I was thinking about this on the way to work this morning.
Leaving aside for the moment the issue of resources required to create a new car, and how to deal with the nasties that live in batteries, and the issue of how the electricity to recharge the batteries is generated, isn't it a bit mad to put extra weight in a car? That gives the engine more work to do, which means it will use more fuel. How can that be "green"?
I think the idea is that an internal combustion engine can be made to work as efficiently as it can (...another topic of discussion...) at a set speed/load, which isn't what you do currently accelerating through the gears/braking/ etc etc. So overall, an IC engine working at constant load charging batteries and running and electric drivetrain may still be more efficient overall - but is not optimal, just a bridging technology with the infrastructure we currently have.
EDIT: A similar technology is used for ships, whereby an industrial gas turbine which is relatively efficient at a given load/speed is used to drive a generator, which feeds an electric motor. There are other issues here around packaging/control of the ship/etc etc, but overall thermal efficiency is a driver too.
Ok. Here's the short answer, let me know if you want the long one 
In most 'hybrid' cars, having a petrol engine coupled with an electric motor allows the petrol engine to be used only when it's most efficient to do so. So:
1. When you are going very slowly, it's on electric only.
2. When you are going at a reasonable pace, you can siphon off energy that would be wasted and put it into the battery
3. When you are cruising, the electric motor doesn't contribute
4. When you boot it, the electric motor provides extra power
5. When you brake, the motor works as a generator and recharges the battery some more.
You don't have to add electricity from a power station - all the electricity to charge the battery gets recovered from places where it's wasted in a normal car.
Bristolbiker is talking about series hybrids (as opposed to parallel hybrids which are in most hybrid cars), which are used in trains, boats and things, for a variety of reasons.
Having just bought a used car and looked into this, the thing that gets me is the fact that the quoted fuel economy for something like a Prius is still worse than a modern diesel engine.
Does rather beg the question, what's the point?
Well the older model Prius came out in 2003. It's good for 60mpg in normal driving, and is larger than a Golf. It's also petrol, which is cleaner and often cheaper. At the time I got mine, in 2006, nothing of its size had anything like its CO2 emissions and could not match consumption either; only tiny little Aygos etc could come close.
Now, you can get bluemotion/eco-tec diesels and so on which, on paper, are more economical. Still only a few of them are lower CO2 emissions than the OLDER mkII Prius.
However the new mkIII Prius gets 70+ mpg, is bigger still, faster and has the lowest CO2 emissions of ANY car, even the tiny ones, and is more economical than most of the bluemotion specials, not to mention more powerful. And being petrol again it's way way cleaner on other emissions like NOx (responsible for smog and poor air quality) and smoke.
That's the point
I'd have a Volvo V50 drive thanks. 70+mpg also, less environmentally harmful to manufacture than a Prius, and more useful space in the car. Probably uses less consumables such as tyres and brake pads etc because of the more reasonable weight. Volvos last a long time as well, which helps.
To me the Prius is cynical solution aimed at those who don't fully think it through. Sorry molgrips. If you really care that much cycle to the shops and run a diesel super mini.
Yeah but the prius looks **** minging! 
Molgrips - ok, I stand corrected 
Samuri - you're not wrong, although the latest model is a little better.
has the lowest CO2 emissions of ANY car, even the tiny ones, and is more economical than most of the bluemotion specials
If it has the lowest CO2 emissions, wouldn't that make it more economical than all other cars at least in fuel terms?
It would if the test used to determine CO2 emissions bore any relation to real world driving. The importance of these test results for marketing also cause ECUs to be programmed to give the best possible test results as opposed to the best real world compromise,, which is why chipped cars can do the seemingly impossible and be both faster and more efficient in reality!
I was travelling in a Prius a little while back, and it was very quiet and very comfortable. Very smooth acceleration at lower speeds, and felt quite different to other cars. I think if they used less electronic gizmos they might be even more efficient. Personally, I feel that the environmental side of things is far more important than fuel economy, but of course in the real world, it's the latter which is the crucial factor.
the thing that gets me is the fact that the quoted fuel economy for something like a Prius is still worse than a modern diesel engine
It depends whether the figures can be compared like for like, if you take the maximum MPG a petrol or diesel car can acheive it only achieves that figure at a speeds and in circumstances that people rarely drive in - faster than you can drive around town, slower than you drive on motorways, with no junctions, no roundabouts no braking or changing gears. So apart from being stuck behind a truck up the A9 between Perth and Inverness its a fantasy value.
