From a cursory scan, your units don't stack up.

Joules are energy or work.
Watts are power or rate of work
Watts are Joules/second
kW/hour is meaningless.
John.

But I know what you mean and entirely agree that electric cars are the most misguided concept.


[Edited on 6/6/09 by MautoK]

We could always harass Honda to bring their hydrogen cars over here, their website says there's a solar/wind home filling kit available too

Not sure about your figures at all, also you ignore the energy required to find the oil, drill for it (not find it, go drill somewhere else), pump it, refine it, deliver it... plus it is a finite product

I think Hydrogen makes much less sense than battery or petrol. The figures are even worse. It takes a lot of energy to split hydrogen, then compress it, all to give the abilty to refill a tank to go further.

Vegetable oil is an inefficient use of agricultural land (but I agree is of benefit if used as a by product).

Another idea not mentioned is compressed air, but compressing air is horrendously inefficient.

I think though that there are bigger problems than the petrol we put in our cars.

Personally I favour electric cars, but I don't think we are there yet with regard to battery technology. Until we are (and we will be) efficient use of petrol is our best bet.

2c

As an aside, I do not think that the truth is ever considered an option in the green debate, and I always consider a lot of commentary with suspicion. Years ago I read an article in New Scientist that examined dust to dust environmental vs £ benefit of recycling. Recycling paper was PROVEN to have been far more energy inefficient than recovering energy through
burning it as a fuel. It also did not have the environmental pollution associated with the extra bleaching required the second time through. A discussion of the findings with the green party at the time produced a comment very much along the lines of "We need to get people recycling, paper is a good clean substance to start with. Burning paper is not something that we would like to see encouraged".
I could see their point, recycling one thing encourages you to recycle more, but personally I fealt their whole mandate ought to have been what was best for the planet now... not in 10 years time.

I've never seen so many assumptions used as "facts" upon which to base an argument. That and the use of kW as a unit of energy lead me to believe that the OP is just 8ollocks. Maybe electric cars are a total waste of time. You wouldn't know from the OP.

For the record, I don't believe that a typical petrol car is anything like as good as 30% efficient, not from Jules in the fuel to miles on the road. Similarly, you can make electric cars way better than 70% A good electric motor can top 95% and a good controller in the same region. Copper losses will be small but you can also factor in regenerative braking Wheel motors mean you don't need any kind of gearbox, diff or prop shafts to lose power.

Another obvious mistake in the original post was to take account of electricity distribution losses but not the diesel used by fuel bowsers or power used by filling stations

You then have to compare oil wells / super tankers / refineries against coil / oil / gas / Uranium mining and power generation. Well to wheel figures they're called. Look them up rather than guessing.

I reckon an electric car to be more efficient than an internal combustion car but I also believe the best solution NOW is an electric car fueled by a small generator, say 30 BHP or so, optimised to run at 1 speed, generating 1 power at 1 throttle opening. Then your engine will exceed 30%.

For the future, who knows. I'll tell you this though, as soon as a good way of making / storing hydrogen is invented, the petrol engine will die. I attended a lecture on the development of the fuel cell powered car. There's still a way to go but the smart money will go into developing electric cars now so that when hydrogen fuel cells are available, they'll slot right in.

hmmm, clockwork....

clockwork cars i wonder how that would work? how much it would take to wind up a car would it be possible for peopl eto wind them up? lol

quote:

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Originally posted by Ivan
I have seen a lot of blurb about electric cars but they never answer the basic question about overall efficiency - so did the following calc for myself using info from Google - any thoughts:

Assume petrol consumption rate = 10 litres/ 100 km

Therefore you use 320 MJ per 100 km or 320/3.6 = 89 kW per 100 km

But Petrol engine is only 30% efficient therefore you actually need 89 X 0.3 = 26.7 kW to move car 100 km

For electric car you get around 70% efficiency therefore need 26.7/0.7 = 38.1 kW from battery.

