum that worked the uppy downy thing that generated the power. However, physics was never my strong point

Behemoth

Joined: 01 Dec 2004
Posts: 19023
Location: Leeds

Posted: Wed Dec 21, 05 9:54 am Post subject:
Physiscs was made up by a Yorkshireman - bascially you don't get owt f' nowt.

Treacodactyl
Downsizer Moderator

Joined: 28 Oct 2004
Posts: 25795
Location: Jumping on the bandwagon of opportunism

Posted: Wed Dec 21, 05 10:19 am Post subject:

sally_in_wales wrote:

I'm still disappointed that it doesnt seem to work

When I read it I was under the impression it was the weight of the car passing over the splunger, rather than the forward momentum that worked the uppy downy thing that generated the power. However, physics was never my strong point

It is, but for the weight of the car to press down something has to power the car up onto the ramp in the first place. If the car is almost stationary, for example in a traffic light queue, then you would have to use extra revs to get onto the ramp.

I'm sure there's more to the story than the article though. i.e. reasons for the ramps that's not been mentioned.

cab

Joined: 01 Nov 2004
Posts: 32429

Posted: Wed Dec 21, 05 10:32 am Post subject:

Milo wrote:

That, depending on the location, can be true.

Quote:

Locations abound where a reduction from 40 to 30 and back to 40, or from 30 to 20 and back to 30mph in an urban setting is entirely appropriate and I don't expect it matters greatly if the ramps are not located right alongside the equipment requiring the electrical power.

But the car is still losing kinetic energy, it is slowing down. To speed up again costs more energy.

If the ramp is the causative agent of slowing the car down, then it might be a good way of getting energy out without waste. That would mean (1) rapid, uncomfortable deceleration, (2) damage to the car, and (3) absorbing one hell of a shock.

Milo

Joined: 16 May 2005
Posts: 342
Location: Oop North-ish.

Posted: Thu Dec 22, 05 12:38 am Post subject:

Quote:

The only way I could see these wroking is in sequence like the 'speed cushions' we seem to have a lot around here.

That's how I imagined these to be.

Quote:

These you can drive over without discomfort if you 'hit' them at under 30mph and straight. Put a sequence of these in along a road and you limit the max speed to 30 without any braking. Any faster and you start to get jarred and enter a stop/start way of driving.

Sounds just fine to me, IF located within a stretch of road where it makes sense for the speed to be 30, (or less).

The photo with the Beeb's article is from a curious angle. From the diags on the inventor's website the burmps do appear to be small and gentle.

Rob R

Joined: 28 Oct 2004
Posts: 31902
Location: York

Posted: Thu Dec 22, 05 12:57 am Post subject:

I think perhaps there is a point being missed on this article- having looked at the article again, the point of the ramps seems to me not to be a way of reducing energy wastage or reducing CO2 emissions from power generation but rather it is about generating *free* power for the local authorities. Or to put it another way, getting the motorist to pay to power the street lights & signs (despite them trying to deny this in an FAQ).

Basic physics shows that energy is constant- it can neither be created nor destroyed, only its form can be changed, not its existance. The clever bit of this invention seems to be in basic economics, however, as a cost cutting exercise for the authorities.

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