The advantage, I would hope, of combining elec and petrol is that you'll travel in an optimum, economical manner for more of of the circumstances of your journey. So in use, rather than in marketing material, something like a Prius should out perform a comparably size car.
The other advantage of the combination is that we are at a very early stage in the transition away from fossil fuels for road travel (if indeed we ever make that transition) and at present we don't have either the driving habits, (in terms of range) or the infrastructure (in terms of charging facilities at home and one the road) that would make drivers feel happy to set off on a journey on battery power alone.
Probably uses less consumables such as tyres and brake pads etc because of the more reasonable weight
Haha, prime piece of forum bullsh*t there, well done Prius weighs about the same as a V50, plus it uses regenerative braking which means the brake pads can last for over 100k miles.
From my own experience, I get between 58 and 62mpg from my mkII Prius in real world driving in the summertime. That includes driving around town and long motorway trips down the M4, all done at the speed limit.
Sorry molgrips. If you really care that much cycle to the shops
What on earth makes you think I don't cycle (or walk) to the shops? You are assuming that because I drive a Prius I think I'm some kind of fabulous eco-warrior who's better than everyone else? No, really, I just wanted a decent sized economical car. That's not a bad thing to want is it? Didn't really fancy shoving my kids and relatives into the back of a supermini. Should I have bought something LESS economical to please you?
If it has the lowest CO2 emissions, wouldn't that make it more economical than all other cars at least in fuel terms?
It is by far the most economical petrol car. All other cars that come close are diesel, and a litre of diesel produces more CO2 and a lot more other pollutants than a litre of petrol. Which is why it's so clean - 15% less CO2 than waverider's V50 and none of that nasty NOx. But that's still a great car, I'd happily drive one. Bit slow too with only 109bhp though as opposed to 138bhp in the new Prius
I dunno why Priuses get such stick. Nice economical car - what's the problem?
porter-jamie - that "study" is widely known to be utter b*llocks
which bit? the battery doing laps of the world?
I very much doubt if any of the Prius' I see get 70 - they're always flying past me at about 80-90 on the motorway
I think the reason Prius's get such stick is that they are promoted as being really green, which they are pretty good at their end use, but surely greenness should take into account the whole of the vehicle's life such as the pollution from nickel mining shipping the nickel for processing by ship, shipping the processed materials back etc. all of which are not green. As on Top Gears demo you can drive an M3 as economically as a Prius. I like the Prius down the road from me. It doesn't have to pay any congestion charge but it permanently has a roof rack fitted but doesn't carry anything and gets thrashed so isn't economical.
I also don't like all this focus on CO2 emissions because it has sod all to do with how much mileage people travel. I did 3000 miles in my car last year. I know it's not the most environmentally friendly car but it causes way less pollution than a Prius or whatever doing normal annual mileage. I don't see why they don't just scrap road tax etc. and put it straight on the cost of fuel. If you drive an uneconomical car or drive more miles it costs you more - or is that just too simple a solution?
there are 2 points in a prius
they have a very green image. this is good for smug people, and also companies wanting to portray a green image
they are much more economical than petrol cars. this is great in places where it's difficult to run a diesel car, for emissions reasons. Ie America and Japan (2 massive markets)
diesel hybrids will obviously be a better choice when they're available. Pug reconned they would be doing one of the rcz that has a total of 200bhp (1.6 diesel iirc) and does 99co2s, so is cheap to tax etc. Seems like a great combo to me
the newer generation (not out here, yet) such as the chevvy volt use a petrol engine, but it has no direct drive to the wheels - ie it only drives a generator which only powers a battery which powers a motor which drives the wheels. This sounds inefficient, but eliminates the drivetrain (30% loss normally) and means the motor can be run at a single rev range (ie 1600rpm the whole time), thus be smaller (50bhp), simpler and cheaper. lotus are doing one of these (called a range extender). obviously it has limitations, ie can't cruise at high speeds for a long time, but for general driving they look pretty good
but surely greenness should take into account the whole of the vehicle's life such as the pollution from nickel mining shipping the nickel for processing by ship, shipping the processed materials back etc. all of which are not green
Well there is a lot more to it than that. Apparently most nickel is recycled, since it's as easy to recycle it as it is to refine the ore. Also a Prius weighs 200kg less than say a Golf, battery included. So that extra 200kg of gubbins has to be manufactured somewhere, shipped somewhere, the raw materials have to be mined and refined just the same.
