Naked Science Forum
Life Sciences => The Environment => Topic started by: Paul Bayliss on 10/07/2008 21:59:51
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Paul Bayliss asked the Naked Scientists:
Are electric cars much more ecologically friendly than petrols ones when you take into account the fuel and carbon dioxide from generating the electricity at the power station? Also are the special metals used in the batteries really sustainable?
What do you think?
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There has been a lot of debate about this lately with neither side really being overly convincing.
One advantage with electric cars is that all the pollution is created in 1 place. If that is controlled properly then it is cleaner.
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it is a very complex topic. Much depends of course on how the electricity is generated. If the electricity is generated by renewable sources such as wind turbines, solar panels, or hydroelectric, then there is no carbon footprint and you are far better off than running a gasoline (petrol) powered vehicle. If the electricial comes from a nuclear plant, again, zero carbon footprint. How about if the electricity is generated by a coal fired electricity station? Well, you are actually still going to generate less carbon dioxide, which may surprise you. The plug in vehicle will charge its batteries overnight usually, a non-peak period for the coal plant. And electrical power is so much more efficient than gasoline- gasoline creates heat, but very little of the energy released actually moves the wheels of your car.
The concept of the plug-in electrical car is very sound in theory. the real challenge is to come up with a battery that is up to the challenge of traveling many miles between charge-ups. Toyota and General Motors are in a race to get it right. if oil prices stay high, the winner stands to make big money. If oil prices slide back down, few people will be interested for now because the battery technology adds to the price of the car. In time, this technology looks like it will inevitably replace the standard internal combustion engine, because it will inevitably become harder to find new oil sources.
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If everyone uses something, they'll tax it.
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Electric cars don't add up and depending on how you generate the electricity can be far from grren.
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Electricity can only be as green as the method by which it was generated. Fossil fueled generation involves exploration to find the deposits, transport of the means by which to extract them and the power used to operate this equipment, transport of the raw material to a processing plant (which in tern means clearing a site, erecting a plant, transport of the equipment to run the plant and the power to operate it)............
It goes on & on & on. I don't think it is possible to calculate how much a kilowatt of electricity costs, lets face it, I started in the middle with the exploration. What about the cost of the equipment to explore with?
That reminds me, I will be working on PETEX soon, at London's Olympia. It's the Petroleum Exploration Exhibition. Real boring to me, but not to worry, I will be working on Erotica in the days before & after. That's always good for a laugh.
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I understand that the generating efficiency of large power stations is maybe 40%, depending on type. The efficiency of an modern Diesel engine maybe 40%, but it is not the best device for providing motive power, as it must operate over a range of speeds and loads. This is why cars have gearboxes and clutches, which lose energy. The final efficiency of a car engine in use is I understand around 25%. A combination of modern 3phase motor (or switched reluctance motor) and electronic controller can achieve an efficiency exceeding 80%, even allowiong for battery charging. It needs no gearbox and clutch and it is even possible to drive each wheel directly, without torque multiplication. It can provide maximum torque over almost the entire speed range. With all these advantages the battery powered car can still make better use of electricity generated by fossil fuelled power stations than can the car mounted fossil fuel powered engine.
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There are losses all the way from the fuel in the power station to the power reaching the wheels.
Heat > Mechanical energy > AC at a few kV > AC at 400 kV > transmission lines > Step down via 2 - 3 stages to 400v threephase (230v) > local distribution > DC > charging process > AC - 3 phase motors > wheels
A long chain with losses all the way.
The US Dep of Energy concludes that electric cars are wasteful and expensive to run.
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A long chain indeed, but the I.C. engine is so poor that the electric car with battery can still be a better match to the load. Also no clutch, gearbox, differential, idling consumtion, emmission control, etc.
Also, an all electric rail loco supplied by overhead cables is still more efficient than one with the I.C. engine on board.
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Yes, but the car is having to cart the weight of the battery around. That is very inefficient. The Wh/kg for fuel is around 100 times greater than the best battery.
Essential first step if electric cars are to have any significant future is a battery pack with 10 times or more the best present Wh/kg figure. Then there are several more snags to overcome.
Have to bear in mind that several energy conversions (heat/mechanical/AC/DC/voltages) at a (good) 90% mean an overall poor figure.
5 x 90% = 60%
5 x 80% = 33% AND with a long chain there might several more than 5 conversions.
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I think that 90% is probably quite realistic for large electrical installations, so at 60% you can loose a good bit more energy before you reach the 30% or less of a petrol engine in a road vehicle.
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Yes but although fossil fuel use in power stations can be more efficient (40 - 50%) than in a car engine you have all that long chain of losses which wipes out the advantage.
90% is more likely %80 for some conversions... AC to DC and the actual charging process.
Eevn with poor calorific to mechanical ..petrol is vasty more practical than heavy expensive limited-life batteries.
If electric cars made sense there would lots of them on the roads. I don't think I have even seen one apart from milk floats..
