[Paul Bayliss]

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?

[DoctorBeaver]

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.

[VAlibrarian]

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.

[lyner]

If everyone uses something, they'll tax it.

[Pumblechook]

Electric cars don't add up and depending on how you generate the electricity can be far from grren.

[Don_1]

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.

[teragram]

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.

[Pumblechook]

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. 

[teragram]

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.

[Pumblechook]

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. 

[teragram]

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.

[Pumblechook]

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..

[teragram]

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."

[Pumblechook]

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. 

[teragram]

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.

[Pumblechook]

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.   

[teragram]

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.

[Rhino337]

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. 

[Pumblechook]

 

"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.

[teragram]

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.