Also the factory in Japan that makes them is something like 70% solar powered; uses water from an adjacent river and puts it back in cleaner than it comes out; and sends nothing to landfill.
As on Top Gears demo you can drive an M3 as economically as a Prius
What does that tell you? Nothing.
I did 3000 miles in my car last year. I know it's not the most environmentally friendly car but it causes way less pollution than a Prius or whatever doing normal annual mileage.
A valid point, but you are missing the real one somewhat. You could be doing 3000 miles a year in an economical car and save even more CO2 emissions We all need to reduce as much as possible - we aren't working to a set CO2 alloawnce.
Re the 'road tax': It's a pretty small component of the total cost of car ownership, but it has a big psychological impact - because you tend to forget about it then all of a sudden bang, it comes out of one of your pay cheques. I had my tracking done the other day, and the mechanic was absolutely stunned that I only paid £15/year for my road tax, compared to his £150 or whatever for 6 months in his Civic Type R. Never mind that I was getting maybe double the fuel economy - he didn't seem to care about that, despite most likely costing him a lot more over a year.
Diesel hybrids could be good, but as far as I can tell the gains would be less. When driving a petrol car at low revs, you have to throttle the intake to reduce engine speed, which is wasteful. In a diesel, you only inject the fuel you need which is not wasteful. In a petrol hybrid, rather than throttle the engine you just divert energy to the battery, and when it gets full you just cut the engine. So petrol hybrids remove some of the advantages of diesel over petrol, and consequently I reckon the percentage gain would be less for a diesel hybrid.
The Chevy Volt is a great idea but it's built on more advanced battery technology that they are apparently having trouble with. It's an electric car with a 40 mile range that has a petrol genny to top it up. And you can plug it in. So the idea is that you drive it purely electric all the time unless you need to do a long journey, whereupon it runs on petrol and (supposedly) has the performance of and somewhat better economy than a normal car. It does not have mechanical drivetrain losses, but it does have electrical losses, so the absence of a gearbox is not really a factor.
Very nice idea tho. This set-up (series hybrid, like trains) would definitely benefit from being diesel I think.
FWIW I'd have been very attracted to a Volvo DRIVe or a VW Bluemotion car if they were out when I was splashing cash on a Prius. And I'd have bought one last year instead of a normal TDI Passat if there had been any second hand.
From my own experience, I get between 58 and 62mpg from my mkII Prius in real world driving in the summertime. That includes driving around town and long motorway trips down the M4, all done at the speed limit.
Prius is a green wash. The greenest car would be small light and longlasting. Aygo or wagonr or similar. Small engine and light body
the prius exists because of an american marketplace where car with zero emission in cities are favoured. Total lifetime environmental cost they are not good. all that extra lithium of whatever in the batteries, they are big and heavy, most of the High MPG comes from the easy rolling tyres and low areo drag.
Edit - a lot is guesswork because toyota wioll not release any info on the batteries - why?
I'm glad you joined in, this is an interesting subject.
What does this mean?
2. When you are going at a reasonable pace, you can siphon off energy that would be wasted and put it into the battery
What is NOx? I thought diesels were cleaner than petrol?
What we really need to do is change our driving habits and not do what I have just done (in my defence it is something I do only very rarely) and that is drive my monster car the few miles to the off licence so as to catch it before it closed.
I'd have a Volvo V50 drive thanks. 70+mpg also, less environmentally harmful to manufacture than a Prius, and more useful space in the car.
hmmm I doubt that. Official figures for a volvo V50 put the extra urban mpg at 50.1 linky. The same site give the prius mpg at 76.4. I'd be interested to know where you get figures of 70+mpg for the volvo.
I think that TJs comment on green washing whilst valid is a bit of an over simplification. This combination of technology had not been achieved before toyota did it with this car. Whist there is an element of green washing someone had to do this first and what if the small cars that you mention were to get this sort of technology too? It certainly isn't the single answer to improving the efficiency of cars but to dismiss it out of hand like that seems a little harsh.
Gone fishin - its the truth tho. Oversimplified it may be but its a fundamental truth. Car amnufacturers won't make a green car - its not good business to make small light cheap car that lasts a longh time
a fiat panda is better than a prius because of the small amount of materials in it.