Now battery conversion rate is 23% therefore you need 38.1/0.23 = 165.8 kW from mains to get equivalent of 10 litres of petrol.


Factors used – Petrol Supplies 32 MJoule/ litre
1 kW/hr – 3.6 MJ/hr

To take it further:

Electric grid efficiency is 92.5%

So you need 165.8/.925 = 179.2 kW generated at source

And coal fired power station is 35% efficient so need 179.2/0.35 = 512.1 kW worth of coal to move your 10 litre/100 km car 100 kilometers

Overall efficiency of electric car is 26.7/512.1 = 5.2 % and its ultimate fuel source is the most polluting there is.

[Edited on 6/6/09 by Ivan]

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I'm afraid I'm not convinced by your figures.

Specific energy of petrol = 44x10^6 J/kg
density of petrol = 720kg/m^3

So, 10 litres/100km = 7.2 kg/100km
equivalent to 3.17x10^8 J/100km

A petrol engine is only 30% efficient, so an ideal car with a 100% efficient engine with the same characteristics would only use:

3.17x10^8x0.3 = 9.5x10^7J/100km

An electric motor is about 90% efficient and a lead-acid battery about 80%, so taking the same car and powering it with an electric drivetrain (all other things being equal) uses:

9.5x10^7/(0.9x0.8) = 1.32x10^8 J/100km

So if we take efficiency at the point of distribution (petrol station or wall socket) then we see that the electic car uses only 41% as much energy as an equivalent petrol-driven car.

Now obviously we should figure in transmission and generation losses too, but these figures are extremely hard to get hold of in the case of the petrol driven car (perhaps why you ignored them?). We need to calculate the efficiency of the transmission, generation and primary fuel source mining in the case of electicity, and in the case of petrol we need to calculate distribution, refining and crude extraction costs.

I understand that the electric car still wins out after these calculations, and clearly if you factor in a clean primary source (nuclear or renewables) is far preferable.

In any case, hydrogen produced using nuclear power is a far more efficient fuel than either grid electricity or petrol, and will be the standard automotive fuel of the future I believe, unless there is a huge breakthrough in battery energy density.

Interestingly, there are several projects on going to produce synthetic petrol and diesel using water and CO2 feedstock.

Perhaps in 50 years time, we will see modern cars running on hydrogen fuel cells, and old classics running on synthetic (and carbon neutral!) petrol produced using almost unlimited electricity from fusion power.

nick

Sorry not convinced by the efficiency of anything said so far.
There is only one environmentally friendly and efficient car that i know of....
Fred Flinstones
Old tinkle toes could beat anything when he put his mind to it.

Electric cars are simply 'toys' in my view until we have a sutainable power network.

Dennis goes into some real world detail on

THIS PAGE

and HERE

If you haven't see the dpcars site before, best you go get a fresh cuppa/beer before you click.

Cheers

Fred W B

[Edited on 6/6/09 by Fred W B]

Another aspect of electric cars is the horrendous amount of heavy metals that go into their construction.

And while I'm here, when will people realise that there's no such thing as 'renewable energy'. All our energy comes from the sun - whether immediate, as direct radiation, or delayed, as captured in the specific energy content of oil or gas, or for example from the gravitational effects of sun + moon giving tides. I'm all in favour of using the energy encapsulated in tidal flow, but tapping that will have an effect on the moon's orbit (eventually.........)

The fatuous use of the wind as an energy source is not like a magic bucket where you scoop out a ladleful of energy and it mysteriously remains full - it gets refilled (i.e. more winds blow) only as a result of more energy from the sun.

All energy ends up as low-grade heat.