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Quite a few large companies (TNT, Argos, others) are using or planning to use battery powered vans and lorries supplied by Smiths, for one.Check out "New Scientist" 20 September 2008:-
An article about battery powered and hybrid cars,"Born to be Wired"....."The (Tesla) Roadster produces no CO2 emissions, and even when you factor in the CO2 released in generating the electricity used to charge its batteries it produces less than half the amount of that emitted by the greenest gasoline cars on the market. Generating electricity from renewable sources would cut the Tesla's CO2 footprint still further."
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Another has fallen for all the hype.
I fail to understand the point of the Tesla car unless it is to make a quick few quid by selling them to rich kids and then scrapping the whole thing.
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The original question was "are electric cars really more elogically friendly than petrol ones when you take into account the fuel and carbon dioxide from generating the electricity at the power station?
I think the qoute from the Tesla article gives the answer.
The Tesla is of course a toy for rich kids, but it is a "proof of concept". In fact the next generation of electric cars will need no reduction gears (let alone changing gears) or differential, further improving efficiency.
I understand that battery vehicles are being ordered or considered by
Translinc,TKMax,BSkyB,DHL,British Telecom,Sainsbury's,Royal Mail,Balfour Beatty, among others.
It will not happen fast ehough for me, but the automomobile WILL move into the 20th(sorry 21st) century eventually, and development is being driven by the electronics and chemical industries, not by the old fashioned mechanical boys.
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Batteries are just too heavy, expensive and unreliable to make electric cars viable.
Even if new batteries come along with much higher Wh per kg they will always take hours to charge domestically and we just don't have the generating capacity to allow electric vehicles to become widespread. You need at least a ten fold improvement in battery Wh per kg.
The limited range will suit very few people.
Who said electric cars are the cars of future and always will be?
What efficiency? The whole process from fuel (power station) to wheel is not very efficient. Carting heavy batteries (themselves not very green) around is not efficient.
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The I.C. engine is such a poor tool as a prime mover for vehicles that electric motors do better per unit fuel used even accounting for having to cart a bettery around.
The average car journey is well within the range of a battery powered car, many people would only have to charge every few days.
The New Scientist article also mention the Chevrolet Volt, the General Motors EV, as well as the Tesla, and some hybrids.
The answer to "are electric cars really more environmentally friendly" is still yes.
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The purpose of the high-priced Tesla car was to recoup engineering costs quickly, so that the company can stay alive financially to make progressively lower priced models. Maybe by the 3rd or 4th generation they'll have something I can afford. However, living in the Texas Gulf Coast region and the having just survived Hurricane Ike, I would not want my one & only car all electric unless I had my own Back-up Generator.
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"The I.C. engine is such a poor tool as a prime mover for vehicles that electric motors do better per unit fuel used even accounting for having to cart a bettery around."
With respect that is nonsense. If it is the same fuel (petrol say) it makes far more sense to use it directly with a IC engine in the car than in a distant power station with the transmission losses and the power conversion losses (AC to DC in a charger and the charging process itself.. then maybe DC to 3 phase for AC motors in the car) even though a modern power station might be more efficient than a small IC engine. And carrying all that weight around is a killer blow.
And regards relatively rapid charging the only way you could do it domestically would be with a large diesel alternator which totally negates any effort to be green.
Manufacturers (like with ordinary cars) quote figures in the best possible light such the cheapest available off peak electricity.
To convince people you need to do a proper analysis with figures. Start with my car for instance which I reckon has about 150 kWh of useful (axle) energy in its petrol tank and gets about 400 miles range from it. I think it weighes about 1300 kg. Need to check.
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I’m no good at sums, so here goes:
If your car does 400 miles on a “tankfull” of 150KWh, consider the following:-
A battery powered delivery vehicle (Smiths Ampere) has a 24 KWh battery, and claims a range of 100 miles, at gross vehicle weight of 2.3 tonnes.
Your car , weight 1300Kg, 400miles/150KWh = 2,7mile per KWh,
Delivery van, weight 2300kg, 100miles/24KWh = 4.2mile per KWh,
so to cover your claimed mileage (I know it's probably approximate)the van would need a batter capapacity of 4x24 = 96KWh compared to your 150KWh even though it's nearly twice as heavy.
However, it’s even worse:-
one litre of petrol contains 34.6MJ of energy,,
your tank is I guess 50?litres, so the energy in your tank is 50 X 34.6 = 1730MJ.
1KWh = 1000W x 3600seconds = 3.6MJ, so the energy in your tank is nearer to 1730/3.6 = 480KWh, which makes your car consumption more like 400miles/480KWh = 0.84Mile per KWh.
The cost of electricity tariffs is not relevant here, because we can’t compare the cost of petrol or Diesel with the cost of fuel in a power station.
The electric van seems to cover five times more per KWh than your car, give or take. Which means that to make them equal on environmental terms, the losses in transmission etc. would have to be 80%. No serious engineer would consider a project as inefficient as that, and yet we see all these different companies going ahead with battery powered vehicles.
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""The electric van seems to cover five times more per KWh than your car""
I am too tired at the mo but that is UTTER nonsense. If it takes X kWh to cover Y miles for vehicle weight Z it will take that whatever the source of the kWh is in the vehicle. kWH is simply a measure of energy.