The prius is about zero emissions in cities and about salving peoples conscience Half the weight of it and use a 500 cc engine and you get closer to the mark.
total lifetime environmental penalty is the key thing - and the prius is bad on that because of the batteries. Toyota will not release any info on the batteries life and recycling - why - because the numbers are rubbish is my guess. they certainly will not last 20 yrs
Volvos are good on this because they last a long time. a significant amount of the environmental penalty is in the manufacture and disposal of cars.
lets put this another way - if petrol was £50 a gallon how long until 100+ mpg cars? if road tax was per kg and escalated rapidly after 500 kg how long till the 500 kg car?
I agree with TJ.. The prius is a bit greenwashy. After maybe 15 years and 200k+ miles it might offset the extra production costs and environmental impacts, but how many are likely to see that?
My ideal hybrid would be a small diesel with a flywheel energy storage system. Light, simple and no dirty metal batteries.
This bit doesn't make sense to me.
"When driving a petrol car at low revs, you have to throttle the intake to reduce engine speed, which is wasteful. In a diesel, you only inject the fuel you need which is not wasteful."
Are you saying that a petrol engine is most efficient at full throttle ?
Are you saying that a petrol engine is most efficient at full throttle ?
the prius exists because of an american marketplace where car with zero emission in cities are favoured
I'm pretty sure that it's also partly because diesel is a dirtier fuel in the US. I know a couple of years ago modern 'clean' diesels like we have in Europe weren't possible over there because of the fuel quality.
I think electric/part electric cars are a good thing, they teach pedestrians to look rather than just listen and that's got to be good for cyclists.
I'd never have a diesel coz they're stinky and dirty, and I've followed too many modern ones belching black smoke at every gear change.
if road tax was per kg and escalated rapidly after 500 kg how long till the 500 kg car?
TJ, I'm surprized you wrote that. Crash preformance of the 500Kg car is ??...Wouldn't the Mondeo already be 500Kg, if it were possible ?, the Manuf would love that.
Modern car weight is not a simple issue. On the one hand, Maunfs want to produce a lighter car, on the other hand, the customer demands more in their cars, not withstanding the crash preformance demanded by authorities in any particular market.
Molgrips, you work in Auto ?.
As I've written before, battery powered cars as we know them today, are not the final solution. Far from it.
GM microbes recycling waste into alcohol based fuels is one credible goal.
As an interim phase, plant material in the form of arable crops, is used to produce fuel, although ultimately, I'd like to see a move away from that. Which is starting to happen, espically at the testing stages.
(Don't even think about whinging about starving masses, I'm not even going to entertain remarks about that cr4p)
Unfortunately, any benefit from producing loads of nigh-on carbon neutral fuel, is p155ed away by producing it using conventionally powered agricultural machinery, then transporting it by conventionally powered vehicles/shipping.
Even then, I wouldn't suggest that carbon neutral should be where it stops.
For the next 50 years, heading towards producing a liquid type fuel to run engines in a similar format to todays motors, is the best we could reasonably hope for, imo, when stepping back and trying to appreciate/consider the Big Picture.
The Honda clarity ws along the right lines, but for the fact it was hydrogen powered.
Again, I have explained why the Hydrogen powered car isn't a real-world solution.
So you're telling me that a Prius is more environmentally friendly over its life than a Series III Landy running on chip fat?
surely it depends where you drive it?
A prius in city conditions is using 0 petrol. Beat that in your conventional car.
solo - a light car uses less energy to make it, to accelerate it and to recycle it.
Manufacturers have no incentive to make green cars - and of course a 500 kg car could be made safe. How heavy is a smart? Whats its Ncap rating? ( well maybe 500 kg is a bit light but you get my point)
It would have to lose all the gadgets so beloved of modern motorists tho. Become a much simpler and more basic vehicle. Think 2cv not Mondeo or a modern cyclocar
Unless you reduce the amount of materials in a car any "greening" remains greenwash
Biofuels from crops can never work - there simply is not enough arable land to make enough fuel
Basspine - but it needs to get tha energy from somewhere - so either the petrol engine has to start up when the battery runs flat or the petrol engine works harder to recharge the batteries once out of town
TJ the energy always has to come from somewhere! sunlight eventually if you look far enough back
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