It's very simple!

quote:

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Originally posted by MautoK
when will people realise that there's no such thing as 'renewable energy'. All our energy comes from the sun

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quote:

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Originally posted by Ivan
Now battery conversion rate is 23%

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quote:

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Originally posted by MautoK

And while I'm here, when will people realise that there's no such thing as 'renewable energy'. All our energy comes from the sun

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Shoddy units aside, I'm really not sure where you get 23% battery 'conversion rate' from. If you mean efficiency, it's much higher. In reality, power station fuel to car wheels, an electric car is about 25% efficient, which slightly beats the crude oil to wheels figure of a conventional car.

But the efficiency of an electric car is rather less important in the long run. Even now we can generate electricity from clean plentiful/renewable/free sources, and will do so much more in the future (I do wish we'd hurry up with nuclear fusion - we're well behind the predictions of Sim City 2000). Burning oil is always gonna be burning oil - until there's none left that is.

Liam

quote:

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Originally posted by cloudy
Nuclear / Zero Point Energy?

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You are all looking at the wrong sort of efficiency, when electric cars become more profitable that petrol/diesel is when they will become viable.

quote:

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Originally posted by Badger_McLetcher
one day, too many people, too few resources, boom

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Why are we arguing over the relative efficiencies of petrol engines v. electric motors here?
I think that we should be promoting electric/hybrid/whatever to all our friends and relatives. The less petrol others use, the more is left for me for the time being.

Sorry to take so long to reply - when I wanted to reply I think I broke the forum because I clicked "Reply" last night and everything ground to a halt.

Firstly - Battery conversion rate = power input compared to output . Edit - whoops - big error here - I misread the article as they where talking about solar energy not Li - yes conversion rate seems closer to 90% so you are looking at closer to 20% efficiency overall.

Secondly - I readily concede that I know very little about the accuracy of my calc but there appears to be an awful lot so called experts who seem to be fudging the truth re the practicalities of purely electric cars, so I put this rough and ready calc out there to see if anyone can correct it and show the true position.

Thirdly - I strongly believe that Hybrids are the way of the future.

Fourthly - This was prompted by an interview on SA TV done at the Paris (I think) Auto show with a potential producer of an all-electric car who spent the whole interview skirting around the questions of practicality and could only say that Wind power generated electricity could be used for charging with little environmental impact. Totally ignoring the fact that in most countries the majority of electricity comes from Coal and the power grids are already overloaded.

Fifthly - Although I will readily concede that my Calcs may be totally wrong and ignore many factors I believe that they are not far from the truth (just a gut feel folks) and if so it is time for the relevant engineering community to publicise the truth with real world studies - or is there too much money to be made in developing unrealistic prototypes?

Sixthly - It is well beyond my abilities to calculate all the cost factors such as crude oil and coal exploration, extraction, transport, beneficiation etc etc so I just worked to the nearest practical point

Seventh - most electric car studies seem to totally ignore the ability of the electric grid to carry the load if everyone switched to them.

Eighthly - I thought it would lead to interesting discussion and I would learn something from the posting, which I did so thanks to all and keep on shooting me down.

Lastly - of course if they eventually succeed in getting electric powered cars to be pervasive I bet that the tax revenues lost to reduced petrol sale will be recovered from taxes on electricity.

[Edited on 7/6/09 by Ivan]

quote:

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Originally posted by Richard Quinn
Why are we arguing over the relative efficiencies of petrol engines v. electric motors here?
I think that we should be promoting electric/hybrid/whatever to all our friends and relatives. The less petrol others use, the more is left for me for the time being.

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Good post Ivan. As a starting point for discussion it was really very good and drew lots of facts, figures, guesses and comment - so it worked.

quote:

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Originally posted by gazza285
You are all looking at the wrong sort of efficiency, when electric cars become more profitable that petrol/diesel is when they will become viable.

quote:

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Originally posted by Badger_McLetcher
one day, too many people, too few resources, boom

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What we need is a good, old fashioned epidemic, kill off a few billion or so. How about swine flu? As long as I'm immune!

---

quote:

---

Originally posted by MautoK
Another aspect of electric cars is the horrendous amount of heavy metals that go into their construction.