If a light car can do 400 miles on 150 kWh (I mean useful energy..not calorific) there is NO way a heavy van can do 100 miles on 24 kWh.
I don't think even the very small G-Wizz can do 100 miles on 24 kWh. They claim (up to) 48 miles and probably it will be more like 30 if you drive at anything like a decent speed.
http://www.goingreen.co.uk/store
Real owners of electric vehicles have found claimed range to be total fantasy.. they get about 1/3 to 1/2 of the
claimed range.
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I think I can see what has gone wrong with your thinking there. You are taking the calorific energy of the petrol and comparing it with the stored energy in battery as if the stored electricity has come from thin air (grown on trees). The same calorific to useful energy efficiency will apply in the power station. You might get slighty better efficiency in a power station but as I had said repeatedly the losses along the way wipe out any advantage. You will get more mpg out of diesel (say) if used directly in a car than you will if the diesel is used in a distant power station or a home generator.
A group of us (including some experienced engineers 50 - 60 years old) have thrashed this out on another talkboard and the conclusion from some was that if there was any efficiency saving with electric cars it was small (only due to modern power stations being more efficient these days). Some agree with me that they are significantly less efficient.
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PumbleChooke, It’s a fair cop guv.!!
Bear with me.
I accept your criticism, I did not account for everything, I was thrown by your reference to KWh in the tank, so I’ve done my sums again with some known data.
Take my car - 65mpg = 14.3 miles per litre
Diesel contains 42MJ/litre or 42/3.6 = 11.7Kwh, so my car does 14.3/11.7 = 1.22mile/KWh.
Accounting for all losses in the electricity supply chain, total input to the battery = 75KWh:-
Generator efficiency = 45%
Three stages of transformation at 97% each
Transmission losses at 7.5%
Charger efficiency at 90% (from my days in fork lift trucks modern high frequency chargers can exceed this).
This results in approx 24KWh in the battery
I don’t think I need to include the DC-AC inverter as this is on-board, ie., part of the motor system.
I have rounded down to avoid overstating my case, in fact large transformers can be 99% efficient. But let’s add a bit to err on the safe side or add an extra transformer, say 80KWh.
This makes the van at 100miles per charge = 100/80 = 1.25miles per KWh, PRETTY WELL A DRAW, but this is carrying it’s battery around, and nearly twice the weight of my car. (with development maybe batteries will become lighter)
Of course the van won’t do anywhere the 700 odd miles my car will on a full “charge”.
I know you don’t believe that electric vehicles achieve their claimed range, I cannot argue, but suspect they would not be dealing with as many of the large companies as mentioned before if they weren’t somewhere near it. We need someone joining in who has some practical experience of using one (I’d be happy to test a Tesla or a Lightning G.T. for a few months).
I would add: My 65mpg is a very respectable figure, not achieved by many cars today (I drive to save fuel). I am retired, so no commuting. Basically, if I did still commute I would expect much less than 65mpg. The cars’ fuel consumption figure is based on a record of it’s mileage and fuel consumption since birth.
Not all of the power generated in the power stations comes from fossil fuel. Some comes from nuclear (low carbon but still bad, and about to start growing) some from wind, even in lagging Great Britain, and this is slowly increasing. The effect on our discussion is that less of the 80KWh comes from carbon producing sources, so the equivalent miles per unit CO2 is less. As more power is generated from non-fossil fuel sources, the battery car will be even better.
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P.S., sorry, Pumblechook not Pumblechooke
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I think it is very difficult to make comparisons between what are different technologies. It can get very complicated.
We have been discussing electric vehicles and renewable energy and nuclear on the Guardian Unlimited(newspaper) Talkbord. I suggest you join. I am a bit wary about giving you a link..it might sign you in as me.
Google.. Guardian Unlimited Talk
One thread is 'How far are we from a sensible, mass market electric car?' Science Folder.. 329 posts. Some threads get 1000s.
One poster agrees with me that a 100 mile range could only be reached with a van if it went pretty slowly. I have worked out it will do 28 miles at full speed. Some say that is optimistic.
Pumblechook is a perfect choice because he is a figure from Dickens who is pompous and a know-all.
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I haven't looked through the maths here, but I did notice that the comparisons seem to be based on calculating efficiency of the entire delivery system for a fully charged battery (mentioning heat/mechanical/AC/DC/voltages).
I think it should be pointed out that even though crude oil contains a great deal of potential energy, distilling petroleum fuels from it, plus transporting & storing them goes along way to offsetting that figure in just the same way as talk about the electricity generating network does. -Comparitively, coal has to be dug out of the ground. But it doesn't need to be distilled as well!
To bring us back to Paul's (who started the thread) question:
Electrically powered (by which we mean chemical battery storage) could be infinitely more environmentally sustainable than our current mainstream solutions IF the energy came solely from a renewable resource such as PV solar.
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Thanks for the link, Pumblechook. I'm away for a few days, will look at it on return.
Based on you're description of the Dickens character, I could probably out-Pumblechook you!
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Interesting points, Peppercorn
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Perhaps a way round the battery problem on future electric vehicles would be to develop a standard sized slot in battery pack that could be exchanged for a charged pack at the equivalent of a petrol station.