And while I'm here, when will people realise that there's no such thing as 'renewable energy'. All our energy comes from the sun - whether immediate, as direct radiation, or delayed, as captured in the specific energy content of oil or gas, or for example from the gravitational effects of sun + moon giving tides. I'm all in favour of using the energy encapsulated in tidal flow, but tapping that will have an effect on the moon's orbit (eventually.........)

The fatuous use of the wind as an energy source is not like a magic bucket where you scoop out a ladleful of energy and it mysteriously remains full - it gets refilled (i.e. more winds blow) only as a result of more energy from the sun.

All energy ends up as low-grade heat.

It's very simple!

---

On the subject of renewable energy, this implies energy is lost and created, which isn't true. All the energy put into an engine, and indeed the logistics network in getting the fuel to the car, is used, and converted, thus everything is 100% effecient in converting energy, just not into the required or saveable form. If the wasted energy from the whole process could be used, then the lack of direct waste from an electric vehicle would render them in many ways deficient.

Either way, i like IC power in my cars.

On a side note, it is possible to get IC engines to around 50% useable effeciency, allbeit very big, diesel 2 strokes.

quote:

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Originally posted by smart51
I reckon an electric car to be more efficient than an internal combustion car but I also believe the best solution NOW is an electric car fueled by a small generator, say 30 BHP or so, optimised to run at 1 speed, generating 1 power at 1 throttle opening. Then your engine will exceed 30%.

For the future, who knows. I'll tell you this though, as soon as a good way of making / storing hydrogen is invented, the petrol engine will die. I attended a lecture on the development of the fuel cell powered car. There's still a way to go but the smart money will go into developing electric cars now so that when hydrogen fuel cells are available, they'll slot right in.

---

quote:

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Originally posted by Ninehigh

quote:

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Originally posted by smart51
I reckon an electric car to be more efficient than an internal combustion car but I also believe the best solution NOW is an electric car fueled by a small generator, say 30 BHP or so, optimised to run at 1 speed, generating 1 power at 1 throttle opening. Then your engine will exceed 30%.

For the future, who knows. I'll tell you this though, as soon as a good way of making / storing hydrogen is invented, the petrol engine will die. I attended a lecture on the development of the fuel cell powered car. There's still a way to go but the smart money will go into developing electric cars now so that when hydrogen fuel cells are available, they'll slot right in.

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Ok paragraph one, I suggested this a few weeks back and got shot down on the basis that the Prius has a 1.5l engine, I think you might have explained it better though.


Paragraph two, they have. Honda FCX, iirc the website is www.problemplayground.com

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BATTERY!

BAT-TE-RY!

Get out of the 80s man........

quote:

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Originally posted by brianthemagical
On a side note, it is possible to get IC engines to around 50% useable effeciency, allbeit very big, diesel 2 strokes.

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If peeps want to make IC engines more efficient look at the stirling engine. Fantastic design and works very well. Their was some research done at fitting them into cars and it went very well ....... just needed a lot more research but is ideal for this conversation.

Philips did a lot of the pushing / development of the idea in the 40's onwards.

quote:

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Originally posted by MikeR
If peeps want to make IC engines more efficient look at the stirling engine.

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Back to post 1 "IC engines are 30% efficient", this is the biggest error. Your petrol engine's maximum efficiency is 30% - but it's never there, most operation is round the 5 to 10% range. Obviously while idling efficiency is zero. The big efficiency improvement with diesels is in their off peak efficiency where they slaughter petrol hands down - due to them not being "throttled" they always work with a higher compression ratio.
All the decent sized BLDC motors are in the 90s % efficient, pretty much all the time even operating down at a few% load.
Basically if you burn the petrol in a power station to make electricity for a battery car, you'll get 30% efficiency from the petrol engine in the power station. If you burn the petrol in a car you get about 3. So if you lose another 50% in the distribution & the battery you're still 5 times better off with battery electric car.